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local weight give rise to shearingforces that lead to longitudinal ten-sions. The shearing force is the forcethat wants to shift the (transverse)plane from one part of the ship toanother. The submerged part of theship clearly shows the difference involume between the midship, the fore-and the aft ship; this is the reason forthe difference in upward force.In the drawing on the right of this

page a part of the aft ship is shownalong with the shearing force near abulkhead. The shearing force at thebulkhead is 400 - 200 = 200 tons.The downward force causes a hog-ging moment of 400 tons x 6 metres.The upward force causes a saggingmoment of 200 t x 3m.The bending moment at the bulk-head is: 2400 tm - 600tm = 124800tm(hogging).

The longitudinal forces occur because:a. the weights in the ship are not

homogeneous in the fore and aftdirection

b. the upward force differs due to theshape of the underwater body.

77K? submerged part of this ship clearly shows the difference in volume between the midships

section and the aft ship. This explains the difference in upward pressure.

weight

200t

4Q0tsheering force

200 tons shearing force at

this bulkhead

The black vectors represent the upward pressure and the w

The red vectors give the resultant per section.

initial draught

ht of the ship

This is how the separate compartments would float. The dashed line gives their actual draught.

The black vectors give, the resultant shearing forces between the different compartments.

The red vectors give the resultant per section.

Ship Knowledge - Chapter 5: Forces on a ship 95

SHIP KNOWLEDGECovering Ship Design, Construction

and Operation

The shape of a ship

Ships' types

1 General

When a ship is moving through thewater, there are many forces actingon it. How they act is largely deter-mined by the purpose the ship wasbuilt for. Forces on a tugboat will bedifferent from the forces acting on acontainer ship. The types of forcesthat occur in waves are the same forevery ship but the magnitudes andpoints of action depend on the shapeof the ship below and immediatelyabove the waterline.

The pattern of forces on a ship is verycomplicated and largely depends onthe following parameters:

- the weight of the empty ship (lightship weight)

- the weight and distribution of thecargo, fuel, ballast, provisions,etc.

- hydrostatic* pressure on the hullapplied by the water

- hydrodynamic* forces resultingfrom the movement of the ship inthe waves

- vibrations caused by engines, pro-peller, pitching

- incidental forces caused by dock-ing, collisions

- ice

A ship with heel in cm unstable situation.

These and other forces cause the shipto deflect. When the force disappears,the ship will regain its original shape.Every ship is different and some havemore or less of this flexibility. If,however, the forces exceed a certainlimit, permanent deformation can bethe result.

2 Longitudinal Strength

2.1 Shearing Forces

When a ship is in calm water, thetotal upward force will equal the totalweight of the ship. Locally this equi-librium will not be realised becausethe ship is not a rectangular homo-geneous object. The local differencesbetween upward pressure and the

*Static and dynamicThe concepts static and dynamic are widely used in this and other chapters.Static means that the work done on an object is absorbed immediately.Dynamic means that the work done on an object is absorbed gradually.

Examples of static:- A swing with a child is slowly pushed forwards from rest. This is a

static movement because the force exerted on the swing is absorbedinstantaneously.

- A crane on a ship is loading a ship with cargo. As the cargo runner isstiffened, the ship lists slowly. This is a static movement because theship absorbs the force that lifts the weight instantaneously.

Examples of dynamic- The same swing is pushed forwards suddenly. The weight of the swing

cannot absorb this sudden burst of force and gets out of control. This isa dynamic motion.

- The same crane has lifted the weight several metres. The weightsuddenly snaps and falls on the quay. This causes the ship to listviolently to the other side. The ship is unable to absorb the suddenchange in weight and, as a result, acquires a dynamic motion.

Ship Know/edge — Chapter 5: Forces on a ship

2.2 Explaining bending

Below is an explanation of how bend-ing moments and shearing forces arecontinuously changing. As an exam-ple a rectangular vessel is used whichis divided into three compart-ments(A, B and C). In figures 1, 2 and 3both outer compartments are filledwith cargo. In figures 4 and 5 theinner compartment (B) is filled withcargo. In figures 2 and 5 the vessel ison a wave crest and in figures 3 and 6the vessel is In a trough. The upwardpressures keep changing because thewave is moving along the barge. Thedownward forces, however, stay thesame. The up- and downward forcesper compartment are shown as vec-tors.

fig. 1

calm water

The mean resultant per compart-ment is given as a vector on the linebelow.The load curve gives the differenceof the up- and downward forces permetre at each point on the baseline.The sum of the areas above the base-line and the areas below the baselineshould be equal.The shearing force curve gives a sumof the shearing forces on the rightpart produced by the left side, goingfrom left to right. If the direction ofthe force is changing (from upward todownward or vice versa), the shear-ing force curve will change from ris-ing to falling or vice versa. The shear-ing force curve has an extreme valueat the points where the direction ofthe force is changing. Converting theload curve to a shear force curve is

fig. 2

wavetop

called summing. The sum of the areasabove the baseline has to equal thesum of the areas below the baseline.The shearing forces are expressed intons.The bending moment is determinedby summing the shearing forces goingfrom left to right.

The bending moment is expressed inton-metre (tra). If the shearing forcecurve changes from rising to falling orvice versa, the bending moment willbend at the bending point from "hol-low" to "round" or vice versa. Whenthe shearing force curve crosses thebaseline, the bending moment line willchange from rising to falling or viceversa. The ship will take the shape ofthe bending moment line if this hasonly one extreme (maximum) value.

fig. 3

trough

resultant

load curve

sheering force

bendingmoment

Ship Knowledge - Chapter 5: Forces on a ship

The situation in figures 1 and 2 iscalled a hogging condition and thesituation in figures 3, 4, 5 and 6 iscalled a sagging condition.Around the half height of the rectan-gular cross-section of the barge vesselthere is a "neutral zone". At that levelthere are no tension or compressionstresses. Further to the top and tothe bottom the stresses have a highervalue, as can be seen from Hook'sLaw stress distribution.On the diagram of the bendingmoment, we find the maximal bend-ing moment at half length, ('/•> L),reducing to zero (0) at the ends.In a ship we find a similar stress dis-tribution.

Hogging:The vertical deflection of a ships'hull, in longitudinal direction,where the hull midships is bentupwards, as a result of cargo dis-tribution and/or the way the shipis supported by a wave at sea. (seepage 96)

Sagging:The vertical deflection of a ships'hull in longitudinal direction,where the hull midships is bentdownward, as a result of cargo dis-tribution and/or the way the ship issupported at sea.

Stress distribution in a beam, during

bending. The neutral axis is ai the level

of the centre of gravity of the sections.

fig. 4

calm water

fig. 5

wavetop

L A 1/\

B |Z\

LclLI

fig. 6

trough

r\ \

•esultant

oad curve

sneering force:jrve

sendingmoment

Ship Knowledge — Chapter 5: Forces on a ship

3 Torsion of the Hull 4 Local Stresses 4.4 Vibration Stresses

Torsion occurs in a seaway and whenthere is an asymmetry in the mass-distribution over the horizontal plane.For example, if there is a weight of100 tons on the starboard side of thefore ship which is compensated byan equivalent weight on the port sideof the aft ship, there will be torsion(or torque). If both weights are 10metres from the centreline, the tor-sion moment will be

100 ton x 10 me te r - 1000 tm.

In adverse weather, especially whenthe waves come in at an angle, thetorsion can increase as a consequenceof the asymmetric distribution of theupward pressure exerted by the wateron the submerged part of the hull.Torsion causes a ship to be subjectto extra stresses and deformations.This can result in leaking hatches anddefects in hatch-coaming corners.Especially "open ships", i.e. shipswith large deck openings, tend to betorsionally weak and are sensitive tothis. A good example are containerships and modern box-hold gener-al cargo ships. Large bulkcarricrs(capesize) with large hatch openingsand enormous torsional forces whenocean-waves come in under an angle,are specially strengthened in hatch-coaming corners.

4.1 Panting Stresses

These occur in the fore-ship duringpitching. The constantly changingwater pressure increases the stress inthe skin and the frames. Panting stressis not a result of hydrostatic pressure,but more a result of hydrodynamicpressure. To reduce the panting stresseffect, panting beams in transversedirection and stringers against theship's shell are added to the forepeak,the area aft of the forepeak and aftpeak structure.

Damage caused by panting strain. Entire

forepeak tank torn off.

Ship size 100,000 ton deadweight.

Forces on the fores hip if the ship is on a

wave top (left) and in a trough (right),

4.2 Pounding

When pitching becomes so heavythat the entire bow comes above thewater, pounding or slamming canoccur. Especially with a flat fore ship,such as in bulkcarriers and tankers,the dynamic forces on the flat bottomwhen that flat bottom beats at the sea-surface, can result in damage to plat-ing and internals. Plates can be set in,and internals can be deformed.To prevent this kind of damage,thicker plates are fitted, and moreinternals, at smaller distances, suchas floors at every frame, and morekeelsons.

4.3 Diagonal Loads

These occur when the ship is asym-metrically laden and during rolling ofthe ship in waves. The effect of thediagonal loads is reduced by the addi-tion of frame brackets, deck beambrackets, cross frames and transversebulkheads.

These can be caused by:- vibrations induced by the (main)

engine,- forces on the aft ship caused by the

rotation of the propeller.- wave impact

Vibration of a construction occurswhen the own resonance frequencyis equal to the first, second or thirdorder of an induction source: the mainengine, the propeller, etc. Addingweight and structure, and so chang-ing the resonance frequency or localstiffening are remedies. Vibrationis a growing concern, as ships arebeing built lighter and lighter, due tothe use of high tensile steel, whichallows thinner construction at thesame strength, and the applicationof better paints, which eliminates theneed of corrosion surplus. Vibrationcan result in fatigue-defects, noise,and discomfort for the crew.Vibration can also be eliminated byinducing another vibration source,with contra-pulses.

4.5 Drvdockim

These forces are the result of verticalupward forces in way of the locationof keel and (to a lesser extent) theside blocks.

Keelblocks are supposed to take thetotal weight of the ship. Side blocksare put in drydock to keep the shipupright, but of course also to takeweight. When calculating block-loads, only the keelblocks are takeninto consideration.

Diagonal loads due to roiling in waves

Ship Knowledge — Chapter 5: Forces on a ship

5.1 Purpose of Stiffeners

To prevent the plate areas (or platefields) of a ship from distorting underinfluence of the shearing loads, bend-ing moments and local loads, theyhave to be stiffened.

Compressing forces on a plate result in

plate buckling.

Compression forces on a stiffened plate.

Buckling requires extra force.

Examples of plate areas are the shell,decks, bulkheads and tank top.

Deformation of plate areas can beprevented by welding of stiffeners(in the direction of the forces).

5.2 Shell plating

The shell plating has as primary taskto keep the (sea) water outside theship. On the outside of the shell thereis water and on the inside air, water,fuel or cargo. Difference in pressureoutside and inside is the result, andthe shell plating has to withstandbending forces.The pressure at the shell from outsidedepends on the draught and varieswith the water depth.The distribution of the pressure forcescan be seen in the drawing.

Parallel frames on a plate subjected to

bending moment

5.3 Decks

The weather deck will deflect underthe load of water-on-deck, ice ordeck cargo. The tweendeck by theweight of the cargo on the deck, andespecially forward by the apparentincrease of weight due to pitching.Also rolling forces have an influ-ence.

5.4 Bulkheads

Bulkheads have to withstand bendingforces when they are the boundaryof a lank or a hold with bulk cargo.When the contents of liquid or bulkcargo is different in height on eitherside of the bulkhead, this will result ina pressure difference, causing bend-ing of the bulkhead. At sea, by theship's movement, and the resul-tingsloshing, these forces can be multi-plied. For the strength calcula-tion ofthis kind of bulkhead it is assumed thatone side is empty, while the other sideis filled with liquid to the height of theoverflow pipe on deck.When a bulkhead also has to function

as a support of heavy deck construc-tions, there are also com-pressionforces. Bulkheads fitted against tor-sion of the hull have to be stiffenedkeeping diagonal forces in mind.

5.5 Tank top

The tank top, the closing plate of thedouble bottom, can be under pressurefrom below from liquids, and abovefrom cargo resting on it. Pressure fromunderneath is caused by liquid in thedouble-bottom tank, and the height ofthe overflow / airpipes which allowthe liquid to fill high in the pipe, oreven to overflow. The height of theliquid column causes pressure on thetank top. See drawing.

5.6 Panel

The water pressure results in forceson the plating, which is so large thatthey cannot be absorbed by the platewithout deformation or even frac-turing. The plates have therefore tobe stiffened by stiffening profiles. Acombination of plate with stiffenersis called a panel.By adding stiffeners, the panel isdivided in strakes, with the widthof the stiffener-spacing. The load onthat area is transferred to the stiffener,which m itself has gained in strength,

106 Ship Knowledge - Chapter 5: Forces on a ship

due to the fact that it is welded to theplate. The thickness of the plating isdetermined by the stiffener spacing. Inbulkheads, therefore, the lower platesare thicker than the upper plates.Classification gives regulations forthe maximum spacing of stiffeners,depending on their function (shellframes).

use the same (vertical) profile sectionover the full hei«ht of the bulkhead.

Each stiffener takes its part of thetotal force working on a panel. Themagnitude of the force is related tothe pressure on the panel, the spacingof the stiffeners and the (unsupported)length of the stiffener. In the drawingbelow a panel is shown where the partsupported by the middle stiffener hasbeen indicated.

To determine the dimensions of thestiffener, the width of the plate carriedby the stiffener, is taken (for a certainpercentage) into the calculation of therequired section modules. The sec-tion modulus comprises stiffener plusplate. The effective part of plate iscalled: contributing plate.

When the unsupported length (span)of a stiffener is so long, that this isresulting in very heavy stiffeners, thestiffeners themselves are getting sup-port from even heavier stiffeners, theso-called stringers or web frames.The table shows various panels withtheir specific stiffeners and suppor-ting webs.

The spacing of horizontal webs, thestringers (flats), increases from asmall spacing at the bottom to a largespacing at the top of the bulkhead, inconnection with the triangular liquidpressure on the bulkhead. We can then

Stiffeners can be chosen from arange of types: most used are flatbars, inverted angle bar and Holland-Profiles or bulb-flat. These are hot-rolled sections.

Constructed T-profile

Web frames and stringers can be madeof similar profiles, but this is imprac-ticable. Normally those beams areconstructed from plate with a flangeor with a facebar.

-Flat

Similar stiffeners have names inconnection with the type of panelthey support.

5.7 Longitudinal Framingand Transverse FramingSystem.

We have seen in this chapter thatlongitudinal forces are present on allships and that they play a larger roleif the ship is longer and/or has lessdepth. This is why ships with a lengthof more than 70 metres are usu-ally constructed in accordance with alongitudinal stiffening system. Thismeans that the primary stiffening ofthe shell plating and the primary stiff-ening of the deck and bottom platingrun in the fore and aft direction. Shipsshorter than 70 metres (for examplefishing boats and tug boats) are usu-ally built in accordance with a trans-verse stiffening system. The decisionof either longitudinal or transverseframing is also under influence ofthe shape. If the parallel mid body isrelatively long, for instance in shipsfor inland navigation and in barges,longitudinal stiffening is cheaper andeasier, also with shorter ships.

Lloyd's Register does not require acalculation for longitudinal strength ifthe ship is shorter than 65 metres.

On the next four pages we see threedifferent kinds of ships. First theaft ship of a container vessel withtransverse framing, then a double-hull tanker built with the longitudinalframing system and thirdly a tug boatbuilt with transverse frames.

Planes:

shell

bulkheads

decksflat bottom

tank top

Stiffening:

(vertical) frames(horizontal) longitudinals

horizontal stiffeningvertical stiffening

deck beam or longitudinalsbottom longitudinals (fore and aft)

bottom frames (transverse)upper frames (fore and aft)upper frames (transverse)

Support:

stringers (horizontal)web frames

stringers (horizontal)web girders

deck girders or deep beamsfloors

keelsonsfloors

keelsons

Similar stiffenings have different names for different planes

Ship Knowledge — Chapter 5: Forces on a ship 107

1. Bulbous bow2. Breasthook3. Floor4. Floor stiffener5. Acces / lightening opening6. Stringer or flat7. Centre keel in bulb8. Stembar9. Transition of flat to shell stringer10. Shell frame (HP)11. Hawse pipe12. Anchor pocket13. Chain locker14. Watertight bulkhead (collision bulkhead)15. Ladder to the forecastle deck16. Weather deck (main)17. Emergency fire pump / bilge pump18. Bilge line in bow-tbruster room19. Forepeak (water ballast)20. Bow-thruster tunnel21. Floor slab in bow-thruster room22. Deeptank (water ballast)23. Floors24. Wash bulkhead at the centre line of the ship

H _

Location of the section in the ship

Assembly drawing

166 Ship knowledge - Chapter 7: Structural arrangement

1. Onboard Cargo Handling Gear

Transhipment is moving cargo into and from a means of conveyance, like aship or a truck. Most cargo is moved with the aid of some type of cargo hand-ling gear. Only very small and lightweight cargo is still moved by manpower.The cargo handling gear is either present on the ship (self-loader/un loader) orat the port. In the latter case the quay has a large array of mobile cranes capableof moving along the length of the quay. These cranes used to move exclusivelyon rails, but today an increasing number of cranes are equipped with ordinarywheels with air-tyres and steering capabilities. This allows the cranes to movefreely across the entire quay.

1.1 The choise for on boardCargo Handling Gear

There are many types of cargo han-dling gear for ships and just as manyincentives for choosing to install oneor the other:

A mobile crane on pneumatic-lyres

- The charterer (who hires the ship)demands it. Why, is not theshipping company's concern, but ifnot in possession of a self-discharging ship, the order goes toa competitor who does have one!

- The area of navigation demands itbecause the ports in that area lackcranes. This is often the case inAfrica, South-America, Asia and insmall ports and factory sites allover the world.

- In order to transport special cargo,too bulky or too heavy to handlewith the available shore-cranes.This requires special attention,however, in general the earningsare higher.

- Special cargo is a one-time, large-scale tran sport like a completefactory, moved in sections, or largeand heavy machinery.

Ship's cranes reduce the stability andthe carrying capacity of a ship; theyalso cost money and require mainte-nance. On a general-cargo ship, two

Mobile crane loading paper rolls slowed on a pallet and handled further by a specialforklift

Ship Knowledge - Chapter 9: Cargo gear /lifting appliances

Container cranes on rails at work

cranes, including foundations, repre-sent 10% of the total building costs.Refrigerated vessels often have 7 ormore (light) cranes on board whichmay cost as much as 20% of the totalbuilding costs. As a compromise itis possible that a ship is built with-out cranes, but with the necessaryfoundation (strengthening in severalplaces on the ship) and piping sys-tems. If cranes are then required,they can be installed without radicalchanges to the ship and without extraloss of time (if the cranes are orderedin advance).

1.2 Statutory demands

The statutory demands for cargohandling gear, including lifts, ramps,hoistable decks etc. are laid down inthe ILO-convention 152 (Interna-tional Labour Organisation). Com-pliance with the regulations is underthe supervision of the Flag state andthe Classification Societies like ABS,GL, Lloyd's and Veritas.

Classification of cargo handling gearcan be according to:- National law. which states that the

ship checks the gear annually and aclass check is done every 5 years.

- International regulations whichstate that the gear has to be checkedannually by the ClassificationSociety for an examination and afunction test. Once in five years aQuadrennial Survey. I.e. a yearlyexamination, including opening upof blocks, etc. plus a load-test.

Division of tasks.The inspections, certification andresponsibilities are divided as fol-lows:- All ILO-152 tasks directly related to

cargo handling (cranes, ramps etc.)are the responsibility of theClassification Society.

- All ILO-tasks related to safety, likeentrance to the ship, hold or craneentrances and safety in the holds aswell as supervising the Classifi-cation Societies are the responsi-bility of the Flag state.

- All tasks that do not result from theILO-152 treaty like hoisting gear inthe engine room, store cranes etc.are the responsibility of theshipping company, In compliancewith national law and ISM.

CertificatesThe items under control of theClassification Society are specifi-cally mentioned In the Register ofShip's Lifting Appliances and CargoHandling Gear.

Excerpts from tie JLO-i 52 treaty:Every seagoing vessel must have aRegister of Ship's LiftingAppliancesand Cargo Handling Gear.The inside cover of this register muststate:- The rules for the five-yearly

insections as stated in the ILO-rulesand the rules of the ClassificationSociety.Rules for the annual inspections

- Test certificates must be present forall parts of the loading gear that canwear through use and ageing, like:• the crane (complete)• the runner and topping lift

wire(s)• the blocks and sheaves• the hoisting winch• the crane hook• attachments

The certificate must show whichrequirements are applicable forevery part.

- Certificates are marked by a name-stamp of the surveyor, covered byhis signature and the date and placeof testing.

- The bottom of the jib must show:• the maximum safe working load

(SWL).• the radius applicable to the load

(the horizontal distance betweenturning point and vertical run-ner).

These figures must be clearly visiblefrom the place where the cargo Ishooked on to the cargo hook.

Example:SWL 60 t (40 t)/16 m (28 m)SWL means Safe Working Load and is60 tons with a radius of 16 metres and40 tons with a radius of 28 metres.

Indication of SWL and range of a large shearlcga floating crane

Ship Knowledge - Chapter 9: Cargo gear / lifting appliances 195

2. Revolving Cranes

The picture on the right shows a shipwith three common revolving cranes.The crane house is bolted to a slewingbearing, which lower ring is bolted toa pillar, the foundation, which is partof the ship's construction. The slew-ing bearing is a large double-turningbearing. An electric or hydraulicmotor grabs with its pinion in therim of the upper turning ring, whichis a large ring-shaped cogwheel thatrotates the crane. Normally the cranecannot rotate unrestrictedly in con-nection with electrical cables runningto and from the crane, inside thepedestal.

The crane cabin is a steel construc-tion with windows that allow thecrane driver a wide view of the areaof activity. The wire drum(s), driveengine(s) and the controls and secu-rity are all located in the crane house.The diameter is 2-3 metres.

The crane jib is hinged to the cranehouse, making lowering and toppingpossible. The crane jib consists of oneor two box beams. Thejib is designedin such a way that it has the desiredstrength, while its weight is minimaland its stiffness is maximal. The dif-ferent types of revolving cranes thatare discussed can be distin-guishedmainly on the basis of where the jibis attached to the crane house.

2.1 The position of Cranes onthe ship.

Masts and cranes used to be placedexclusively on the centreline, buttoday they are increasingly movingtowards the side of the ship.

The following remarks can be madeon this subject:- Positioning on the centreline of the

ship is best for the ship's stability.With cranes at centreline, the cranedriver has a good view of the holds,but not of the quay. Thereis also no preference withwhich side the ship should comealongside.

- If all the cranes are positioned onone side of the ship, there is anadverse effect on the position of the

Container feeder with revolving deck cranes

Deck crane

ship's centre of gravity. Therefore,only large ships, where the mass ofthe cranes is very small comparedto the ship's total mass, can havethis kind of arrangement. Forthe crane driver the view of theholds is not so good compared tothe situation where all the cranesare on the centreline, but the viewon the quay is greatly enhanced.In addition, the reach of the craneon the quay is also much im-proved.An alternative is, to position onecrane on portside and one onstarboardside, (or two and two,alternating). They are still offcentre, but now half the number ofcranes are not on the side of thequay, which is bad for the view andreach of these cranes.

Feeder with deck cranes

1. Crane foundation / pedestal2. Slewing bearing3. Crane house4. Jib5. Jib-crutch or boom rest6. Topping cylinder

- If remote controls (wireless!) areused, the view from the crane cabinis of no importance. The cranedriver can position himselfwherever the view is the best.

2.2 Securing the Cranes

All crane jibs are subject to additionalforces when the ship is in waves.Therefore jibs have their own cradle,a support, where they can be securedduring the voyage. This can be donein several ways:- a fixed or moveable support, some-

where on the deck

196 Ship Knowledge - Chapter 9: Cargo gear / lifting appliances

the jib falls down, and when thecrane is revolving it will bedifficult to stop it.

- Emergency stops shall be present.Red emergency stop buttons shallbe present within reach of the cranedriver and wherever the regulationsrequire them. When pushed, allmovement of the crane is madeimpossible. Emergency stops canonly be reset locally.

- A hoist-limit switch shall bepresent. This is a limit switch thatdefines the highest position of thehook.

- Empty-drum safeguard. The hois-ting cable shall be wrapped aroundthe drum at least three times inorder to keep sufficient liftingcapacity (friction).

- Sometimes an inclination-limitswitch is present. This shuts downthe crane when the angle ofinclination becomes too large.

Specifically for revolving cranes:- A limit switch for the highest and

lowest position of the jib. This isalso the maximum and minimumoutreach limit.

- Turning-limit switch(es) to preventthe crane-jib from touching somepart of the ship's structure.

2.6 Drives

Every crane has at least three motors:one for the runner, one for the toppingof the jib and one for slewing. Themotors can be hydraulic or electric. Tncase of hydraulic power to the crane,the hydraulic supply is created by aso-called power-pack, driven by anelectric motor.

a. Hydraulic Crane DrivesThe runner and the slewing bothrequire revolving hydraulic motors;the topping of the jib is done usingone or two hydraulic cylinders. Themain slide valve is controlled with themain lever via the driver valve. Themotor automatically stops moving ina direction when the crane reaches anextreme position. This is done withthe aid of a limit-switch and an end-switch. Of course, movement in theopposite direction is still possible.

To lay down the jib in the crutch, theresting position, an over-ride switchis necessary, as this is normally belowthe allowed lowest position of theJib.The main slide valve often has a veryingenious construction adapting theforce and velocity of the winch engineto the position of the control lever.The main slide valve also lifts thebrakes of the particular motor whenmovement is wanted. Furthermore,if the oil lines of a hydraulic motorare closed, the main slide valve canabsorb the extra load.

b. Electric drivesThe electrical drives of the ship'scranes receive their power from theship's switchboard. For this purpose,the ship's 3-phase current is changedby an adjustable converter into eitherdirect current (DC) or an alternatingcurrent with an adjustable frequency.

The control lever operates the convert-er, which sends current to the motorand lifts the brakes off. In contrast tothe hydraulic engines, the electricalmotor cannot absorb the forces of aload if the power supply is cut off. Incase of a stop-command, the brakesare applied instanta-neously to over-come this short-coming. However, asa result of this, the brakes of an elec-tric winch engine wear faster than thebrakes of a hydraulic winch motor.

As in hydraulic drives, excessive lift-ing, slacking, topping and slewingis prevented by a limit-switch. Ofcourse, moving in the opposite direc-tion is still possible.

2.7 Classification of Cranes

Revolving cranes can be distin-guished into the following types:- conventional type (section 3)- low type (section 4)- heavy-lift cranes (section 5)

3. Conventional Type Crane

The advantage of the conventionalrevolving cranes over the low types isthat during topping and slacking, theload remains at the same height. Thishorizontal level luffing / load travel isachieved by using the high position of

the pulley block and the way the run-ner is reeved through. This ensuresthat it slacks the same distance as thetop of the jib rises. When lowering,the same correction is carried out inreverse.

In the case of double runners, hookblocks are used instead of hooks.

Conventional cranes can differ inthe ways that the jib is slacked andtopped:- with a cable (topping lift wire)- with (two) hydraulic cylinders

3.1 Topping with a Steel Cable

In topping and slacking with a cable,the crane jib is attached to the cranehouse as low as possible, just abovethe slewing bearing. A longer dis-tance between the end connection ofthe topping-lift wire and the lowerhinge-pin of the jib means a lowerforce in that wire. Further-more, thecentre of gravity will be lower.

A possible danger in these types ofcranes is that in case of a sudden list,a steep crane jib can smash against thecrane cabin. This effect is amplifiedby the forces in the runner (runningpart). To prevent this, rubber stopsare used, but if there is a load hangingfrom the runner, both the load and thecrane-jib can be damaged.

The topping-lift wire can be connec-ted to the top of the jib, or to a pointhalfway, or a combination of both,preventing vibrations in the jib.

3.2 Topping with HydraulicCylinders

The jib-fulcrum is attached higherto the crane house if the crane jib ismoved vertically by hydraulic cylin-ders. This is because the cylinders areattached to the lower part of the jib atone end and to the base of the cranehouse at the other end. The cylindersare positioned such that they arebeside the crane cabin when the jib iscompletely topped. This means thatalthough the load can touch againstthe crane cabin, it cannot damage thecylinders.

198 Ship Knowledge — Chapter 9: Cargo gear / lifting appliances

Topped cranewith the top-ping cylindersadjacent to thecrane hut

1. Crane house2. Cabin3. Jib4. Pedestal5. Slewing bearing

8. Hoisting safetydevice

9. Hanger (topping lift)10. Runner11. Pulley (sheave)

6. Turning point of the jib 12. Light cargo block7. Light runner 13. Swivel

(auxiliary hoist) 14. Rams horn hook15. Heavy cargo block

Ship Knowledge - Chapter 9: Cargo gear / lifting appliances 199

Some typical figures that apply tothese cranes are:- maximum lifting capacity of 16-60

tons- maximum reach 22-34 metres

Using hydraulic cylinders for the top-ping of the jib has a number of advan-tages over topping with a steel cable:

- Slamming of the jib as a result ofwaves is prevented becausedouble-acting hydraulic cylinderscan absorb both pulling andpushing forces.

- Cylinders are easier to maintainthan cables. The latter have to bereplaced every five years.

- The jib cannot shoot through thetop-position. This allows craneswith hydraulic cylinders to have asmaller range (2 metres) thancranes with runners (3 metres).

3.3 The Crane Cabin

The drawing below shows the arrange-ment of the crane winch, which isdriven by an electric-hydraulic motor.An electric motor drives the hydrau-lic pump that, in turn, supplies oil tothe hydraulic lifting and revolvingmotors.

The oil absorbs the heat that is gen-erated in this process and it is sub-sequently cooled in an oil-cooler byan automated ventilator; then it ispumped back to the hydraulic oiltank.

1.2.3.4.5.6.7.8.9.10.11.12.

Crane cabinLever for topping and revolvingLever for liftingJibHydraulic motorOil tankOil filterOil coolerLimit switchDrum for toppingDrum for hoistingPulley block

1. Pedestal2. Slewing bearint3. Crane house4. Jib5. Grab6. Cabin

3.4 Bulk Crane

The bulk crane isa unit designed forloading and / or dis-charging using grabsand logs on standard(handy size, 30,000tons) bulk carriers.These are usuallyconventional revol-ving cranes, up to 20ton SWL.

P.wL

Ship with bulk cranes

Crane cabin

200 Ship Knowledge- Chapter 9: Cargo gear/lifting appliances

tight and that it exactly follows the cargo-hook. This cable reelis controlled by the crane driver with the same (right) leverthat the driver uses to control the hoisting winch.

4.2 The advantages of the lowcrane

The jib of a low crane is much higher compared to a con-ventional crane where the top of the cranehouse is at thesame height. This way the crane can still operate,even ifthere are many containers stacked on top of each other.

- The low crane has a lower weight and a lower centre ofgravity compared to a conventional crane with the slewingbearing at the same height. This offers more stability andincreases the cargo capacity.

- If containers are stacked at the same height, the low cranegives the bridge a better view.

§o Cranes for heavy cargo

The cargoes to be transported by ship are continuously increas-ing in weight. The shipping industry therefore builds ships forheavy cargo, where eveiy new generation of ships gets craneswith a higher capacity than the previous generation.

The cargoes this type of specialised ships are built for, canbe complete installations for the petro-chemical industry, orpower stations and suchlike, as long as there are heavy com-ponents amongst the total package.Nowadays, cranes with a lifting capacity of 150 tons or more,are called 'cranes for heavy cargo'. The lifting capacity can beas high as 800 tons (2006).

There are two basic types of heavy-cargo cranes:- conventional cranes,- mast cranes.The conventional crane, has a cranehouse. mounted on andrevolving through a slewing roller bearing, with the crane jibconnected to the cranehouse. The slewing bearing is bolted toa pedestal which is part of the ship's construction and has totake the full tilting moment of the crane plus cargo. This bear-ing usually is a 3-row roller bearing. This type of crane hasthe advantage that the winches are located inside the crane-house, and slewing can be carried out unobstructedly.

The mast crane is installed around a mast, which is weldedto the ship's construction. At the lower part of the mast a plat-form is mounted, which can rotate around the mast. On thisplatform the jib, or derrick is mounted. On top of the mast is afree-turning swivel-head, with sheaves for the hanger and run-ner wires. The winches are installed inside the mast, or insidethe pedestal of the mast, or even below deck.

1. Mast2. Jib3.Topping lift and running

part of the hoisting rope4. Cargo-hook

202

5. Hook of auxiliary hoist6. Slewing bearing7. Mast foundation / pedestal8. Top slewing unit.

Mast crane

A heavy-lift ship with a heavy piece o , working in tande.

Ship Knowledge — Chapter 9: Cargo gear /lifting appliances

The hanger and runner wire gothrough the mast to the top-swivel.This arrangement restricts the slew-ing ability. Normally to + or - 270°.

In connection with the cost of theslewing bearing, conventional cranesare built to a maximum of 400 tons.Higher lifting capacity is not eco-nomic, and technically too difficult.Above 400 tons the mast crane ismostly used.These cargoes have impact on theship's construction. The double bot-tom and the tanktop have to be adapt-ed to a large number of tons per m2.Stability requires anti-heeling tanks,with high capacity pumps to preventlisting of the ship during cargo liftingfrom outside the ship. Usually side-tanks are used for this purpose.To increase the stability, sidepontoonscan be used, attached to the ship'sside, enlarging the moment of inertiaof the waterline, and which can beempty or filled with water.

The cranes are often used in tandem,to load a heavy part together. The loadcontrol therefore is computerised andboth crane drivers have informationon display about their own crane,but also about the other crane. Reachand load are maximised, via the load/ moment curve calculated for eachindividual crane, and they are not tobe exceeded.

For the heavy cargoes, the ship is pro-vided with special tools: heavy slings,shackles, spreader beams, etc. Alsosuitable lashing gear has to be pro-vided. All these tools are load-tested,marked and certified.

5.1 Hoisting diagram

The capacity of a crane depends onthe range and the maximum load ofall the parts of the crane, together aswell as apart. The right side of thegraph shows the important impact ofthe range. The heeling angle is alsoclearly visible.

Heavy-lift ship with hatch covers fitted as portable funks to enkand thus the stability

5.2 Stabilising pontoons

Stabilising pontoons are employedwhen the heeling tanks fail to reducethe list to an angle of less than 3°. Thepontoons are necessary when the GMmay gel smaller than 1 metre. Theyare rigidly attached to the sides ofthe ship at a distance of 0.5 metre insuch a way that the ship and pontoonessentially become one.

A pontoon consists of tanks that canbe filled and emptied indepen-dently.

The pontoon increases the GM of theship at the picture by 0.4-0.8 metres.The pontoon can transfer both down-ward and upward forces. After use.the pontoons are emptied and liftedback on board.

.'• "•';'!':,-,••';;-.- - " . ; v

Stabilising pontoon for increasedwaterline

0.00 SCO 10.00 15.00 20.00 25.00 30.0

Radius [m] at main deck level

Hoisting diagram for a derrick

Jib angle 83°

Lift capacity 275 t

Range 5 . 0 m

49°

275 t

18.6 m

27°

2031

25.0 m

13°

186 t

27.0 m

0"

162!

27.5 mSpreader beam

Ship Knowledge - Chapter 9: Cargo gear / lifting appliances 203

6 Gantry cranes

Gantry cranes are deck cranes that cantravel, over the cargo, along the shipin longitudinal direction. Many dif-ferent types of cranes can be attachedto the gantry. Ships without owncargo gear often use a simple gantrycrane as a hatch cradle.Gantry cranes specifically for the han-dling of cargo can be distinguishedinto three main types:- gantry cranes with a revolving

crane on top- gantry cranes with a moveable

cable trolley with jib- gantry cranes with a double portal

and cable trolley without a jib.

Gantry cranes are always sensitive totrim; 2° often is the maximum. Cranesthat have a cable trolley are evenmore sensitive and in this case a listof 2° is the maximum.

Multi-purpose ship witi

If there is a revolving crane on topthis maximum may be a little bit high-er, but it will never be more than 5°.The four-point suspension of thehoist gives a gantry crane an excel-lent load control. This ensures thatthe load stays in line so that it can bedeposited at the right location.

A disadvantage of gantry cranes istheir massive weight that shifts thecentre of gravity to a higher point.This reduces the stability and the car-rying capacity. An advantage is thatthe ship hardly needs any strengthen-ing; only the guide rails on deck needa strong foundation.

Gantiy crane with a cable trolley and a fixed jib, front view and side view

U-gantry with trolley on a container-ship

A characteristic of gantry cranes is thelarge reel on the side for the feedercable.

The portal uses train wheels to travelover the guide rails. The travellingpart uses pinions to mesh into atoothed rack, which is attached to thelongitudina! beam, which is usuallythe foundation for the rails. Clampson the sets of wheels fit around therails without actually touching themin order to prevent the gantry fromtipping over.During the voyage, heavygantry cranes are lifted free from therails by hydraulic jacks, in order notto damage the wheels (ball-bearings)and rails by the ship's vibrations.

7 U-Gantry with a cabletrolley without a fixed jib

The forces in a crane are distrib-uted more equally in gantry craneswith two beams and a cable trolleywithout a jib than in a gantry cranewith a fixed or rotating jib; there aremore torsional forces in the latter.This allows the structure to be onlyslightly heavier than structures withonly one beam. However, the cranecabin should be placed higher than inthe other two types of gantry cranesbecause the load always remainssome distance below it.

Similar to the other types of gantrycranes, this type can best be used formoving:- containers- parcels of timber or paper- rolls thin steel- other bundled cargo.

8 Side loaders

Side-loader systems are used for thetranshipment of small cargo unitslike pallets, rolls of paper and generalcargo. The system comprises one ormore doors in the side of the ship,and one or more elevators situatedbehind these doors to transport thecargo from the ramp, at quay level,to the holds and vice versa.

The advantages are:- it has minimum impact on the

ship's stability because it addsalmost no weight.

- Furthermore, the ramp lies low.- a high transfer capacity. The cargo

docs not have to be transportedover unnecessary distances. Thisminimises the waiting period.

- if the route over the quay to theship is covered, loading anddischarging of delicate cargo(paper rolls) can continue diningrain or snow.

204 Ship Knowledge - Chapter 9: Cargo gear / lifting appliances

HYDRAULIC LIFTING GEAR S | D E D 0 0 R o p E N

QUAY MAXIMUM HEIGHT

HOLD

COUNTERWEIGHT.

PAPER REELS

LOADING PLATFORMGUIDING

Side and top view of an elevator-system

1. Opened side door2. Cargo (paper rolls)3. Elevator4. Quay5. Tweendeck

Paper rolls on the elevator. The cargo is transported by the lift to thetweet? deck or the lower hold

A fork lift picks up paper rolls to convey them to the holds

Ship Knowledge — Chapter 9: Cargo gear / lifting appliances 205

The disadvantages are:the doors in the side of the shipreduce the longitudinal strength.This has to be compensated byapplying thicker plates around thehole in the ship's side.

- the elevators reduce the availablecargo volume.

- the elevators are unsuitable forheavy loads.

- there is a maximum size for thecargo to fit the dimensions of theelevators.

Some characteristics of side-loadsystems- the maximum work load (of the

elevator) is 8-20 tons- the lifting speed of the elevator is

0.33-0.66 m/s (20-40 metres/min.)

Fork lift places paper rolls on the loadingplatform

9 Ramps

Ro-Ro vessels are ships where thecargo is brought on board on wheelsvia ramps. Loading and dischargingcan take place quickly, due to thespeedy and mainly horizontal trans-port.

An advantage of this is that the ship isindependent from the shore facilities.

In general, ramps have sufficientlength to be used both in high andlow tides. Opening and closing isdone with a winch or hydraulic cyl-inders. Closing and securing is doneusing hydraulic sequence lockingsystems, when the ramp is brought inclosed position, the locking wedges,bars, hooks etc, come in, operated byhydraulic cylinders.

The most important types of rampsare:- straight ramps, extending straight

from the forward and aft ends orfrom the side.

- quarter ramps, having an angle of45° relative to the centreline.

- slewing ramps, here the angle canbe varied between +45° and -45°relative to the centreline.

Driving from the loading deck to theother decks also proceeds via inter-nal ramps.

These can be distinguished into:- fixed ramps- adjustable ramps- car decks that also serve as ramps.

Ro-Ro vessel:1. Straight stern ramp/door2. Hoistable ramp3. Shell door4. Fixed ramp with cover5. Door6. Car-deck access ramp7. Hydraulic Power Pack8. Hoistable car decks

9.1 Ramps between ship andshore

- Straight rampsThe use of straight ramps means thatthe ships sometimes depend on a spe-cially designed, sloped quay, with alanding area for the ramp. If loadingand discharging is done via the fore-ship or the aft-ship, the full lengthof the ship has to fit in the berthingplace. However, this is not necessaryif the straight ramp is lowered fromthe side of the ship.

- Straight ramp in the fore-shipA straight ramp forward, is normallycombined with a watertight door,behind bow doors or sometimes abow visor. The bow-doors have avery complicated shape as this is partof the shaped profile of the ship'sbow. The inside of these doors havea flat edge with a rubber seal to makethe door watertight. The bow-doors/visor absorb the forces of the waves,and are therefore subject to stringentrequirements for its strength, lock-ing system, seals and security. Rulesstipulate that the bow ramp and thewatertight door, positioned at the col-lision bulkhead, must be separatedfrom each other. This is normallyaccomplished in one of the two fol-lowing ways.

206 Ship Knowledge - Chapter 9: Cargo gear /lifting appliances

1. Outer bow door= ships shell

2. Watertight door atcollision bulkhead

3. Lower ramp, afterpart also a watertightdoor, forward of 4.

4. Inner ramps to uppercardeck

Principle of two-part rump

Ship Knowledge - Chapter 9: Cargo gear / lifting appliances 207

Straight ramp in the off-ship Straight ramp in the side

Inboard ramp

1. With a folding frame bow ramp arrangement the collisionbulkhead door can be completely separated from therest of the ramp. This implies that no part connected to thedoor will extend forward of the correct position for thecollision bulkhead. A steel frame is positioned forward ofthe collision bulkhead door and controls the foldingmovement through hinge connections with the outer partof the ramp. In the fully outfolded position the frame,together with the outer section, forms the load carryingstructure. (See figures and photos.)

2. A normal bow ramp/door arrangement is fitted behind thebow-doors/visor. Behind this ramp, at the position of thecollision bulkhead, another set of doors is fitted.

- Straight ramp in the aft-shipThe aft-ship can suffice with just one watertight door,which, if it is flat, is used as a ramp. In the picture on theright this is the case. The closed ramp protrudes above theaft-ship.

- Straight ramp in the sideStraight ramps can also be located on the side and they arecomparable to the straight ramps in the stern and to the sideloaders discussed earlier. The ship designer tries to makethe side ramp in such a manner that, when closed, it formsa seamless whole with the ship's skin. There are also highdemands for locking, sealing and safety measures for thesetypes of ramps.

Ship with quarter ramp in dry-dock

Hoisiable car deck

1. Holstable car deck2. Hingeable hangers3. Hoisting wire4. Ramp5. Deck

208 Ship Knowledge — Chapter 9: Cargo gear / lifting appliances

- Quarter rumpsA quarter ramp makes an ang/e ofapproximately 45° with the ship's cen-treline. This limits the orientationsof the ship in berthing to the sidewhere ramp is located.

9.2 Inboard ramps

- Fixed inboard rampThe figure on page 206 shows a shipwith a fixed ramp that leads to thelower hold. Economically a disad-vantage, as nothing can be storedunderneath the ramp.

- Hoistable car decksA hoistable car deck is shown inthe figure to the right. These can beused as Lwecndecks, allowing twolayers of cars to be transported aboveeach other. When the tweendeck isfull, the ramp, complete with cars,is hoisted to the tweendeck position.The space below the movable cardeck can be loaded when the ramp hasbeen hoisted.

- Hoistable Inboard RampsBetween decks, inside the ship, hoist-able ramps are used, which are closed,by lifting the ramp, herewith clos-ing the upper-deck or the free-board-deck. This has implications for tight-ness, strength, certification. This typeof ramp can be very long, dependingon angle when lowered and height ofthe cargo-space below.

- Cargo liftsTrailer lifts provide the only solutionto the problem of transferring trailersbetween deck levels in areas of Ro-Ro ships where longitudinal space islimited. The trailer lifts are availablein a wide variety of configurations tosuit individual applications. The lay-out of the installation can be arrangedto enable the lift platform to act as awatertight hatch cover when securedin its upper level position.

- ElevatorsPersonnel elevators need yearly to betested and certified by a recognisedcompany.

10 Registers andCertificates

Ever\; ship with cargo-gear has to beprovided with documentation:- Register of Ship's Cargo Gear and

Lifting Appliances, accompaniedwith the relevant testing certifi-cate:• Certificate of Test and

Examination of Winches,Derricks, and Accessory Gear,

• Certificate of Test andExamination of Cranes or Hoistsand their Accessory Gear, beforebeing taken in use.

• Certificate of Examination andTest of Wire Rope (for eachrope!)

Cranes, used in the Offshore Industry,i.e. the petroleum winning, are sub-ject to more stringent regulations, inconnection with being in use at anOffshore Unit, ship or platform, at sea,and subject to the unit's move-ments.These cranes are called OffshoreCranes.

In case of repairs earned out to anycargo-gear item, this has to be doneunder supervision of Class or Flagstate, and generally re-testing and re-certification has to be carried out.

Movable or hoistable ramps betweendecks are in some cases also cargo-space. A lorry is placed on the ramp,before it is hoisted. In that case, the

Slewing ramp

ramp is cargo-gear, and subject to thenormal cargo-gear inspections andtesting. In that case the ramp needs tobe registered in the cargo-gear book.Wires and locking devices need tobe tested by ship's staff regularly, asper ISM requirements. If this is aramp between a lower-deck and thefreeboard-deck, the ramp is a water-tight closing, and also subject to theregulations for load-line, with theinspections and tests as for weather-tiehtness.

Lloyd's Register of Shipping

Register of Ship's Lifting Appliancesand Cargo Handling Gear

Class Notation of Lif tin'

Lloyd's

First page of cargo gear book

Ship Knowledge - Chapter 9: Cargo gear /lifting appliances 209

11 Load testing equipment.

All equipment intended to be usedin lifting gear needs to be certified.Regulations for lifting equipmentand testing are internationally harmo-nized. This means that material qual-ities are checked, workmanship isjudged and that a load test has to becarried out under the supervision of aregulating body. For ships this is nor-mally the Classification Bureau.

All the items in hoisting gear mustbe covered by a certificate, statingan identification and a test. The loadtest is carried out to guarantee a SafeWorking Load (SWL) or the WorkingLoad Limit (WLL).

A crane as a complete unit is testedby lifting a weight, and carrying outthe normal movements like hoisting,lowering, slewing and topping. Whenthe power to the crane Is interrupted,the brake has to hold the load. Theweight for testing is heavier than theWLL. For the smallest cranes thismeans 25% overweight, for the big-gest cranes it is 5 tons more than theSWL.

Individual small items belonging tothe crane, such as blocks, hooks,shackles, etc. arc normally tested at aload in accordance with 1LO and theClassification:- single sheave blocks at 4 times the

SWL- multi sheave blocks below SWL 25

ton, at 2 x SWL- multi sheave blocks between SWL

25 and 160 ton at (0.933 x SWL) +27 ton

- multi sheave blocks over 160 ton,at 1.1 xSWL

- hooks, shackles, chains, ringsbelow SWL 25 ton at 2 x SWL

- hooks, shackles, chains, ringsabove SWL 25 ton at (1.22 x SWL)+ 20 ton.

Test weights can be steel weights witha known mass; the modern variantis a water bag, which can be filledwith water till the required mass isreached. A certified load cell indicatesdie weight. Water bags are availableup to 35 tons.

Testing the crane using •vatcr ba''s

Testing with water-bags has a maximum.For bigger loadsspecial constructedpontoons are used.

Testing lifeboat davits using water bags

Ship Knowledge — Chapter 9: Cargo gear /lifting appliances 211

1 Overview of Anchor and Mooring Gear

Anchor windlass on general purpose ship with mooring drum and warping head

1. Storage part of the 6. Warping head 13. Chain stopper withmooring drum 7. Chain in the gypsy security device

2. Pulling section of the wheeldrum (working part) 8. Dog clutch

3. Brake band 9. Anchor4. Gearbox 10. Hawse pipe5. Electro hydraulic 11. Spurling pipe

motor 12. Chain locker

14. Guide roller15. Bollard16. Guide roller17. Deck18. Hatch to chain

locker

(see also next page)

Ships' Knowledge - Chapter 10: Anchor and mooring gear

Maindeck

Longitudinal cross-secfion uj

the fore ship

The equipment number can hecalculated with the equation:

(A2/3 + 2HB + 0.LA)

A = displacement (weight of the ship)this term gives the influenceof the displacement and thecurrents on the ship.

HB = width and height, this term whichdetermines the influence of frontalwinds, (m2)

A = the lateral surface of the ship(above the water), whichdetermines the influence of sidewinds, (m2)

2. Anchor Equipment

The purpose of the anchor gear (orground tackle) is to fix the position ofa ship in shallow water by using theseabed. Reasons for doing so can be:- The ship has to wait until a berth

becomes available.- To load or discharge cargo when a

port does not have a berth for theship, either temporarily or perma-nent.

- To help with manoeuvring if theship does not have a bow thrusterand/or no tugboats are available.

- In emergency cases to avoidgrounding.

2.2 Legal demands on theAnchor and Mooring gear.

Each bow-anchor needs to be pro-vided with a certificate, issued byClass, based on type, materials used,weighing, and testing. The same is

applicable to chain-cables. A certi-ficate for the anchor and mooringequipment is only issued after allthe requirements of the ClassificationSociety are met. The original cer-tificate has to be on board. The tablebelow indicates equipment num-bers used to determine the mini-mum weights and dimensions ofthe anchors, chains, ropes, etc. Theequipment number can be found onthe Midship Section drawing.

EQUIPMENTEQUIPMENT LETTER

STOCKLESS BOWERANCHORS STUDLINK CHAINCABLES

WEIGHT PER

ANCHOR DIAMETER

EXCEED-

ING

550

600

660

720

780

840

910

980

1060

1140

1220

1300

1390

1480

1570

NOTEXCEED-

ING

600

660

720

780

840

910

980

1060

1140

1220

1300

1390

1480

1570

1670

P

QR

S

T

UV

wX

Y

zAt

Bf

Ct

Dt

CONV.

ABS DNV GL

NUMBER

OF

ANCHORS KGS.

HHP

KGS.

SPEC. EX.SP.

STEEL STEEL

TOTAL (GRADE (GRADE

LENGTH U2) U3)

METERS MM MM

U16U17

U18

U19

U20

U21

U22

U23

U24

U25

U26

U27

U28

U29

U30

Pqr

s

t

u

V

wX

yz

A

B

C

D

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

1740

1920

2100

2280

2460

2640

2850

3060

3300

3540

3780

4050

4320

4590

4890

130514401575171018451980214022952475265528353040324034453670

440440440467.5467-5467.5495495495522.5522.5522.5550550550

3638404244

5050525456586062

3234363638404244

46464850505254

Ships' Knowledge - Chapter 10: Anchor and mooring gear 215

Poof, anchor (IMP) Type HG "Pool N

Hall anchor (convenUonal anchor)

1. Crown / shackle2. Shank3. Flukes4. Crown pin5. Crown piate6. Anchor chain with swivel

2.3 Anchors

Anchors are the final safety resourceof a ship. From the ancient times ofthe first boats, the men using themhad a stone on some sling to keepthe boat in position. Later devel-opments show combinations withwood, ending in the stock-anchor(fisherman's anchor) with woodenstock. When propulsion or steeringfails, the seafarer has to rely on hisanchoring equipment. It is thereforeof utmost importance that this equip-ment is in good condition. A regularcheck of the condition of the anchoritself, the crown, anchor shackle, thechain cable, windlass, brake bandand anchor securing arrangements isa master's obligation.

In genera!, ships have two bow-anchors and sometimes a stern anchor.There are two bow anchors for safe-ty. Under normal circumstances oneanchor is sufficient, but under severeweather conditions or in strong cur-rent both anchors may be needed.Also, if one anchor fails, the secondanchor is a back-up. A ship is not

allowed to sail from any port whenone anchor has been lost. Tn generalthe Classification Bureau may allowdeparture, under the condition thatreplacement is carried out at the ear-liest opportunity and that the vesseltakes additional tug-assistance leav-ing and entering port.

The stern anchor is used to preventships (coastal-trade liners for exam-ple) from rotating due to the changesin a river-current.

- Anchors can be distinguished as:Conventional anchors

- HHP-anchors (high holding pow-er)

- SHHP-anchors (super high hold-ing power)

Common conventional anchor typesare: Spek, Hall, Union, Baldt.

Spek anchors have the advantage ofbeing fully balanced.

A fully balanced anchor has the fol-lowing advantages:- an anchor recess that completely

envelops the anchor, can be used- the shell cannot be easily damage

during heaving when the anchorflukes leave the water vertically.

Accepted HHP anchors are AC14,Pool and Danforth. CQR and Plow-type anchors are only used on smallcraft. Various copies of acceptedtypes are made all over the world.

The lota! holding force is supplied by the

anchor and (the weight) of the chain

The dashed lines in the drawing show-

that it is not dangerous if a ship floats

away for a certain distance (a ship's

length) from the original anchor-posi-

tion.

Fully balanced anchor means thatwhen the anchor is being weighed,lifted from the seabed, into the hawsepipe, that is comes up with the flukesvertical, by the weight of the head,being a counterweight. Such ananchor never comes foul, i.e. with theflukes pointing into the ship's shell.

The conventional type is still used alot and serves as a standard for newertypes of anchor (see table).

Conventional anchors are always cast.Newer types like Pool, can also con-sist of plates (or other components)that are welded together. If the flukesare hollow, they tend to be moreresistant towards bending forces.

The crown plate ensures that theflukes of the anchor penetrate the seafloor. In certain types of anchor, theflukes prevent the anchor from bury-ing itself too deep in the sea bottom.

The navy uses a specially developedHHP-anchor with an open crownplate (bottom plate). The advantageof this type of anchor is that it digsinto the bottom more rapidly.

HHP-anchor with an open crown plate

216 Ships' Knowledge - Chapter 10: Anchor and mooring gear

Stevin anchors on a deck of an Anchor handling fug

supplier (AHTS)

Hall anchor

Anchor d'hone

AC-14 anchor

Ships' Knowledge — Chapter 10: Anchor and mooring gear

Spek anchor

Poo! TW anchor

Danforth anchor

I!l.

Flipper anchor

111

HHP-anchors are allowed to be 25%lighter in weight because their hold-ing force is twice as strong as that ofa conventional anchor. The SHHP-anchors can be 50% lighter in weight,because their holding force is evenlarger, namely 4 times as large aswith a conventional anchor. However,this type of anchor is not accepted byClass for normal ships and can onlybe used on yachts and special craft.

For Offshore and Dredging specialvery high holding- power anchors arein use, which have to be laid downin position by a tugboat, a so-called'anchor-run boat', and also have to belifted out by the same boat, using aseparate wire attached to the crown ofthe anchor. These anchors are certifiedas Recoverable Mooring System.An example of such an anchor is theFlipper Delta-anchor.

2.4 Anchor chain

The chain runs from the chain locker,through the spurling pipe, via thegypsy wheel of the windlass throughthe hawse pipe, to the anchor. Theanchor chain consists of links withstuds to prevent kinks in the chain(stud-link chain).

The required strength and length ofthe chain can be determined withthe aid of the equipment numbers inthe previous table. This table alsodistinguishes two main types of male-rial-quality, namely U2 and U3. Notincluded in the table are the qualitiesUl, which has become obsolete, andU4, which is an offshore quality.

The anchor chain is composed oflengths (shackles), each with a lengthof 15 fathoms (15 x 1,83 = 27.5meter). The shackles are interconnec-ted by a kenter shackle.

In order to keep track of the outboardchain-length, the paying out and heav-ing in of the anchor can be monitoredby markings near each kenter shackle.The markings can be white paint and/or wire wound around the studs. Thekenter itself is red.

Description of the images below:1. Anchor shank2. Anchor / link

Swivel4. Open link

Enlarged linkKenter shackleCrown shackle

1. Half link2. Locking pin3. Stud

81 mm U3 Cham Quality 1. 3 rd length or'shackle7

2. 6th length or 'shackle'

3. 7th length or 'shackle"

218 Ships' Knowledge - Chapter 10: Anchor and mooring gear

The paid out chain length can alsobe monitored electronically, by sen-sors that carefully register how manytimes the gypsy wheel rotates. Anadvantage of this system is that whenthe anchor is hove in, the winchautomatically slows down when theanchor chain is almost completelyinside and stops completely when theanchor is home.

A D-shackle connects the anchor andthe chain. A swivel is usually fixedon the chain and allows the anchor torotate independently from the chain.The swivel can also be connecteddirectly to the anchor.

A water-spray installation in the hawse pipe

Anchors in pocket

220

2.5 Hawse-Pipes and AnchorPockets

The hawse-pipe is a tube that leadsfrom the shellplating to the forecas-tle deck. A water-spray in the pipecleans the chain during heaving ofthe anchor.During heaving, the flukes of theanchor should be parallel to the ship'sshell. A collar protects the part of theship's shell around the hawse-pipe. Inaddition to this, the plating is extrathick in this area.Anchor pockets or recesses are some-times made in the bow into which theanchors can be completely retracted.

The advantages of the anchor recesses:- the anchors are protected from

direct contact with waves- a loose anchor cannot bang against

the shell (important on passengerliners)

- damage to the shell by floating icecan be prevented.

- prevention of fatigue damage to theanchor itself

- mooring wires do not get fouled

2.6 Chain stopper / Cablestopper

The chain stopper absorbs the pull ofthe chain by diverting it to the hull.The chain stopper's holding forceshould be min. 80% of tensile break-ing strength of the anchor chain.Furthermore, the hawse pipe's resist-ance absorbs 20% and the windlassshould have a holding force of 45%of the minimum break load.

In most types of chain stoppers, thechain runs over a roller, sometimesequipped with a tensioner. The actualstopper mostly is a heavy bar, laidover the flat link, and secured witha strong pin. The securing consistsof a hook onto which both eyes of asteel wire are attached. This wire isput through a link of the chain andtensioned. This securing fixes theanchor in the recess thereby prevent-ing banging of the anchor against theshell.

Cable stoppers are to be divided intoanchor securings for when the vesselis at sea, and for when the vessel is

riding at anchor. When the vessel isat sea, the anchor is held by the brakeband, and a securing wire or prefer-ably a high tensile chain, through thechain cable and attached to a strongpoint on the fo'c'sle deck. The wind-lass should not be engaged.

When riding at anchor the chain forceon big ships is held by a transverse,hingeable bar, a strong back, incor-porated in the guide roller above thehawse pipe secured on top of a flatlink of the anchor chain, so that avertical link cannot pass. The chainforces are then transferred to theship's construction. A wire as anchorsecuring at sea is insufficiently strongand vulnerable to chafing especiallywhen not lashed through a link of thechain under a stud.

Chaw stopper with tensioner

Chain stopper

1. Tensioner2. Cable stopper

3. Chain4. Guard

Ships' Knowledge - Chapter 10: Anchor and mooring gear

Winches on the forecastle and on the

quarter deck of a car ferry

The main shaft is rotating, the warping

end is the only part that is also rotating.

The gypsy wheel and both drums are

disconnected.

2.7 Winches

Anchor winches are used to heave inand pay out the anchors and anchorchains in a controlled way. The samewinch can be used to operate a moor-ing drum. A clutch is used to connect/ disconnect the gypsy wheel or themooring drum to the main shaft. Theanchor can be hove in if the gypsywheel is coupled to the main shaft.

Anchor winches normally are provid-ed with a mooring-drum, via a sepa-rate clutch. The winch turns either thegypsy, or the mooring drum, or both.The main shaft in most cases is hori-zontal, however, in rare cases it canbe vertical, like a capstan.

The winches can be powered by:- electricity; an electric motor rotates

a cogwheel. The advantage of usingan electric motor is that the noise islimited. Especially on passengerliners this is important.

- hydraulic systems. The cogwheelsare driven by a hydraulic motor,which is connected to a hydraulicpump system located below thedeck. Advantages of this system arethat there is no risk of (electrical)sparks and furthermore, the systemis gearless.

- electric-hydraulic. The set of pumpsis incorporated in the winch insteadof below deck. This means thatthere is no need for piping systemsfor the hydraulic oil.

- steam.

Anchor and mooring combined

windlass / mooring winch

1. Main shaft2. Gear box3. Electric motor4. Warping drum5. Drum (storage part)6. Drum (working part)7. Gypsy wheel8. Control lever for the band brake

ClawcluTch out and in

1. Bearing2. Sliding claw3. Fixed claw

Ships' Knowledge - Chapter lth Anchor and mooring gear 221

A rope should never stay on thewarping drum because then the forceexerted by the ship may well exceedthe pulling force of the warpingdrum. The warping drum can absorbequal amounts of pulling force andbrake force; the brake force of thedrums, however, is three times asmuch as the pulling force due to theband brake.

Below:1. Working part2. Storage part3. Warping end

The anchor chain enters the chainlocker via the spurling pipes. Chainlockers are high and narrow, makingthem self-trimming. This means thatthe stacked chain can not fall over inbad weather. The end of the chain,the bitter-end, is connected to anend-connection in the chain focker,with a release possibility outside thelocker. On very large ships, often theconnection is a weak link, to breakwhen the chains runs out accidentally.This way the chain locker and fo'c'sledeck will not be damaged, because aheavy chain, when running, cannotbe stopped.A grating (plate with holes) on thebottom of the chain locker makessure that water, rust and mud can fallthrough, to a space below the chainlocker. This has a separate manholeentrance, for cleaning purposes. A(manual) bilge pump can drain off thewater. In emergencies, the chain canbe released by the bitter-end outsidethe chain locker.Possible types of chain release devic-es (bitter-end connection):- remove the pin out of the last link of

the chain with a hammer. The pin islocated either below deck outsidethe chain locker or on deck, next tothe windlass.

- a weak link in the bitter-endconnection ensures that the chainbreaks loose when the stressbecomes too high. The breakingforce must be less than themaximum holding force of thechain.

- the hand wheel can be used torelease or attach the chain.

Windlass with anchor securing, guide roller and hitter-end connections

Anchor windlass, with on the same shaft as the gipsy a mooring drum and a wharping head

222 Ships' Knowledge - Chapter 10: Anchor and mooring gear

3 Mooring gear

A ship's mooring system, is designedto moor a ship with a standard lay-out, on a standard jetty, with bollardsat regular distances. A ship is there-fore equipped with winches, withwires or ropes on drums (no hands)and with additional ropes, which canbe paid out by hand, and tightenedusing the warping heads.Tankers have, through an internatio-nal standard system of the oil compa-nies, a standardised mooring system.

3.1 Winches

- Dru mA winch drum can be made in twoways: a straight drum, and a drum intwo parts, for tensioning and for stor-age. If the drum is made of one part,it serves both as head (storage) andas drawing and pulling drum. Thesetypes of drums are only suitable forsteel wire and certain synthetics. Ifforce is applied to a synthetic hawser,it may not slip through the layers ofrope below. If this does happen, therope gets foul. Sorting the rope outagain takes a lot of time. If the drumconsists of two parts, then the smallpart is the working drum and the otherpart is the storage part. The tensionin a rope (with a maximum of twolayers) may only be applied on theworking drum.

Suppose that the diameter of the drumis 30 cm, and 5 windings fit next toeach other in two layers, then the pull-ing drum can pull in 10 m. of rope.

)f the MBL (minimum break load) ofthe ropes is 100%, then the holdingcapacity of the drum is 80%, and thepulling force is approximately 1/3 ofthis. This ride applies to all the drumsmentioned.

- Warping HeadThe warping head is used:- to heave in extra ropes, set them up

and fasten them on the bollards.- to move the ship alongside the quay

over short distances. Tf the warpingdrum is used, the gypsy wheels andthe drums must not be coupled tothe main shaft which would engagethe anchor cable.

Foredeck of a tanker

- Self tensioning winchesSelf tensioning winches can beadjusted to maintain a certain holdingforce. If this value is exceeded, thenthe winch automatically adjusts thelength of wire to the new force (toomuch holding force: slacking; too lit-tle holding force: heaving). This sys-tem is frequently used by ships thatload and discharge quickly (containerships and Ro-Ro vessels) or if there isa large tidal range in the port.

Control for the self tensioning winch.

1. Control lever for the winch2. Cooling fan3. Control for the self-tension settin;

1. Warping head2. Drum3. Bollards4. Eyes to connect the stoppers5. Guide roller (fairlead)6. Centre lead7. Lead way8. Head line9. Forward spring

- CapstansThe capstan consists of a warpingdrum with a vertical drive shaft thatis driven either electrically, hydrau-Hcally or elcctro-hydraulically. Thecapstan is usually placed on the aft-ship and, if the ship is very long,on the sides. If the capstan is com-bined with a gypsy wheel, it can beused to control the (stern) anchor i.e.a vertical anchor windlass.

Capstan

Ships' Knowledge - Chapter 10: Anchor and mooring gear 223

3.2 Mooring Gear Auxiliaries

One or more winches can be placedon the fore-ship, depending on thesize of the ship and the preference ofthe owner. As shown in the picture,the warping drum, bollard and fair-lead are preferably positioned in astraight line.

Rollers, chocks, guide pulleys and bol-lards.A rope is guided from the shore via apanama chock, through the bulwarkto a bollard or winch. The pana-ma chock must be able to withstandlarge forces, because the direction ofthe rope changes inside the panamachock. The panama chock must becurved to prevent wear of the rope.

Roller fairleads can also be made ofvertical and horizontal rollers. Theirfunction is the same as the panamachock. However, the roller fairleadcauses less wear to the ropes.

Panama chock and roller fairlead

Bollard

1. Guide roller2. Nose3. Stopper eye

Panama chock

Rollers on deck serve to change thedirection of the ropes. Both the rollerfairleads and the guide pulleys areable to withstand a maximum of 32tons of pulling force depending onthe ship's size.

Bollards transfer the mooring for-ces to the ship's hull. The outsidesof the bollards have a nose, whichprevents the first few windings of therope from slipping upwards. Aboveor below this, there is an eye to whichthe rope stopper can be attached. Thestopper absorbs the forces in the ropetemporarily so that the rope can betaken off the warping drum and pla-ced on the bollard. The double bollardis provided with two ridges to preventthe rope from moving. A stopper lughas been fitted as rope stopper.

For the non-moving parts like panamachocks, the allowed force is 1/5 of themaximum static force that this part isable to sustain.

3.3 Emergency towing systemfor tankers

In recent years a number of environ-mental disasters involving tankershas shown how difficult it is to makea connection with a ship in distress.The IMO demands that tankers with acarrying capacity of more than 20,000tons have an emergency towing con-nection forward and aft. Forward thisis a stopper, which holds a standardchain, when pulled through from out-side to inside (the same stopper as thetanker uses when mooring on a singlebuoy). Aft it has to be a preparedsystem. This means a rope or wirein the water, with a messenger buoy,ready to be picked up and fastened bya tugboat, and that can be deployedby one man.

of an emergency towing system

4. Rigging

4.1 Cables and ropes

GeneralCables are used on ships:a. to moor the ship and maintain its

position at a jetty, and for towing.b. for the cargo gearc. in fishing and dredging

The cables mentioned in a. are usu-ally made of rope and called hawsersor lines. The cables used in b. and c.generally are steel cables. The lat-ter are described in more detail inthe section "description of commoncables".

Rope can be made from either naturalor synthetic fibres. Nowadays, with afew exceptions, most ropes are madefrom synthetic fibres. The syntheticfibres are manufactured from mineraloil products that have undergone achemical process.The rotation of the threads is oppo-site to the strands, preventing therope to unlay. Below some (of themany) types of ropes are categorisedaccording to the way they have beenstranded (plaited).

Some rope-types have a mantle. Thepurpose of the mantle is to keep thestrands in the core together. This hasthe advantage that the strands in thecore can be arranged in a parallelfashion: this gives the maximum ten-sile strength. The mantie itself rarelycontributes to the tensile strength.The threads in the core need not beresistant to wear as the mantle provi-des the wear resistance. Therefore itis important that the wear resistanceof the mantle is higher than the wearresistance of the core. A mantle keepsthe cable round and compact, whichreduces sensitivity to wear.

224 Ships' Knowledge - Chapter 10: Anchor and mooring gear

• I_E : - EQUIPMENT FOR SELF-PROPELLED OCEAN GOING VESSELS

_: ; : ;:_.:pment iir.ks the so-called equipment number to the composition, sizes and quality of anchors, chains

L- ; - : • : - -3 ropes on ocean-going vessels. The equipment number is normally calculated in the design stage o! the

- ••-. ~- s table is accepted and used by all main classification societies.

-

: .- -.

• ~ - T 7 9 0

• • G LINES

264028503060330035403780405043204590

5250

19802140229524752655283530403240344536703940

467,5495495495522,5522.5522,5550550

550

577,5

505052545658606264

40424446464850505254

•

1901902002002002C0200200220220220

•

520560600645SSO

7407858358909401025

. . •

EACH

170170130180180180180180190190

200215230

2502702353G5325325335

Some core-lypes that can be presentin core-with-a-mantle-cables:- braided- stranded- parallel strands- parallel threads

The characteristics that are importantwhen using or buying rope:

- MBF(MiriimumBreakForce).Thisis the minimum force in kN needed(o break the rope.

- Elasticity.- Density. The larger the density, the

heavier the rope. It is important toknow whether the density is smalleror larger than 1,000 t/m3, in otherwords: docs the rope sink or float.

- UV-re si stance. After several years,sunlight can degrade a rope.

- Wear resistance.- Construction. The number of strands

and the way that the rope is plaited,the presence of a mantle.

Water-absorption, expressed as aweight percentage of the rope.Backlash or snapback. This indi-cates if, in case of breaking, the ropefalls "dead" on the deck, or snapsback. Rubber has a large backlash.Creep limit. This is the lengtheningof the cable in lime under constanttension.Chemical durability. This indicateshow well the rope can resist (theaction of) chemicals.A knot or splice in a cable can re-duce the strength by as much as50%.TCLL-value (thousand cycle loadlevel). This is the cyclic load level asa percentage and as an absolutevalue of the maximum load underwet conditions. This is the load atwhich a cable will break when it hasundergone the load a 1000 times.For example, if the TCLL-value of a100 ton/f cable is 50%, or 50 lon/f,then the cable will break if subjectedto a 50 ton/f load a 1000 times,

- 4x2-strand braided

- Braided

1. Fibre2. Thread3. Rope yarn4. Strand5. 3-Strand rope

3.

2.

- 1.

The drawing above shows how a cope

can be composed

Ships' Knowledge ~ Chapter 10: Anchor and mooring gear 225

4.2 Description of commoncables

a. High-grade cablesb. Polyamidec. Polyesterd. Polyolefmese. Natural ropef. Steel cables

a. High-grade cablesAramide and High Module Poly-Ethylene (I1MPE) are high-gradecables. Kevlar, Twaron and Technoraare aramide brand names andDyneema and Spectra are HMPE-brands. The difference between thetwo types is that aramide has a lower(thus better) creep, but aramide sinkswhereas HMPE floats. High-gradecables are relatively new productsand strengthwise (hey are comparableto steel cable of the same diameter.However, the price is 5 -10 timeshigher than steel cables.Advantages over steel cables are:- light weight- easy to handle- non-conductive- small backlash

GRIPOLENE3 M OCTOPLY(Poiyprop)

PHILLYSTRAISTPSP(Polyester)

*t» *£. t±

These graphs show that the elasticity

of polypropylene is greater than that of

polyester. At maximum load, the poly-

propylene stretches by 20% and the

polyester by 12%.

1"•uc

O)

6?

—

100

90

80

70

60

50

40

30

20

70

0

i~® TCLL valuesj—J (8 strand plaited):

polypropylenepolyamide

1 sleet (laid)polyester

—1 aramid

52%55%60%70%70%

Dyneema >1OO%

A official end of lestdetermine residual sire

8 eno of Dynesma leslinciesi<Ju,ir slrencjin I 3 0 ° I

i 2 j i 5 6 7 S

cycles Cx 1000J •

g i h

This graph shows the TCLL -values for a

number of rope-types

All relying on one bollard

b. PolyamidePolyamide is better known as nylon.Polyamide ropes sink (density >1,000 kg/m3) and absorb water afterbeing a few days in contact withwater. The absorption of water adds4% to the rope's weight. This canreduce the MBF by 20%. Polyamideshave a large elasticity. A consequenceof this is the backlash when parting.The rope sweeps over the deck andendangers the people present there.Certain types of polyamides can bespliced and re-used after the rope hassnapped. However, especially cheapropes are disposed of when they snap,and a new rope is ordered.

c. PolyesterPolyesters are very resistant to wearand very durable, both in wet anddry conditions. In mechanical char-acte-ristics polyester resemblesnylon, except that it is more resist-ant to wear. Furthermore, polyesteris more expensive. The density ofnylon (1.14) is lower than of polyes-ter (1.38) and the energy absorbingcapacity of nylon is higher, makingit more suitable to absorb large forcevariations. For this reason, nylon isoften used as a stretcher, to protectsteel cables from large shock loads.

d. PolyolefinesThere are two types of polyolefmerope, namely "High PerformanceRopes" and "Standard Ropes". Thedifference between these two liesnot just in the MBF, but also inthe qualities like UV-sensitivity andwear resistance, which increase thedurability of the rope. High perform-ance ropes can also be found with amantle.

Polypropylene, polyethylene andmixtures of these compounds arepolyolefmes. Many high performanceropes like the Tipo-eight are alsopolyolefmes. Poiyprop is a polyole-fine-rope that is often used.

Its advantages are:- h floats- it is relatively cheap

The disadvantages are:- not very resistant to wear- low TCLL-value- short lifespan

Towine wire with a stretcher

226 Ships' Knowledge — Chapter 10: Anchor and mooring gear

6X36WS + IWRC I960 N/MM:

QUALITY

TENSILE STRENGTH

TOTAL NUMBER OF STRANDS

TOTAL NUMBER OF WIRES

TYPE OF CORE

NUMBER OF OUTER WIRES

NUMBER OF OUTER STRANDS

galvanised

1960 N/dim'

'3265

IWRC

84

6

TYPE OF LAYDIRECTION OF LAY

GREASING

ON REQUEST

>re, general purpose me

• regular lay• right hand

•yes

• [ang fay

• ungalvanised

• dry

• left hand lay

7X19

QUALITY

TENSILE STRENGTH

TOTAL NUMBER OF STRANDS

TOTAL NUMBER OF WIRES

TYPE OF CORE

NUMBER OF OUTER WIRES

NUMBER OF OUTER STRANDS

• galvanised

• 1770 N/mrrr

•7

•133•WSC

•36• 6

TYPE OF LAY

DIRECTION OF LAY

GREA5ING

ON REQUEST

• regular lay• right hand lay

• no

• ungalvanised

• greased

• left hand lay

Standard wire rope, mainly used in small diameters on winches

6X19 + FC

QUALITY

TENSILE STRENGTH

TOTAL NUMBER OF STRANDS

TOTAL NUMBER OF WIRES

TYPE OF CORE

NUMBER OF OUTER WIRES

NUMBER OF OUTER STRANDS

• galvanised

-1770 N/mm!

• 6

•114

• fibre

•12

• 6

TYPE OF LAY

DIRECTION OF LAY

GREASING

ON REQUEST

• regular lay

* right hand lay

* no

• ungalvanised

• greased

• left hand lay

Wire rope with JiHre cart

NominalDiameter

(mm)

910

11

12

NominalDiameter

(mm)

10

12

14

NominalDiameter

(mm)

10

12

14

MBF{kN)

44,751,069,884,4

100,0

MBF(kN)

3 7 , 6

5 8 , 7

84,6115

• / • • - • ' •

- • '-1

19X7

QUALITY

TENSILE STRENGTH

TOTAL NUMBER OF STRAND5

TOTAL NUMBER OF WIRES

TYPE OF CORE

NUMBER OF OUTER WIRES

NUMBER OF OUTER STRANDS

• galvanised

• 1960 N/mm1

• 1 9

•'33•WSC

•72• 12

TYPE OF LAY

DIRECTION OF LAY

GREASING

ON REQUEST

• regular lay

- right hand lay

• yes

• !ang lay

• ungaivanised

• dry

• left hand lay

Rotation resistant wire, used as hoisting rope

NominalDiameter

(mm)

1012

14

MBF

41,164,392,6

126

Ships' Knowledge — Chapter 10: Anchor and mooring gear 111

e. Natural ropeNatural fibre rope has been replacedon most ships by synthetic ropes. Ingeneral, the only type of natural ropestill in use on ships is manilla rope.Manilla rope is manufactured fromthe abaca fibre that is present in theleafstalks of the manilla plant.

Although the resistance to chemicalsand UV-light is good, the MBF isabout 2-8 times smaller than the MBFof synthetic ropes.

Manilla on ships is used for the pilotladder, boat ropes of lifeboats andhelicopter-nets.The reason for this is:- manilla is less sensitive to fire and

burns slower.- manilla is rough and hairy, therefore

it does not slip easily, especiallywhen wet.

f. Steel wire ropesSteel cables or wire ropes haveadvantages and disadvantages. Theyare strong, cheap, have little elonga-tion under tension, have a high wearresistance, but they are heavy, andthey rust.

They are used where the circumstanc-es allow or demand it, for instance forhoisting and luffing wires in cranes,mooring wires for tankers and bulk-carriers, anchor wires in dredging andoffshore, towing wires for fishing andtugboats. In case of fire they are notimmediately destroyed.

Steel wires are available in numer-ous constructions, depending on therequirements.

There are basically two steel tensilestrength grades: 1770 N/mm2 and1960 N/mm2. Cables are made of anumber of strands, turned in a longspiral around a core. The strands con-sist of a number of usually galvanisedwires.

An eye. is spliced into a rope

For flexible wire, the core is rope,and when flexibility is not necessary,the core is steel. A steel core makesa stronger wire. Rope core whenoiled, lubricates the wire, but allowsdeformation under stress and ben-ding. Steel wires need maintenance.Regularly greasing is essential.

The strength is optimal when dif-ferent sizes of wires are used in onestrand, so that the space betweenthe wires is optimally filled. This isdone in cables made according to theWarrington-Scale (WS), the sectionis then optimally filled with steel andthe permeability for water is less.Like ordinary rope, there are righthand and left hand laid cables.Analogue to synthetic rope, the direc-tion of rotation of strands and wiresis mostly opposite, called "ordinarylay".Other constructions are Cross-lay,Lang's Lay, Non-Rotating, etc.When wires and strands have thesame direction of rotation, there isthe possibility of turning open. Thesetypes of wires are only to be usedwhere the ends, both sides, are fixed,like as mast-stays, and bridge sus-pensions. Non-Rotating cables arealways cross-lay.

During the fabrication process thewires in the strands can be pre-formedinto the helical form which they get inthe finished state, to reduce internalstresses in the rope. That preventsunspinning, and a broken wire doesnot stick out. The construction ofsteel wire is given in a formula.

For example: Galvanised, Diam. 36mm, 6 x 36 ws - iwrc.It means 36 mm diameter, 6 strandswith each 36 galvanised wires, warXrington seal (ws), and an independent \wire rope core (irwc). Warrington seal/is a means of constructing a wire ropefrom wires with different diameter, sothat water ingress is limited.

Steel wire is mostly galvanised, butuntreated steel wires also exists, andfor special purposes stainless steelis used.

4.3 Various parts

Various rigging parts are explained onthese pages:- end connections- shackles- turnbuckles or bottle screws- thimbles- sockets.

A Talurit clamp is an aluminium bush,which is pressed under high pressureat the position where normally a splicewould be, replacing the time-consum-ing splicing. The pressing makes theoriginal oval shaped bush into a cylin-drical clamp, with the strength of thereplaced splice. A talurit clamp is notto be used in bending situations.

Life-boa! hoisted with 19x7 steel wires

228 Ships' Knowledge - Chapter 10: Anchor and mooring gear

1.

End links

- End connectionsEnd connections are needed to con-nect a wire to something else. Oftenshackles are used for the connection.

- Safety hookA safety hook is shown in the figurebelow. It prevents the load from fall-ing out of the hook, even if the load isresting. The hook can only be openedby pressing the safety pin.

Safety hook

1. Brand or type marking2. Chain size (chain 7/8 of an inch)3. Class, grade 8 (high-grade steel)4. Safety pin5. Spring

- ThimblesA thimble is a ring inside a splicedeye, to enlarge the radius of the wirein a splice, where this comes arounde.g. the pin of a shackle, and thus pro-tecting the wire and is usually madeof galvanised steel. Its function is toprotect the eye of a cable from wearand damage.

1. Gaff socket with rolledconnection

2. Cast spelter socket3. Rolled eye terminal4. Thimbled taiurit eye5. Spliced eye with thimble6. Thimbled flamish eye, swaged.7. Wedge socket (not allowed in

hoisting).

- ShacklesShackles can be divided into Bow-shackles and D-shackles. The lighttypes can be closed with a screwedbolt, the heavy types with a bolt anda nut. These can both come with orwithout a locking pin. Their generalpurpose is to connect certain parts toeach other or to the ship. The SafeWorking Load (SWL) can vary from0.5 ton up to 1000 tons and more.

a'I-High tensile steel shackles. To obtain

this high strength, after forging'

shackles are subjected io heat treat/net

(Quenched and Tempered)

1. Bow shackle with safety pin2. Bow shackle with screw-bolt3. D-shackle with safety bolt and nut4. D-shackle with screw-bolt

- TurnbucklesTurnbuckles are used to connect andtension steel wires or lashing bars. Thebottle screw consists of two screws,one with a left screw thread, and theother with a right screw thread. Theseare connected by a house.

Tumbuckle

1. Gaff2. House3. Thread, one left-, one righthanded4. Eye

Thimble

Ships' Knowledge - Chapter 10: Anchor and mooring gear 229

This is the correct way of applying the wire clamps to a cable (all U-bolts on the non-

pulling part of the cable)

- Steel wire clampsA steel wire clamp can be used toquickly make an eye in a cable.The U-boIt of the clamps should beattached to the part of the cable thatis free from pulling forces. The boltsshould be attached to the "dead" part,where no pulling forces are acting onthe cable.Steel wire clamps may not be usedfor lifting purposes, with an exceptionfor guys and keg sockets to make surethat the cable does not slip.

(Compulsory) wire clamp on a kegsockel

- SlingsWhen lifting objects, often slings areneeded. A sling is a wire with at eachend an eye spliced or clamped. Theeye can be long or short, all depend-ing on the purpose. When the item tobe lifted has lugs welded on it, a slingwith talurits and shackles can be used.In other cases long eyes are moreversatile. These eyes can be talurit-clamped, but better is a flamish eye,with a swaged clamp. A flamish eyeis a very simple but very strong splice.From a wire with an even number ofstrands, the strands are turned looseover the double length

of the eye. Over that length the wireis split in two sets of strands. Half thenumber of strands are laid in a bendin one direction, the other half intothe other direction, meeting togetherin opposite direction, forming an eye.The strands are turned into each other,forming a wire. Where the ends cometogether a conical steel bush is placedon forehand, which is pressed togeth-er, preventing the wire ends fromjumping loose.

The strongest sling is the grommet.A wire is turned around a circularrod, say six times the circumference,forming a cable, after which the rodis pulled out, and the wires, acting asstrands, remain, turned around them-selves. The ends are put awray insidethe rope. A grommet is very flexibleand very strong. The heaviest grom-mets, for offshore lifts, reach a calcu-lated MBL of 7500 tons. Testing isnot possible, but the MBL of the indi-vidual wires is a known Figure, foundfrom a breaking test of a sample.

Cable-laid slings are very heavycables, constructed from steel cableswith varying diameters, to fill theavailable diameter as solid as possi-ble. Eyes are spliced at each end. Thebuilt-up rope diameter can go as highas 350 mm. The calculated MBL cango as high as 4000 tons.

- Fabric SlingsModern slings are fabric. Woven frommodern fibres very light and strongband-type slings are made, with onedisadvantage: they can easily be dam-aged by sharp items. But strength-weight ratios can be extremely high,when modern fibres as Dyneema,Aramide, or other carbons are used.Very flexible and soft slings aremade from Dyneema in long straightthreads, not laid, inside a canvastubing. This type of sling is veryfriendly to machined or polished steelobjects.

Cable-laid slim Spreader wills hook, SWL 6000 Ions

230 Ships' Knowledge — Chapter 10: Anchor and mooring gear

» -

4.4 Forces and stresses

- Some definitionsSafe Working Load (SWL) or WorkingLoad Limit (WLL) is the maximumacceptable load on an item (shackle,hook, wire, derrick, crane, etc.).

Minimum Breaking Load (MBL)is the guaranteed minimum load atwhich an item, when tested to destruc-tion as a sample for a large number ofidentical items, will fail. So, on aver-age, most items will fail at a higherload. The load-stretch diagram belowshows that the tested chain actuallyfailed at a higher load than the MBL.The diagram also shows that proofloading by the manufacturer is doneto 2.5 times the safe working load.For a re-certification test, the proofload will be 2 times the SWL.Figures normally used for the ratioWLL/MBL (or SWL/MBL) are:For chains: 1 : 4For steel wires and shackles: 1 : 5For ropes: 1:6 or 1 : 7

SWL

Load/stretch diagram of a grade 8 chain

- Forces in wiresThe figure on the right shows the forc-es in a wire when a weight of 1000 Nis lifted, and how the force in a ropeor wire increases as a function of theangle between the components. Whenthat angle exceeds 90° the increase isexcessive. Between 120° and 150" theforces run up to 1950 N. The angle istherefore not allowed to exceed 120°.The material used for the wire doesnot influence the forces.

Heavy-duty bow shackles ready for testing

Blocks with rams horns of heavy cargo gear (400 tons SWL)

For heavy or large loads spreaders are met

Ships' Knowledge — Chapter 10: Anchor and mooring gear 231

SHIP KNOWLEDGECovering Ship Design, Construction

and Operation

Shipwise

The shape of a ship

The building of a shi

Hi'1""

Page 24

Page 48

•

ppliam

Cargo gear / lifting appliances

Page 192

Anchor and mooring gear

Engine room

Page 212

Page 232

Propulsion and steering

I installation

QUESTIONS:

www.dokmar.com

1. Ship resistance

The power required to move a ship through the water depends on the propul-sive efficiency and on the total resistance of the ship. The resistance is a com-plex function of displacement, shape and speed.

The various components of resistancecan be divided as follows:

a. Frictional resistanceThe friction between the water andthe ship's shell is the cause of thistype of resistance. The water in theboundary layer is accelerated by theship's speed, dragged by the molec-ular friction. This boundary layeris thicker, and the resistance higherwhen the shell is fouled.The frictional resistance is the small-est directly after delivery of the ship.During the ship's lifetime, the rough-ness of the hull normally increases,due to paint-layers covering olderpaint-layers, damage, corrosion, etc.This results in a gradual drop in speedand efficiency.

boundary layer

wake

The wake of the .ship

b. Pressure (form) resistanceThe ship's momentum pushes thewater aside at the bow and as a result,the pressure of the water increases.This increase in pressure will alsotake place aft. The pressure will dropwhere the boundary layer is released.

c. Wave resistanceThis is a result of wave-systems alongthe hull that originate from the differ-ences in pressure.On certain ships the use of a bulb atthe bow can significantly decreasethe wave-making resistance. Thebulb generates its own wave-system,which is designed to interfere nega-tively with the ship's wave-system.The two wave-systems then neutral-ize each other.

d. Added resistance in wavesThis type of resistance is caused bythe pitching, heaving and rolling ofthe ship.

e. Air resistanceThis depends on the vertical areaabove the waterline, which varieswith the draught. Resistance compo-nents as mentioned in 'd' and 'e' arevariable, depen-ding on wave direc-tion and wind direction as experi-enced by the ship.

Supplier without a bulb

Containet •ship with

wBm

• - - * .

a bulb

Trailering hopper suction dredger wit-

hout a bulb

Ship Knowledge — Chapter 12: Propulsion and steering gear

The propulsion system

N.B. With regard to frictional resist-ance, the newest hull paint, the so-called non-stick paint, silicon-based,which does not allow fouling to holdonto the paint, keeps the frictionalresistance constant through the life-time of the paint. This paint can alsobe applied on the propeller, resultingin a smooth hull and propeller, and inthis way keeping the hull efficiencyconstant. Speed does not drop withtime passing and the fuel consump-tion of the engine remains constant. Ttis, however, a very expensive system,only paying off on large, fast ships.

Looking at oil tankers, bulk carriersand container ships it can be veryclearly seen that the bulb preventsan increase in pressure near the bow.The improved streamline of the ship'sunderwater body reduces a wave-system around the ship. In suppliersand hopper suction dredgers, there isa large wave-system present aroundthe ship.

Tf the rate of flow of water (or air)is higher, then the pressure will belower compared to the pressure inparts of the water where the rate offlow is lower. So in waves, water in atrough has a higher speed than waterin a wave top. See also chapter 4'design' and Bernoulli's law.

2. Propulsion

2.1 Propellers

In order for a ship to obtain a certainconstant speed, a force needs to beexerted on the ship. The magnitude ofthis force depends on the ship's resist-ance applicable to that particular

speed. If the ship is moving throughthe water at a constant speed the forceexerted on the ship equals the resist-ance of the ship. The force that movesthe ship can come from an outsidesource like a towing line or the wind,but generally the force is generatedby a power source on the ship itself(engine). The propulsion system usu-ally consists of an engine or turbine,reduction gearing, if applicable, pro-peller shaft and propeller.The efficiency of a propeller takes animportant place in the design processof the propulsion, because its effi-ciency and the ship's fuel consump-tion are directly related.

The efficiency depends on the flowfield of the propeller, which dependson:

- the shape of the ship's underwaterbody

- the power delivered to thepropeller

- the number of blades- rotations per minute- the maximum possible propeller

diameter- the blade surface area and

smoothness of the blade- the ship's speed.

For a given ship-speed and power, ifthe diameter of the propeller increas-es, the rotations per minute decrease;this generally increases the efficiencyand thus reduces the fuel consump-tion.

Briefly said, the diameter of the pro-peller should be as large as possibleso that a maximum amount of wake,caused by the ship's hull, is used.

1 Engine2. Engine shaft and flexible coupling3. Reduction gear-box; this reduces

the number of revolutions of theengine (e.g. 1000 rpm) to anacceptable rotation rate of thepropeller (e.g. 200 rpm) Thereduction is 5:1.

4. Shaft generator; this supplies theship with electricity when theengine is running

5. Stem tube with bearing6. Propeller shaft7. Propeller

The choice for high efficiency witha large-diameter propeller and a lownumber of revolutions per minute iseasily justifiable, but requires a sig-nificant investment.The propeller pitch is the distance inthe direction parallel to the propel-ler shaft that a point on the propellercovers in one revolution in a solidsubstance. Similar to a point on acorkscrew turning in a cork. Whenrotating in a fluid a propeller willhave a (small) slip. Rotations orrevolutions per minute are abbre-viated as 'rpm'.

RPM and the number of blades haveinfluence on vibrations on board andthe resonance frequency of the ship.Most small single-screw ships usea 4-bladed propeller, while 5-bIad-ed propellers are more common onbigger ships, where a large power(20,000 kW) is necessary.However, today, more and more shipsuse the 5-bladed version, even whenless power is needed, to reduce vibra-tion. 3-Bladed propellers are usedon twin-screw vessels and on shipswith a high number of revolutions perminute and a low power (700 rpm.600 kW).

Ship Knowledge - Chapter 12: Propulsion and steering gear 261

Fixed right-handed propeller on a tanker (deadweight 30,000 tons). Propeller being

polished to reduce roughness, for less rotation friction and less fuel consumption.

reduces the efficiency, but it is veryfavourable for the ability to stop theship and for the reverse propulsionforce.Blade 4: Is used in nozzles.Blade 5: Is also used in nozzles if thenoise and vibration levels have to belimited to a minimum.

2.1.2 Pressure and suction sidesof the propeller

The approach velocity of the wateris a result of the ship's movementthrough the water. If the ship haszero speed, this Ve = 0. The approachvelocity can be calculated by sub-tracting the wake velocity from theship's speed. The speed of rotation ofthe propeller and the approach veloc-ity result in the speed (V).This V hits the propeller blade at acertain angle:a = 9°-l()1' at service speed

The speed of the incoming water cre-ates an under-pressure on the forwardside of the blade (suction side) andan over-pressure on the aft side of theblade (pressure side). The propellerblade acts similar to a wing profile.Propellers are usually viewed fromaft, therefore the pressure side is alsocalled 'the face1 and the suction side'the back'.

Different types of blades attached to

a hub. This combination can never he

used for actual propulsion

2.1.1 The shape of the blades

Every propeller is designed individu-ally, based on the specific demandsset for this propeller. As a result ofthis, there is a large variety in shapesof blades.

The remarks tor each shape of bladeapply to both the fixed and the con-trollable pitch propellers.

Blade I: is hardly used anymore.Blade 2: Is used when there are strictdemands regarding noise and vibra-tions on board.Blade 3: Is used when the rpm ishigh and, consequently, the diameteris small.A large blade surface area somewhat

A drawing of the upper fixed propeller

blade of a right-handed propeller seen

from above

1. Cross-section of propellerblade

2. Propeller shaft3. Suction side4. Pressure side5. Leading edge6. Trailing edge

Ve = approach velocity =ship's speed - wake speed

U = speed of rotation of thepropeller

03*r - angular velocity * radiusV - resulting speedA - liftW = dragP = resulting forceS = propulsion force (thrust)T = shaft moment

P ,'

Forces an the upper propeller blade

when the propeller is rotating and the.

ship is moving

262 Ship Knowledge -~ Chapter 12: Propulsion and steering gear

Cavitation damage on a propeller blade

on a CPP due to missing plug.

2.1.3 Cavitation

As described above, the propellerpressure of a rotating propeller is notjust the result of the water-pressureon the pressure side, but also of theunder-pressure on the other side ofthe propeller. Propellers that rotaterapidly can create an under-pressurethat is so low that water-vapour bub-bles are being formed on the suctionside of the propeller. These gas-bub-bles implode again when the pressurerises, and they do this continuouslyon the same spot. When this is locatedon the blade surface, it causes damageto the suction side of the blade. Thisis called cavitation. Severe cavitationresults in:- increase of blade roughness

a reduction in propulsion force- wear of the blades- vibrations that bend the blades- noise in the ship- high cost to rectify.A properly working propeller oftenshows light cavitation at the bladeedges which is not harmful.

2.1.4 The influence of the propeller'sturning direction on the ship'smanoeuvring.

Propellers can be divided into right-handed and left-handed propellers.Ships with a fixed-pitch propellerusually have a right-handed version.A right-handed propeller can be rec-ognised in the following way. Standaft of the propeller, look at the face

Cavitation damage on a rudder blade

and hold on to the top blade withboth hands. If the right-hand sideof the blade is furthest away, it is aright-handed propeller. If the ship isgoing ahead, a right-handed propelleris rotating clockwise.When a propeller is rotating, the shiphas the tendency to turn to a particu-lar side, even if the rudder is in themid-ships position and there are noadditional forces acting on the ship.This effect is called the propellereffect or wheel effect (see the sectionon manoeuvring).

Propellers with adjustable blades(controllable-pitch propellers, abbre-viated CPP) are often left-handed.When the propeller is in the asternmode, turning anti-clockwise, theeffect of the propeller is the sameas in a right-handed propeller goingastern, also turning anti-clockwise.Going ahead they have the sameeffect as a left-handed propeller. Thisis done in order not to confuse pilots.When going astern, the efficiency ofthe propeller can drop below 50%of the ahead efficiency, dependingon the type of blade and the type ofpropeller.

2.1,5 Alternative propeller designsApart from the blade form and thenumber of blades, many alternativedesigns have been tried and tested.Propellers with tip plates have beeninvented around 1850, but have onlyrecently been rediscovered. Tip platesare attached to the blade tips.The plates prevent the water from

flowing too fast from the pressureareas to the suction areas of the pro-peller, resulting in vortices. Tip platesincrease the efficiency by reducingthe energy loss. The improved hydro-dynamics of the water-flow caused bythe tip-plate propellers also contributeto the reduction of vibrations andnoise of ihe propeller.Another development is the contra-rotating propeller. This system con-sists of two propellers placed onebehind the other, which are driven bymeans of concentric shafts (inner andouter shafts) with opposite directionsof rotation. Both the number of bladesand the diameters differ.

Propeller with tip plates

Model test of a contra-rotating propeller

Propeller

right-handedright-handedleft-handedleft-handed

Turningdirection

rightleft

rightleft

Sailingdirection

aheadasternasternahead

Direct propellereffect

Aftstarboard

portstarboard

port

Foreport

starboardport

starboard

Indirect propellereffect

Aft

portstarboard

Fore

starboardport

Wheel effect of propellers

Ship Knowledge - Chapter 12: Propulsion and steering gear 263

The principle this system is basedon, is that normally water is broughtinto rotation by the propeller, whichresults into a loss of energy. Addinga second propeller rotating m theopposite direction reduces the loss ofenergy. The combined propellers canreduce the fuel-consumption by 15%.It stands to reason that this configura-tion is very vulnerable.

2.2 Fixed pitch propellers

The propeller blades of a fixed pitchpropeller have a fixed position. As aconsequence the direction of rotationof the propeller has to change if theship stops or must go astern. This isrealised with a reversing clutch or areversible engine. A reversing clutch,and therefore also the fixed pitchpropeller, is economical in ships upto 1250 kW.

The diameter of fixed pitch propellersvaries between 25 cm and 12 metres.The choice of a fixed or a control-lable-pitch propeller (CPP) dependson, among other things, the need for ashaft generator and the need for easymanoeuvring qualities.

Installation of a fixed right-handed pro-

peller with shaft

Advantages of a fixed propeller over acontrollable-pitch propeller are:- they are less vulnerable to damage- the propeller does not revolve

when berthing, so it imposes lessdanger to mooring boats and thereis less risk of ropes gettingentangled in the propeller.

Fixed right-handed propeller of a container vessel (GT 80942} with a reversible engi-

ne. The propeller weighs 95 tons, has 6 blades and a diameter of 8.95m.

Disadvantage of the fixed propellerover a CPP are:- in adverse weather, the propeller

may turn with too many rpm, thiscan hamper propulsion.

- fixed propellers also have a limitedrange of rpm for manoeuvring, andso with their power range.

2.3 Controllable-pitchpropellers (adjustable-pitch propellers)

The blades of this type of propellercan be turned around the blade-axis,thereby changing the propeller pitch.These propellers are internally com-plicated. The mechanism that adjuststhe propeller pitch is located in theboss of the propeller. It is activated

from the engine room, and remote-ly controlled from the bridge by ahydraulic cylinder. The most strik-ing feature of the controllable-pitchpropeller is that it only rotates inone direction, making the reversingclutch or the reversible engine unnec-essary. Unlike the fixed-pitch propel-ler, the controllable- pitch propelleris an integrated part of the propulsionsystem. This makes it possible thatpower and necessary propulsive for-ces can all be controlled by simplychanging the positions of the blades.The figure next page shows cross-sections of a propeller blade and theforces that act on that part of a rotat-ing propeller blade.On the left are the cross-sections andforces when the ship is going ahead.

264 Ship Knowledge - Chapter 12: Propulsion and steering gear

All the vectors point backwards, theship is going forward.Now the blades are rotated towardsthe zero-position. This means that thepropulsive forces above and beloware equal in magnitude, but oppositein direction. The nett propulsive forceis zero, but the propeller still absorbsa large amount of energy that is con-verted to turbulence of the wake. Togo astern, the blades are rotated evenfurther, resulting in a forward propul-sive force.

Safety precautions1. The position of the blades can be

changed manually without loss ofpropulsive force.

2. If the hydraulic system fails, theblades can be locked in the aheadposition.

Advantages of a controllable-pitch pro-peller:- It can propel the ship at all speeds,

even at very low speed withoutstopping the engine.

- It can change quickly from aheadto astern and vice versa.

- Improved efficiency on ships withchanging power demand likefishing craft and tugs.

- It can easily be combined with ashaft generator (see on the right).

- It can stop a ship with maximumpower.

- In case of propeller damage,changing a blade is sometimespossible afloat depending on theship's type and trim possibilities.

Neutral Backwards

Drawings of a .single propeller blade and its cross-sections. The pictures show the

controllable pitch propeller; the upper blade is the blade in the drawings.

n

The shaft generator can supply theelectrical power on a ship as longas the main engine keeps running.With controllable pitch propellersthe generator frequency can bekept constant because the rpm ofthe engine remains constant. Theengine drives the shaft generatorvia the reduction gearbox.

When a shaft generator is fitted whichalso can work as an electric motor,with power supply from the auxiliarydiesel-generators, the electric motorcan produce propulsion power, i.e. incase of major main-engine problemsfor emergency propulsion.

Class does not require this systemand/or the maximum speed it canobtain. The system is sometimes usedon small ships.

A shaft generator can produce elec-tric power also during manoeuvring,which is an economical advantage.

Disadvantage:CPP systems are vulnerable due to thehydraulic components and many seal-ing rings. A damaged sealing ring canresult in oil pollution.

1. Propeller blade (tip speed 31,4 m/s)2. Boss or hub3. Watertight / oil tight seal4. Stern frame5. Propeller shaft, 240 rpm6. Stern tube7. Intermediate shaft (to engine shaft)8. Reduction gear box (1:2.5)9. Mechanically driven lubricating

oilpump10. Collar shaft (thrust)11. Actuating motor, coupled to a12. mechanism of bars that serves the

blades

Drawing of a controllable pitch pro-

peller with propeller shaft. The pitch

adjustment of the blades is done via oil

pressure though the hollow shaft. The

figures apply to a propeller with a diam-

eter of 2.5 metres.

Ship Knowledge — Chapter 12: Propulsion and steering gear 265

2.4 Nozzles

The purpose of a nozzle is to increasethe propulsive force. This increaseresults from the fact thai the propel-ler forces water to flow through thenozzle. This water-flow has a highervelocity in the nozzle than the wateroutside and the resulting pressuregradient then creates the additionalpropulsive force. The efficiency ofthe nozzle is at a maximum when thewater can pass unobstructed. Thisis why the top of the nozzle shouldalways be as free as possible in rela-tion to the aft body.Not only does a nozzle increase thepropulsive force, it also reduces noiseand vibration levels.

Controllable pilch pwpeUer m afixed'nozzle

Furthermore, the incoming water-flowis more homogeneous in a nozzle,minimising local pressure differencesthat are responsible for cavitation andvibrations.The combination of a propeller in anozzle is often called a ducted pro-peller. In principle, the nozzle can beused on every type of vessel excepton very fast ships like high-speedferries where they have no increas-ing effect on the propulsive force.If the frictional resistance (causedby the nozzle) becomes larger thanthe increase in propulsive force, thenozzle is not effective. Nozzles areoften used on inland vessels, hoppersuction dredgers, tugs, fishing vesselsand suppliers. The advantages anddisadvantages of fixed- or control-lable-pitch propellers are the samefor propellers in a nozzle and propel-lers without one. For shallow-draughtships the same thrust can be deliveredwith a smaller system diameter.

Nozzles are fitted as:- fixed versions- nozzle-rudder-propellers: the

whole system including propellercan rotate around a vertical axis,360°

- nozzle rudders: Propeller fixed,nozzle can turn as a rudder

- (35° a 40° max.).

One particular type of fixed nozzleis the wing-or Schneekluth nozzle.Only applied for ships with a fullbody, which lack wake velocity in theupper half of the propeller circle. Thisnozzle is fitted forward of the upperpart of the propeller against the stern-frame, in two halves, with differentaxis-angles in relation to baseline andcenterline. The nozzle works anti-rotating and brings water to the top-

Fixed propeller in a nozzle rudd

Two rudder propellers in a nozzle, with

360" rotation.The lift force, created by the nnder-pres-

sure on the outside of the nozzle

halve of the propeller circle, wherethe velocity of the incoming water ina full ship is low., in spite of its mod-est dimensions, this still increases thepropulsive force if the speed exceeds12-18 knots.

2.5 Rudder propellersThe main characteristic of rudderpropellers is their ability to rotatelike a rudder, if unobstructed, thefull 360". Rudder propellers are alsocalled 'a7imuthing thrusters' or 'Z-drives'. To achieve this freedom ofrotation, a right-angle underwater-gearbox is driven by a vertical powershaft. This vertical shaft is centered inthe rudder stock.A gear driven by a pinion is attachedto the top of the rudder stock. Thismakes the unlimited rotation pos-sible.

Nowadays, rudder propellers canhave a power up to 7500 kW. Thereare several versions of rudder propel-lers, namely:1. Afixed unit assembled in an assem-

bly box. It can be equipped with adepth-adjustment system. Whenthe ship is empty, the propellercan be lowered in order to get suf-ficient propulsive force efficientlywithout the need for ballast.

2. Deck units. The diesel-drive unitsare placed on deck; the rudder pro-peller is attached to the back of thedrive unit. These types can alsohave a depth-adjustment system.

3. A retractable unit. It can be with-drawn entirely into the ship and isonly lowered when the ship is atsea. When in top position, the pro-pellers can then be part of a tunnelthruster and are then called 'retract-able thrusters'. Not used for mainpropulsion.

4. Bow thrusters or stern thrusters.Also called tunnel thrusters. Theyare based on a transverse propellerand a right-angle underwater gear-box. These are used exclusively toposition the ship with a starboardor port side thrust. Wlien the ship'sspeed is above 6 knots, their influ-ence is negligible.

Types 1 and 2 function as main pro-pulsion units, while type 3 is an aux-iliary propulsion unit. Type 4 is for

266 Ship Knowledge — Chapter 12: Propulsion and steering gear

Tug boat equipped with two azimuth ing thrusters and a bow thruster

Cross-section

of a rudder

propeller

low-speed manoeuvring.The most important advantage of arudder propeller is its ability to giveoptimal thrust in each rudder posi-tion.With exception of the tunnel thruster,all rudder propellers can steer theship 360°, thereby giving the shipexcel-Ient manoeuvrability. Today,modern electronic equipment for sat-ellite navigation can be employed tocouple the rudder propellers to thedynamic positioning system (DP-sys-tem). This can keep a ship in a pre-determined position irrespective ofthe influences of currents, waves andwind. Retractable thrusters are oftenused for this purpose. When the shiphas arrived at its position, the azimuththrusters are lowered and the shipswitches to DP.

Schematic presen-

tation of the com-

mand path from

bridge control

to the rudder

propeller

MtKUCT J*(!0 C0KI1IW.

1. Driveshaft from engine, with gears2. Vertical driveshaft3. Propcllorshaft with gears4. Kort-Nozzle5. Rotation point in ships construction6. Controllable Pitch Propeller7. Hydraulic lines to CPP8. Oil-Filled gearbox

Ship Knowledge — Chapter 12: Propulsion and steering gear 267

Other advantages of the rudder pro-peller are the very compact engineroom (because there is no need for along propeller shaft); this results inlower installation costs as comparedto a conventional propeller.

Rudder propeller installations areoften used on passenger ships, cableships, floating cranes, suppliers,dredgers, barges etc.

The joy stick on the control panel is aso-called 'one-man operated joy sticksystem1, which controls the entire Aeriai} holograph of a supplier shows the optimal manoeuvring capabilities of a md-propulsion system and the rudders. ckr propeller in combination with a how thruster

Good manoeuvrability of electrical rudder

propellers The turning circle of a ship with

electrical rudder propellers as con/pared to

the sister ship thai uses separate rudders

and propellers

Control pane!

1. Joystick2. Control automatic pilot3. Read-out of daughter-

compass Aerial photograph of a ferry showing thriftier wash

268 Ship Knowledge - Chapter 12; Propulsion and steering gear

Drive via rudder propeller••

Conventional diesef-direct

Direct-drive engine to propeller

Conventional dieset-electnc

Diesel-electric drive

2.6 Electrical rudder propeller

(Brand names: Azipod, Dolphin.Mermaid, SSP)

The difference between the rudderpropeller of paragraph 1.5 and theelectric rudder propeller or poddedpropulsor is that the latter has itspropulsion engine located outside theship hull. The electrical engine withadjustable rpm is placed in a pod thatis attached to the bottom of the ship.Every pod has a propeller attached toit, driven by the electric motor insidethe pod. There are two main types:a fixed pod with a rudder or a 3600rotating pod without a rudder. Bothtypes can either push or pull. The pro-peller is then located at the back or atthe front of the pod, respectively.The electric rudder propeller does notrequire gearboxes, clutches, propellershafts and rudders.

A cruise ship with 2 electrical rudder propellers that can rotate 360".

Wheelhousecontrols

Generatorsets

Automation

Mainswitchboards

transformersPropulsionmotors

Frequencyconverters

The diesel generators can be placedanywhere on the ship, as long as thereis space available, unlike the shipswith a mechanical drive where theengines are connected to the propellerby a long shaft and other parts.

This makes this propulsion systema compact system that simplifies thedesign and construction of the ship ascompared to conventional propulsionsystems. Although the system wasoriginally developed for icebreakers,it is now in use on suppliers, cruiseships, tankers, ferries and ships witha DP-system.

Arrangement of a diesel'-electric pro-

pulsion-system using electrical azipods.

with the power-supply by dieselgenera-

tors.

Advantages are:1. It is possible to separate the power

source and the propulsion system.2. It can combine the power supply

of the auxiliaries and the propul-sion system.

3. Few vibrations and little noise.4. Excellent manoeuvring

capabilities.5. Lower fuel-costs.

Ship Knowledge - Chapter 12: Propulsion and steering gear 269

4:

Large pod Small pod

1. Propellor2. Bearing and shaft labyrinth (seal)3. Hydraulic steering unit with

toothed rim4. Collector rings for the

transmission of data and power5. Ship's bottom6. Electro-motor7. Bearing (radial and thrust)

2.7 Propeller shafting

The stem tube contains the bearingsin which the propeller shaft is rotat-ing. Usually, there are two bearings,the one most aft being the longer.Close to this aft bearing is the sealingsystem that keeps the seawater out ofthe stern tube and the oil inside.

The front side of the stern tube iswelded to the aft peak bulkhead,the aft part to the stem or propellerpost. After welding, the tube ends aremachined in situ, in accordance withthe alignment of the shafting in rela-tion to the main engine.The sealing system must be able towithstand extreme conditions like:- circumferential speeds up to 5 m/s- water-pressure up to 3 bar- axial and radial propeller shaft

displacements of approximately 1millimetre

- the ship's vibration- 7000 hours of rotation-time per

year, during 5 years.

Shaft alignment can be complex. Insmall ships it usually is a straight line,but in large ships with heavy shaftingsystems, the alignment is calculatedand bored in accordance with the flex-ible line of the installed and coupledshafting.

The lubricating agent between the pro-peller shaft and the shafting can be:

a. waterb. oil

a. Water as a lubricantWhen water is the lubricant for thepropeller shaft, the bearings are madeof rubber or synthetics. Water lubri-cation can be achieved with bothopen and closed systems. In the opensystem, there must be flow, usuallygenerated by a pump, through thestem bush from forward to aft, thuspreventing seawater from entering theship. In the closed system, the water is

pumped round the shaft, from fore toaft. This means that the water insidethe stern tube always has a slightover-pressure as compared to the out-side seawater. The Navy prefers waterlubrication because seals, in use withoil lubrication are vulnerable to pres-sure shocks, from, for instance, depthcharges. The seals arc then blowninwards, and the sealing propertiesare lost.In some countries water lubricationis compulsory for local shipping toprotect the environment.

Bearing: that part of a machinein which a rotating part rests

1. Propellor2. Tailshaft3. Shaftbearing (Rubber, lignum-

vitae, tufnol)4. Sterntube

Water lubrication tailshaft system

270 Ship Knowledge - Chapter 12: Propulsion and steering gear

1.2.•]

4.5.6.7.8.9.

SternRudderPropel leu capPropellerSkegAft stern-tube sealsShaftingForward stern-tube sealsIntermediate shaft bearlnss

10. Propeller shaft

b. Oil Lubricated ShaftingApproximately 70% of all ships useoil as a lubricant for the propellershaft. In that case, the bearing is usu-ally made of white-metal, and some-times of synthetic material. White-metal is superior.

The disadvantage of synthetic mate-rials is that they poorly transmit thefrictional heat between bearing andshaft. The oil-filled tube, with theshaft in centre, has sophisticated sealsat both sides, to keep the oil in thetube, and the water (aft) out.

The sealing system at the backsideconsists of a sealing case and mostlythree sealing rings. These sealingrings are made of synthetic rubber.The space between the two bearingsis completely filled with lubricant.The aft seal prevents oil from leakingto the outside.

Stern with a controllable pitch propeller.

The stern tube is brought into the stem.

Ship Knowledge — Chapter 12: Propulsion and steering gear 111

10.

5.11

3.

Stern bearing and seals

outer seal inner seal

5. 3.

Outer and inner seals

3.4.

'• 7.Closed system with lubricating oil

1. Propeller boss2. Propeller shaft3. Chrome-steel liner4. Seawater seal5. Oil seal6. Stern frame7. Aft bearing

8. Stern tube9. Clamped ring10. Stern tube bearing11. Fastening at stern tube12. Fastening at stern tube, where

meeting the aftpeak bulkhead

The lubricant pressure is only slightlyhigher than [he water pressure. So ifseawater should somehow enter thetwo water-seals, the higher lubricantpressure prevents it from reachingthe propeller shaft. Seawater couldseriously damage the unprotectedpropeller shaft. The higher lubricantpressure is maintained by a smallpressure tank (A), which is placed afew metres above the load line.

Tank A is part of the main lubricatingsystem, tank B contains lubricatingoil for the seawater sealing rings.The oil in the main lubricating sys-tem is self-circulating due to the factthat warmer oil rises upwards. TankC is both the drainage tank and thestorage tank. If oil leakage shouldsomehow occur, it is usually limitedto small amounts. If not, drydockingis necessary. A chrome steel bush isfitted around both the propellershaftaft near the propeller and forward inway of the aft peak bulkhead. Thespace between the bush and the tubecontains lubricant.

The aft chrome steel liner is attachedto the propeller boss with bolts, thechrome-steel liner of the forward bushis attached to the propeller shaft via aclamped ring. Around both bushes,are non-rotating housings, bolted tothe stern tube, and inside the sealingrings are fitted.

During dry-docking, the position ofthe shaft, relative to the stem tube,has to be measured, to ensure thatthe shaft is more or less, within afew tenths of a mm, in the verticalsame position as when built. Thisis indicative of the wear of the aftbearing. A special depth gauge, theso-called 'poker gauge', is present onboard and is designed to measure theposition of the shaft. Normally thereis no sagging.

272 Ship Knowledge - Chapter 12: Propulsion and steering gear

Forward propulsion Zero speed Reve-s ":

2.8 Water-jet propulsion

Water-jet propulsion is based onthe reaction force of a high-velocitywater-jet at the stern of a (light dis-placement) ship, blown in aft direc-tion.

The main principles of the water-jetare:- the impeller (propeller) draws in

seawater through an inlet, usuallyin the (flat) bottom

- the same impeller boosts the waterpressure for the water flow

- the water is pushed through a noz-zle

- the nozzle converts the water pres-sure into a high-speed jet

- the acceleration of the water-flowgenerates a thrust force that givesthe ship its speed

- for sailing astern, the water-flowexiting from the nozzle can bereversed in the forward directionwith reversing plate(s).

The water-jet has an electronic steer-ing system. This means that theorders from the bridge are immedi-ately processed by micro-processors.

The same principle as for a waterjet is applied in an aircraft jetengine, but here air is the mediuminstead of water. The principle isbased on Newton's law F = m x a,where F is the force in Newton, mthe mass of the water and a is theacceleration of the water.

Steering port Steering starboard

Ship driven by waterjet propulsion

Waterjet with reversing bucket down

Full speed ahead

This makes it possible for the water-jet, engine and gearbox to be control-led directly from the bridge.

Along with yachts, many passengerand ear ferries, rescue and patrolboats are nowadays equipped withwater-jets. In 1998 the first cargo-ships were built with water-jet pro-pulsion. The maximum speed ofmodem water-jets lies around 70-75knots (approximately 135 km/h). Thefastest ferries can reach a speed ofapproximately 50 knots.

The advantages of water-jets are:- no rotating parts under water. This

makes it safe to manoeuvre inshallow waters.

- less resistance, especially at high-er speeds, because there are no fit-tings (e.g. the rudder)

- not protruding below the ship.- excellent manoeuvring capabili-

ties. For instance, a jet-poweredship can navigate sideways.

- less sensitive to cavitation thanpropellers on fast ships.

- high propulsion efficiencies of upto 72%.

Ship Knowledge — Chapter 12: Propulsion and steering gear 2 "3

Cross-section of water-jet (Wartsild Propulsion Jets)

3. Stabilisers

Rolling of a (fast) ship during sailingcan be reduced by using stabilisingfins, by as much as 80 - 90%. Thevelocity of the water stream along theships-side can be used to reduce therolling, by installing such fins, witha configuration of a flap-rudder, ina sideway direction protruding fromthe bilgestrake, and which can rotatearound a shaft. The maximal rotation-angle is up and down approximately25°. When having an angle with thewater-direction, they produce liftingforces, similar to a rudder upwardsor downwards. When a ship is rol-ling, water tlows along the sides in anondulating way.The fin is operated such, that at anymoment, a reactionforce is produced,upward or downward, contrary to theacceleration of the ship side. Theangle of attack of the fin profile isadjusted to the flow direction.

upward or downward, depending onrolling speed and -time, and shipspeed. The fin is oscilated by ahydraulic piston or vane-type motor.The angle of attack, the rotation speedand -period are dictated by a compu-ter, receiving signals from sensors inthe rotating shaft, comparing the pro-duced force with the required force,and from a gyro. The working forceis maximised, but cavitation is pre-vented. They are in use on passen-gerships and yachts, for the comfortof the people on board, and on ro-roships and containerships to reducethe acceleration forces on the cargo.Some heavy cargo ships use stabili-sers for the same reason. A decreasein fuel consumption is claimed also.Normal installation comprises onefin on each side, but 4 fins are alsoinstalled. The fins can be retracted,in order not to stick out from the shipside when moored.

1. Bridge control unit2. Main control unit3. Pump motor starter4. Local control unit5. Fin6. Stabiliser machinery

unit7. Oil header tank8. Hydraulic power unit

1. Inlet2. Driving shaft3. Impeller4. Hydraulic steering cylinder5. Jetavator, steering part6. Hydraulic cylinder that alters the

direction of the propulsion7. Reversing plate, can be moved

by the cylinder8. Reverse section9. Sealing box to prevent water

from entering the ship10.Combined guide and thrust

bearing11 .Nozzle

274 Ship Knowledge - Chapter 12: Propulsion and steering gear

4. Rudders

The function of a rudder is to devel-op a transverse steering force on theaft side of a ship, using the reactionforce of the water flowing along theship (and the rudder). The rudderis usually located in the water-flowaft of the propeller. Depending onthe type of ship, the area of the rud-der ranges from 1.5% to 10% ofthe underwater lateral area (length xdraught).

The rudder should be shaped in sucha way that the water-flow can bedeviated as effectively as possible, incombination with minimal resistance.

Giving the horizontal cross-sectionof the rudder a wing-profile satis-fies these two demands. In fact, therudder is a vertical wing, on whicha lifting force is generated by thewater-flow in the same way as anaeroplane wing, propeller blades anda nozzle get a lift. This is also knownas the rudder force. The drag shouldbe as low as possible. The liftingforce gives a turning moment aroundthe ship's centre of displacement: thisis what rotates the ship.

For slow-speed manoeuvring the rud-der should cover the propeller diam-eter as much as possible in order tomake optimal use of the water-flowr

of the propeller.

The force that the steering enginemust supply depends on the torque(force x distance) that must be appliedto rotate the rudder.

This force is the resultant (N) in thedrawing. The total moment dependson:- the position of the rudder stock

compared to the point of applica-tion of Nthe distance between the rudderstock and the leading edge of therudder (balance).

When the rudder is free-hanging(spade type), the rudder stock mustalso be able to absorb the total bend-ing forces of the rudder.

Selling in the heel of a flap rudder

A controllable pitch propeller and a flap

rudder of a multi-purpose vessel. The

underside of the rudder stock can be

seen in the rudder.

N

Horizontal cross-section

of the. rudder blade of a

balance rudder

Conical connection between the rudder

stock and the rudder blade

Depending on the rudder-profile, therudder stock is located at 25 - 40%abaft the leading edge of the rudder.

Most rudders are hollow and empty.The inside is stiffened with hori-zon-tal and vertical profiles.

The next sections will only describefree-hanging rudders. In smaller ves-sels (like fishing boats), however,rudders are still supported in spe-cially constructed heels, or in ease ofmariner rudders at half height (biggerships)

Rudder stock moment: N

V = velocity of water- N —flow

L = lift + =D = drag

— resultant force— under-pressitre

over-pressure

distance betweenthe rudder-stock and thepoint ofapplication ofN

Ship Knowledge - Chapter 12: Propulsion and steering gear 275

Top view

Construction of part of the lower stern

of a container feeder

1. Transom2. Steering flat3. Aft perpendicular = rudder axle4. Rudder5. Rudder trunk6. Space for the rudder stock7. Ice-protection8. Rudder dome (deadwood)9. Stern frame10. Wash bulkhead on centre line11. Stern frame centre12. Centre line propeller shaft13. Side girder14. Floor plate

Side view of the ship s centre line

Frame at aft

perpendicuki}

(frame 0/

Side girder

in stem

276 Ship Knowledge - Chapter 12: Propulsion and steering gear

The drawings and photos will give anidea of how rudders are supported.

The most common rudder-types are:1. spade rudder2. flap rudder3. mariner rudder4. fish-tail rudder

4.1 Spade rudder

In terms of construction, the spaderudder is very simple because it hasno supports. For this reason it is avery cheap rudder and it is widelyapplied, from yachts to fast ferriesand tankers. The rudder usually beco-mes narrower from top to bottom, toreduce the bending moment in therudder shaft.

A spade rudder on a reefer, freely sus-

pended from the rudder dome

4.2 The Flap rudder

The flap rudder has a hinged flap atthe back of the rudder blade. This flapis moved mechanically by the flapguide at the top of the rudder in sucha way that the flap's turning angle istwice as large as the turning angle ofthe main rudder blade. The steeringmethods of the flap differ per typeof flap rudder. When the maximumrudder angle is 45°, the flap has amaximum angle of 90° with respectto the ship. In this rudder position itis possible that 40% of the ship's pro-pulsive force is directed sideways. Incombination with a bow thruster sucha ship can navigate transversely.

A flap rudder under a large cargo ferry

I

- JI

\ ! ;\ i i

3.

4

1

i f

Ji of Q

OM

!

\ ^10.

rE-

r—ii

y-9.

1.2.

3.4.5.6.

7.8.9.10.

vai

Rudder bladeRudder-stock in ruddertrunkFlapHinge lineSteering engineSteering enginefoundationGland and bearingRudder domeSteadiment bearingFlap actuator

itages of flap rudders arc:

]1111

Flap rudder- extra manoeuvrability (that is, if

the main rudder blade is as largeas the spade rudder)

- course corrections can be perfor-med with smaller rudder angles.This means that the ship

- loses less speed and therefore con-sumes less fuel.

Disadvantages are:- the price- vulnerability- the larger rudder forces require the

rudder stock to be bigger.

Rudder Blade

Rudder stock

Pivot

Flap

Water flow when rhe 'ifi'm is turned

Current flows at maximum rudder angle

Ship Knowledge - Chapter 12: Propulsion and steering gear 277

4. 3 The Manner rudder

The Mariner rudder is used on largeships like container ships, bulk carri-ers, tankers and passenger liners. Therudder horn is integrated in the ship'sconstruction and the mariner rud-der is attached to the stern post withthe ability to rotate. This results in arobust rudder. Disadvantages of thisconstruction arc that there is a largerrisk of cavitation at the suspensionpoints and that the cast constructionis more expensive.

actuator -

rudder trunk

cone block — -

I stock

rudder blade -

pintle blank-

C onstmction

of a mariner

rudder

4.4 Fishtail rudder

The fishtail rudder has been devel-oped for ships with a slow speed,less than 14 knots. The after edge ofthe rudder blade is provided with afriction increase, to give extra dragto the water around the rudder. Thisimproves the manoeuvring abilities.

'Stratus' in drydock

Removal of complete rudder, weight

approximately 120 ions

Fitting of pintles to new bushings

Alignment of rudder and stock in shop

Flow acceleration delays stali Stabilising forces

STREAMLINEDMID BODY

FISHTAILTRAILINGEDGE

Top view of a fish tail rudder

278 Ship Knowledge — Chapter 12: Propulsion and steering gear

Double-acting cylinders in a rum stee-

ring gear of a small vessel

5. Steering gear

5.1 General

When on the bridge it is decided toalter the course, the automatic pilot orthe helm is used to activate the steer-ing engine, which, in turn, rotates therudder-slock and the rudder. The rud-der carrier supports the rudder-stockand the rudder. The rudder carrieralso functions as a bearing around therudder-stock, and it seals the ruddertrunk to prevent seawater from enter-ing the ship by a gland.

SOLAS demands that every steeringengine should be equipped with 2 setsof pumps with separated power sup-ply, and, consequently; also 2 servosets, serving the hydraulic pumps.Both the ram and the rotary-vanesteering engines operate by hydraulicpower.Both types of steering gear are equal-ly common in shipping. The magni-tude of the steering or rudder momentis expressed in kNm (kilo-Newton-metre). In general the greatest ruddermoment occurs at 30°-35°.

5.2 Ram steering gear

In ram steering gear, the rudder-stockis rotated by a tiller that, in its turn,is controlled by rams. A ram consistsof a cylinder and a piston, the pistonbeing moved by hydraulic pressure.The tiller and the rudder-stock areoften linked by a conical connection.

1. Rudder stock2. Tiller3. Ram (piston + cylinder)4. Hydraulic lines5. Electro-motor6. Protection of coupling between

e-motor and hydraulic powerpack

7. Pump in tank filled with oil(power pack)

Ram steering gear can have 1 ram, 2rams or 4 rams. If, in the case of oneor two rams the cylinders are double-acting, the steering engine can stilloperate through one of the cylinderswhen the other one fails. A 4-ramsystem can be split in two and twofor the same reason. This is a require-ment of SOLAS.

Ram steering gear of a large, ship

Ship Knowledge - Chapter 12: Propulsion and •steering gear 279

5.3 Rotary-vane steering gear

A rotary-vane steering engine con-sists of a fixed casing, with insidethe casing a rotor to which wings areattached. The casing is provided withtwo similar fixed wings as are on therotor. This arrangement divides thehouse into four chambers, two high-pressure and two low-pressure ones.A valve block directs hydraulic oilat high pressure into the chamberssimultaneously, pushing/rotating therotor and subsequently the rudder. Ifthe rudder is rotated to the other side,the high-pressure chambers becomelow-pressure chambers and viceversa. The rudder-stock is locatedin the centre of the rotor; the rotor ispressed onto the conical section ofthe rudder stock. The wings and thefixed division blocks are providedwith spring-loaded plates which arethe seals between the high- and low-pressure oil chambers.

Advantages of a rotary-vane steeringgear engine over a ram-steering engineare:- it takes up less space- it is easier to build in

it has an integrated bearing- it has a constant rudder moment.Disadvantage:- it is quite complicated to repair it.

_ • • _ . :

e ©

Rotery vane:1.2.3.

4.5.6.

Rudder stockRotor with wingsFixed division blockslinesChambers (filled withElectric motorHydraulic pump

with oil

oil)

Below:

1. Rudder2. Rotary-vane steering gear with

valve-block3. Electric motor with main hydrau-

lic pump4. Power units (to supply the hydrau-

lic power to operate the valves inthe vaive-block)

5. Hydraulic oil tank6. Emergency manoeuvring console7. Starterboxes electric motors8. Bulkhead between engineroom

and steering gear room9. Bottom10. Entrance from engineroom11. Hydraulic oil lines for manoeu

ring and cross connections

1

280 Ship Knowledge - Chapter 12: Propulsion and steering gear

totally dissolved, and the substrate isat the surface, fouling starts. The totalnecessary layer thickness, can be cal-culated from the polishing rate andthe ship's service speed. For classesof ships each with their own speedcategory, different polishing rates aredeveloped, to achieve a taylor-madeanti-fouling. Containerships with aspeed of 25 knots need another typeof anti-fouling than the dredger with5 knots or the bulkcarrier with 15knots. The thickness of the layer anti-fouling decides the working time.To enable overcoating in drydock,it is important that this layer is stillpresent. If not, so-called "polishedthrough", the substrate, usually anepoxy with an adhesion coat of anepoxy/vinyl mixture, is becoming toohard, (and possibly fouled), and pro-vides insufficient anchoring for thenew paint.

Self-polishing anti-fouling creates,due to the polishing effect, a smoothsurface. This, in itself is an advan-tage, as it keeps drag at a constant

•rI /

Skin 1— ^ " J Q 1Primer

Binding agent I

Antifouling

Seawater1

Freshly applied After exposure to seawater

Self-polishing antifouling

level, and so the friction-resistance.

- Hard Anti-fouling.This anti-fouling consists of a matrix-type binder mixed with biocidc. Whenthe ship is in the water, moving or not,the biocide is leaching out, and killingthe larvae of the marine-growth.When the biocide is not leachinganymore, the fouling starts. Normallythis process goes on for two to threeyears, whereafter another coat of anti-fouling needs to be applied. Throughthe years there is a huge build-up ofpaint, and a growing roughness.

- Non-Stick Paint - Fouling ReleasePaint

A new development (2006) is a fin-ishing underwater paint, so smooth,that fouling, when it has settled, startsto drop off when the ship's-speedexceeds 5 knots.

At 15 knots it is all gone.The paint is based on a silicon elas-tomere, and is a two- or three-compo-nent paint, depending on the supplier,it should not be called anti-fouling,but a fouling release coat. Whenundamage, theoretically an unlimitedlifetme.Not only ship's hulls are painted withthis kind of paint, also the propellers,as they also tend to get fouled. Thepropeller smoothness is as importantas the hull smoothness: the revolu-tions times of the area of the propelleris a figure of similar magnitude as theunderwater hull area times the ship'sspeed.

The above paint system is proven tobe very cost-effective on fast ships,such as the large containerships, navyships, and fast ferries. With this typeof anti-fouling, the newbuilding con-dition of the hull (or even better) canbe maintained throughout the ship'slife, whereas ships with conventionalanti-fouling through the years slowlybuild up the hull roughness resultingin higher frictional resistance with thedisadvantages as listed above.

- Hybrid SystemsBetween the various principles, thereare also mix-forms.Biocides are heavily under pressure.Tin containing anti-foulings werebanned through IMO some years ago.In future copper will probably go thesame way.

5.5 Economy

Decisions about application of expen-sive paint systems are mostly takendepending on the answer to thequestion who is paying for the fuel.Companies using their own ships intheir own trade, such as large con-tainerships and passengerships, paytheir own fuel. Tankers and bulkcar-riers, when in voyage charters, also.However, the latter ships often dotheir work in time-charters, and thenthe charterer is paying the fuel.

6 Cathodic protection

To understand how cathodic protec-tion works, it is necessary to look inmore detail into the corrosion proc-ess. In this undesired chemical effect,the material can react with differentchemicals in its surroun-dings. Thereactions can be divided into:

- chemical reactions- electro-chemical reactions

These reactions take place exclu-sively at the surface of the metal. Itis possible that microscopic pits areformed by corrosion on the metal'ssurface. The corrosion can also occurin existing cracks.

Antifouling at the end of its life and worn out. Time for repainting. The .spraying pat-

kirn on the skin is still visible. The outermost layer of antifouling is still partly visible

on the overlap. In between it has disappeared completely.

Ship Knowledge - Chapter 14: Materials and maintenance 319

6.1 Chemical reactions

In almost all chemical reactions, thereis a charge transfer between the reac-tants. If this exchange of charge is alocal effect, then the reaction is calleda chemical reaction, and the resultingcorrosion chemical corrosion.

An example of this is the reactionbetween bare steel and oxygen fromthe air. A thin oxide layer rapidly cov-ering the metal, is formed at the sur-face. All metals form such an oxidelayer. The characteristics of this first(dry) layer are of great importanceto the further course of the corrosionprocess, and to the adhesion of thepaint layer.

If water comes into contact with theiron oxide, the compounds react togive the product iron hydroxide(rust). The rust is very porous, andtherefore oxidation continues.

The first oxide layer of stainless mate-rials is not affected by water. Betweenthe metal and the oxide layer a lackof oxygen arises which is the reasonthat the oxide layer cannot developany further.

6.2 Electro-chemical reactions

Many compounds have the tendencyto dissolve charged particles (ions)into water. Ions can move freely inwater. Compounds that always behavein this way are acids, alkalines, solu-ble salts, metals and some gases.A consequence of the ion-mobilityis that chemical reactions and theincidental electrical current are not

Water

Positively chargedmetal-ions

y^ hydrogen-bubbles

o

necessary local, they can stretch outover a much larger area. These elec-tro-chemical reac-tions do not justcome to a halt.Every metal in contact with waterhas the tendency to generate posi-tive ions. This makes the water morepositive and the metal more negative.If a metal is less noble, it will have astronger tendency to generate theseions and thus become more negative.Alternatively, if the metal is morenoble, then it will have a weaker ten-dency to generate positive ions andwill thus be less negative.

In general:gold is more noble than copper

- copper is more noble than tin- tin is more noble than iron- iron is more noble than zinc- zinc is more noble than alumini-

um.

6.3 Sacrificial element (galvaniccorrosion)

When two different metals are in con-tact with each other and with water(even a small amount), then the lessnoble metal will have a lower elec-trical potential than the more noblemetal. This potential difference andthe contact between the metals gener-ates an electric current between thetwo metals, running from the preciousto the less noble metal.

The continuous flow of current to theless noble metal causes it to generatemore ions that dissolve into the water.This way the metal slowly disappearsinto the water. This dissolving ofmetal ions is called an anodic reac-tion and the metal that is dissolving iscalled the anode.

Electro-chemical corrosion can alsotake place if a metal is not composedhomogeneously. Objects in seawaterthat are made of brass (an alloy ofzinc and copper) are very sensitiveto this; the zinc dissolves leaving aporous copper behind. This is calledde-alloying. If there is no interven-tion, then all the anodic material(zinc) will dissolve until all of it iscompletely dissolved.

ANODE e-

Al

AL

CATK

A!

OxidationAluminium Steel

[-'

DC power supply

Galvanic corrosionZINC STEEL

320 Ship Knowledge - Chapter 14: Materials and maintenance

Electro-chemical reactions on shipscan occur in the following places:

- between the propeller and the sur-rounding steel

- between copper-containing parts(e.g. heat-ex changers) and thesteel parts of a piping system.

- between aluminium parts and thesteel parts of the ship.

Electro-chemical corrosion mainlyoccurs at places where the paint isdamaged, for example by soft contactwith a muddy river bottom (Missis-sippi), ice, after contact with debrisin the water alongside a jetty, and thenormal wear through mooring anddeparture, tugs that come alongsideetc. Turbulence, speed of the waterand higher temperatures of the waterand salinity increase the corrodingprocess.

Eliminating the corrosion current canprevent electro-chemical corrosion.This goal can be achieved in severalways:

- Insulating the metal on the waterside by painting it. This preventsthe metal from contact With theoxygen and the electrolyte. If thepaint-layer stays intact, this works.As soon as the layer is damaged,the corrosion begins.

- Reversing the current by usinga sacrificial anode of a very basemetal

- Reversing the current by creatingan opposite potential, (ICCP sys-tem:Tmpressed Current CorrosionProtection).

6.4 Sacrificial anodes

Cathodic protection using sacrificialanodes is called passive cathodic pro-lection. Blocks of zinc and/or alu-minium are connected to the ship bywelding of cast-in steel strips, in dif-ferent places. These anodes have sucha low potential that they "suck" thecurrent out of the ship's exposed steel,faster than currents can enter the skinvia the copper-containing parts. Theprotection works by the wastage ofthe sacrificial anodes as they are lessnoble, so as long as there is anodematerial present the anodes work. If

the paint-layer below the waterlincis damaged, there will be an electriccurrent from the water into the metal.If the damage is extensive, then theanodes will dissolve faster. Whenthe anodes have been dissolved, theother metals (ship's steel) will startto dissolve.

Sacrificial anodes have the follow-ing:Advantage:- low investment costsDisadvantages:

the limited life-span of the anodes;1 to 5 years and difficult to predict

- floating ice, irregularly dissolvingand other damaging factors candiminish the protection quite unex-pectedly. This can lead to damag-ing of the steel.

Sacrificial anodes on the propeller nozzle

Reference electrode of impressed current

svstem seen from inside the hull

- there is a chance of overprotection,especially when the anodes havejust been applied. This can damagethe paint-systems.

6.5 Impressed current

In the impressed current cathodic pro-tection system (ICCP), a large posi-tive current is applied to the hull andpassed through the adjacent water. Asa result, current flows into the ship'ssteel whereas it has a direct unprotect-ed contact with the seawater inducinga cathodic reaction that protects thesteel against corrosion. To achievethis, a rectifier is connected to theship's steel with the negative exit. Thepositive exit is connected to two ormore anodes in the ship's shell. Theseinsulated anodes are embedded in theshell to prevent damage by floatingice and are made of inert materials(inert is another word for non-reac-tive). Sometimes the very noble (butvery expensive) metal platinum isused, but more often the anodes aremade from a mixture of high-grademetal oxides (MMO, mixed metaloxides). Oxides cannot oxidate again.The selected oxides do not dissolvein water. If the anodic reaction has nometals to consume, the reaction willproduce smali bubbles of oxygen,which are not without harm to theshell. The strength of the impressedcurrent can range between 10 A and600 A, the exact value depending onthe size of the ship, the amount ofdamaged paint layer, the speed of theship and the salinity of the seawater.The voltage can be as high as 20-30V, depending on the number and posi-tioning of the anodes. Where the shellis in direct contact with the seawater,this voltage reduces to 1.5-2.5 V.

Anode in the shell Regulator

Ship Knowledge - Chapter 14: Materials and maintenance 321

Activeanode

Referenceelectrode

Reference electrode

Active anode

Current collectors on thepropeller shaft and rudderstock

Principle of impressed current corrosion protection system

The ICCP-system has the following:Advantages:- a minimum of maintenance is re-

quired- high reliability- action can be control led at any mo-

ment- an automatic regulator can adapt

the current with the use of refer-ence electrodes if a change in thewater-composition (fresh, brack-ish, salt) or damage to the paint-layer requires this.

- the high investment costs (com-pared to a sacrificial system) willrecover itself in approximately 6years.

Disadvantages:- the costs of acquisition are signifi-

cantly higher than those of a sacri-ficial system

- if the ICCP-system is wrongly-tuned it can cause extensive dam-age to the ship below the water-line.

- some paint systems are damagedquickly when the ICCP-system isoverprotecting (the current is toohigh).

Some remarks on cathodic protectionand related matters:

- ICCP-system is mostly used onships with a length exceeding 40metres

- Fast ships like patrol vessels andhydrofoil boats are always protect-ed by the ICCP-system

- Aluminium ships cannot be pro-tected passively

- In ships with a lubricated propel-ler shaft, the shafting should beequipped with a strong current col-lector. If this is not the case, thecurrent will flow from the propel-ler to bearings or gear wheels ofthe engine or gearbox. This cancause extensive damage.

- If the current collector is tunedwrongly and the shafting has afaulty earthing, the gear wheels andthe bearings can be damaged veiyquickly.

- The rudder stock has to be equippedwith a good earthing if the rudderis to be part of the cathodic protec-tion system

- Stainless steei, for instance in thepropeller shaft, is protected againstcorrosion by a dense oxide layer-called the neutralisation layer. Ifthis layer is damaged it will not ful-ly restore itself. The new layer isnot impermeable, so corrosion can-not be stopped. A wrongly tunedICCP- installation can destroy theneutralisation layer of the stainlesssteel if it comes into contact withseawater. This does not happen in alubricated propeller shafting.

7. Dry-docking

7.1 Why dry-docking?

- The SOLAS Convention requires it.(Chapter 1, Reg 10-V)This chapterstates that every ship should be dry-docked for inspection of the underwater parts at least twice every 5years. The maximum time-lapsebetween two dry-dockings should

Special paint layer around the anode

Earthing brush

not exceed three years. Only whenspecial provisions have been madeduring construction, one of the dry-dockings may be replaced by an in-water survey.

- Demanded by the bureau of classi-fication. The demands from theClassification Societies are gener-ally in compliance with SOLASrequirements.

- To repair damage below the water-line as a result of for instance:• collision• running aground• bad or no maintenance• propel)er-shaft seal leakage• rudder damage

- Inspection when the ship is goingto be sold.

7.2 Methods of dry-docking

- floating dock.- excavated dock (graving dock)- patent slip.- lift and subsequent horizontal trans-

port of the ship.

Floating dockA floating dock is, in fact, a pontoonwith a vertical sponson on both sidesin longitudinal direction. The pon-toon and a part of each dock wall aredivided into a number of tanks.

To dock, the following has to bedone:- the tanks are filled with water so

the dock submerges sufficiently forthe ship to safely enter it

- the ship navigates into the dock

322 Ship Knowledge - Chapter 14: Materials and maintenance

Repair-department of a dockyard with

two floating docks

Tanker being built it} a drv-dock

Construction t/l an excavated dock

- the tanks are emptied, the dockrises to the surface and the ship islifted out of the water.

The front and/or the back of the spon-sons are usually equipped with hinge-able walkways to provide access toboth sides. On top of the sponsonsare found:- pump control room- travelling crane for handling, load-

ing/onloading of parts- capstans and bollards to control the

ship's movements into the floating-dock.

Electric motors are located in theupper part or dry room of the spon-sons. These motors operate the bal-last pumps that are located low in thetanks.

The manual controls of the inletand outlet valves are also located inthis compartment. Opening the inletvalves fills the tanks and lowers thedock. To raise the dock, the pumpsare started and the outlet valves areopened.The ship rests on the keel blocks thatare placed on the tanktop of the dock.These keel blocks are 1 - 1.25 metresapart and each can carry a weight of100-200 tons, height 1.5-2 metre.

Side (bilge) blocks are used to keepthe ship stable in the dock. They keepthe ship in balance and are placedtowards the turn of the bilge. All sideblocks have to be placed in such away that the forces they exert on theship's hull are absorbed by the rein-forcements present in the ship, likeside girders and longitudinal bulk-heads. The centre line bulkheads andthe web frames of the dock also haveto be taken into account.

The positions of the blocks, the riseof bottom, the bottom tank drainplugs and other important data haveto be indicated in the docking planof the ship. The rise of floor makes itnecessary for the side blocks to havethe correct height so that the weightof the ship is distributed over the keeland the side blocks. The dock masteris responsible for the placing of theblocks as indicated in the dockingplan of the ship.

Excavated dockThe excavated dock (graving dock)is closed using a caisson or door. Thedock floor slightly slopes towardsthe opening. The pump room is alsolocated near the opening. Most char-acteristics of the excavated dock arethe same as those of a floating dock.The ship's trim is limited more thanin a floating dock. The differencebetween the slope of the dock andthe trim should not exceed 1 metre,to prevent high loads in the stern areaof the ship.

A floating dry-dock. Data: length = 21 /

metres, width (internal) 32 metres,

draught above blocks = 7.5 metres, lif-

ting capacity — 25,000 ions.

1. Keel blocks2. Side blocks3. Side sponson4. Rails for the crane

A view under the ship in a dock (normal

dock block-arrangement)

Ship supported by special dock block-

arrangement with enlarged height (in a

graving dock.

Ship Knowledge - Chapter 14: Materials and maintenance 323

Anchor and mooring gear

Engine room

Page 212

Page 232

Propulsion and steering gear

Page 258

1. General

1.1 General

Safety on board ships is an importantissue. Normally, at sea and often veryfar from any possible assistance, thereis nobody who can be called upon forhelp. Of course, the ship should beof good design, well maintained inseaworthy condition with sufficientstability, watertight and weather tightand properly equipped. However,safety on a ship is not guaranteedby availability on board of the (com-pulsory) safety items and systems.Safety cannot be bought. Most of theaccidents on board ships are the resultof human error.

Preventing by recognition, rectifica-tion and avoidance of unsafe actionsand/or situations, at all times and atall places on board by all personnel isof utmost importance.

Since July 2002 all ships (and theirashore offices) have to be certi-fied under the International SafetyManagement Code (ISM Code) andthe crew has to work in accord-ance with the Safety ManagementSystem (SMS). The SMS is a setof rules, describing in detail how toapply safety in general, and how touse the safety gear.

Courses and regular drills are to beheld in order to achieve that the crewis safety-conscious. This trains the

Train/fig in how to walk and climb pro-

vided with a BA-set (breathing appa-

ratus'!

crew to use the right equipment incase of an accident. In a crisis situ-ation people are not logical thinkers.They tend to act instinctively usingthe things they learned during thecourses and drills. When some situ-ations have not been trained, and thecrew are unfamiliar with the situationthey tend to panic. In case of fire,especially on tankers, inadequatelytrained people have jumped over-board, often with fatal consequences.

Chapter T: General provisionsChapter II-l: Construction - Structure, subdivision and stability,

machinery and electrical installationsChapter 0-2: Construction - Fire protection, fire detection and fire

extinctionChapter III: Life-saving appliances and arrangementsChapter IV: Radio communicationsChapter V: Safety of navigationChapter VI: Carriage of cargoesChapter VII: Carriage of dangerous goodsChapter VIII: Nuclear shipsChapter IX: Management of the safe operation of shipsChapter X: Safety measures for high-speed craftChapter XI: Special measures to enhance maritime safetyChapter XII: Additional measures for bulk carriersAppendix: Certificates

\n overview of the index of SOLAS

Ship Knowledge - Chapter 15; Safety

Oxygen

1.2 Regulations

Regulations concerning safety onships are formulated by the IMOdepartment called the Marine SafetyCommittee (MSC), responsible forthe SOLAS-Convention. The sub-committee on Standards of Trainingand Watchkeeping, have regulatedthe certification of seafarers, in theSTCW Convention, shortwriting for(International Convention for) Stan-dards of Training, Certification andWatchkeeping (for Seafarers). Thisinvolves the certification of all sea-farers.The SOLAS Regulations apply to allships over 150 GT for radio and over500 GT for radio and safety equip-ment. Ratification by the relevant flagstates means that they will adopt theregulations in their national laws.

2 Fire protection, firedetection and fireextinction

2.1 Purpose

The most important issue of course,is protection. Protection through con-struction is, as said above, arrangedin Chapter II-1. It prescribes the posi-tions of bulkheads, materials of subdi-viding structures, in combination withthe use of non-flammable materials,fire-proof doors, fire-proof insulationetc. The three elements for combus-tion: flammable material, heat andoxygen, should not be allowed tocombine and create fire.

2.2 Combustion process

For a better understanding of thisparagraph we will look more closelyat the theory of combustion.

Combustion is a chemical reactionwhen a flammable compound reactswith oxygen. This compound willform a chemical bond with oxy-gen under the release of heat andthe formation of new compounds.This process is known as oxidation.Combustion is happening everywhereunnoticed, for example in the humanbody or in corrosion like the rustingof iron.

Fuel

The fire triangk'

An actual fire will only occur incase of a combination o[ all of thesefactors. If one of these factors isremoved, there will be no fire andif there already is a fire, it will beextinguished. Fire prevention and firefighting are based on this principle.The required factors are shown in thefire triangle. If just one side of thetriangle is taken out of the equation,then the fire will cease.

The ignitionTo start a process of combustion morethan the three factors are needed. Theheat that is necessary to start the firemust fulfil some requirements. For asolid or a liquid to ignite there has tobe some vapour or gaseous product.This is the case when the compoundis heated until enough vapours andgases have been generated to form aflammable mixture.

To ignite a liquid, there has to be gasabove the liquid. The liquid itself can-not bum, though the gas can, whenthere is also oxygen and the tempera-ture is sufficiently high.

The lowest temperature at which thissituation occurs is called the flash-point.

However, it is possible that when theflashpoint is reached, the combus-tion will cease after ignition. Thereason for this is an incomplete mix-ing of gas and air. The lowest tem-perature at which combustion willcontinue after Ignition is called theignition temperature. At this tem-perature, enough vapour is formed tosustain combustion; the heat balanceis in equilibrium. A necessity forsus-taining combustion after ignitionis that a sufficient amount of heat isreleased in the process. This is thecase when more heat is produced thancan be absorbed by the surroundings.Combustion is also possible withoutignition from outside. If enough heat

Gas ) CH

CHO

Vapour

Air

Heat beams

Liquid

Jombustion of a liquid

}Gas

Heat beams

Air

p& Pre ignition

WoodIgnition and combustion of a .solid

is pumped into the fuel, the tem-perature may become so high that itwill ignite spontaneously. The lowesttemperature at which this can occur iscalled the (spontaneous) combustiontemperature.

The fire pentacleFrom the preceding it becomes clearthat the fire triangle alone does notsuffice; the oxygen/fuel ratio is alsovery important in the ignition andsustaining of a fire. Next to this, a firecannot start without a catalyst.If there is no catalyst in the vicinity ofthe fuel then (over-)heating can stillstart the combustion process becausethe fuel will form its own catalyst.The general catalyst in combustionis water vapour, present in the (air)atmosphere. If the two factors oxy-gen/fuel ratio and catalyst are addedto the fire triangle you obtain a firepentacle.

Temperature

The fire pentacle

Ship Knowledge - Chapter 15: Safety 335

A catalyst is a compound that accel-erates a chemical process withoutbeing consumed.

An everyday example of this is thecombustion of a sugar cube. You cannot light a sugar cube with a matchor Hghter. However, when you putsome ash on the cube, you will beable to set fire to the sugar. The ashis working as a catalyst. In essence,a catalyst reduces the energy neededfor a process in comparison with theprocess in the absence of the catalyst

Fire classesFire classes highlight the characte-ristics of combustion depending onthe type of fuel. The fire class isused to determine which method offire-fighting is most suitable for theparticular fuel.

Class of flammable goods

A

B

C

D

Solids

Liquids

Gases

Metals

Wood, paper,textile, plastics

Liquifyinggoods, petrol,alcohol, stearine,fat, tar, paint

LPG, butane,propaneMagnesium, alu-minium, titani-um, zirkonium,sodium, potassium

Overview of fire classes and the Types

of fuels

2.3 Fire-fighting

When there is a fire, all attempts mustbe made to extinguish it.There are various means of fire-fight-ing, like:- take away heat, (2.3.1)- take away oxygen (2.3.2)- take away flammable material.

2.3.1 Take away heat

This can be done by:a. Solid Water. When the water evap-orates by the heat of the fire, thistakes a large quantity of energy fromthe fire. When there is sufficientevaporation, the fire will die.

b.Foam. Foam is a mixture of waterwith foam-making liquid. The proc-ess and the result is as under a.c. Mist. Mist is consisting of veryfine droplets of water. The result is asunder a.d. CO2. When released into a closedspace, it will form, a mist. The drop-lets need to become gas, and this proc-ess uses heat. (This is a side effect offire-extinguishing with CO2)

2.3.2 Take away oxygenWithout oxygen a fire cannot contin-ue. The Oxygen quantity (percentage)can be reduced by adding anothergas, without oxygen. The percentageoxygen will reduce.

a. CO2. Releasing CO2 into a closedspace, pushes the air, depending onthe quantity of CO2, out. When theoxygen is below 8 percent, a fire cannormally not exist.b.FM 200. As above,c. Close the space completely wherethe fire is. The present oxygen will beused till the percentage is too low tomaintain a fire.

2.3.3 Take away flammable materialMany ways can be thought of. Forinstance, close a valve in a pipelinewhere oil comes out onto a very hotsurface.

2.4 Fire-fighting Means

2.4.T Portable fire extinguishersThe first line of defence on board isusually the portable fire extinguisher(dry-powder, CO2 or foam).Dry-powder extinguishers, usuallywith 6 kg powder, are placed inthe accommodation and other easilyaccessible spaces. In the engine rooma 20 kg unit has to be available, andalso on tankers in way of the mani-fold, during loading and dischargingoperations.The powder is suitable in three fire-categories:A for fire in solids,B for fire in liquids, andC for fire in gases.

Cross-section of a powder extinguisher

Cross-section of COn-extinguisher

\. Carrying handle2. Control lever3. Outlet pipe4. Snow horn5. Blow-out pipe

336 Ship Knowledge - Chapter 15: Safety

Usually Ihe extinguishers are filledwith a mixture of the three powders,making them versatile. The extin-guisher consists of a closed containerwith powder, and inside a compressedgas (carbon dioxide) cartridge. A pinwhen hit, opens the cartridge, bring-ing the container under pressure, andblowing the powder out.CO2 portable extinguishers arc tobe used in case of electrical firesin a switchboard, and oil fires, forinstance in the uptake of a galley.

Portable foam extinguishers are inuse in engine rooms, but are moreand more being replaced by powderextinguishers.

Foam trolley

Spare charges for the extinguishers ora sufficient supply of all types of fireextinguisher are required to be storedon board.

When a fire is too big to be dealt withby portable extinguishers, systemswith more capacity are available.

2.4.2 Watera. Main fire line system and hosesThe most versatile, easiest and at seathe cheapest medium available forextinguishing a fire.

Therefore ships are provided with:- fire pumps- pipe-line system for water under

pressure, to reach every location ona ship

- hydrants at regular distances.- hoses.

So when hoses are connected to theappropriate hydrants all parts of theship can be reached.The pipe-line system must be sup-plied by two fire pumps, situated inthe engine room, each having suf-ficient capacity and pressure for thewhole system. An emergency firepump, individually driven, is locatedin a separate fire protected compart-ment. This pump is to have a suffi-cient output to supply two hoses.

Near each hydrant a hose must bestored, fitted with a dual-purpose noz-zle: for a solid jet, and for spray. Thehydrants and the hoses are providedwith fast-fit standard connections.(There are three systems: Snap-on,Storz, London Fire-Brigade).To enable to be assisted by the shorefire-brigade, in case of a fire inport, there has to be the so-called:International Shore Connection, astandardised piece of pipe, to whichthe local fire-brigade can connecttheir water supply to pressurize theship's fire main.

The International Share Connection for

the fireline. (SOLAS requirement)

Disadvantages of fire-fighting usingwater:- the ship's stability can be endan-

gered due to large quantities offire-fighting water entering it

- water itself also can result indamage

- water is not suitable for all fires

h.Fixed pressure water spraying sys-tem

Various systems have been developedto spray water in or over areas, whichare vulnerable in case of fire, such aspublic spaces in passenger ships.

- DrenchingRo-Ro vessels have throughout theircar decks open sprinklers, operat-ed from a central fire-control room.When a fire-alarm comes in, the fireis located by the related alarm head,and after inspection, by an officeror via closed circuit TV; the valveof the relevant area of the car deckcan be opened manually. The capac-ity is much higher than of ordinarysprinkler systems. The cargo, trucks,trailers, vehicles are much more dan-gerous than a cabin. Deck scuppersmust have the capacity to cope withthe water quantity, so as not to causeloss of stability due to the free surfaceeffect of the water. This system is alsocalled a: Deluge system.

- SprinklersIn each cabin, depending on its area,one or more sprinkler heads are fit-ted in the deck head. These sprinklerheads are connected to a pipelinesupplied by a pressurised vessel filledwith water. A glass crystal closes thepipe. When heat is developed in thespace, the glass crystal breaks, waterflows out and is diverted by a rosettein to an umbrella shaped water foun-tain. When the pressure in the watervessel drops, a pressostat starts afire pump, providing the vessel withwater, to keep the flow going. Thepressostat also triggers the fire alarm.

Sprinkler with heat detector. If a risein temperature causes the red liquid toexpand, it will break the glass and shootdown the nozzle. Subsequently, the wateris driven out in the form of mist.Colour of the liquid indicates the work-ing temperature, for example 68 °C.

Ship Knowledge - Chapter 15: Safety 337

Fire on the fore ship of a large crude tanker. Foam has been used in an effortto extinguish the fire

c. FoamWater can be mixed with chemicals,so that when expelled through a noz-zle where it can be mixed with air,foam is developed. There are threesystems:- high-expansion foam,- pre-mix ordinary foam and- foam made in a proportionator.

The foam-forming chemical is nor-mally ox-blood or an artificial equiv-alent. The mixing rate is 3 - 6%.Both low and high expansion foamcan be used in spaces like enginerooms. It can fill the whole space,through a system of nozzles, strate-gically placed, without doing muchharm to the equipment. The water isthe coolant.

Ordinary foam, pre-mix or mixedwith water is applied via a propor-tionator, which is a venturi-tubewhere in the narrow part of the tubethe foam liquid is injected. This isused on tankers to lay a blanket overthe deck. It separates a fire from theair. and thus from oxygen. Foam insmall quantities can be used via FoamApplicators, usually available in anengine room. It is a small drum withfoam liquid, connected to the throat ofa venture-tube which is connected toa fire hose. When spraying water, thefoam liquid is sucked up and mixedwith the water, producing foam.

d. FogA relatively new development iswater fog. Fresh water is pressu-rised through very fine nozzles sothat the water comes out as a fog.Whereas sprinklers splash everythingfrom above with water, the fog fillsthe space with a cloud, going every-where, also underneath furniture, etc.

Since 2002 the 'local watermist sys-tem' is compulsory on new shipslarger than 2000 GT and an engin-eroom larger than 500 m3. As from2005 the system has also to be avail-able in existing passenger ships fromon 2005.

This system is meant as a meansof extinguishing between a manualextinguisher and a 'total flooding sys-tem", like CO2. It has to be fitted nearfire-risky equipment like the mainand auxiliary engines, boilers, sepa-rators, etc. Each section is separatelyoperable. Near each protected itemsmoke and flame detectors are fitted.When one detector detects smoke orflame, an alarm is activated. When asecond detector detects, the systemwill be activated The control unitopens the valve of the subject section,starts the fire-mist pump, and throughspecial nozzles the equipment will beenclosed in water mist.

The system can be activated in threeways:- Fully automatic.- Manually, locally by a push-but-

ton,Remote from a panel outside theengineroom.

Advantages:- hardly any damage from the water

"large water area" making fogvery effective causing more heatextraction

- oxygen depletion by steam form-ing.

- the action can be repeated

Disadvantages- high capital cost compared to tha:

of CO,- a bilge system must be provided to

discharge the water- the water could cause some

additional damage.

338 Ship Knowledge — Chapter 15: Safer.'

2.4.3 Fixed gas systems

a. C02 (Carbon dioxide)Fixed gas fire-systems: filling aspace with a gas which reduces theoxygen content, or which is an anti-catalyst which will extinguish a fire.It reduces the oxygen content to alevel at which fire cannot exist. Sucha system can only be used in closedcompartments.

Carbon dioxide, although very effec-tive, is very dangerous to people.A large number of fatal accidentshas necessitated the search for lessharmful alternatives, first found inHalon. For a number of years thiswas in use, but being a CFK, wasabandoned in connection with envi-ronmental consequences. There area number of Halon replacements, butthese are so expensive that CO2 todayis mostly installed in new-buildings,again, since Halon is forbidden. CO2

is most frequently in use for extin-guishing fire in engine rooms andcargo- holds.

The system consists of a battery ofbottles of CO2 under high pressure(200 bar), which can be blown empty,first to a manifold, and after openingthe main valve into the engine room,using pilot bottles with compressed

air or CO2, supplying the force to pullopen the bottles, and releasing CO2

to the engine room or a cargo-hold,creating an atmosphere with insuf-ficient oxygen to allow combustion.

The bottles for a cargo hold are partof the battery for the engine room.The content of the bottles have to bechecked yearly, by weighing, or bylevel check using radiation throughthe bottle, by a radio-active isotope.

Advantages of CO2

- no consequential damage- transport over long distances

through pipelines possible- a relatively low cost material

Disadvantages:- High risk for personnel- High quantity gas needed- Cylinders have to be stored in an

isolated space, outside the protect-ed space

- Many safety devices needed- The action is not repeatable

AdmissionBefore CO2 gas can be released,various safety measures have to betaken.- a head count to ensure that no

people are left in the engine room

VOL% CO2

0.030.51.82.53

4

5

89

101220

Symptoms after breathing CO2

normal CO2-concentrationTLV and MAC-valueIncrease in lung ventilation by 50% (hyperventilation)Increase, in lung ventilation by 100%Light stupefaction, less accurate hearing, faster heartbeatand higher blood pressureIncrease in ventilation by 300%, heartbeat andblood pressureSymptoms of poisoning after 30 minutes; headaches,dizziness, transpirationDizziness, stunning and unconsciousnessBreathing difficulty, drop in arterial blood pressure,congestion, death within 4 hoursDisorientation and dizzinessImmediate unconsciousness, death within minutesNarcosis, immediate unconsciousness, death bysuffocation

- all openings to open air have to beclosed, mostly manually.

CO2 can be released from more thanone position:- from the CO2 room- remotely from a cabinet some-

where else in the accommodationpreferably in a special safety roomor on small ships outside.

When the door of the locked cabinetwith the release system is opened, theCO2 alarm is triggered, and claxonsand flashing lights are started in theengine room. By opening the doorof the cabinet, all ventilation stopsautomatically.

The system can be released fromthe CO2 room, where the bottles arestored, and from a remote space, inlarger ships the fire-fighting controlroom (see under paragraph 2.8).In all locations, the vital releasevalves are inside a locked cabinet. Inthis same room there are possibilitiesto close valves at the various oil tanksin the engine room, stopping all oilflow towards machinery. There arealso remote stops for all oil pumps inthe engine room.

CO2 release to a cargohold has to bedone in the CO2 room, as only part ofthe battery is involved, and the bot-tles have to be selected manually byfitting pins.

TLV = Threshold Limit ValueMAC - Maximum Allowable ConcentrationCongestion - accumulation of blood CO? -cylinders

340 Ship Knowledge — Chapter 15: Safety

To" .eguipped wi:h a WaterLock

No.

01

02

03

04

05

06

07

08

09

10

11

12

13

14

15

16

17

18

19

20

Description

CO2-Release Station

Emergency Release Station

C02-Pilot Cilinder

Shuttle Valve

High Pressure Time Delay

CO2-Cilinder

Check Valve

Manifold

Safety Valve

Pressure Gauge

Shore Connection

Section Valve

Smoke Detecting Cabinet

Fan Unit

Ball valve 3/2-ways

CO2- Nozzle

Acoustic alarm sounder

Key Box

Pilot Piping

Distribution Piping

CO? total flooding system

COi-cvlhiden Main hand-operated valves to release CO-, to the cargo holds.

Ship Knowledge — Chapter 15: Safety 341

2.6 Personal protection for fire-fighters

Each cargo-ship has to be providedwith at least two firemen's outfits,complete with breathing apparatus.This is a heat-resistant suit, withboots, gloves and helmet, to go closeto a fire, when necessary for fire-fighting or for evacuation of peoplein danger. In case of smoke, theBreathing Apparatus (BA) set is tobe used. The BA set comprises acompressed air bottle, and a smokemask. (A normal tanker has 4 BAsets, Chemical tankers more).

Modern ships are provided with afire-control station. Tn big ships this isa room in the accommodation, acces-sible from outside, with a fire-door tothe rest of the space. The fire-con-trol station, depending on the type ofship, comprises the following:

- a display of the fire alarm system,- the cabinet with the operation han-

dles of the quick-closing valves,- stop-buttons of the mechanical

ventilation.- the smoke extraction cabinet,- the remote operation cabinet of the

CO2 fire-extinguishing system,- a firemen's outfit including a

breathing apparatus set,- other related equipment.

The fire control station is normallyalso the mustering point for the fire-fighting team.

The Fire control plan is a gen-eral arrangement drawing of the ship,showing all the safety appliances.This plan is at various places postedon the walls for all persons on boardto see. The Fire Control Plan is also ina red container near the gangway, forthe shore fire brigade, when the shipis in port or at a shipyard.

3.

MouthpiecePressure regulatorManometer for bottle pressureMask

Cylinder containing the safety plan,

easily accessible for the fire-fighters Light-weight aluminium fireproof suit, enabling to get close to fires and heat.

344 Ship Knowledge - Chapter 15: Safety

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An example of a Muster List

2.7 Fire alarm

The Fire Alarm, a bell ringing loudly,at intervals of a few seconds, canbe activated manually by pushinga button in a little red box, behindglass. The alarm buttons are installedthroughout the ship. Also, whenfire has been detected by a detec-tion system, it activates the alarm.Resetting of the alarm can only bedone at the main display, usually onthe bridge. On the display can be seenwhich button, in which zone or detec-tion-loop, was activated. A zone orloop can be isolated when repairs arecarried out especially if smoke at thatlocation is inevitable (engine roomworkshop).

2.8 Muster list

A Muster list, for everyone on boardto look at, with names and functionsof everybody, updated every voyage,and the special tasks during fire orother calamities, is fitted on the wallsat various places: wheel house, mess-rooms and fire-control room .

3. Lifesaving Appliances

3.1 Regulations

Regulations for lifesaving appli-ances are laid down in the SOLASConvention. See Chapter 6.Chapter 111 of SOLAS handles thelifesaving, backed up by the Life-Saving Appliance Code.The Marine Safety Committee hasissued a document with the testingregulations.

3.2 Lifeboats

Lifeboats have to be installed oneach side of the ship, each side capa-ble of accommodating everybody onboard. Alternatively a free-fall life-boat maybe installed on the stern,large enough to accommodate thewhole crew. In case of lifeboats onboth sides, one boat is designatedas man-over-board boat, or rescue-boat. In case of a free-fall lifeboat,an additional man-over-board boatis needed. On passenger ships theremust be capacity for each person on

w oSRDE

» « •

ps

F«6R

omEW

board, but only 50% on each side .The inventory of the lifeboats is accu-rately laid down in SOLAS, and hasto be checked regularly. Main itemsare food, water, a first-aid kit, medi-cines, a searchlight, diesel fuel for24 hours, two bilge pumps, distresssignals, fishing gear, tools like axesand engine-tools, spares etc.Since a few years lifeboats have to betotally enclosed. On passenger ships,partly covered boats are in use.

On tankers the lifeboats have to beprovided with an internal air-supplythrough compressed air bottles, sothat the boat can pass through burn-ing oil on the water. Therefore also asprinkler system is installed, to coolthe outside of the boat.

Every lifeboat must have a die-sel engine, started by batteries andbacked-up by manual-start.Lifeboats have lo be able to belaunched or lowered at a listed ship,from the high side, with a maximumlist of 20° and a trim of 10°. An(enclosed) lifeboat must have suffi-cient stability to upright itself.

Ship Knowledge — Chapter i5: Safety 345

a Lv .1. 1These drawings show stepwise howa lifeboat with occupants is embar-ked and lowerd into the water.

Lifeboats launched with storedpower davits

Launch of a free-fall boat from aheight of 20 metres

346 Ship Knowledge - Chapter 15: Safen-

1. Freefall lifebuoy with light- and 4.smoke signal 5.

2. Firehose box. near hydrant 6.3. Lifebuoy 7.

Rescueboat (man-over-board boat)Liferaft (crane launched)Crane for MOB-Boat and LiferaftFreefall Lifeboat

New type lifeboat, catamaran type, capacity'

40 persons. Note the dome, offering a 360 °

mundview. The lifeboat is self-tightening.

Lifeboats and davits are made in vari-ous ways. All systems are made suchthat no power is needed from theship's systems to lower a lifeboat.

Free-fall type. The installation is posi-tioned at the aft of the ship, ensuringthat trim and list have a minimum ofinfluence on the launching.Prior to the launching, the wholecrew enters the boat, seats them-selves. Boat securings are released,whereafter the mate moves a lever upand down which lifts the release hookhydraulically. At this point, the dieselengine is already running so that theboat can navigate away from the shipimmediately after the launching.

Interior

The seats in the boat are positionedwith the backs facing towards thefront of the lifeboat, to prevent inju-ries due to impact.

From July 2006, new bulkcarriershave to be fitted with free-fall life-boats.

Apart from falling, the free-fall boatcan be lowered using the recoverycrane, usually an A-frame. This isarranged for testing or maintenance.The A-frame is provided with a winch,for recovery.

This lifeboat can also be used as a ten-

der on passengers/rips.

The "auxiliary launching facility"is manoeuvred using hydraulic jacksand an electric hoisting winch.Tn case the ship sinks or rolls over, thelifeboat must have sufficient buoy-ancy to detach itself from the launch-ing system.

The most common lifeboat/davit com-bination is 'gravity davits' at eitherside of the ship. The boat goes downby its own weight, after removing anumber of securings and seafasten-ings, by simply lifting the brake han-dle of the winch.

Another launching method is to use"stored power davits". This systemis mainly used on passenger linersbecause the system does not requiremuch space. The lifeboats are hang-ing in the davits.

During launch, these telescopic davitsextend until the lifeboat is clear fromthe ship. The lifeboats can be low-ered into the water afterwards. Thedavits are extended by a hydraulicsystem that obtains its (stored) powerfrom batteries.

On passenger ships, the lifeboats arealso in use as tenders, to transfer pas-sengers between ship and shore. Theboat on the picture is certified for 120people when in use as a lifeboat, andfor 150 passengers when in use as atender.

Ship Knowledge - Chapter 15: Safety 347

3.3 Man-Over-Board boat /Rescue boat.

Man-Over-Board boat / Rescue boat(MOB-boat). In case of a free-falllifeboat, there has to be a separateMOB-boat. under a crane. Againwith compulsory inventory. Specialsurvival suits for 3 crewmembersare important. Ships carrying pas-sengers need to have a fast rescueboat, capable of being lowered intothe water when the ship has a speedof 5 knots.

Raft in contains

The sinking ship pulls the boat line and

the raft is inflated.

MOB -boat with crane. The crane can

also bring the haul hack on board.

Explanation of the numt eiused in the image

Permanent MOB -boat. If the ban! is

suspended from the crane, it can be

lowered by pulling the triangle.

3.4 Life rafts

Inflatable life rafts are located oneach side for the whole complement.Davit launchable rafts are requiredwhen the embarkation level exceeds4.5 m above "lightest seagoing con-dition of the vessel.Also rafts may be deployed of thetype to be thrown overboard.In case of overboard thrown rafts, aline should be attached to the vessel.On a normal cargoship, with life-boats, they are of 'throw overboard'type.

Lashing strap around :_Pelican hookConnecting linePainterWeak linkRing

7. Hydrostatic release un8. Expiring date of

certificate

Hydros tatic re I east

350 Ship Knowledge - Chapter 15: Safety

In case of a free-fall lifeboat, one ofthe rafts needs to be davit-launched,usually the MOB davit. This allowsthe liferaft to be lowered in inflatedcondition. The davit has a specialhook, which cannot be opened whenthere is load. Only unloaded, whenthe raft floats, it can be released. Alsovibrations may not open the hook.

A throw-overboard liferaft needs tobe connected to the ship by a line,and seafastened with a band, closedby a hydrostatic release. Pullingthe line by dropping the closed raft,triggers the pressurized bottle, and

Life buoy with light

inflates the raft. If the ships sinks,the release opens and the raft floatsup. The connected end of the line hasa 'weak link', so that the line can bepulled free.Large ships have an additional 6-per-son liferaft forward, and some verylarge container ships with midshipsaccommodation, another one aft.

3.5 Life jackets

Life jackets are provided for every-one on board. They must be providedwith a light and a whistle. They arcmostly stored in the cabins, but some-times in boxes near the lifeboats. Alsoa few life jackets are to be stored inplaces where people work: in theengine room, on the bridge and in theforecastle space. A life jacket has tobe made of watertight and fire retard-ing material with sufficient buoy-ancy. Furthermore, it has to uprightan unconscious person who is facedown in the water and has to keep hismouth 12 cm above the water.

They have to be provided with reflec-tive material. In case of children onboard, special, smaller life jacketsneed to be provided. In case of inflat-able life jackets, they need to havetwo air chambers and are to be serv-iced every year.

3.6 Life buoys

A number of life buoys, the numberdepending on the ships length, arepositioned around the ship, hookedon the handrails. Some provided witha light and/or line.On both bridge wings there has tobe a life buoy, installed such, thatwhen released, it drops by gravityinto the sea. Attached to these buoysare a floating smoke light and a lightsignal.

Ship Knowledge — Chapter J5; Safety 351

Light and smoke signal

Survival suit. It has to be worn in com-

bination with a life belt to stabilise the

head in case the person wearing it beco-

mes unconscious.

3.7 Immersion suits (Survivalsuits)

From July 2006, everybody on boarda cargoship, including bulkcarriers,shall have an immersion suit. Up tothat date at least three per lifeboat arerequired.Hypothermia is the most dangerousthreat to people in lifeboats. Espe-cially in open lifeboats, which are stillvery much In use on older ships. Inthat case there must be for everybodya Thermo Protective Aid (TPA), aprotecting bag, keeping the body heatinside, for the people who do not havean Immersion suit.An immersion suits has to be worntogether with a life jacket. The insu-lating quality of immersion suits hasto be such that the body temperaturehas not dropped more than 2 °C after6 hours in water with a temperaturebetween 0 and 2 °C.

4 Precautionary measures

4.1 Training

To work professionally with all theabove equipment and items, the ship'screw needs to be educated. Beforesigning on, everyone must have acertificate of competency.

This certificate can only be obtainedwhen the individual is in possessionof the proper diplomas, sufficient sea-service and a number of certificatesobtained after fulfilling certain safetycourses.

4.2 Tests and drills.

To respond fast and efficiently incase of an accident, people need to betrained. Regular drills, fire-drills, andabandon-ship drills, are compulsory.It is important that the drills are asrealistic as possible. On completionof the drill an evaluation should bemade, where the shortcomings of thegroup or the Individuals are to bediscussed, and, if necessary, sometheory is reviewed. The drills areto be entered in the ship's logbook.Drills on board with life rafts isimpractical, and are therefore done atshore institutes. The same counts fordistress signals.

Exercise

Abandon shipFire-fightingMan over boardEmergencySteering

How many times?

MonthlyMonthlyMonthlyOnce every threemonths

Abandon ship drill

Fire drill

4.3 Personal safety gear

During normal daily work, varioussafety measures have to be taken.Personal safety items for normal workare: safety helmet, ear-protection,eye-protection, gloves, safety-shoes,coveralls, lifebelt, etc.

Working with cargo, requires the rel-evant safety measures related to thatcargo. Especially when working withchemicals. Often special suits haveto be worn, special gloves and boots,breathing apparatus, etc.

352 Ship Knowledge - Chapter 15: Safety

4.1 TRAINING MATRIX CARGO SHIPSfamilia-rization

(ship

proficiency proficiency advancedfire

fighting forseafarers

shipmanage

ment

Holders of Dutch diploma's only

.vatch keeping offic;hief engineer

,',-atchkeeping eng'.st maritime office

validity in months

LEGEND:

on

= initial training as part of the curriculum of nautical colleges in the Netherlands

= applicable to ships certified for an unlimited area (GMDSS sea areas A3 and A4)

- required for at minimum 2 officers in charge of a navigational watch (presently ait officers in charge of a navigational watch)

j= mandatory

1= mandatory only for designated crew (according to the vessel's manning plan or muster list)

|= not applicable to certificates of competence < 3000 GT and/or < 3000 kW

- not applicable

= no refresher training required in case of 1 year sea service during the past 5 years

Water and chemical proof boots

Training matrix in accordance with 1995

STCW-treaty. The table shows an over-

view of required exercises for working

on passenger ships, safety exercises are

included. The table is made by the Royal

Association of Dutch Owners (KVNR),

in collaboration with the Association

of Dredging am! Civil engineering

companies (VBKO) and the Shipping

Inspectorate. The data in the table has

a temporary stains and is based on

the situation in 2005. The matrix for

cargo ships is somewhat different. No

training in handling large groups of

people in emergencies is included here.

Safety helmet and a self-inflating life.

jacket. This life jacket is specially to be

used during work.

MARS 200031Saved by a Safety HelmetA 2nd Mate was in charge on the deck of

a ship which was at anchor and loading

containers from barges. As a container

was being loaded on to the 3rd layer by

stevedores a twistiock fell from a height

of about 8 metres, it hit the 2nd Mate on

his helmet and touched his booy causing

an abrasion on his chest and a contusion

on his left thigh. Because of trie heavy

impact on his head he was sent ashore

to see a doctor.

An X-Ray was taken and he was declared

fit to return to the vessel but put on light

duties. This emphasises the importance

of wearing personal protective equip-

ment, without his helmet the 2nd Mate

would probably have died.

Some examples of filter masks. The left

one also protects the eyes from poison.

Ship Knowledge - Chapter 15: Safety 353

4.4 Tankers

for tankers there are special safetymeasures, like additional fire-fightingsystems, such as:- a foam system to cover the deck;- fire and / or explosion prevention-

by inert gas above the cargo- alarms for full tank or risk of over-

fill (95% and 98% full),- special safety measures for the car-

go-pump room.

5 Markings

Many items on board ships are identi-fied by markings, often stickers. Allsafety gear, wherever stored, has to beindicated by a sticker. Escape routesare identified by a sticker.

Near the life rafts instructions on howto use the life rafts must be displayed,i.e. showing preparation and launch-ing.

Markings should be clear, simple andfast to understand. For instance, onships carrying passengers, stationnumbers are useful for orientation ofthe passengers on the ship. However,the markings are important for bothcrew and passengers in case of anemergency. The markings show theexits and the location of life-savingappliances. This is made easier bythe use of arrows on the walls or alighting-system for passenger waysand staircases. These escape routemarkings (green) in the accommo-dation are compulsory according tothe IMO-regulations. Not only theescape route must be marked, but alsoall means of safety. The markings onthese should be photo-luminescent.This means that they light up when nolight shines on them.

There are pipes running throughoutthe ship, many of them in the engineroom. A large variety of liquids isbeing pumped through these pipesand in the interest of safety it shouldbe clearly indicated what liquid runsthrough what pipe. This is not onlyimportant for the crew, but also forpeople less familiar with the ship. Toachieve this all the pipes have a col-our (either paint or coloured tape) thatstands for the liquid in that pipe.

Testing the foam pump on a tanker

Farbcode:Colour code:

Farbe:Colour:

Medien (allgefriei-::Media (generail:

(mcht a im Kraftstoffgebr-aijch)O;her than fjel

rai. Laugensi kali 5

Michibrennbare GasoNon flammable gases

Medien (trotken und fencht)M s (dry and wet)

Entrance door with name and technical

markingColour code far pipes

Pipe, with colour code and arrows indi-

eating the direction of the liquid flow

BEN

JO

-MY-

m •;•

CHREE

Slicker showing your position on board Emergency lighting system

There are many large and small roomsand spaces on a ship. In general eachhas a door or an entrance hatch. Butbefore the door or hatch is opened, itis important to know what is in that

particular space, especially at nightor in bad weather. This is why everydoor or hatch carries the name of theroom behind it, sometimes with sometechnical marking.

354 Ship Knowledge - Chapter 15: Safety

6 Communication Safety

6.1 Global Maritime Distressand Safety System(GMDSS)

A GMDSS installation is legallyrequired, by the SOLAS 74 Amend-ment in which the distress and safetyradio traffic is regulated. All passen-ger liners and ships larger than 300GT are obliged to have GMDSS.GMDSS ensures that, irrespective ofthe ship's location, reliable shore toship and ship to shore communica-tion is possible in an emergency usingradio and/or satellites. All informationregarding transmitting and receiv-ing, and the frequencies used, canbe found in the "Admiralty List ofRadio Signals", Volume 5. GMDSSalso includes the NAVTEX receiver,which receives and prints weatherforecasts and warnings as well asdistress messages, and watertight(GMDSS) walkie-talkies for commu-nication in case of distress.

6.2 SART (Search and RescueTransponder)

Life rafts and lifeboats are difficultto see on radar because of their poorradar-reflecting properties. To over-come this problem, a device (SART)has been developed that, on receivinga radio signal, answers by transmit-ting a radio signal of the same fre-quency. This makes the life raft orlifeboat visible on the radar screen.When the ship is evacuated, oneindividual, indicated on the MusterList, is responsible for bringing theSART from the bridge, to the life raftor lifeboat. The SART has a range ofapproximately 30 miles.

DSC2, GMDSS Control Panel

Ship Knowledge - Chapter 15: Safety

1. SART2. Powder extinguisher3. CO->-extineuisher 2

6.3 EPIRB (EmergencyPosition Indicating RadioBeacon)

The EPIRB is of use in case the shipis sinking so fast that the crew doesnot have the time to warn the world ofthe disaster. As in the case of the liferaft, the water pressure will activatea hydrostatic release and the EPIRBwill rise to the surface. As soon asthe EPIRB is activated it will start totransmit the MMSI-number* of theship to a satellite which, in turn, willwarn a ground station. The groundstation then warns the nearest coastguard station. (-MMSI= MaritimeMobile Ship's Identification)The coast guard will direct ships andaircraft as soon as the approximateposition of the ship in distress isdetermined. When the EPIRB startstransmitting, a bearing can be takenand the position can be determined.

Aft side of the bridge

1. EPIRB2. Firehose box, with contents:

hose, nozzle and spanner.

355

6.4 Voyage Data Recorder(Black Box)

At present phasing in for ships of3000 GT and upwards, starting with20.000 GT and upwards, ships arerequired to have a Voyage DataRecorder (VDR).This is an apparatus storing in asecure and retrievable form, the dataof navigation, such as position, move-ment, speed, course, command andcontrol (recordings of voice on thebridge, etc.) leading upto and after anincident or accident.

7. Pyrotechnics

A visual form of emergency commu-nication are the Distress Signals:

Red Parachute Signals, must be avail-able in or near the wheel house (12)and in each lifeboat (4). They arerockets, which can be fired out ofhand, and can be seen from a greatdistance. To be fired in the hopesomebody notices. The general mean-ing is: I need help.

Hand flares, in lifeboats (6) and res-cue boat (4). These are very brightburning torches, which are to be heldin the hand. Used to draw attention, orto let know the own location.Smoke signals, in each lifeboat (2). Atin can, when lit to be put in the water.They remain afloat and produce athick orange smoke, clearly visiblefrom airplanes.

Line throwing apparatus, 4 pieces inor near the wheel house. These arerockets, which when fired by a gun.draw a long thin line behind them.The purpose is to shoot a line toanother ship, as a first step to estab-lish for instance a towing connection.With the thin line a somewhat heavierline can be pulled in, connected to ahawser.

Liueihruwing apparatus (four in one

box)

. ' - • . . 2'"'.

•

Smoke signal

356 Ship Knowledge - Chapter 15: Safen-

SHIP KNOWLEDGE 1. IntroductionCovering Ship Design, Construction

and Operation

Shipwise

The shape of a shi|

Ships' types

R B H H H H H ^ H ^ ^ H I I ^ H

• • ( • • • • • • • • • • • • •

R

^ ; ^ -

• •

Cargo gear/lifting appliances

: . . . Page 192

Anchor and mooring geari

Page 232

Propulsion and steering gear

Page 258

•iflMiin

Electrical installations

12

3

4

5

6

7

8Qy

11

12

13

14

15

QUESTIONS:

www.dokmar.com

Why does a ship float in spite of being constructed from heavy materials suchas steel? The reason for this is that the gravitational force that pulls the shipdownwards is balanced by the upward water pressure on the hull. Of course aprerequisite for this is that the ship is watertight below the waterline. When theweight of the ship becomes so large that the upward pressure is less than theactual weight, the ship will sink.

The water around the ship exertsa force on the ship that is directedperpendicular to the water sur-face. If the ship floats, this forceequals the weight of the waterthat is displaced by the ship.This is called Archimedes' lawwhich states that an object that istotally or partially submerged ina liquid, expe-riences an upwardforce that equals the weight ofthe liquid displaced.

The magnitude of the upward forcedepends on the volume of the ship'sunderwater body. The displacementresulting in an upward force is calledthe buoyancy. If the ship has onlybuoyancy (B) and no reserve buoy-ancy above the waterline, then theslightest increase in weight of the shipwould cause it to sink. It is thereforevery important that the ship possessesa certain amount of reserve buoyancy.The reserve buoyancy comprises thehull volume above the waterline, butalso the accommo-dation, deckhous-es and other deck erections. All thespaces that contribute to the reservebuoyancy must meet the demand thatthey are wateitight or can be closedwatertight.

Stability is the ability ofa totally submerged orpartly submerged body tofloat upright, and whenforced from the uprightposition, to come back tothe upright position whenthe reason for the list nolonger exists.

2. Intact stability

Ships are designed to float upright,what is depending on its stability.

Difference is made between longi-tudinal stability and transverse sta-bility. The longitudinal stability isnormally sufficient, it will thereforenot be taken into consideration. Wewill look at transverse stability only.When in the following discussion theword stability is mentioned, trans-verse stability is meant.

Stability for small list angles ofheel (less than 6°) is called InitialStability.

When a floating body is forced intoa heeled position without adding orremoving weight, a buoyancy wedge(2) is formed and filled at the lowerside of the body, and at the high sidea wedge (1) is lost. When the volumeof the submerged part during listingdoes not change, both wedges havethe same volume.

Due to the above water movement(from wedge 1 to wedge 2), thecentre of buoyancy (B) of the wholesubmerged part has moved. B is thecentre of gravity of the displacedliquid, and at that point the vector,representing the buoyancy has itsorigin.

Ship Knowledge - Chapter 16: Stability

The locations of B at varying anglesare all on a virtual curve.

A ship can be forced to a heel in alldirections. Not only transversely orlongitudinally. We only consider twomodels, transverse and longitudinal,which are at right angles to eachother, and we look at the ship's body.

The following pictures show a trans-versal section of a ship. In the figurebelow, we see the points TG' forGravity and 'B' for Buoyancy, bothorigin of a vector, representing theforces of weight and buoyancy.

By a strong wind, from transversedirection, the ship gets a small list,resulting in a transformation of thebuoyancy, and relocation of vector Bto the low side of the ship, but trans-versally to the waterline.

Where the buoyancy vector crossesthe centreline plane of the ship, wefind the point M, or the Metacenter

For every angle of list and displa-cement, there is 1 metacenter-point.In case of larger heel, the position ofM can vary considerably in compari-son to M for small angles of heel.That location of JVl is called the FalseMetacenter.

Metacenter (M): The point fromwhere the ship is virtually sus-pended. The location height of Mis important for the magnitude ofthe initial stability of the ship.

2.1 Determination of thedistances MB, KG and KB

MBThe vertical distance between M andB can be determined using the for-mula:

MB =V

! = transversal moment ofinertia of the waterline-area= l/12LB3[m4] (Only in

case of a rectangular barge.)V = volume submerged part of

the ship [m3]L = length of the submerged part

of the ship [m]B = breadth of the submerged

part of the ship [m]

MB can be found for every draughtT in the hydrostatic tables for theship, or can be calculated.

KGThe distance KG of the center of grav-ity of the complete ship to the keel 'K1

is (initially) a figure produced bythe building yard. Each added weightafterwards, results in a change of KG.(Unless added at the level of G)Added weights can be cargo, stores,fuel, drinking water, ballast, personalbelongings, everything not belongingto the empty ship.

M

,G

KBKB can be found for each draught Tin the hydrostatic tables of the ship.The tables are found in the Hydro-static Particulars, supplied by thebuilding yard, and which have to beon board as part of the obligatory doc-uments, (stamped and signed by theFlagstate as appropriate and approvedfor the particular ship).

This cargo hold of a multi-purposeship is being loaded with piles forthe offshore industry. The length ofuric pile, is as long as the cargohold.Division bulkheads are removed.This type of piles are used to attacha jacket to the seabed. The firis pilesare loaded down in the hold, G willgo down and KG decreases. Afterone layer of piles, with as conse-quence a gradually decrease of KG,the next layers will increase KG. Ifthe hold is filled completely, KG willhave a comfortable value.

Ship Knowledge — Chapter 16: Stability 361

2.2 GM values

GM can have three values:- GM positive: M above G- GM negative: M below G- GM zero: M and G are at the same

location. (KM = KG)

MG is positive

.G

MG is negative

2.3 The location of G in rela-tion to M (GM)

When the afore mentioned distancesare determined, the distance betweenG and M (GM) can be calculat-ed. This distance is decisive for thelength of the 'righting arm' which isdecisive for the 'righting moment' or'stability moment'.

The value of GM comes from theformula:

GM = KB + BM - KGGM - K M - KG

The above alternatives are only appli-cable for small angles of heel. i.e. lessthan 6°, this is the Initial Stability.

2.4 The importance of thelength of the righting leverof the stability moment

In the figure (next page) a ship underheel is drawn. The cause of the listis external: a wave or windpressure.This results in B moving to the lowside of the ship. The stability momentis shown as (A x GZ).The length of the righting lever canbe calculated.

C 7Sin cp = > GZ = GM sin cp

From the figure can be seen that themagnitude of the stability moment isdepending on the horizontal distancebetween the two forces (buoyancyand displacement), the so-called stat-ic lever of stability, GZ.

These levers can be calculated fordifferent angles of heel. When setagainst a baseline, a curve is found,the 'curve of levers of static stability',or the stability-curve. The values areusually given in meters.

The stability curve gives a clear pic-ture of the ships stability.

The curve has to fulfil legaldemands.

A = displacement

! \

w I

A couple is a system of two iden-tical forces, working on a body,in counter-direction along parallellines. The magnitude is "force xlever". In the case of a ship thisis: A x GZ

Relation between waterline areaand metacenter (M)From the formula MB=I/Vol canbe concluded that the location ofM, with a constant ship-weight,completely depends on the water-line area.

When a ship heels, the breadth onthe waterline will increase, and sothe area of that waterline, result-ing in a increase of MB. Thisway, a small negative initial MB,can become positive, preventingthe capsizing of the ship.

The opposite can occur when forinstance by ballasting a forepeakthe trim of a ship changes, result-ing in a decrease of waterlinearea. Fast ships normally usuallyhave forward a smaller waterlinearea than aft.

362 Ship Knowledge - Chapter 16; Stability

angle [degrees]

""

The points of ongm of the resultants of all weights ofihe ship itself and on board weight (G) and theresultant of Ihe buoyancy (B) are positioned on oneline, resulting in a zero lever of static stability fGZ}.

Ship is upright

G

-_.

In all situations, the basic assumption is thatthe position of the weight on board does notchange. The listing is caused by an externalforce.

As soon as the ship starts to list, the leverGZ increases.

\

When the list increases, the vector B wi: move further to the low side, resulting in a; larger lever of static stability (GZ), which meansa larger righting moment.

Point B moves to the low side, tothe place where the ship gets thelargest upward buoyancy force.

Ship Knowledge — Chapter 16: Stability 363

The stability will decreasewhen the bilge comes abovethe water, or when the watercomes on the deck (or both!).

In this drawing, the bilge is coming abovethe waterline, resulting in a decrease of thewaterline area, and in a smallerdistance B-M

When the vectors of weight and buoyancy areon the same line, the lever is zero, and therighting moment also.

364 Ship Knowledge - Chapter 16: Stability

NB. In reality, as soon as the ship starts listing, thepoint M will move away from the midships plane. Forsimpler calculation the assumption is made that withlisting-angles up to 6 degrees, point M remains in themidships plane. The explanation of this phenomenon isoutside the range of this book.

When the list increases, the vector of the buoyancyforce will move to the wrong side of the vector of theweight force. KM is in that situation smaller than KG.GM is then negative, and the ship will capsize.

2.5 Notes on stability

2.5.1 Influence of Depth onstability

In the figures below is explainedwhy a greater Depth (D), or agreater freeboard are inportant forstability.

Both ships have the same GM-Value, but a different stability-range, 34° and 47° respectively.The beam of both ships is thesame. The Depth of hull nr. 2 islarger than the Depth of hull nr. 1

2.5.2 Influence of GM0

The minimum and maximum val-ues of GM,, is largely depen-dingon the type of ship. Varia-tionsbetween 0.5 m and 8 meter arenormal. When the GM0 value

is below or above these values thiscan have negative stability effectson the ship.

Ships with a small GM0 havea long rolling period, which isadding comfort to the people onboard. But a too small GM0 forinstance, can result in capsizingafter a collision. Passengcrsbipshave a small GM0 value to achievea long rolling period, for the com-fort of the passengers.

Ships with a large GM0 are usu-ally ships with heavy cargo, (steel,iron-ore) with the cubic capacityof the cargo-space hardly used.When the cubic capacity is usedcompletely, with grain, or coal,GM0 will be smaller. The highaccelerations due to a large GM0

value are uncomfortable and couldresult in shifting of carso.

To prevent the ship to have a too large stabilityafter loading, the steel rolls are partly stowed in thelower hold, and on the tweendeck, to get the posi-tion of point G at an acceptible height, and there-with reducing the GM value. When all the steel isstowed in the lower hold, this could result in a roll-ing-period so short and abrupt, that life on hoard isvery uncomfortable, and even damage to ship andequipment is possible.

L .1 4- J._ L. 1_ _L J_ _L A _J

Higher ships have higher stability

Ship Knowledge - Chapter 16: Stability 365

Rollingperiod:The period of time, needed tomove from port to starboard andback to port, or counter/wise. Therolling period varies from 30 sec-onds for passengerships to 8 sec-onds for wide ships, or ships witha low KG, due to heavy cargo lowin the ship. Partly filled tanks(cargo, ballast, fuel), result in avirtual higher KG, and a smallerGM. This can be dangerous forsmall ships with a (too) small sta-bility, but adding comfort on largeships with a (too) large stability.

2.5.3 Influence of Beam(Breadth) on GM

Ships with a large beam and shallowdraught such as barges, have a largeGM0. Slender, narrow ships such ascontainerships or passengerships witha large draught, have a small initialstability. (Preferably in combinationwith a high freeboard).

As earlier mentioned, the initial sta-bility GM0, has nothing to do withthe stability at greater angles. Anextreme example is the floater of afishing rod. This floater has a verysmall initial stability, but will nevercapsize.

2.5.4 Negative influences onstability

- heavy cargo on deck- ice on deck, superstructures, masts,

etc, due to freezing spray or fog(icing) in arctic regions.

- loading or discharging heavypieces of cargo with the ships owncargo gear.

- the emptying of tanks low in theships hull (double bottom tanks).

- free liquid surface(s).

The last item, the free-liquid-surfaceswill be explained in part 3, in particu-lar because this is the most importantreason for stability problems, with agrat number of casualties.In the design-stage all possible cir-cumstances, such as loading and bal-last conditions and adverse weather

Spray over the bow becomes ice when it is cold outside. The weight of the ice adds

weigh! to the ship, at a not-warned location. Under had circumstances, A increases

substantially, and GK becomes larger. Small ships with high and extensive rigging can

easily come in danger in severe fog and bad freezing conditions.

conditions have to be carefullyreviewed and calculated with respectto stability.

3. Stability of DamagedShips (Damage Stability)

for cargo handling longitudinal andTransversal bulkheads are unwantedfeatures on (dry-cargo) ships.Loading and discharging are hampe-red, and there are limitations forcargo with extreme dimensions.Bulkheads are however necessary tolimit the amount in-flowing water incase of a leakage, for instance after acollision.In case in-flowing water could spreadslowly and evenly through the ship,there would not be immediate dangerto the ship. However, it is normal thatin a collision case, the water flows

Permeability:The extent to which a compart-ment can be filled with water isthe permeability. The effect ofincoming water on the stabilitywill be:- maximal if the compartment is

empty (permeability - 1)- minimal if the compartment is- completely filled with for in-

stance Styrofoam or a liquid,(permeability = 0).

The permeability of an engineroom is approximately 0.85.The higher the permeability of acompartment, the more volumecan be occupied by leakage, thelower the remaining buoyancy.

fast into the ship, often from portto starboard or reverse. This createsa listing moment, with an impactdepending on the quantity of thewater and the distance the water canflow unobstructed, mainly in trans-verse direction. The severity of thesituation is greatly depending on thedistance it can flow transversally andthe permeability of the space.

The magnitude of a moment isdetermined by a force (weight) andthe distance of that force to a fixedpoint. Example:

1. A child (30 kilos) and his father(60 kilos) are sitting on a seesaw.The distances to the turningpoint of the seesaw are 2 and imetres respectively. In spite ofthe difference in weight, boththe father and the child exertthe same moment on the turningpoint of the seesaw. (30x2 and60x1 respectively). The seesawis in equilibrium.

2. Tf a weight of 100 tons is moved1 metre on a ship, the same ef-fect on the trim can be achievedby moving 1 ton a hundred me-tres. In both cases the momentis 100 tm.

This illustrates how even a limitedamount of liquid can cause a largemoment on the ship if the liquidis allowed to move freely over thefull width of the ship.

366 Skip Knowledge - Chapter 16: Stability

Two slack tanks

Explanation of the abbreviations used inthe above drawings:

(,BoIkp

/%

KGMKM

KAfcpG0G"GZ

I

- ('entre of gravity= Centre of buoyancy (no list)= Buoyancy by heel to port or

starboard (external force)= Buoyancy by list to port or

$ larboard (internal force)= Initial metacentre= Metacentrec height- The height of initial

metacentre above the keel= Keel= Displacement (D)= -Displacement (-D)--- heeling angle- virtual loss ofGM= lever GZ, righting lever, the

horizontal distance betweenthe centre of gravity and thevertical through the centre ofbuoyancy.

= moment of inertia of the freesurface area of water on deck

Moment of static stability= A x GZ = A x GM sin cp

The distance that G moves dependson the length and width of the holdwhere the liquid is freely moving.De (virtual) movement of G can becalculated using the formula:

_ J_ length tank * (breadth tank)1

V 12 * vessel displacement

This formula shows clearly the influ-ence of the width (to the third power)on the movement of G. See drawing3. In drawing nr 4 the width of thetank is halved by a longitudinal bulk-head. The negative influence on thestability is considerably reduced andis only % (=2 x (l/z)3) of the originaldistance GG" In case 2 bulkheadsare installed, i.e. 3 tanks beside eachother, the effect will be reduced to1/9 x GG"

Leakage of one or more compart-ments can have the following conse-quences:- heel- draught increase- change in trim- change in stability

A Ro-Ro ship which has capsized due tothe free surface effect

Ship Knowledge — Chapter 16: Stability 367

Resulting from this weight increaseat one side of the ship, a large listcan develop in a short period oftime. A ship can capsize in a fewminutes. In recent years a number offatal accidents occurred with Ro-Roships. Due to bow-door (ramp) fail-ures seawater could enter freely intothe ship.

Below a short explanation is follo-wing about the foregoing.

The water, flowing from port to star-board and vice versa has a free-sur-face effect. This can be seen as aweight, causing a heeling moment,working on the ship.

(1 m3 = approx. 1 ton = 1000 kg.)

The effect a Free Surface Moment(FSM) can have on the stability of aship will be (somewhat exaggerated)explained in the following figures.

NB: The list as drawn is a randompicture of a complete roll of the ship.This roll, from port to starboard andback to port lasts only a few seconds,and can be caused by waves, wind,current, etc.

All these changes are acting from themoment the water in-flow starts.

On the car deck of thero-ro ship is a small amountof water. The influence of this amount of water

can easily be seen on the stabilitycurve: it gives a small list andreduces the GZ-curve.

' I i i * i I I I 1 &E "tl 'b : t ! 1b UC ifi 40 ^-- -n ••••' sS)

The water quantity has increased.This results in a negative initialstability.

When the amount of water at thecar deck remains constant, the shipwiii have a constant list of approxi-mately 19 degrees. In case thewater quantity further increases,the ship finally will capsize.

368 Ship Knowledge - Chapter 16: Stability

The choice not to install bulkheads,for economical reasons, needs atten-tion. At some types of ships thenumber of bulkheads is minimisedin connection with hamper on load-ing and discharging, for instance atRo-Ro ships and at ships for heavycargo.In tankers, the presence of bulkheadsis needed to separate the variouscargo-parcels and to reduce the influ-ence of the free surface effect in thevarious, sometimes only partly filledtanks.

The drawings to the left show theeffect of a free liquid surface in a car-deck of a Ro-Ro ship, and the effectof same at the stability curve.

4. Rules and regulations

Tt is obvious from the previous sec-tion that the free-liquid surface result-ing from a leak in a compart-mentshall not pose a direct danger tothe ship. The size of a compartmentis therefore subjected to regulationsas determined by the IMO-SOLAS-Convention.There arc three types of regulations:

4.1 Calculations of submersionand trim.

These calculations check if there isenough reserve buoyancy to keepthe ship floating after a compart-ment has been completely filled withwater*. The assumption was madethat a ship sinks vertically as a resultof the flooding. The reserve buoy-ancy is enough to compensate forthe increased draught. So the numberand the positions of the bulkheadswere related to the buoyancy and

SOLAS vs IMOThe SOLAS-treaties must beincorporated into the nationallaws. The IMO-regulations areoptional. However, in practicemost nations also incorporate theIMO-regulations into their natio-nal laws.In the past, many computationalmethods have been used to deter-mine the number of bulk heads ona ship that are necessary for thesafety. These are called damagestability calculations.

the reserve buoyancy**. After theTitanic disaster these calculationswere implemented in the first issueof SOLAS. The experiences of theSecond World War proved that theseSOLAS-rules were not adequatebecause of the assumption that a shipsinks vertically. Instead, many shipsfirst capsized before sinking.

*The reason was that a ship withflooding compartments should notsubmerge below the maximumimmersion line. This is an imaginaryline on the hull that runs 76 mmbelow the bulkhead deck. The bulk-head deck is the deck above whichthe bulkheads are not water-tight.This deck should remain above thewaterline across its entire length, thuspreventing flooding from one floodedcompartment into others resulting inthe sinking of the ship. It is assumedthat the ship sinks vertically, that is,without heel.

**The maximum distance (floodablelength L) between two watertightbulkheads is calculated for a largenumber of points P going from aftto the forward. Every space that is

created in this way has the point P athalf this length. The volume of thesecompartments is chosen in such away that the ship has enough sparebuoyancy after the compartment hasfilled up. The ship submerges a littlebut the bulkhead deck remains abovethe maximum immersion line. Inorder to get a quick view of the maxi-mum distance between the watertightbulkheads across the entire lengthof the ship, the lengths L are plottedvertically against the points P. Theresulting curve is called the Curve ofFloodable Lengths

A (shortened) calculation of thefloodable lengths, beginning in theaft perpendicular and the resultingbulkhead graph is shown below. Thetable and the curve arc for the yachton the picture.Depending on the regulations, theship should be able to survive a one-compartment damage or a two-com-partment damage.

Distancefrom APP in

metres

00.0005.0010.0015.0020.0025.0030.0035.0040.0045.0050.0053.75

Floodable lengthin metres

20.3210.3211.3513.4217.5617.0911.5409.1408.9614.0624.0231.52

distance from APP (m) 1/250

Floodable length curve

Ship Knowledge — Chapter 16: Stability 369

A one-compartment-ship cansurvive the (accidental) floodingof one compartment. Regardlesswhich compartment.

A two-compartment damage canoccur if the ship is struck at a bulk-head separating two compartments.The combined length of the two com-partments should then be smaller thanthe floodable length to survive thedamage.

4.2 Calculation of FloodableLengths.

(Trim and stability in case of a dam-age assuming certain well definedtypes of damage)A drawback of the method describedin a) is that a possible heel is not takeninto account. The method describedhere to determine the number andpositions of the bulkheads does takethe loss of stability into account andalso assumes some well-defined typesof damage. These calculations arecalled deterministic flooding calcula-tions.A drawback of this method is theexact definition of the damage. A shipthat is designed by this method canlive up to all the demands, but stillsink if the damage is 1 cm bigger thanthe assumed damage.

4.3 Probabilistic damagecalculations

(Calculations of the chance of survi-ving in case of damage)This method attempts to apply thepossibilities that the damage is notthe same throughout the length ofthe ship. A probability is assignedto every type of damage, as is the

probability of surviving this damage.The sum of all these probabilities is anumber between 0 and 1 and repre-sents the chance of surviving in casethe ship is damaged. The regulationsderived from this method also includea minimum survival chance. Theseprobabilistic damage calculationscurrently apply to:- passenger Ships (IMO resolu-

tion A265) as an alternative to theSOLAS rules (resolution A265 stillencompasses some deterministicrules).

- cargo Ships with dry cargo, longerthan 80 metres (measured over theclosed hull).

In order to estimate the centre ofgravity of the flooding, a numberof uncertain parameters are of majorimportance.For instance:- what positions does the water oc-

cupy, especially in rooms with anirregular shape?

- trim, list- the possibility of trapped air-bub-

bles.

5. How to take damage stabilityinto account on board.

The stability must be calculated forevery voyage a ship makes, and ofcourse the stability has to fulfil thevarious rules and regulations. Theweight distribution can differ per tripas can many other parameters. Factorsthat are of importance to the damagestability are:- kind of cargo (permeability)- wing and double-bottom tanks; fil-

led or empty- does the liquid stay in a damaged

tank or does it flow out?

A lot of calculations and thoroughknowledge of rules and regulationsare required in order to determine theinfluence of all these factors. Further-more, the chances of survival (proba-bilistic calculations) should also beincorporated into these calculations.In practice it is impossible to executethe calculations without the aid of acomputer.

A computer with a loading pro-gram-me, capable and programmed to cal-culate longitudinal strength, shear-force, intact- and damage stability isgenerally required on all ships longerthan 65 meters to make the requiredcalculations After all the weight datahave been fed into this computer theposition of the centre of gravity (G)above the keel (K) can be calculated.

The regulations concerning damagestability usually only mention themaximum allowed heeling angles.Sometimes the possibility of counter-flooding is incorporated.

Counter-flooding is the deliberate fil-ling of a compartment or tank at theopposite side of the ship to offsetany heel resulting from flooding dueto damage. Often used in passengerliners, even automatic systems areused.

The maximum KG is the numberthat indicates how high point Gmay be above the keel in agree-ment with the requirements madein SOLAS with regard to thestability of a ship.

NB: the maximum KG dependson the draught/displacement andthese factors must be taken intoaccount.

. ' .'. \. ;

Car deck of a Ko-Ro with doors to reduce the extend of any liquid flooding the deck.

2 1 - The doors in closed position2. The doors in stored position

370 Ship Knowledge - Chapter 16: Stability

summer freeboard

SHIP KNOWLEDGECovering Ship Design, Construction

and Operation

Shipwise

Structural arrangement

Closing appliances

Cargo gear / lifting appliances

Anchor and mooring gear

Engine room

Propulsion and steeri

I \\ "1

QUESTIONS:

www.dokmar.com

1. Principal Dimensions

1.1 Definitions

Length over allLength of the ship over its extremi-ties.Length between perpendicularsLength from aft perpendicular (centre ofrudderstock) to forward perpendicularLoad line LengthLength as used in freeboard calcula-tion,BeamWidth of the hull, usually inside shellplatingDepthHeight from baseline to uppermostcontinuous deck at side, inside ofplatingDraughtThe maximal depth underwater, incl.shell plating.

PerpendicularsImaginary lines, perpendicular to thebase line or plane (and the waterline). On a ship there are:- Forward Perpendicular (FPP or Fp)

This line crosses the intersection ofthe water line and the front of thestem.

- Aft Perpendicular (App or Ap)This line usually aligns with thecenter line of the rudder stock (theimaginary line around which therudder rotates).

The perpendiculars are used when thelines plan is made. They are the endsof the 'block' where the underwaterpart of the hull fits in.

Load LineThe water line of a ship lying in thewater. There are different load linesfor different situations, such as:Light water lineThe water line of a ship carrying onlyher regular inventory.Deep water lineThe water line of maximum loaddraught in seawater.

Construction (Scantling) water line

The water line used as the limit towhich the various structural compo-nents are designed.

summer draught

/; Plimsoll mark2, Timber mark3: Plimsoll line4: Draught marks5: Deckline

Ship Knowledge - Chapter 2: The shape of a ship

Tropical3 SummervV WinterMMA Winter North Atlantic

Explanation of abbreviations used on the mark:

Tropical Fresh (for water with a density of 1.000 t/m3)Fresh (ditto)Tropical (for water with a density of 1.025 t/m3)Summer freeboard (ditto)Winter (ditto)

TF:F:T:S:W:WNA : Winter North Atlantic (ditto), only for ships, less than 100 meterGL/NK/ LR: Germanischer Lloyd / Nippon Kaiji Kyokai / Lloyd's Register

Deck lineExtended line from the upper side ofthe freeboard deck (or deck-covering)at the ship's side.

Moulded dimensionsDistance between two points, meas-ured at inside of shell plating (oroutside framing).

Base LineTop of the flat keel plate.

Plimsoll MarkThe Plimsoll mark or Freeboard markis a symbol indicating the maxi-mal immersion of the ship in thewater, leaving a minimal freeboardfor safety. The mark consists of acircle with a diameter of one foot(one foor=0.3048rn.), through whicha horizontal line is drawn with itsupper edge going through the centreof the circle. This level indicatesthe minimum freeboard in salt watersummer conditions. Beside the circle

is the load line mark consisting of anumber of horizontal lines indicatingthe minimum freeboard as above.All load lines are connected by avertical line. The ship may load cargotill the upper edge of the relevant loadline is at the water level.

The freeboard is marked according tothe result of the freeboard calculation,where the summer freeboard in saltwater is established. The main param-eters in that calculation are length,width(beam), sheer, length of super-structures, length/depth ratio, etc.Allowances are made for fresh water.

The minimal freeboard depends on:- The location on earth (latitude)- The time of the year (summer,

winter)

The Plimsoll Mark is basically to bechecked by the crew. The origin liesin the safety of the people on board.The abbreviations of the marked load

lines have to be in the language of theflag state of the vessel.

For easy checking of the positionof the Mark (during the yearly loadline survey), above the mark a refer-ence line is drawn: the Deck Line.Normally at the level of the weatherdeck, but in case the weather deck isnot the freeboard deck (e.g. RoRo,passenger ships), at the level of thatdeck. When the distance between thedeck line and the mark is unpractical-ly large, or the connection deck shellplate is rounded off (tankers, bulkcar-riers), the reference line is positionedat a lower level. The Mark and theDeck line are to be marked perma-nently on the port and starboard-side, mid-length. (See also load-lineCertificate, Chapter 6)When a ship carries a deck cargo oftimber, and certain demands are met,this ship is allowed to have moredraught (less freeboard). This in con-nection with the additional reservebuoyancy provided by the deck cargo.To indicate this, the ship has a specialFreeboard Mark for carrying a deckcargo of timber, the so-called TimberMark.

Tankers carrying liquid cargoes andbeing completely watertight, alsohave allowance for less freeboardcompared with other cargo ships withthe same length.

The lines plan shows the shape ofthe ship. However, at the outsideof the frames and other internalsthe shell plating is laid around theinternals. The thickness of the shellplating is not taken into conside-ration for certain measurements.Those measure-ments are called'moulded'

The draught marks, load line mark.Plimsoll mark and deckline haveto be marked permanently on theshell plating. Usually this meansthat they are outlined on the plat-ing by bead welding or by weldedplate.

Ship Knowledge — Chapter 2: The shape of a ship 27

1.2 Dimensions

Length between perpendiculars(LPP)Distance between the Fore and the AftPerpendicular.

Length over all (Loa)The horizontal distance overextremities, from stem to stern.

the

Length on the water line (Lwl)Horizontal distance between thepoints where bow and stern arc goingthrough the water plane, at sum-mer mark, less the shell plating, i.e.moulded.

Draught Forward (Tfwd)Vertical distance between the waterline and the underside of the keel,as measured at the forward perpen-dicular.

Draught at the stern (Ta)The veitical distance between thewater line and the underside of thekeel as measured at the aft perpen-dicular.

TrimThe difference between the draught atthe stem and the draught at the stern.Down and trimmed by the head.Vessel, and the draught forward islarger than at the stern.Down and trimmed by the stern.Vessel loaded with cargo, to the mark,and the draught aft is larger, thanforward.

On an even keel, in proper trim.The draught of the stern equals thedraught of the stem.

1. Length over all (Loa)2. Length between the for and aft

perpendicular (LJJ)3. Length on the water line4. Breadth over all5. Depth6. Draught7. Freeboard8. Air draught

Breadth or beam (Bmld)The greatest moulded breadth, meas-ured from side to side at the outsideof the frames, but inside the shellplating.

Breadth over allThe maximum breadth of the ship asmeasured from the outer hull on star-board to the outer hull on port side,including rubbing bars, permanentfenders etc.

DepthThe vertical distance between thebase line and the upper continuousdeck. The depth is measured at halfLpp at the side of the ship.

FreeboardThe distance between the water lineand the top of the deck at the side(at the deck line). The term SummerFreeboard means the distance fromthe top of the Summer Load Line orthe Plimsoll Mark and the upper edgeof the deck line.

Air draughtThe vertical distance between thewater line and the highest point ofthe ship. The air draught is measuredfrom the summer mark. If the shiphas less draught one can ballast untilit reaches the summer draught and soobtain its minimum air draught.

28 Ship Knowledge - Chapter 2: The shape of a ship

77ic sheer line is good visible

SheerThis is the upward rise of a ship'sdeck from mid length towards thebow and stern. The sheer gives thevessel extra reserve buoyancy at thestem and the stern.

CamberThe transverse curvature of theweather deck. The curvature helpsto ensure sufficient drainage of anywater on deck.

Rise of floorUsual to some types of vessels liketugboats and fishing boats. This is theupward deviation from the baselineof the lower edges of the floors fromthe keel towards the bilges, in orderto collect water inside the hull nearcenter line, for easy pumping. Thiswas used in all ships but out of fash-ion in large ships to-day. They haveflat bottoms.

Camber*— isamuer

• Bilge radiusRiseoffloor

1.3 Proportions

The ratios of some of the dimen-sions discussed above can be usedto obtain information on resistance,stability and manoeuvrability of theship. Some widely used ratios are:

L/BThe ratio of length and breadth: L/Bcan differ quite significantly depen-ding on the type of vessel. Commonvalues:Passenger ships 6-8Freighters 5-7Tug boats 3-5

A larger L/B value is favourable forspeed, but unfavourable for manoeu-vrability and stability.

L/DThe length/depth-ratio. The custo-mary values for L/D vary between10 and 15. This relation plays a rolein the determination of the freeboardand the longitudinal strength.

B/T(T = Draught)The breadth/draught-ratio, variesbetween 2 and 4.5. A larger breadthin relation to the draught (a largerB/T-valuc) gives a greater initial sta-bility.

B/DThe breadth/depth-ratio, varies be-tween 1 and 2. If this value becomeslarger, it will have an unfavourableeffect on the stability (because thedeck edge will be emerged when thevessel heels) and on the strength.

1.4 Volumes and weights

GeneralThe size of a ship can be expressedby using terms which describe thecharacteristics of the ship. Each termhas a specific abbreviation. The typeof ship determines the term to beused. For instance, the size of acontainer vessel is expressed in thenumber of 20' containers it can load;a Ro-Ro carrier's size is given bythe total lane metres and a passengership in the number of passengers itcan carry.

Measurement TreatyAll aspects concerning the meas-urements of seagoing vessels arearranged in the Certificate of RegistryAct of 1982. Part of the Certificateof Registry Act is the Internationaltreaty on the measurement of ships,as set up by the IMO-conference in1969. The treaty applies to seagoingvessels on international voyages witha minimum length of 24 metres andcame into force in July 1994.

At the IMO-conference in 1969 thenew measurements for the "GrossTonnage" and "Nett Tonnage" wereintroduced, to establish a world-widestandard in calculating the size of aship. In many countries the GrossTonnage is used to calculate harbourdues and pilotage, or to determine thenumber of people in the crew.

Register ton.To determine the size of a ship theRegister Ton is used. It is based onvolume where one register ton equals100 eft, or 2.83 m3

Bilge radiusGives the bilge radius of the ship. An example of a ship with a small depth

Ship Knowledge - Chapter 2: The shape of a ship 29

/;; the drawing NT is given a different colour wit-

hin GT (which is moreless the whole ship), to indi-

cate the difference between NT and GT.

Gross Tonnage (GT)

Nett Tonnage (NT)

Gross Register TonnageThe Gross Register Tonnage (GRT orGT), usually called Gross Tonnage,is calculated using a formula thattakes into account the ship's volumein cubic metres below the main deckand the enclosed spaces above themain deck.

This volume is then multiplied by acoefficient, which results in a non-dimensional number (this means novalues of T or in3 should be placedafter the number). All measurementsused in the calculation are mouldeddimensions.

In order to minimize the daily expens-es of a ship, the ship owner will keepthe GT as low as possible. One wayof doing this is by keeping the Depthsmall, so more cargo can be placedon deck, This strategy is in particularused in container-feeder ships. Asa consequence, dangerous situationscan occur as the loss of reserve buoy-ancy can result in a loss of stabilityand more "water on deck11.

Nett Register TonnageThe Nett Register Tonnage is also anon-dimensional number that descri-bes the volume of the cargo space.The NT is derived from the GTby subtracting the volume of spaceoccupied by:- crew- navigation equipment- the propulsion equipment(partly)

- workshops- ballastThe NT may not be less than 30% of the GT.

Underwater volume or carenc (in3)The moulded underwater volume of a ship is the displacement in m3 minus thecontribution of the shell, propeller and rudder. Or: the calculated volume of thepart of the hull which is immersed in the water, on the outside of the frameswithout extensions.The influence of the shell in weight, is compensated by the extra displace-ment.

Displacement {my)The displacement is the volume of the part of the ship below the water lineincluding the shell plating, propeller and rudder.

Displacement D or A (ton)The displacement is the weight of the volume of water displaced by the ship.One could also say: the displacement equals the total mass of the ship.

Displacement (ton) = waterdisplacement (m3) * density of water (t/m3)

Lightship weight (ton)This is the weight of the ship including the regular inventory, but without anycargo, fuel or crew. The regular inventory includes: anchors, life-saving appli-ances, lubricating oil, paint, etc.

Deadweight (ton)This is the weight a ship can load till the maximum allowable immersion(to summer load line). This is a fixed value, which is unique for each ship.Through the years, there is usually a build-up of mud in the ballast tanks,additional spares are taken on board, and less is going off. There is also water,which cannot be pumped out. The total weight of all this, is called the ship-constant, and has to be subtracted from the deadweight.

Deadweight (ton) = design displacement A(ton) - iight ship weight (ton)Deadweight (ton) = maximum weight A(ton) - actual weight A(ton)

30 Ship Knowledge - Chapter 2: The shape of a ship

Cargo Capacity (t)This is the total weight of cargo a ship is designed to carry, at a certain time.The actual cargo loaded (in ton) is not a fixed number, it depends on the ship'smaximum allowable immersion at the relevant season, which will include thecapacity (in ton) of fuel, spares, provisions and drinking water. For a long voy-age a large quantity of fuels has to be taken, which reduces the cargo capacity.If. on the other hand, the ship refuels (bunkers) underway, the cargo capacityis larger upon departure. The choices for the amount of fuel on board and thelocation for refuelling depend on many factors, but in the end the master hasfinal responsibility for the choices made.

Cargo capacity (ton) = deadweight (ton) - ballast, fuel, provisions (ton).

2. Form coefficients

Form coefficients define the characteristics of the vessel's shape below thedesign waterline. This makes it possible to get an impression of the shape ofthe underwater body of a ship without extensive use of any data. However, theform coefficients do not contain any information on the dimensions of the ship,they are non-dimensional figures.

2.1 Water-plane coefficient. Cw (a)

Waterplane-coefficient (Cw) =L p p xB mid

2.2 Midship Section coefficient, Cm. (J3)

Midship-coefficient (Cm) -xT

The cargo capacity largely determines

the amount of money a ship generates.

The water-plane coefficient givesthe ratio of the area of the water-plane (Aw) and the rectangular planebouded by Lpp and breadth moulded(Bmiti)- A large watcrplane coeffi-cient in combination with a smallblock coefficient (or coefficient offineness) is favourable for the stabil-ity in both transverse and longitudi-nal direction.

The midship coefficient gives theratio of the area of the midship sec-tion (Am) and the area bounded byBmld and T.

A ship with a large midship coefficient

and a large block coefficient.

Ship Knowledge - Chapter 2: The shape of a ship 31

2.3 Block coefficient, coefficient of fineness, Cb. (5)

The block coefficient gives the ratio of the volume of the underwater body (V)and the rectangular block bounded by LpD, Bmld and draught (T). A vesselwith a small block coefficient is referred to as 'fine1. In general, fast ships havesmall block coefficients.Customary values for the block coefficient of several types of vessels:

Ship typeLighterBulk carrierTankerGeneral cargoContainer shipFerry boat

Block coefficient C^0.900.80-0.850.80-0.850.55-0.750.50-0.700.50-0.70

Appr. ship speed5 - 1 0 knots

12 17 knots12-16 knots13 - 22 knots14-26 knots15-26 knots

Block coefficient (Cb) = Volume

pp X 'mid x T

Graphical representation of the block coefficient.

2.4 Prismatic coefficient, Cp. (phi)

The Prismatic Coefficient gives the ratio of the volume of the underwater bodyand the block formed by the area of the Midship Section (Am) and Lpp. The Cp

is important for the resistance and hence for the necessary power of propulsion(if the Cp decreases, the necessary propulsion power also becomes smaller).

The maximum value of all these coefficients is reached in case of a rectangularblock, and equals 1. The minimal value is theoretically 0.

A ship with a small block-coefficient and

a large midship section coefficient

A ship with a large block-coefficient and

a large midship section and prismatic

coefficient

I1

w

f

Vx A

Lpp x B x T x CLpp X D X 1 X L-

C tWaterlines, ordhmtes, verticals, diagonals

Graphical representation of the prismatic coefficient.

32

Waterlines, animates

Ship Knowledge — Chapter 2: The shape of a ship

3. Hull-form (Lines plan)

When the principal dimensions, dis-placement and hull-form coefficientsare known, one has an impressiveamount of design information, but notyet a clear image of the exact geome-trical shape of the ship. The shape isgiven by the lines plan.

The shape of a ship can vary inheight, length and breadth. In orderto represent this complex shape onpaper, transverse sections of the hullare combined with two longitudinalsets of parallel planes, each one per-pendicular to the others.

Ordinates.Evenly spaced vertical cross-secti-ons in transverse direction are calledordinates. Usually the ship is dividedinto 20 ordinates, from the centre ofthe rudder stock (ordinate 0) to theintersection of the water line and themould-side of the stem (ordinate 20).The boundaries of these distances arenumbered 0 to 20, called the ordinatenumbers. Aprojection of all ordinatesinto one view is called a frame plan.

Water lines.Horizontal sections of the hull arecalled water lines. One of these isthe design water line. This is thewater line of the ship at the level ofimmersion in full cargo. Between thebaseline and the design water line areusually 3 to 4 other water lines drawn,counted from the baseline, which iscalled number 0. The constructionwater line, or the scantling waterline, can be higher. When the waterlines are projected and drawn into oneview from above, the result is called awater line model. Verticals / Buttocks

Vertical sections in longitudinal direc-tion are called verticals or buttocklines. These longitudinal sections areparallel to the plane of symmetryof the ship. When the buttocks areprojected and drawn into one particu-lar view, the result is called a sheerplan.

Apart from the rectangular sections,sometimes planes are used, in longi-tudinal direction, but at an angle withthe midship plane. They are calleddiagonals, or sent-lines.

The diagonals

DiagonalsThe diagonals are longitudinal secti-ons that intersect with the hull surfaceat a certain angle. On the longitudinalplan they show up as curves.

The curvature of the frames (ordi-nates), water lines and buttocks arecompared to each other and modifieduntil they are consistent, and developsmoothly in all directions. When thisprocedure is executed, the results canbe checked using the diagonals. Themost common diagonal is called thebilge diagonal.

Ship Knowledge - Chapter 2: The shape of a ship 33

Heavy cargo ship, multi-purpose

PP

'mid

mid

= 134 meter= 28 meter- 7 meter

Volume - 18644 m3

-0.710= 0.992= 0.715- -2.24 %= 14.46 meter

Frigate

Lpp

B m | d

TmldVolume

cbCm

C PLCBKM

= 96 meter= 11.5 meter= 3.25 meter= 1620 m3

= 0.452= 0.752= 0.601= -2.30 %= 6.17 meter

Abbreviations used in the drawings:Lpp = length between

perpendicularsBmld = breadth mouldedTmld = draught mouldedCarene = volume of the

underwater body, asmeasured on the lines,to the outside of theframes (nv).

C PLCB

block coefficient orcoefficient of finenessmidship sectioncoefficientprismatic coefficientlongitudinal positionof the resultant of allupward buoyancyforces:

Longitudinal centre ofbuoyancy (forward oraft of ordinate 10) in%ofLp p

VCB = Vertical position of theresultant of all upwardbuoyancy forces;

KM = Height of meta-centrcabove the keel (meter).

36 Ship Knowledge - Chapter 2: The shape of a ship

4. Drawings

4.1 Drawing list

To build a ship, hundreds of draw-ings are often needed. A selectednumber of drawings are to be submit-ted for approval to the Flagstate andthe relevant Classification Society.The construction drawings have tobe approved by the ClassificationSociety, the drawings concerningsafety in general by the Flagstate.Which drawings have to be submittedis depending on the type of ship.

Drawings have to be submitted toClassification and Flagstate.

Classification requirements:- General Arrangement Plan,- Lines Plan- Construction Plan(s) Profile and

Decks- Transverse Sections, incl. Midship

Section,- Double Bottom Construction- Fore and Aft ship,- Rudder, Sternframe

- Engine foundation,- Crane foundations, if applicable,- Deckhouse

Capacity Plan.- Loading Manual for longitudinal

strength- Pumping and Piping,- Shafting,- Etc.

The Flagstate requires:- General Arrangement Plan,- Capacity Plan,- Safety Equipment Plan,- Stability calculations.- All Class approved drawings.

Above is very much depending on theflag the ship will carry. One flagstateor the other has completely differentrequirements, and can delegate it allto Class.

4.2 General Arran(GA)

lenient Plan

The General Arrangement plan rough-ly shows the division and arrange-ment of the ship.

The following views are displayed:- a (SB) side-view of the ship- the plan views of the most impor-

tant decks- sometimes cross-sections, or a front

and back view are included

The views and cross-sections men-tioned above, display among otherthings:- the division into the different

compartments (for example: tanks,engine room, holds)

- location of bulkheads.- location and arrangement of the

superstructures.- major equipment (for example:

winches, loading gear, bow thrus-ter, lifeboat).

In addition to these, some basic dataare included in the drawing such as:- principal dimensions- volumes of the holds- tonnage- deadweight- engine power- speed- class.

The general arrangement plan of this ship is shown at the next pages

Ship Knowledge - Chapter 2: The shape of a ship 31

SHIP KNOWLEDGECovering Ship Design, Construction

and Operation

Shipwise

Ships1 types

The

I Cargo gear / lifting appliances

Page 192

Anchor and mooring gea

Engine room

Page 212

Page 232

Propulsion and steerim

Electrical installations

Materials and maintena

HHHHH

3 gear

e258 \k\m

. • 13-M M

0m Mm

,332 1 5

QUESTIONS:

www.dokmar.com

1. The International Maritime Organization (IMO)

1.1 General

International shipping, and nationalshipping to a lesser extent, are subjectto stringent laws and regulations, byinternational and national regulatorybodies.Internationally those bodies areunited in the International MaritimeOrganization, TMO.

Within the United Nations, mari-time affairs are taken care of by theInternational Maritime Organization,in abbreviation, IMO. The mainobjective, from the first conferencein 1948 up to its entry into force in1958, is improvement of safety atsea. SOLAS (Safety Of Life At Sea)goes back as far as 1914, but due toWorld War I never came into force.There were even earlier internationaltreaties, but they were not very suc-cessful.

Seafaring has, through history,always been one of the most danger-ous occupations. Many countries hadunilateral regulations on safety, butas sea trade is of international nature,the rules and regulations were betterset up internationally, instead of byindividual countries. In 1948 a con-ference was held where the basis waslaid for IMO.

The slogan is: Safe, Secure andEfficient Shipping on Clean Oceans

The first objective was to improvesafety of life at sea: SOLAS, fol-lowed by the subject of cleaneroceans, resulting in the MARPOL-Convention about marine pollution,accelerated by the Torrcy Canyonaccident (1967).

1.2 Assembly / Committees

In IMO the governing body is theAssembly, with has installed Com-mittees for the different objectives.

- MSC, the Marine SafetyCommittee, with safety relatedConventions and Codes as theirworking area, resulting in theSOLAS Convention.

- MEPC, the Marine EnvironmentProtection Committee, withenvironmental subjects as theirworking area, resulting in theMarpol regulations, first in 1973,afterwards 1978.

Other Committees are: LEGAL(Security), TCC (Training) andFAL (Electricity).There are some 10 sub-committees.

Up to May 2006 there were 166member states.

ASSEMBLY

COUNCIL

SECRETARIAT

MEPC MSC LEGAL TCC FAL

Sub Committees - BLG, DSC, FP, COMSAR, NAV, DE, SLF, STW & FSI

Basic stmcture of IMO

Ships' knowledge - Chapter 6; Laws and regulations

L-=ue raisedMSC/MEPCwill discuss

-*CAssembly foradoption

Sub-Comm. Sec. Gen.Ratification

Keep updated andensure ratification Implementation by

member states

nv of I MO processes

Through the years many conventions,protocols, codes and amendmentshave been adopted. After adoption,individual governments must ratifythe protocols or conventions. Depen-ding on acceptance by the number ofgovernments and the gross tonnagegoverned by them, a Conventioncomes into force, after a certain timefrom the acceptance date.

Then it is followed by the imple-mentation, when the new regulationbecomes law under the responsibilityof the flagstate. The whole processcan take many years.

Flagstate:Flagstate is the country that the shipis registered. Each country is respon-sible for the law and rules applicableto ships sailing under their flag. Oftenthe control of the rules are delegatedto the Classification Society of therelevant ship.

Port State Control:Flagstates around the North-Atlanticand in the Mediterranean (Europeanand Canada) have set up (in 1978)a system of ships inspections, relat-ed to the international regulationsregarding Loadline, SOLAS, Marpol,Tonnage, Colreg, Living and wor-king conditions of crew, DangerousGoods, Class, etc.The target is to inspect 25% of theships coming to their ports. In casedeficiencies are found, they normallyhave to be rectified before departure,or are to be checked in the next port.Important deficiencies result in theships detention, which means that theship is not allowed to depart beforethe deficiencies are made good.

• • "

Designed, approved and surveyed to withstand the roughest seas.

1.3 Conventions and Codes

The Conventions and Codes result in worldwide recognised certificates whichships have to carry, after being surveyed to ensure that they meet the require-ments, as applicable for the relevant ship. A variety of compulsory equipment hasto be type-approved by Flag state(s) and/or Classification Society.

The following IMO-CONVENTIONS have been adopted (not all have beenimplemented):- The International Convention on Load Lines 1966- The International Convention for the Safety of Life at Sea, SOLAS 74, '88- The International Convention on Standards of Training and Certification of

Watchkeeping for Seafarers (STCVV)- The Convention on the International Regulations for Preventing Collisions

at Sea, (Colregs)- The International Convention on Tonnage Measurement,- The International Convention for the Prevention of Pollution from ships,

1973, modified as per Protocol 1978 (Marpol)- The International Convention on the Control of Harmful Anti-Fouling

Systems- The International Convention for the Control and Management of Ship's

Ballast water and Sediments- The International Convention on the Safety of Fishing Vessels

Each of the Conventions is, where necessary, more precised in Codes.However, some Codes are independent without reflection to a Convention.

Examples of CODES:- The IMO Code for the Construction and the Equipment of Ships Carrying

Dangerous Chemicals in Bulk,- The ILO/SMO Code of Practice on Security in Ports- The IMO Code of Safe Practice for Solid Bulk Cargoes (BS Code)- The International Safety Management Code (ISM)- The IMO Code of Safe Practice for Ships Carrying Liquified Gases in Bulk

- The FAO/ILO/IMO Code of Safety for Fishermen- The IMO Code of Safe Practice for Cargo Stowage- The IMO Code of Practice for Atmospheric Oil Mist Detectors- The IMO Code of Practice for the Safe Carriage of Irradiated Nuclear Fuel

- The IMO International Code of Signals- The IMO Code of Equipment of Mobile Offshore Drilling Units

(the MODU Code)

Ships' knowledge — Chapter 6: Laws and regulations 115

ti

2. Certificates

Before any Certificate can be issued,a ship must be registered in a certaincountry, the Flagstate. This meansthat the flag state accepts a ship ascarrying their flag and belonging totheir 'fleet'. Against a certain fee, andtaxation on the earnings, the authori-ties allow the ship to sail under theirjurisdiction. The port and countrywhere the ship has been registeredhas to be marked on the stern.

The certificates can be divided incertificates every ship must have onboard, and certificates which are con-nected to the type of cargo the shipis intended for, or the area the ship isallowed to sail.

2.1 Compulsory Certificates inaccordance with SOLAS

The SOLAS Convention requires everyship on international voyages (above500 GT) to have on board:

On cargo ships:- Cargo Ship Safety Construction

Certificate- Cargo Ship Safety Equipment

Certificate- Cargo Ship Safety Radio

Certificate

A Cargo Ship Safety Certificate,combining 1, 2 and 3.These can be issued to replace 1, 2and 3 above. All above certificateshave to be accompanied by a Recordof Equipment, giving a list of itemswhich need to be on board of therelevant ship.

In SOLAS the ship's constructionis also regulated, with regards tostrength, maximum size of flooda-ble compartments, intact and damagestability, covered under the Safer;'Construction Certificate.

On Passenger ships:- Passenger Ship Safety Certificate

Earlier in use than the cargo shipsafety certificate, the passenger shipsafety certificate with the same con-tent.

Rules and regulations and certificatesare more stringent for passenger shipsthan for cargo ships.

2.2 Certificates, compulsoryin accordance with otherConventions:

2.2.1 LoadlineThe Loadline Convention requiresthe International Loadline Certificate,evidence of meeting freeboardrequirements, as prescribed in theConvention, and in the relevant Code.Loadline requirements started in theUnited Kingdom by a member ofparliament, Mr Plimsoll, after whichcertificates have been issued by theClassification Societies since 1876,when the Freeboard Mark or PiimsollMark became compulsory. The regu-lations to comply with at present arelaid down in the Loadline Convention1966. On the basis of ship's length,size of openings in deck, sheer, door-sin heights etc., a minimum freeboardis calculated, and has to be displayedat the ship's side. The carriage of tim-ber as deck-cargo, or oil in an oiltank-er, gives relaxations. The PlimsollMark shows minimum freeboard, andis a safety mark.

2.2.2 TonnageThe Tonnage Convention requiresevery ship to be provided with TheInternational Tonnage Certificate. Asproof of the registration the Flagstate issues this certificate, or theClassification Society issues this cer-tificate on their behalf. This certifi-cate is worldwide accepted as givingthe official details of the ship: maindimensions and volumes of the vari-ous spaces, in particular the spaces inconnection with cargo, cargo holds,tanks, etc., all in accordance withregulations set out in the TonnageConvention.It shows Gross Tonnage and NettTonnage, figures with a high legalvalue. Nett Tonnage is the GrossTonnage minus the spaces which donot directly contribute to the earnings,like ballasttanks and the engine roomfor a certain percentage. Details canbe found in the Convention. Harbourdues and many other financial chargesare often based on GT.Every ship is provided with a so-called

Survey to verify freeboard marks on side

of ship.

Inspecting a hatch on a life boat for

compliance with the latest regulations.

Surveyors check links and shackles of an

anchor chain.

In a manufacturer's workshop a local

surveyor reviews the fit-up and align-

ment of intermediate and thrust shafts.

116 Ships' knowledge — Chapter 6: Laws and regulations

IMO-number, a 7-digit number as anidentification, the idea for the numberborrowed from Lloyd's Register. Thenumber stays with the ship for itslifetime, and has to be marked offclearly visible, and is printed on allcertificates.

Apart from the International TonnageCertificate, the Suez Canal and thePanama Canal have their own wayof establishing 'tonnage' to base theirfees on. Therefore, special tonnagecertificates are issued for Suez Cana!and Panama Canal.

2.2.3 MarpolThe Marpol Convention requiresunder Annex I, to have on board,a valid International Oil PollutionPrevention Certificate (1OPP). Seealso under Section 7.To comply with the Marpol regula-tions, every ship has to be providedwith the International Oil PollutionPrevention Certificate, for oil tankersof 400 GT and above and for othercargo ships above 400 GT. This cer-tificate deals with oil pollution. Seeunder 7.

Marpol has been provided withAnnexes.- Annex I as above,- Annex El gives regulations for

liquid chemical cargo in bulk,resulting in the Certificate ofFitness,

- Annex III is dealing with HarmfulSubstances, in packed form,resulting is the certificate forDangerous Goods,

- Annex IV is dealing with Sewage,- Annex V is dealing with Garbage,- Annex VI is dealing with air pol-

lution.

2.3 Examples of Certificates inconnection with the ship'sdesignation:

2.3.1 Dangerous GoodsInternational Certificate of Fitness forthe Carriage of Dangerous Chemicalsin Bulk (IBC Code Certificate) accom-panied by a Cargo list, is issued whenthe ship is found applicable to theregulations in the relevant Code. Achemical tanker has to be providedwith equipment to minimise residues

in cargo tanks, various measurementtools and special equipment related tothe cargo they are intended to trans-port. The cargo list gives the names ofthe chemicals the tanks comply with.This relates to closing appliances,cargo tank coating, gasket materials,protective clothing, breathing appara-tuses, gasmasks, etc.

2.3.2 Certificate of Fitness for theCarriage of Liquified Gasesin Bulk

Gas ships have a similar Certificateof Fitness for the Carriage of LiquifiedGases in Bulk, in accordance with theInternational Gas Code, or for olderships the Gas Carrier Code.

2.3.3 Certificate of Compliance forthe Carriage of DangerousGoods

The carriage of dangerous goods inall forms: packaged form, in solidform in bulk, explosives, dangerousliquid chemical cargoes in bulk inchemical tankers, gases in gas-tank-ers and packed radio-active materials,is regulated in SOLAS Chapter VII.In the subdivisions A-D all kinds ofrules and provisions are given, withrequirements for the ship's construc-tion, stowage requirements and pack-ing, labelling, etc.

On the certificate is clearly statedwhich dangerous goods the ship isallowed to carry. An approved cargolist gives the specific names.

2.3.4 Certificate of Compliance forthe Carriage of Solid BulkCargoes

For bulk carriers a special certificatehas been created in connection withthe transport of Solid Bulk Cargoes.These cargoes have been categorizedA, B and C, depending on their haz-ards. A is the least harmful, C themost harmful. For each of these car-goes there are special requirements.

2.3.5 Minimum Safe ManningCertificate

The Flag state is also responsible forstating the minimum number of crew,and their required qualifications, whohave to be on board when the ship isunderway.

[MO 9289518ON 8000901NET 14378

O. N.: Official Number

NET: Net Tonnage

3. Classification

Ships are built in accordancewith Rules and Regulations of aClassification Society, chosen bythe prospective Owner. The Societyapproves the relevant drawings, andinspects the actual construction.Classification is controlling strengthand quality of materials and work-manship in connection with the ship,when built "under Class".The Classification Society issues acertificate upon completion of con-struction:The Certificate of Class, for Hull andMachinery.The Certificate of Class is the hasis forunderwriters to insure a ship.At the same time a trading Certificateof Class is issued with a validity of 5years which has to be endorsed everyyear, on completion of the AnnualSurvey.

Every year, in a window of threemonths before the birthday and threemonths after, an Annual Survey has tobe carried out, covering Class, SafetyConstruction, Safety Equipment,Loadline, Radio, Marpol, Fitness.Dangerous Goods, Cargo-gear, etc.Normally all done at the same portof call.

Birthday:The date at which the first timecertificates were isssued.

Ships' knowledge — Chapter 6: Laws and regulations 117

When at the end of the three monthsafter the 'birthday'one of the tradingcertificates has not been endorsed bythe relevant Classification or Flagstate the ship is not allowed to leaveport.

To carry out the different surveys,the Class Societies each maintaina worldwide network of surveyors,centralized by their main offices.The main Societies have beensince 1968 grouped under IACS,the International Association ofClassification Societies. Since 1970they are consultative to IMO, contrib-uting their expert technical knowl-edge.

The members are (in alphabeticorder):- American Bureau of Shipping

(ABS)- Bureau Veritas (BV)- China Classification Society(CCS)- Det Norske Veritas (DNV)- Germanischcr Lloyd (GL)- Korean Registry (KR)- Lloyd's Register (LR)- Nippon Kaiji Kyokai (ClassNK),

Japan- Registro Italiana Navale (RINA)- Russian Maritime Register of

Shipping (RS)

The division between Classificationcertificates and statutory certificatesis as follows:- the Classification Society looks

after the technical condition of theship

- the Flagstate (country of Registry)after the people on board, and theirbehaviour in connection with safe-ty, environment and communica-tion.

Initial(special

annual

The interest of the Classificationis the safety of the ship and thecargo. The interest of the Flagstate is the safety of the peopleon board.

However, many flagstates delegatetheir tasks to the ClassificationSociety. Therefore, on many ships,apart from the Class certificates, alsothe statutory certificates are issued bythe Classification Society.

The validity of the important cer-tificates have since 1999 been har-monised, as per IMO Assembly res-olution A.883 (21). All certificateshave a validity of five years, startingfrom the ncwbuilding date, and arerenewed at each Special Survey, i.e.after 5 years. The 'birthday' remainsthe same.

4. ISM-Code (InternationalSafety Management)

4.1 Introduction

A issue of IMO is the InternationalSafety Management (ISM). This cer-tificate, for both ship and office, isa statement that Owners/Managersand the ship's staff are committingthemselves to maintain the vesselas required, and to fulfil obligationsconnected with safety and pollution.Most regulations in shipping concerntechnical aspects of the ship andthe required training of the crew.The ISM-code, applicable to all shipssince 2002 is a list of regulations forthe organisation of the ship, so basi-cally it concerns the management-system,

For Class and ISM, ships have to dry-dock two times in five years

Inter mediate

Special

2nd annual 3rd annual 1 Hi annual

6 m tli 6 mth

3 months; either side

max o vear sClassification Special Survey Cycle

118 Ships' knowledge — Chapter 6: Laws and regulations

The management-system comprises:- the organisation on board the ship- the organisation ashore

- the organisation of the shippingcompany

- the communication between shoreand ship

The importance of good managementfor safety in general is illustrated bythe fact that 80% of all accidents inshipping are the result of humanerrors.

4.2 Objectives

The objectives of the iSM-code are:- to satisfy all relevant national and

international regulations likeSOLAS, MARPOL, ISM, Classand Labour laws

- creating a permanent awareness ofsafe behaviour by the personnel onboard and ashore

- ensuring a readiness to acteffectively in emergencies

- guaranteeing safety at sea- preventing accidents and damage

to environment

The ISM-code is a standard of safe-ty consisting of 13 elements, eachdescribing a business operation thatis relevant to safety and environment.The elements can be considered asparagraphs of the ISM-code. Theycan deal with:- (planned) maintenance- office personnel and crew

4.3 How ISM works

a. The Shipping CompaniesEvery shipping company must pos-sess a Document of Compliance(DOC). This document states that theshipping company is found fit toexploit the ship in accordance withthe demands of the ISM-code. Oneof the demands is that the shippingcompanies must develop, execute andmaintain a Safety Management System(SMS).The Flag state issues the DOC, butonly after a Classification Societyhas approved the safety managementsystem. The DOC remains valid for aperiod of five years, provided that theannual surveys by the ClassificationSociety yield good results.

b. The ShipsThe ships can get a Safety- Manage-ment Certificate (SMC) if the DOChas been issued to the shipping com-pany. The SMC also remains valid fora five year period. During this periodthere should be an inspection betweenthe second and third years.

4.4 The Audits

The SMS is inspected by means of anaudit. An audit is a prescribed surveyto check whether the organisations onshore and on the ship are able to suc-cessfully execute the regulations andhave reached certain goals. Audits canbe distinguished into internal auditsand external audits.

The I SO-organisation grants one cer-tificate to the entire organisation, con-trary to the ISM which has separatecertificates for the organisa-tion onand off shore.

a. Internal AuditsInternal audits are performed by theshipping company and can comprisematters like:- the overlap between the way of

working on board and the SMSregulations applied

- checking if the measures taken forsafety and the environment are inaccordance with the SMS

- testing the SMS for efficiency andtaking measures if necessary

All relevant personnel must beinformed of the results of these auditsand the measures taken. The manage-ment must correct all shortcomings.Internal audits are usually performedannually.

b. External AuditsExternal audits are performed by thebureau of classification under super-vision of the Flag state. If the organi-sation lives up to the standards set,the shore organisation receives theDOC and the ship the SMC.

5. InternationalOrganisation forStandardisation (ISO)

ISO has drawn up the:- ISO 9000 (standard)- ISO 14000 (environment)- ISO 18000 (labour circomstances)These standard sets demands for mat-ters that an organisation should haveor do in such a way that the customercan be confident that the productmeets the standards of good quality.

A company will voluntarily use theI SO-standards, possibly under pres-sure of the free market. The companywill draw up a Quality ManagementSystem (QMS) that can be certified bya bureau of classification.

The ISO-9000 standard is a generalstandard aligned to the ISM-code.This means that every company drawsup and executes its own QMS basedon the demands.

6. ISPS-Code

By various regulatory bodies, meas-ures have been taken in connectionwith the growing threat of terroristattacks. IMO has compiled regula-tions under the name:International Ship and Port FacilitySecurity Code (ISPS-Code).Applicable to:- Passenger ships

- Cargo ships above 500 GT- Mobile Offshore Drilling Units- Harbour Facilities, and means of

transport.

Above ships need to have on board anInternational Ship Security Certificate.Fishing ships and Navy ships areexempted from the Code.

Objective of the ISPS-Code is thatrisk of a terrorist activity is mini-mised."Security officers" have to be appoin-ted:- Company Security Officer (CSO)- On a ship the Ship Security Officer

(SSO)- On a harbour facility the Port

Facility Security Officer (PFSO).

Ships' knowledge - Chapter 6: Laws and regulations 119

All ships which are obliged to carryan ISPS certificate, and the relevantharbour facilities have to compile asecurity scheme, comprising all secu-rity measures, such as:- To know at each moment who are

on board or on the facility;- To control entrances and perform

visitor identity checks;- To control loading and discharging

cargo and stores.

The ISPS-Code acknowledges 3threat-levels:- level 1: No specific threat — > no

additional measurements needed,- level 2: Enhanced, general threat

—> increased security- level 3: Terrorist threat —> further

increased measures.

7. Marine Pollution(MARPOL)

In 1973 IMO adopted the InternationalConvention for the Prevention ofPollution from Ships, modified againin 1978. The Marine EnvironmentProtection Committee (MEPC) doesthe daily work and has given clari-fication. The actual regulations toprevent pollution by environmentunfriendly substances are given in"Annexes".

The following applies to ships. Forplatforms and other stationary equip-ment at sea, other regulations apply,also specified under Marpol.

Note: At January I, 2007, a updatedand revised Annex I will come intoforce.

7.1 Annex I

This Annex of Marpol deals withregulations in order to prevent thepollution of the seas by oil fromships. Oil is defined for this Annexas petroleum in any form includingcrude oil, fuel oil, sludge, oil refuseand refined products. AH such sub-stances are listed in the appendix 1 tothis Annex.

We have two basic situations:- Oil and oily mixtures generated in

the Engine Rooms of a ship notbeing an oil tanker of 400 GT and

above, and engine rooms of any oiltanker

- Oil and oily mixtures resultingfrom cargo pump rooms, cargohandling, cargo tank cleaning, etc.on Oil Tankers.

All Engine Rooms generate waste oil,sludge and oil-polluted bilge water.Waste oil and sludge will be collectedin waste oil tanks and sludge tanks,and the bilge water via the bilgewells, in bilge water holding tanks.After settling, the water in the bilgewater holding tank can be pumpedinto the sea, under the followingconditions:- the oil and oily-mixture is not

mixed with cargo residues- is not coming from cargo pump

rooms- the vessel is not in a Special Area- the vessel is underway at sea• the oil content of the effluent

without dilution does not exceed15 parts per million (PPM), andthe ship has in operation a filteringequipment as required byregulation 16 of the Annex.

To be allowed to discharge oil andoily-mixtures from engine roomswhile sailing in a Special Area, theremust be a filtering equipment onboard, with an oil content meter,and a device that automatically stopsthe discharge when the oil contentexceeds 15 PPM.This oil content meter and stoppingdevice is already a requirement forvessels larger than 10,000 GT. If avessel of less than 10,000 GT wishesto discharge in a Special Area, it alsomust be equipped with an oil con-tent meter and an automatic stoppingdevice.

The content of the bilge holding tankis pumped to a bilge separator. Thisis a vertical settling tank, where theoil separates from the water, oftenfollowed by a filter which filters theremaining oil (if any) out. In the set-tling tank, a probe measures if oil isfound, and starts a pump, discharg-ing the oil to the waste oil tank.When the probe does not find oil, thepump stops. The remaining water ispumped overboard via the oil-contentmeter which checks via a full flow, or

via a bypass flow the oil content inthe processed bilge water. If the oilcontent is more than 15 PPM, a pre-alarm is generated, but the dischargeis still not stopped. If the oil contentis consistent over 15 PPM, after ±20 seconds a second alarm is gener-ated. This second alarm will stop thedischarge.The automatic stopping device canbe a three-way valve, a combinationof two alternating working valves,or a pump stop. The automatic stop-ping device must be so arranged, thatin case of a failure or in power-offcondition, no discharge into the seais possible.

All the equipment must be TypeApproved, and kept well maintained.

All operations like fuel bunkering,transfer of waste oils and sludge,handling of bilge water, defects onthe filtering equipment, accidentaldischarges must be recorded withouthesitation in the Oil Record Book(Part I).

The Special Areas can be found inregulation 10 of the Annex. TheNorth-West European Waters, theBaltic Sea and the Mediterranean areSpecial Areas, to give some exam-ples.

Oil Tankers generate cargo residues,remains from cargo line blowing,manifold-drip trays, tank washings,pump room bilge water, etc. Thoseoily-residues are collected in the sloptank(s) of the vessel. It is under nocondition allowed to transfer suchoily-residues to the engine room.

Oil Tankers have apart from theengine-room generated oils, anotherproblem. When an oil cargo is dis-charged, there is always residue, andoften the tanks must be cleaned toprepare them for a next cargo.

Washing is done with rotating waterjets in the tanks, generating an oilywater mixture which is pumped to theso-called slop tank. There it is left tosettle into oil and water.Tank washing is performed using tankwashing machines. These machinesare water pressure driven, and give

120 Ships' knowledge — Chapter 6: Laws and regulations

Sewage treatment plant

rotating waler jets, which reach everycorner of the surface of the tank.While washing, the washing water iscontinuously pumped to another tankor the slop tank.

Water washing is carried out to ena-ble tank entry. To achieve a gas-freecondition, all the oil which can gen-erate gas, needs to be away. This isbest done by washing the tank. Afterwashing and pumping away the slops,the tank is to be properly re-inerted,after which the tank has to be venti-lated, till the oxygen content is 21%.By following this procedure, there isnever an explosive mixture.

After settling, it is allowed to pumpthe contents of the slop tank into thesea, under the following conditions:

- the tanker is not within a SpecialArea,

- the tanker is more than 50 nauticalmiles from the nearest land,

- the ship is underway at sea- the instantaneous rate of discharge

of oil content does not exceed 30litres per nautical mile,

- the total quantity of oil dischargedinto the sea does not exceed:

- for existing tankers 1/15,000 of thetotal of the particular cargo ofwhich the residue formed a part,

- for new tankers 1/30,000 of thetotal quantity of the particular car-go of which the residue formed apart.

- the tanker has in operationOil Discharge and MonitoringEquipment and a slop tank arrange-ment as required by regulation 15of this Annex.

The Oil Discharge and MonitoringEquipment (ODME) must be typeapproved. Oil tankers over 150 GTmust be equipped with an ODME.

All operations must be recorded inthe Oil Record Book (Part II) withouthesitation.

The remaining oil is to be retainedin the slop tank. Either to be pumpedashore later, or when the next cargois suitable, usually only possible withcrude, to be mixed with that nextcargo, (load-on-top-system). If this isnot allowed, the content of the sloptank has to be pumped ashore, at areception facility.

Crude tankers during discharge washtheir tanks with cargo, to prevent theaccumulation of sediment. The cargooil is pumped through the rotating jetswith high pressure, and the sedimentsare kept mixed with the cargo andpumped ashore with the cargo. Thisis called Crude Oil Washing (COW).The rotating jets are the same as usedduring tank washing.

A problem connected with high pres-sure water washing and COW is thatstatic electricity is generated. CrudeOil Washing (and water washing) istherefore only allowed at an atmos-phere with reduced oxygen (5%),below the level that explosions orfire can occur. COW is compulsorythrough Marpol legislation, and InertGas is a consequence. To achieve anatmosphere above the cargo, or inthe empty tank of below 5% oxygen,the exhaust gas of the boiler is, afterwashing, led into the tank duringdischarging.

All tankers need their cargo and bal-last water to be kept in complete-ly separate tanks. These are calledSegregated Ballast Tanks (SBT). Allhandling of oils and ballast water hasto be accurately administrated andentries are to be kept on board forthree years.

Restricted areaRestricted area is an area at seawhere nothing may be pumpedoverboard, also not over 50 milesfrom shore. The Mediterranean asa whole is a restricted area.

Incinerator

The minimum SBT capacity of atanker is regulated to ensure sufficientballast capacity for safe navigation.

7.2 Annex II

This Annex of Marpol regulates theprevention of pollution by NoxiousLiquid Substances, in general called'Chemicals'. These 'Chemicals' arecategorized. Depending on the dangerfor the environment in case of pollu-tion and the fire hazard properties, theregulations arc more stringent.

A special booklet, issued by IMO, theso-called International Bulk ChemicalCode (IBC-code) gives a listing ofrequirements for the ship which hasto carry the noxious liquid substanc-es. For chemical tankers with a keellaying date before 1 July 1986 theBCH-code is applicable.The noxious liquid substances arefor the purpose of the regulations inthe Annex divided in four categories:A, B, C and D.Category A is the most toxic one,and category D practically non-toxic;when discharged into the sea fromtank cleaning or de-ballasting opera-tions they would be a major hazard(cat. A) up to a recognizable hazard(cat. D) to either marine resources orhuman health.Depending on the cargo category,the ship's cargo tanks have to meetspecial requirements, with regard tolocation, distance from ship's side orbottom, i.e. double hull requirements.Therefore the ships are divided intoTypes 1, II and IN.

Pumping, piping and unloadingarrangements are regulated. Slophandling and mandatory pre-wash

Ships'knowledge ~ Chapter 6: Laws and regulations 121

WASTE MANAGEMENT

Getting rid of waste in the proper wayis a huge problem. Nearly everythingcoming on board is packed, from meatto toilet-paper. In cartons and woodenboxes, plastics, in foil and hardware-glass, tin, other metals, etc. Especiallya passenger ship is a waste generator.The remains of food seem easy to getrid of. The sea takes care of them.This idea changes when a large pas-senger vessel is in port. Then theycan't just dump it.Port authorities of ports where dailypassenger ships are calling, are

strongly objecting to waste dumping,and have stringent requirements toprevent it. Not only for passengerships, though, but for all ships, yachtsand boats.

So getting rid of waste in the properway has been a problem for manyyears.

For cartons and paper the incinera-tor has been developed. Nowadayscommon on all ships, althoughburning sludge is sometimes

problematic. Sewage has aiso beendealt with. Numerous firms supplyan efficiently working treatment unit.Dry waste compactors are commonlyinstalled.

Sewage can be divided into grey andblack liquid. Grey is the washingwater, and water generated in the gal-leys. This can be stored in a tank, andis, subject to regulations, allowed tobe pumped in the sea. Black water,that comes from toilets, must betreated biologically and chemically,

RECYCLING i FOODBURNABLE WASTE

Ash Bagging Oily Water Sepa

122 Ships' knowledge - Chapter 6: Laws and regulations

before it goes overboard. Passengerships can not do this in port, so theyhave to store it and keep it on boardtill they are (far) at sea.

Nowadays there are firms which sup-ply the whole package, as shown inthe picture. The various problems aresolved in the following ways:- Liquid waste, grey and black water,

undergoes biological treatment,before going overboard.

- Food and wet waste is collected,made free of water by condensingand drying. The water goes to thegrey water system. The dry residue

is bagged automatically andburned.Tin and glass is crushed, shredded,cleaned, dried and split, forcollection and transport ashore, andas far as possible to be burnt in theincinerator.Engine-room generated sludge isdealt with in the incinerator.

In the end ashes and flue gas areremaining. Ashes go ashore, com-pacted tin and plastics as well.

Incinerators are complex furnaces.The initial heat in the furnace isgenerated by oil burners, the wasteto be burnt dropped from above ona travelling bed, bringing the ashesdown. The necessary heat is partly-produced by the waste itself. The endproduct is ashes and flue gas. Fluegas disappears into the atmosphereand the ashes are cooled, bagged andtransferred ashore.

. .YET WASTE „ HEPBURN BIO SHIP CARE LIQUID WASTE

Ships' knowledge - Chapter 6: Laws and regulations 123

(cleaning and discharge of the tankwashings ashore after unloading) areprescribed.

Stability in intact and damaged con-dition is an important issue.

Another important requirement for allchemical tankers is the total quantityof residue on board after discharg-ing. Special cargo pumps, or built-indevices in the cargo pumps allowemptying of the tanks till only aminor quantity (some litres per tank)is left behind; this is called the mini-mum stripping quantity. Pumping thelast drops out goes via a small pipeand not via the normal discharge lineto the manifold.

As with all other tankers, all cargohandling has to be accurately admin-istrated in the Cargo Record Book,without delay. The relevant equip-ment required for chemicals, and therequired procedures, are described ina specific book: The Procedures andArrangements Manual.

Each chemical tanker has to be pro-vided with a International Certificateof Fitness for the Carriage of DangerousChemicals in Bulk, with a attached listof cargoes that the ship is fit to carry,a tank plan, tank groups, and a list ofadditional requirements. On BCH-code chemical tankers this certificateis called the Certificate of Fitness forthe Carriage of Dangerous Chemicalsin Bulk. This certificate has a valid-ity of five years and runs parallelwith the ship's Special Survey cycle.Annual survey of the equipment ismandatory after which the certificateis endorsed.

NB: The Marpol Annex II has beenrevised and will enter into forcewith 01-01-2007. All noxious liquidsubstances are reviewed and recate-gorized in new categories called X.Y and Z.In the existing categories for examplethe edible oils are categorized as cat.D, so a 'recognizable hazard', butbecause the cargo residues are mainlysolidifying, they are judged to be amore serious hazard for the environ-ment.

7.3 Annex III

This Annex of Marpol regulates thecarriage of Packed Harmful substan-ces. The carriage of harmful sub-stances is prohibited, except whenin accordance with the provisionsin this Annex. Packages have to belabelled with the correct name anddurable mark or labelled as a marinepollutant.The packing must be adequate. Thereare stowage requirements and quan-tity limitations. Throwing overboardis only allowed in case the safety ofthe ship is at risk or in case of savinglife at sea. This type of cargo is to bereported (type, quantity, location) toharbour authorities in each port theship calls at, also when the cargo isnot handled.The relevant certificate is called:Document of Compliance for theCarriage of Dangerous Goods.

7.4 Annex IV

This Annex regulates the Preventionof Pollution by Sewage, applicable toships of over 400 GT. Every shipshall be equiped with a sewage treat-ment system, communiting and dis-infecting system, or a holdingtank.

Two criteria:- When a ship has a treatment sys-

tem sewage can be discharged- Ships having a communiting

system can discharge sewageoutside 3 miles of the nearest land.

The size of the holding tank dependson the ship's normal operating scheme,and there must be adequate connec-tions for discharge into a receptionfacility. The content of the holdingtank can be discharged overboard atleast 12 miles from shore, and onlyat a moderate rate of speed of at least4 knots.

7.5 Annex V

This Annex regulates the Preventionof Pollution by Garbage. Garbagemeans all kinds of victuals, domesticand operational waste, liable to bedisposed of continuously or perio-dically, except substances definedunder other Annexes.

(jarbage

Disposal into the sea of plastics isalways prohibited. This includesropes, fishing nets, and plastic bags.Floating waste like dunnage, liningand packing material is allowed tobe disposed of at least 25 miles fromthe nearest land. Food waste, paper,rags etc. at least 12 miles from shore.When the last is ground into smallparticles, max. 25 mm, 3 miles issufficient.

Ships operating in special areas haveto comply with more strict dischargestandards.On ships intended for longvoyages waste from packages, i.e.wood, carton, plastics, etc. can be dis-posed of by burning it in an incinera-tor. This is a simple stove, where thewaste is put into the fire-space, andwhere a simple gas-oil burner ignitesthe waste, and if necessary keeps itburning. The ashes may be disposedof in the sea.A ship must have a garbage manage-ment plan and a record must be kept,similarly to substances describedunder other Annexes.

7.6 Annex VI

Annex VI deals with airpollutioncaused by ships. This Annex cameinto force the 19th of May 2005. Itrestricts the emission of:- Substances which attack the ozo-

ne-layer,- Nitrogen-Oxygen compounds

N0(x)- Sulphur-Oxygen compounds

SO(x).- Volatile Organic Compounds

(VOC)- Exhaust of incinerators.

124 Ships' knowledge - Chapter 6: Laws and regulations

When the danger of oilpollution exists, harbour authorities will require precautions toprevent spreading of the oil. Normally a flowboom' is laid around the ship.

The NOx and SOx emissions are directly related to the quality of the fuels burntin ships dicsels or boilers, which quality is very much under economical pres-sure. Fuels available for ships are the leftovers of the refinery. The alternative,low-sulphur dieseloil is too expensive. However, in certain areas and ports, thepollution is drastically restricted, and clean dieseloil has to be used to fulfil therequirements. Tncmerators have to be provided with type-approval, which isrelated to the quality of the burning process. !MO is trying to standardise therequirements from the various involved governments.

Air pollution

8. Ballast Water Managment(BWM)

Ships need ballast water for many rea-sons: to achieve a sufficient draft andstability, to reduce stress, to correctlist or trim, etc. Ships normally takeballast during or after discharging car-go, in the port of discharge. Mud andthe local organisms come aboard withthe ballast water. During the voyage toa port of loading, the mud settles andthe organisms may grow. In the portof loading, the ballast water, or a partof it. has to be pumped out. Most of

the mud stays on board. The majorityof the organisms, however, are dis-charged with the water at the port ofloading, and may harm the local envi-ronment. Due to the growing amountof ballast water transported over theworld from port to port and region toregion, a great environmental problemhas been created. Species arc broughtto places where they become dominantto the existing species and this resultsin environmental unbalance or evendanger to the environment. ThroughIMO, a resolution has been adoptedwith regulations and guidelines to stop/ minimise this transport of species.

The aim is to reduce this transport ofspecies drastically. This resolution isexpected to come into force globallyin phases in 2009, depending on bal-last capacity and the date of build ofthe particular ship (see table). Somecountries, however, let the resolution

come into force at an earlier date.

The subject has been divided in asediment problem and the problem oforganisms. The amount of mud has to

Sediment is the collection of veryfine particles of all kinds of sol-ids, dispersed in river- and coastalwater. Most is soil, but all kind ofparticles can be part of it. Whenwater is pumped into a ship as bal-last and comes to rest, the mud inthe water settles down because ofgravity, thus forming a layer ofsediment on all horizontal surfac-es. In uncoaled tanks, rust from thetank construction will also be partof the sediment.The quantity of sediment dependson the ship's size and on the loca-tion where ballast is taken

be minimised by taking ballast in deepwater, and by removing mud when ithas settled. Getting rid of sediment isnot easy. The best way is manually:use a fire hose with low pressure andhigh volume, hose the mud towardsthe suction of the ballast pump, andsimultaneously pump the water withthe mud overboard. This process israther easy in large ballast tanks, butnearly impossible in low double bot-tom tanks, and very impracticableduring a voyage.

Apart from the environmental prob-lem, the ship's loading capacity is re-duced by the weight of the mud. Thisweight can vary from just a few tonsin a small coastal vessel, up to 2000tons in case of a capesize bulk car-rier, or a large tanker. Therefore, thesediment content has to be monitored.The amount of sediment normally sta-bilises, and is the main content of the'ships constant'. This is the differencebetween what the ship should be ableto load, and what it actually can loaduntil the limits indicated by the free-board requirements are reached.

Ships' know/edge - Chapter 6: Laws and regulations 125

Ballast water managementTable 1 summarizes the implementation schedule ol the type of treatment requiredaccording to the age of ship and its bsiiast capacity as per the provisions of theConvention f regulation B-3 ].

Table 1 - Ballast water Implementation Schedule

BallastCapacity (m3)

. . ' . . • . . . .

Construction

Firs

t In

term

edia

te o

r R

enew

al S

urve

y,w

hich

eve

r occ

urs

firs

t afte

r an

nive

rsar

yda

te o

f d

eliv

ery

in th

e ye

ar:

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

< 1500 m3

<2009

D1orD2

£2009

>1500m3but $ 5000 m3

<2009

D1orD2

£2009

> 5000 m3

<2012

D1orD2

£2012

Ballast Water Exchange Standard, D1- 35% voiumetic exchange- or pumps through tree times the volume of each tank-

Ballast Water Treatment Standard, D2- Approved treatment systems are to treat ballast water.

Removal of sediment can be done invarious ways. In the resolution dis-posal is allowed at sea at a minimumof 200 nm from shore and in water ofminimal 200 meter depth. In port, orduring repairs at a shipyard, disposalneeds to be carried out at special re-ception facilities.

In order not to arrive in a loading portwith the ballast water taken on boardin the discharge port, the ballast has tobe changed at sea during the voyage.Water taken in at 200 nm from shoreand where the water depth is 200 me-ter or more, is considered 'clean'.

Changing the ballast water can beperformed in three ways which areacceptable to the TMO;

1. Sequential method, emptying andrefilling each individual tank,

2. Flow-through method, replacingthe water by adding to and simulta-neously overflowing of the tank,

3. Dilution method, filling over thetop and simultanuously pumpingwater out the normal way.

A tank content is considered changedwhen 95 % of the water has been ex-changed. When method 2 or 3 is cho-sen, changing is considered completewhen three times the volume of thetank has been pumped through. Dur-ing the whole procedure various top-ics are to be looked at:free surface effects, draught, trim,propeller immersion, minimal draughtforward to prevent slamming, visibil-ity from the bridge, stability, stress,sloshing, possible over-pressurizing,prevention of internal transfer of bal-last water, etc.Changing ballast has to be planned,and has to be part of the voyage plan-ning. Once started, it has to be com-pleted, otherwise the organisms maygrow again.

Electrolic cells for chlorination,(test Installation)

CLEAN WATER

Centrifugal mud disposal unitSedimentor (100 mifhr)AP = 2weight: ca, 200 kg

126 Ships' knowledge — Chapter 6: Laws and regulations

An approved Ballast Water Manage-ment Plan has to be on board everyship, explaining how to change bal-last, and taking the above in account.A designated person in charge of bal-last water management and responsi-ble for the training of other personnelhas to be appointed. The form of theplan and the record of BWM activi-ties is stated in the IMO resolution. ABallast Water Record Book has to bekepi.

Where large gas tankers have fully au-tomatic computer programmes to runthe pumping sequence, on small shipsthis still may have to be done manu-ally. Precautions have to be taken thatno contamination of water in alreadychanged tanks with water from a tankthat still has to be refilled when thepumping is changed from one tank toanother.The quantity of organisms and mudcan be reduced by not taking ballastduring the night, when the organismstend to come to the surface, in shallowwater where propellers are stirring upthe sediment or where dredging is inprogress or recently done.

Filling an empty ballast tank with'clean' water straightaway is the idealsolution for the sediment and the or-ganism problems, and the objective inthe end. Heat treatment of water dur-ing filling, chlorination, or ultra-violetlight, are considered as solutions, butthese methods only kill the organismsand so only solve part of the prob-lem.Prevention of the intake of mud. andthe killing of organisms arc possibleusing a centrifugal separator to sepa-rate the sediment from the water. Thesediment goes back into the sea andthe clean water goes into the ballasttank. Most organisms do not survivethe centrifugal forces. The remain-ing organisms still have to be killedby chlorination, but only with a frac-tion of the toxic chlorine (obtained byelectrolysis of seawater) that wouldhave to be used without separation.This system is type-approved.

Facilities for ballast exchange andmonitoring should be provided onnew ships. These facilities could en-compass tank entrance hatches withsampling opportunities, remote con-

tent measuring, additional filling 9. Documentspipes, etc. The construction of tanksshould minimise sedimentation, by On the following pages some com-fifting horizontal areas like frames, pulsory documents are shown,flanges and girders with a slope. An-other way to get rid of the sediment isto get the mud dispersed into the wa-ter during de-ballasting.Certain countries with long freshwa-ter rivers, like Brazil, require the bal-last exchange to be carried out twice:once before entering coastal waters,and again before going up river.

ISSUED UNDER THE PROVISIONS OF THEINTERNATIONAL CONVENTION ON TONNAGE MEASUREMENT

OF SHIPS. 1969UNDER THE AUTHORITY OF THE GOVERNMENT OF THE

REPUBLIC OF PORTUGALREGISTO INTERN ACIONALDE NAVIOS DA MADEIRA

for which the Convention came into force on lit September 1987

bv

Name of Ship

S1DERFLY

Official Numberor

Distinctive Number or Letters

CQUT

IMO No.: 8412405

Port of Registry

Madeira

Da:e *)

27.08.1984

''•) Date on which the keel was laid or the ship was at a similar stage of construction [Article 2(6)]. or-datc or. wbidi die -Jiipcations ui'a major character [Artick-3 (2)(h)K-ttti-appidprial.eT

MAIN DIMENSIONS

Length[Article 2 (3)]

95.09 m

Breadth[Regulation 2 (3))

14.60 m

Moulded Deprh amidshipsto Upper Deck

[(Regulation 2 (2)!

6.95 m

The Tonnages of the ship are:

GROSS TONNAGE 2881

NET TONNAGE 1371

This is to certify that the tonnages of this ship have been determined in accordance with the provisions of the InternationalConvention on Tonnage Measurement of Ships, 1969.

Issued at Hamburg on 22lld April, 2002

The undersigned declares thai he is duly authorized by the said Government lo issue this certificate.

Ships' knowledge - Chapter 6: Laws and regulations 127

Side view

8 Miscellaneous

8.1 Ventilation Louvres

All the vents of the holds, the engineroom and the accommodation areshielded by gratings, often louvres.These have to be provided with meansfor closing weather-tight and air-tightby a cover in case of bad weather orfire.

Ventilation louvre with cover

Ventilation louvre for the accommoda-

tion

•Vi

Cross-section and top view of a manhoh

cover

Manholecover of topwingtank nr I. portside. in the maindeck of a bulkcarrier, looking aft.

Cross section and top view of a cargo oil

hatch with cover

Some types of vent terminals

A rotating cover on a cargo oil hatch

8.2 Manhole CoversManhole covers close the accessopenings that are part of every tank,except for the cargo tanks. Manholesmake it possible to inspect a tank.

8.3 De-aeration devices

- Tank vent / overflowEvery liquid-containing tank musthave a means of venting in order toprevent over- and under- pressureduring emptying or filling. For thispurpose, every water and oil tank hasa venting possibility. This pipe endson the freeboard deck at a vent termi-nal with a closing device, preventingseawater entering the tank.

In case of submersion of the tankbleeder, a floating ball inside thetank bleeder will float upwards untilit is pressed against a rubber ring.

Ship Knowledge - Chapter S: Closing appliances 187

laised tank vents

Drawing of (he inside of a vent terminal

1. Plastic ball2. Rubber gasket3. Vent opening4. Air and water release pipe

This mechanism seals the pipe fromthe seawater. When, during filling thetank is overfilled, the surplus water oroil discharges via the vent terminal ondeck. Tank vents / overflows can beimplemented with:- an overflow, capable of guiding

the contents of the tank to anotherlocation

- a sounding opening where thedepth of the liquid in the tank canbe measured

- in case of a vent / overflow of anoil-tank, a flameproof mesh iscompulsory, and a save-all to keepoil inside.

Cargo tanks of tank vessels havecomplicated venting systems, in con-nection with inert-gas and the influ-ence of outside temperature on thepressure of the possible huge gasquantity in the (empty) cargo-tank.

- Mushroom shaped ventsMushroom shaped vents are onlyused for the ventilation of dry spaceslike the bosun's store or the accom-modation. They have to be providedwith a fire-flap for protection againstfire or bad weather. Often the wholemushroom-head can be screweddown to close the vent. There are twoways of closing them, either manu-ally rotating the top part or with avalve. They are a mechanical back-upwhen the air-conditioning does notwork; under normal circumstancesthey arc closed.

Mushroom shaped vent with a handw-

heel

- High speed pressure valvesHigh speed pressure valves are tankvents with the special characteristicthat they let the gas escape only whena certain overpressure is reached,and not before that. The velocity ofthe escaping gas is so high (with aminimum of 30 m/sec) that it cannever catch fire. The gas rapidlydiffuses into the air and will not fallback to the ship.

They will also let air into the tank incase of under-pressure, for exampleduring the emptying of the tank. Toensure that no flames can get insideof the tank via this route, a fire resist-ing wire mesh covers the inlet sideof the valve. The type of high speedpressure valve discussed here is themost widely used type on tankers.It is a safety device against over- orunder-pressure, which ought to betaken care of by the inert-gas system,or damp-return system.

All the parts mentioned in this sectionarc cither bronze, galvanised or madefrom stainless steel. The classifica-tion society determines which type ofmaterial is to be used.

High speed pressure valve. The arrows

depict the path of the escaping gas

High speed pressure valve- The arrows

depict the path of the gas flowing inPressure / vacuum valve (P. V. valve)

188 Ship Knowledge - Chapter 8: Closing appliances

9. Coming on board /Access to the ship

- Accommodation ladderEvery ship needs means of gettingpeople on board safely. Most vesselshave two accommodation ladders,one on starboard and one on portside,preferably where the ship's side isflat. In general, the accommodationladder is made of lightweight alu-minium that makes it easy to handle.The top of the accommodation ladderis attached to a platform with a slew-ing connection, so that, if necessary, itcan be turned away from the ship, incase of a large gap between the shipand the quay. On the quay the accom-modation ladder rests on a roller,which is at the bottom of the stairs.This roller allows the accommodationladder to slide on the jetty as a resultof changes in draught or movementsof the ship. Lowering and lifting ofthe accommodation ladder is done bya winch.

Compulsory safety measures:- a safety net hanging under the

gangway.- a life buoy at the gangway with

light

- Gangw ayMany vessels have an aluminiumgangway in addition to an accommo-dation ladder. This gangway comesin use whenever the accommoda-tion ladder cannot be used, for somereason of location or jetty lay-out.The gangway is put into the wantedposition by either a crane or by man-power.

Unfolded accomodation ladder.

Gangway on a passenger liner

1. Top platform2. Steps3. Bottom platform4. Roller5. Hand-rail6. Stanchion7. Synthetic rope8. Steel cables attached to

the winch

Side view of an accommodation ladder and top view of the platform

Ship Knowledge - Chapter 8: Closing appliances 189