1) Draw a typical block diagram of compressed air system of a motor ship, Labeling all the components

2)a)Draw a P-V Diagram, for various types of compression b)Explain each type of compressiona.)

Compressor work for various types of compression indicated in a P- V diagram:b.) . ISOTHERMAL COMPRESSION:

It is the compression at constant temperature. In practice, it means that the temperature by of gas (air) remains constant throughout the compression. It means that heat of compression is immediately taken away. This would necessitate infinitely slow compressor. This type of compression theoretically is most efficient compression, but difficult to achieve. Very slow moving piston in a well-cooled small-bore cylinder can approach Isothermal compression.

2. ADIABATIC (ISENTROPIC) COMPRESSION:

It is the compression under constant enthalpy conditions, i.e. no heat is given to or taken from the gas through the cylinder walls and all the work done in compressing the gas is stored within it. During this compression the temperature raises progressively causing increase in rate of pressure rise, which calls for increased power input to piston. This gives it poor efficiency. A very fast moving piston in totally insulated cylinder will give adiabatic compression.

3. POLYTROPIC COMPRESSION:

It is the compression process which lies-in between two extremes of isothermal and adiabatic compression. Here, some parts of heat of compression is usually extracted by Jacket cooling and multi-staging with inter cooling is used to reduce work of compression. 3)Why multistage compression is used on air compressors?*MULTISTAGE COMPRESSION: If we had an infinite number of stages of compression with coolers in between each stage returning the air to ambient temperature, then we would be able to compress over the desired range under near isothermal conditions. This of course is impracticable so two or three stage compression with inter-stage and cylinder cooling is generally used when relatively high pressures have to be reached. *4)a)Why intercooling is used in multistage air compressors?* *b)What are the advantages of intercooling?*a.)Inter-cooling:To avoid excessive temperature rise associated with higher compression ratios, and to approach isothermal compression, inter-cooling is adopted after each stage of compression in a multistage compression. Usually, delivery temperature from final stage is limited to 93*C (Lloyd's Rules). b.) Advantages of Inter-cooling:1. Compression work is reduced.2. Volumetric efficiency and hence compressor capacity is increased.3. It approximates isothermal compression.4. The volume of air delivered is reduced, requiring reduced sizes of cylinder, piston and delivery pipes.5. The temperature of air delivered is reduced, which gives less thermal loading onto material and better lubrication of piston and cylinder.6. Due to less temperature suction and delivery valves remain cleaner without being fouled with carbonized oil.7. Moisture separation is easier through intercooler drains.8. Use of after cooler allows smaller receivers.

5)Explain i) a) clearance volume b)Volumetric efficiency c)compressor capacity. ii)Enumerate the factors affecting volumetric efficiency. iii)Draw a simple sketch , showing the effects of clearance volume a) CLEARANCE VOLUME: To provide for thermal expansion and for machining tolerances, a small clearance, called, Bumping clearance, is left between cylinder head and the piston. This clearance must be as small as possible, as its increase will reduce the volumetric efficiency and hence capacity of the compressor. b)VOLUMETRIC EFFICIENCY: Volumetric efficiency is the ratio of the actual volume of air drawn in each suction stroke to the stroke volume. Referring to the figure:

Pressure Volume Diagram of a Compressor with clearance (without flow resistance).Volumetric efficiency = v = vs/vpc.) COMPRESSOR CAPACITY: Compressor capacity is determined as volume of the free air actually discharged by compressor in one hour. It is termed as F.A.D. (free air delivery) in m3/hour.

ii) Factors Affecting volumetric Efficiency:

1. Clearance volume (Bumping clearance) adversely affects volumetric efficiency. High-pressure air remaining in the cylinder after compression and delivery will expand on the return stroke of the piston. This expanding air must fall to a pressure below that in the suction manifold before a fresh air charge can be drawn in. Hence, part of the return or suction stroke of the piston is non-effective. This non-effective part of the suction stroke must be kept as small as possible in order to keep capacity to a maximum.

2. Sluggish opening and closing of valves.

3. Leakage past piston rings.

4. Insufficient cooling water.

5. Cooling water temperature high.

6. Air inlet temperature high.

7. Throttling of air intake. (Due to dirty intake filter, insufficient or excess suction valve lift, suction valve spring too strong).

iii)

Effects Of Increasing Clearance volume.

6) a) What are the statutory requirements for Air Compressors?

AIR COMPRESSOR REQUIREMENTS: 1. Two starting compressors must be fitted, of sufficient total capacity to meet the engine requirements. Each compressor must be able to press up Air receiver from 15 bar to 25 bar in thirty minutes. Two air receivers must to be provided. Total air receiver capacity is to be sufficient for Twelve (12) starts of Reversible engines and six (6) starts for non-reversible engines.2. Additional one Diesel driven or hand operated (or if possible, both) emergency air compressor must be fitted to start auxiliary engines of a Dead Ship.3. Safety valves or preferably bursting discs must be fitted on the cooling water casing to give ample relief of pressure, should an air-cooling tube burst.4. 4.Each compressor must have a safety valve designed so that the accumulated pressure, with the outlet valve closed will not exceed 10% of the maximum working pressure.5. 5.The air compressor cylinders, covers, intercoolers and after-coolers, are tested by hydraulic pressure to twice their working pressure.6. 6.The casing of the inter-cooler and after-cooler is hydraulically tested to 1.5 times cooling water pressure. Thus, for 4 bar cooling water pressure, the casing will be tested at 6 bar pressure.7. 7. A water separator or drain should be fitted on the airside of each intercooler. The drain cock should be used at regular intervals to prevent water from one stage being carried into the following stage. b) How are compressors classified?

CLASSIFICATION OF AIR COMPRESSORS:Compressors can be classified according to principle of compression as follows: 1. Positive Displacement Compressors: They increase the pressure of gas by decreasing its volume. These can be further subdivided intoa) Piston Compressors: In which the gas volume changes due to the action of one or two reciprocating pistons, moving axially in cylinder e.g. Reciprocating air compressors. b) Rotary Compressors: In which the gas volume changes due to rotation in the cylinder of rotary vanes of an eccentrically placed rotor.c) Membrane Compressors: In which the volume variations are effected by deflection of an elastic partition. 2. Dynamic Compressors: These increase the pressure of gas by imparting to it the kinetic energy, which is converted into pressure energy into a diffuser. These are multi-blade compressors and are further subdivided into:a). Centrifugal Compressors: In which a high peripheral velocity is imparted to the gas being compressed by the blades of the impeller, which rotates at a speed of 3000 - 27000 r.p.m. The centrifugal force developed in this way partially compresses the gas. Further compression happens in diffuser by reducing its velocity. Depending upon the direction of gas flow at outlet from impeller compressor can be radial or axial compressor.b). Jet Compressors: In which a driving vapour attains a high supersonic velocity in a Laval nozzle and is mixed with the gas to be compressed in a mixing chamber and leading it at high velocity to the diffuser where kinetic energy is converted into pressure energy. 7)a)Describe a two stage air compressor with a line diagram.

The two-stage compressor arrangements below show the single acting pistons acting in conjunction with an intercooler.Lubricating oil for air compressors should have, among many other properties, a flash point minimum of above 2000C for safety.High temperatures can carbonise the oil and form a gritty deposit which will cause severe wear on piston rings, and cylinder liners, -- expensive replacement parts. This also causes the compressor valves to coke up which can restrict their operation and sealing, thus reducing the compressor efficiency.Modern practice is to use a synthetic oil for lubrication.

By using intercooling and cylinder cooling (usually Air or Water with air compressors) the oil is kept in a fluid condition (i.e. it does not vaporise or carbonise) so it may lubricate properly.

Operation

On the downward stroke of the piston in a single cylinder compressor, air is drawn in through the suction filter and the suction valve, to fill the cylinder. The downward motion of the piston causes a partial vacuum in the cylinder so the atmospheric pressure of the outside air pushes the suction valve open against the light force of the spring that holds it closed when the machine is stopped.As the piston begins its upward stroke the suction valve is pressed shut as the air pressure inside the cylinder rises. Continued upward motion further raises the pressure until at a designed pressure the discharge valve is pushed open against the larger spring force that holds it closed when the machine is stopped, and the compressed air will then pass through an intercooler to a second stage.

The piston-reciprocating compressor has a more positive sealing arrangement (rings) than any other type of compressor and consequently it can achieve higher compression ratios than any other form of compressor.The two-stage compressor arrangements below show the single acting pistons acting in conjunction with an intercooler.Lubricating oil for air compressors should have, among many other properties, a flash point minimum of above 2000C for safety.High temperatures can carbonise the oil and form a gritty deposit which will cause severe wear on piston rings, and cylinder liners, -- expensive replacement parts. This also causes the compressor valves to coke up which can restrict their operation and sealing, thus reducing the compressor efficiency.Modern practice is to use a synthetic oil for lubrication.

By using intercooling and cylinder cooling (usually Air or Water with air compressors) the oil is kept in a fluid condition (i.e. it does not vaporise or carbonise) so it may lubricate properly.Multi-stage air compression have the following advantages:1. They can maintain a moderate range of air temperature by cooling the air between stages. Cylinder cooling also assists this to a smaller extent.2. By cooling between stages (and cylinder cooling), less work input (i.e. less electric motor or diesel power) is required to compress a given quantity of air to a specific pressure.3. Lubrication difficulties can be minimised by keeping the air temperatures as low as possible, (above 200C the oil tends to carbonise onto piston rings and in delivery valves, seriously impairing their operational efficiency).It is common practice to use synthetic oils rather than mineral based oils to avoid carbonisation, despite their much higher prices.

b) State the typical air pressures & temperatures for each stage.

stagesDelivery Pressure Air. temperature

Before the coolersAfter the coolers

First stage4.7 bar130C35C

Second stage26.7 bar130C35C

8) a)Name the main components of a reciprocating air compressor & the materials they are made of.

The main components of a reciprocating air compressor_ area) Bedplate - cast ironb) Crankcase - cast ironc) Cylinder block - cast irond) Cylinder cover - cast irone) Piston - cast iron or alurninium alloy.f) piston rings - cast iron (wet liner) and bronze or phenolic plastics (dry liner) g)connecting rod - forge steel or alurninium alloyh) crankshaft - forge steel.i) top ends bearing - brass bushj) bottom ends bearing - thin shell white metal linedk) gudgeon pins - case hardened steel1) suction and delivery valves--valve seat - carbon hardened steel, hardened and polished working surfaces. valve - nickel steel, chrome vanadium or stainless steel, hardened andpolished.valve spring - hardened spring (tempered)c) Enumerate the various mountings fitted to the air compressor.

The following mountings are fitted to the air compressors to ensure safe and efficient operations:1)Air Filters2)Intercoolers 3)Drain Valves4)Relief Valves5) Bursting Discs 6) Fusible Plug

9)a)What are the consequences of unfiltered air getting into the compressor suction side

Air contains suspended foreign matter, much of which is abrasive. If this is allowed to enter the compressor it will combine with the lubricating oil to form an abrasive-like-paste which increases wear on piston rings liners and valves. It can adhere to the valves and prevent them from closing properly which in turn can lead to higher discharge temperatures and the formation of what appears to be a carbon deposits on the valves, etc. Strictly, the apparent carbon deposit on valves contains very little carbon from the oil; it is mainly solid matter from the atmosphere. This carbon like deposits can become extremely hot on valves which are not closing correctly and could act as ignition points for air-oil vapor mixtures, leading -to possible fires and explosions in the compressor. Hence air filters are extremely important, they must be regularly cleaned and where necessary renewed and the compressor must never he run with the air intake filter removed. b) Describe the effect of a dirty air filter in a multistage air compressor.*

Dirty filter causes pressure drop in air intake, which causes higher compression ratios resulting in higher delivery temperature, which can cause fire and explosion.

A choked filter causes a vacuum on the compressor inlet, which reduces the out put, raises air temperature and may cause filter element sucked in cylinder with inherent dangers.

c)Explain why the air inlet filter need to be maintained in good working order.

It is essential that the filter is kept in a clean condition so that the air pressure drop across the filter is kept to an absolute minimum. If clean, imposes very little resistance to airflow. With most types, regular cleaning or renewing filter elements is necessary. A choked filter causes a vacuum on the compressor inlet, which reduces the output, raises air temperature and may cause filter element sucked in cylinder with inherent dangers.

10)a)Sketch an automatic valve forAir delivery and Air suction

Air delivery

Air suction b) Name the materials used in their construction.

Valve seat: 0.4% carbon steel hardened and polished working surfaces. Valve: Nickel steel, chrome vanadium steel or stainless steel, hardened and ground, then finally polished to a mirror finish. Spring: Hardened steel (N.B. all hardened steel would be tempered).

11) Describe the principle of operation of an automatic drain trap , fitted to air compressors and air receivers with a sketch.

Principle of Operation : With water under pressure at the inlet the disc will lift, allowing the water to flow radially across the disc from A to the outlet B when the water is discharged and air now flows radially outwards from A across the disc, the air expands increasing in velocity ramming air into C and the space above the disc, causing the disc to close on the inlet. Because of the build-up of static pressure in the space above the disc in this way, and the differential area on which the pressures are acting, the disc is held firmly closed. It will remain so unless the pressure in the space above the disc falls. In order that this pressure can fall, and the trap re-open, a small groove is cut across the face of the disc communicating B and C through which the air slowly leaks to outlet. Obviously this gives an operational frequency to the opening and closing of the disc which is a function of various factors, e.g. size of groove, disc thickness, volume of space above the disc, etc. It is therefore essential that the correct trap be fitted to the drainage system to ensure efficient and effective operation.

12)What are the safety devices fitted to an air compressor? Mention their requirements.

Safety devices Relief valveFitted to each stages on air side and set to lift at pressure 10% more than stage pressure.Bursting disc / Bursting Valve Fitted to water side on coolers, will relieve excess pressure in the water casing in the event of failure of an air tube.Oil relief valve (Inside Crankcase) Fitted in the oil system to relieve pr. more than 25% of normal working pr. to protect oil pump from overloading, during cold start up.Fusible plug On air delivery pipe or on air reservoir a fusible plug is also fitted which melts at 121*c, this ensures the safety of after machine system against temperature rise.L.O.Pr.cut out switches Protects the compressor machine from damage due to loss of lubrication oil.Air high temperature cut out switches Protects compressor and air system from damages due to high temperature air.13) Enumerate the various methods used for unloading the air compressor cylinders.

Ans.Unloader :A compressor, during starting and stopping must be in unloaded condition. This reduces starting torque (current for motor)for the machine, also it clears out any accumulated moisture.If the compressor is required to be running continuously, it has to be unloaded after the reservoir is filled to full pressure.Methods of unloading Compressor1.Throttling of suction 2)Speed variation 3)Depressors to hold suction valve plates on their seats.4)By-pass, discharge to suction 5)Changes in volumetric clearances of the cylinders6)Step unloading of cylinders in a multi cylinder machine

14) Sketch & describe the unloading method, by throttling the suction side. Unloading by Throttling the Suction Side

Operation: The compressor discharge at maximum pressure will move the valve to the left, stopping the air intake. So no air is delivered. 15)How is the running gear of reciprocating air compressors lubricated? Some air compressor piston are connected to the connecting-rod through a gudgeon pin and are similar to trunk pistons. With such an arrangement the cylinders are lubricated by oil splashed from the crankcase.condition of scraper rings is of the utmost importance in this type of compressor. When air compressors pistons are connected to the running gear through piston rods and crossheads, the piston rings,pistons,and cylinders are lubricated with lubricator pumps similar to those fitted on crosshead engines for cylinder lubrication .the oil is passed through a quill fitting to the cylinder liner.

16)What are the two basic designs of rotary compressors? Briefly describe a sliding vane compressor with a sketch.

1.positive displacement type in which power is converted directly into pressure energy.2.Dynamic type in which a fast moving impeller causes the air to move at a high velocity and the kinetic energy so created is subsequently converted into pressure energy by the diffuser.eg:centrifugal blowers.SLIDING VANE COMPRESSOR:In this design a slotted rotor carries a number of blades, which maintain contact with the bore of the casing by sliding in and out as the rotor turns with the help of springs backup. Inspection of the diagram will make the operation clear. During the first half of a revolution, the space bounded by a pair of blades is gradually increasing to a maximum. After this it gradually reduces until it is almost zero at the point where rotor and casing are in close contact. During the first half of the revolution air is aspired from the inlet port and is trapped when the blade passes the cut-off point. While the suction opening occupies almost half the periphery of the casing, the delivery port occupies a much smaller arc. There is a period of time during which the air cannot escape and is gradually compressed as the space between the blades is reduced in volume. The delivery is so arranged that the air has already been compressed to a suitable pressure before it is allowed to escape into the discharge port.

17)What are the effects of leaking suction & delivery valves of first & second stage, in a two stage air compressor.

Valves can leak and finally fail. Valves may fail due to wear and fatigue, wrong selection, insufficient or over lubrication, presence of foreign particles, oil decomposition and excess valve lift. Effects of valves leaking: First stage suction: Reduced air delivery, increased running time and reduced pressure in the suction to the second stage. If the suction valve leaks badly it may completely unload the compressor. First stage delivery: With high-pressure air leaking back into the cylinder less air can be drawn in. This means reduced delivery and increased discharge temperature. Second stage suction: High pressure and temperature in the second stage suction line. Reduced delivery and increased running time. Second stage delivery: Increased suction pressure in second stage, reduced air suction and delivery in second stage. Delivery pressure from first stage increased.

18)Sketch a line diagram for Main air bottle, indicating all the mountings & their welding arrangements. b)What are compensation rings & why are they necessary?Whenever a hole is cut

(b)The mountings of the air bottle are fitted on a circular plate with hole drilled of same dia as drilled on air bottle for the mounting. These circular rings are welded to the outer shell of the air bottle and fitted whenever a hole is cut to regain the reduced strength due to drilled hole.19)a)What are the basic requirements for steering gear? b)Represent the steering gear system of a ship, by a block diagram.THE BASIC REQUIREMENTS FOR STEERING GEARS:In brief, a steering gear is required to:a) Be continuously available;b) Move the rudder rapidly to any position in response to the orders from the bridge during manoeuvring, and hold it in the required position;c) Have arrangements for relieving abnormal stress and returning the rudder to its required position,d) Maintain the ship on course regardless of wind and waves. The first three points are now governed by complicated statutory requirements and the last is of particular interest for economic reasons. A steering gear is provided for steering a ship and therefore its perfect ness of design is of utmost importance. Even a small fault cannot be overlooked as this may subsequently result in failure of the system, which in turn would result in collision or grounding of the ship. (b)

20)Explain the Telemotor hydraulic transmitter with a sketch. Indicate the materials of the components.

Material: Casing Gunmetal. Rams Bronze. Pipes Copper. Cups (old type) Leather.In the new Transmitters the rams are lapped to the cylinders.The transmitter consists of two rams ending in racks, which mesh with a primary pinion attached to the steering wheel shaft and housed in a casing. The unit consists of two parts:The top which houses the racks and the pinion and serves as the replenishing or make up tank, the racks and pinion being lubricated by this fluid.The bottom half which is made of two cylinders in which reciprocate the rams passing through sealing glands.

21)Explain the construction & working of the Bypass valve of the Telemotor transmitter. Why it is provided?

Since the cylinders are always full of the hydraulic fluid a device has to be fitted to allow for the variations in the oil volume due to temperature changes,relief in case of a build up of pressure and for equilibrium between the two cylinders when the wheel is at midships. This device is called a Bypass Valve.The working is as follows: When the steering wheel is at midships the cam depresses the operating rod, which in turn depresses the two valves, which connect up both the cylinders, and any pressure difference is equalized.This equalising connection is also connected to the replenishing tank at the top of the telemotor transmitter as shown in the attached diagram.

22)Explain the Telemotor hydraulic receiver with a sketch. Indicate the materials of the components.

It consists of two hollow rams in line, fitted to two fixed crossheads. A cylinder closed at mid length and open at each end, fits over and floats between the rams. Sealing glands (construction described later) are fitted at each end of the cylinder and air cocks provided on both sides. The crosshead and the rams are kept fixed and aligned by two parallel rods. The rods have two sleeves each fitted over them and sliding through the cylinder casing. The stopper nuts as shown restrict the movement. Each set of sleeves carry a strong spring between them. The crossheads are connected by supply/return pipe, to the telemotor transmitterSlight movement of the moving cylinder causes the left hand sleeve to butt against the stopper nut and further movement causes the spring to get compressed. When the steering wheel is returned to midship the springs, which are under compression, return the moving cylinder to its mid position.

23) What are the desirable properties of Telemotor hydraulic oil?The Hydraulic oil should have the following properties:Low pour point around -50*C.Low viscosity (30 Redwood sec. at 60*C).High viscosity index (110).High flash point (closed flash point 150*C).Non-sludge forming.Non-corrosive.Good lubricating properties but not too thin that will make gland sealing difficult.Density about 880 kg/m3 at 15.5*C.

24)Explain the construction & working principle of Hele Shaw Pump, used in steering gear system.

Operating Principle

This pump consists of a shaft which is stationary and a cylinder body which rotates around this shaft. Cylinder body is provided with odd number of cylinders spread around it Each cylinder has a plunger, connected to slippers, which in turn run in annular grooves inside two circular rings on either side of the plungers. Only one cylinder of the cylinder plunger assembly at four different positions during one rotation is shown. Plunger, in addition to rotating along with the cylinder, may also have in and out movement, depending upon the position of the circular ring. If center of the circular ring is concentric with center of stationary shaft; as shown by O, the plungers will have no in and out movement. Thus plunger will act like a pump sucking in oil from chamber at top (T) and pumping into the oil chamber at the bottom (B) of the stationary shaft. As the stroke of the plungers can be varied with the change in eccentricity of the circular ring, the pump therefore is a variable delivery pump. Cylinder body is rotated at constant speed and direction by an electric motor. Odd number of cylinders, usually seven or nine are provided, to produce more hydraulic flow and to give better pump balance.

25)a)Make a labeled sketch of a two ram steering gear.

b)State the purpose of hunting gearThe tiller arm is connected to the bottom portion of the floating lever by a buffer spring and link. This is called the hunting gear. Hunting gear acts as a feedback system of rudder movement to the control system.

26)Discuss the mechanical stops & limits in a Steering Gear system.

A. mechanical stops & limits in a Steering Gear system: As per regulations a steering gear system should be capable of putting the rudder from an angle of 35* on one side to 35* on the other side (statutory requirement is to put rudder from 35* on one to 30* of the other side) in 28 seconds. To ensure that these limits are maintained there are a number of stops and limit switches. the mechanical stops that are provided are in the following actuating order: 1. Auto pilot mechanical stop. 2. Local control mechanical stop, where local control provided. 3. Actuating system mechanical stops that limits on the ram travel, provided as stops against tiller arm movement or some thing similar. 4. Bridge Telemotor transmitter mechanical stop (Rack travel limited). 5. Finally, stern- post mechanical stop. Extra movement of the rudder due to heavy seas or some other reasons is finally or lastly limited by the stern post stops which are set at 36* on each side.

27)Describe the construction of crosshead arrangement of a ram type steering gear, with a sketch, labeling all parts & clearances.

A. The ram ends are usually forked and each pair of rams are bolted together at these ends forming bearing halves as shown. These are bushed to form the top and bottom vertical bearings, which take or clamp the pins or trunnion arms of the swivel block. The swivel block and the pins together are called the crosshead . The swivel block has a horizontal gunmetal bush through which passes the tiller arm. Provision is made by the way of clearances as shown between the swivel block and the ram fork ends for wear-down of the rudder and tiller arm and also to accommodate the vertical movement of the rudder. These two clearances are of utmost importance for the safe working of the cylinders and rams. Any vertical movement of the rudder should not reflect by the virtue of forces on the crosshead. To ensure this (ie. No force coming on the crosshead) it is important to make sure: 1) Wear down clearance as shown above, should be at all times, more than any pintle wear down provided, in the Rudder.2) Jumping clearance as shown above should be at all times, more than the allowable vertical play clearance permitted by the rudder, that is clearances at the striking pad or clearance at the pallester bearing. If striking pads are fitted between the rudder top and the stern-post, one should make sure that this stopper arrangement is effective for all positions of the rudder from hard port to hard starboard. It is of utmost importance that all the clearances are measured and recorded with date, during the vessels routine dry-docking

28)What are the regulations for Steering gear on Tankers & LPG Gas carriers?*A. Oil tankers, gas tankers & chemical tankers are required to have a safematic design of steering system i.e. no single failure on a steering should make the steering of the ship inoperative and thus give the rudder a chance to become free. 29)Explain the Rotary vane Steering gear system, with a line diagram, labeling all the parts.

A.

It consists of a rotor which is a taper fit on the rudder stock and keyed to it and a stator of larger internal diameter than the outside diameter of the rotor, to form an annular space between them. The stator is firmly fixed to the ships structure by anchor bolts to prevent it from rotating. A variable delivery pump delivers into one side and receives from the other side, till the rudder is at the required position. At this point the feed back lever L3 brings the pump to neutral (zero pumping position) and the rudder gets hydraulically locked. Compared with the 4 ram hydraulic steering gear, the cost of the rotary vane type to produce the same torque on the rudder stock is generally less. It is lighter in weight, takes up less space and requires less maintenance.

30)In electrical steering gear system, show with a sketch, how the power is transmitted .

31)a)What is follow up and non follow up steering system?* b)What is the function of Auto Pilot ? * c)What is a gyrocompass?*

A) .Follow Up steering system the angle or amount through which the rudder turns is dependent on the amount of turn of the steering wheel. In a Non-Follow Up steering system, the steering gear and hence the rudder will move as long as the control is held in an actuating position, and will only stop when it is moved back to an OFF position or until the gear has reached the hard-over position.Thus in a non-follow up system the amount of rudder movement depends upon how long the control is held in the operating position and therefore this system can also be termed as "The time dependent steering system." b)The function of an Automatic Helmsman or Auto Pilot is to steer a ship on a preset course (aided by a gyrocompass), with a minimum of deviation, which could be caused by heavy seas or bad weather. The maximum deviation allowed is 3* on either side.c)A Gyrocompass is a compass fitted on a Gyroscope, which consists of heavy swiftly rotating wheels so mounted that its axis can turn freely in all directions and the compass would still maintain its position with reference to the true north.

32)Explain the non follow up system with a line sketch, labeling all parts.

The above figure is a line diagram of a non-follow up system using fixed delivery pumps. The control on the bridge is by means of a spring-loaded lever. The control position is the off position and when it is on one side it gives a starboard movement to the rudder and when on the other, a port movement. The lever operates a switch, which energizes one of the two solenoids, depending upon the direction of movement required. These solenoids operate a pilot valve which causes the main control valve to move so as to divert oil pressure from a continuously running fixed delivery pump to the steering gear in order to give the desired direction of rudder movement. When the switch is released, it springs back to the central position, the control valve moves to a position where it bypasses the pump delivery, and the steering gear stops. At the same time, the control valve seals off the pipes to the main cylinders so as to hold the rudder. If the system is on autopilot control then the lever is held over by the autopilot and springs back to off position as soon as it stops acting. Thus the autopilot acts as the hunting gear, stopping rudder movement as soon as it has reached the desired angle as signaled by the rudder indicator

33)Describe the Electro Mechanical Auto Pilot, with a sketch.

It is a separate unit to the hydraulic telemotor and fitted in the steering flat. The bridge console has a switch or control lever with three positions; Off, Hand and Gyro. In the Off position the autopilot is out of action and operation can be done using the hydraulic telemotor. In the Hand position the control lever or push buttons of the non-follow up system can be used and in the Gyro position, the automatic steering is engaged. In both Hand and Gyro positions the bypass valve of the telemotor transmitter is opened so that the receiver can move freely. The auto pilot unit is linked to the steering gear control and consists of a drive motor (servo motor), a rack, magnetic clutch, limit switches, a synchro-transmitter and gear trains. The motor is fed from the ship's mains and is of the reversible type and to ensure quick stopping -dynamic braking is used. The motor drives the rack through gearing and an electro magnetic clutch, the rack being coupled to the telemator receiver actuating or moving cylinder. The clutch is necessary so that the motor and rack will be disconnected when the gyro pilot is not in use and it also acts as a safety device, designed to stop under excessive torque load. (The coil of the electro magnetic clutch in connected through a control switch, operated by the control lever, the circuit being completed only when the control lever is in the Hand or Gyro positions. The limit switches are cam operated, turned through gearing by the movement of the rack and are set to trip in the hard-over positions, inside the stops on the telemotor receiver. They are so arranged that when one has tripped in one direction, no further movement can be made in that direction but the unit would respond to a reverse signal. The auto pilot servomotor has a feed from the Gyrocompass. Once the course is set, and deviation of more than three degrees (3*) makes a contact in the compass which actuator, the servomotor and hence results in the rudder movement. The operation between the rack and the rudder has been explained earlier on, under the non-follow up steering system.

34)Enumerate the rules governing Steering Gears.

All vessels must be provided with efficient main and auxiliary steering gear of power operated type. An auxiliary gear is not required if the main gear is provided with duplicate power units and duplicate connections up to the rudder stock. The main steering gear must be able to steer the ship at maximum ahead sevice speed and be capable at this speed, and at the ships deepest draught, of putting the rudder from 35 degree on one side to 30 degree on the other side in no more than 28 seconds. The vessel must have means provided to allow steering from a position aft. Two tillers, or their equivalent, are required unless the working tiller is of special design and strength. Power operated gears must be fitted with a device to relieve shock. Any lead connections, steam, hydraulic or electric should be independent to the gear only. Electric leads and fuses are to allow 100% overload. Moving parts of steering gears should be guarded to avoid injury to personnel. Hydraulic systems should employ non-freezing fluid. Steering room floors should have wooden gratings to provide for easy movement of personnel in case of ol spill. A clear view from the steering position is required and the wheel, tell-tale indicators, and rudder movement must correspond in the correct amount and in the correct direction for the ships head. Operating trials should be carried out on steering gears to ascertain degree of action, time of operation, angle of heel at various speeds, etc.

35)Describe a steering system for a Tanker ship, with automatic changeover within 45 seconds, with a line sketch.

Safematic Design: Method No.1 (Also called 100% redundancy method), refer figure All valves are automatically controlled and electrically operated valves. In this arrangement System I supplies to ram No. I &2 . System 2 supplies to ram No. 3 &4 . However, as it is not practical to have both systems work simultaneously, and therefore the only combination of operations available are: Combination No. 1: Isolating valve I & 2 open, By pass valve 5 shut; system No. I In operation. Isolating valve 3 & 4 shut, By pass valve 6 open; system No. 2 stopped Top two rams are in operation, working on system No. I and are providing 100% torque. Bottom two rams & system No. 2 is shut. Combination No.2: Isolating valve 3 & 4 open, By pass valve 6 shut, system No. 2 in operation. Isolating valve 1 & 2 shut, By pass valve 5 open, system No. stopped Bottom two rams are in operation, working on system No. 2 and are providing 100% torque. Top two rams & system No. l is shut Now the logic circuit of safematic design in this method will cause the condition of operation to change from Combination No. I to Combination No.2 or Combination No.2 to Combination No. 1 (depending on which Combination was in operation when the heavy loss of oil LLL (Low low level) alarm is actuated). Example If Combination No.1 is in operation, (i.e. system No.1 & rams No. 1& No. 2 are in operation) & LL (Low level) alarm actuates. This alarm takes care of normal leakage & can be set right by filling in some oil in the tank during the watch. However, if LLL (Low low level) alarm follows immediately, it indicates a heavy loss of oil and logic circuit will cause the condition of operation change from Combination No.1 to Combination No.2. It may be noted that as said earlier even though we have 4 rams, only 2 rams are in operations at any given time. Thus each set of 2 rams should provide 100% torque. Most ships will not employ this method to take care of single failure criteria, as this method means a 100% duplication and a costly one. *36)Explain the test procedure that should be carried out on an electrohydraulic steering gear a)before leaving port *b)before arriving port.

Prior Departure:1. Steering gear should be checked at least one hour prior departure from a port.2. The duty officer and the senior duty engineer should carry out the tests together.3. Telemotor transmitter oil level to be checked.4. Oil level of the actuating system tank should be checked and replenished if necessary.5. Pallester bearing and bottom sea gland checked and greased.6. All links on the steering gear checked to be in order.7. First one pump is started from the bridge and the wheel turned from port to starboard to check the telemotor response.8. Next with both the officers in the steering flat the wheel is turned from hard-a-port to hard-a-starboard and the running checked.9. Check made to see if the helm angle indicator on the bridge and the local mechanical one correspond correctly to each other for all positions.10. The first pump is shut off and the second one started and cheeks 8 and 9 repeated.11. Then both the pumps are put in parallel operation and checks 8 and 9 repeated.12. After testing is satisfactory one pump is shut off. With one pump running and if it is of the Hele Shaw type it should be ensured that the wheel is actuated every 15 minutes, so that the pump parts get properly lubricated.13. Operation of the auxiliary steering gear or use of the second pump, which acts as the auxiliary.14. Operation of the remote control (telemotor) system or systems from the main bridge steering positions. 15. Operation of the steering gear using the emergency power supply.16. The alarms fitted to the remote control system and the steering gear power units should he checked for correct operation. 17. During these tests the rudder should he moved through its full travel in both directions and the various equipment items, linkages, etc., visually inspected for damage or wear. 18. The communication system between the bridge and the steering gear compartment should also be operated.

Before Arriving Port: 1. One hour before picking up the pilot, the speed should be reduced and engine maneuvers and astern running checked. Also steering gear actuation checked.2. Both pumps are put on and the movements on either side checked.3. Helm angle indicator and local indicator in the steering gear compartment checked for correct and matching response on either side.

36)Explain the test procedure that should be carried out on an electrohydraulic steering gear a)before leaving port * b)before arriving port.

Ans:TESTING OF STEERING GEAR PRIOR DEPARTURE AND BEFORE ARRIVING PORT:

Prior Departure:1.Steering gear should be checked at least one hour prior departure from a port.2.The duty officer and the senior duty engineer should carry out the tests together.3.Telemotor transmitter oil level to be checked.4.Oil level of the actuating system tank should be checked and replenished if necessary.5.Pallester bearing and bottom sea gland checked and greased. 6.All links on the steering gear checked to be in order.8.First one pump is started from the bridge and the wheel turned from port to starboard to check the telemotor response.9.Next with both the officers in the steering flat the wheel is turned from hard-a-port to hard-a-starboard and the running checked.10.Check made to see if the helm angle indicator on the bridge and the local mechanical one correspond correctly to each other for all positions.11.The first pump is shut off and the second one started and cheeks 8 and 9 repeated.12.Then both the pumps are put in parallel operation and checks 8 and 9 repeated. 13.After testing is satisfactory one pump is shut off. With one pump running and if it is of the Hele Shaw type it should be ensured that the wheel is actuated every 15 minutes, so that the pump parts get properly lubricated.14.Operation of the auxiliary steering gear or use of the second pump, which acts as the auxiliary.15.Operation of the remote control (telemotor) system or systems from the main bridge steering positions. 16.Operation of the steering gear using the emergency power supply.17.The alarms fitted to the remote control system and the steering gear power units should he checked for correct operation. 18.During these tests the rudder should he moved through its full travel in both directions and the various equipment items, linkages, etc., visually inspected for damage or wear. 19.The communication system between the bridge and the steering gear compartment should also be operated.

Before Arriving Port: 1.One hour before picking up the pilot, the speed should be reduced and engine maneuvers and astern running checked. Also steering gear actuation checked.2.Both pumps are put on and the movements on either side checked.Helm angle indicator and local indicator in the steering gear compartment checked for correct and matching response on either side. *37) What are the objectives of shaft alignment?*

Ans: Shaft alignment objective1. To transmits the power output from the Main Engine to the propeller in most efficient way. 2. To prevent undue stresses and vibrations3. To transmits the thrust developed by the propeller to the ships hull in correct direction.4. To withstands the transient operating, loads.

38) Sketch and describe a method adopted for shaft alignment on board ship.

Ans:During the construction of the ship, the main shafting is aligned and mostly remains unchanged till the life of the ship, unless affected by any accident or wear. There are various external factors which can alter the alignment even during the construction and the entire operating period of the vessel.

During building, the common causes are, stern tube aperture incorrectly machined, Any contraction-expansion of hull owing to temperature variation along with changes caused by welding.

Shafting Alignment in ShipReference datums here are the height of the shaft above the keel aft, and the height of the crankshaft centre above the keel extended to the forward machinery space bulkhead (also centre athwartships) forward. These two datas are taken from the ships drawings The rough bore of the stern frame is fitted with a plate flange, this flange has a small hole (say 1 mm) drilled at the correct height above the keel. With this centre the reference circle can be drawn for the setting up of the exact boring of the frame. Similarly at the engine room forward bulkhead a small flange in the bulkhead has the small hole drilled at the correct engine height above the keel and at the midship point athwartships

An electric light is sighted behind the hole in the forward machinery space bulkhead and by looking from outside through stern frame this light can be seen through the two sight holes. Now at the aft peak bulkhead and the aft machinery space bulkhead and any water-tight bulkhead through which the shaft passes, sighting plates are used . At these points the horizontal plate is moved vertically up until the light line of sight is masked, a horizontal reference mark is now made across the bulkhead. The plate is moved vertically down until the light is masked and another horizontal reference mark made, bisection of these two lines gives the horizontal centre .

The same procedure is now repeated using vertical boards, moved horizontally port to starboard, bisection of these two lines gives the vertical centre. Rough bores are now bridged, the centre is fixed temporarily with a tin plate and a small hole is centred. Now from aft to forward a continuous light should be visibe through all bulkheads, the reference circles can now be drawn for exact boring. The exact borings are now made

*39)What are the stresses in a tail end shaft?*Ans:STRESSES: Steady Stresses: Stresses due to thrust and shear stress due to torque (continuous), radial loads due to the weight of the propeller such as centrifugal force etc. form the major part. Centrifugal force on the coupling bolts although relatively smaller creates steady stresses on the shafting. Alternating Stresses: Alternating stresses are due to bending and torsional vibrations. Alternate bending stress is very pronounced in the propeller shaft due to weight of propeller and is in maximum intensity at a point forward of the propeller. Portion of shaft under greatest stress is aft part of stern tube bearing. The stresses an shafting also depend upon dynamic bending moment caused by number of blades in the propeller and natural frequency of vibration Induced by the blades with respect to resonance. It should be noted here that aft bearing of stern tube is subjected to more load due to tipping moment of propeller and if it wears out excessively in due course the forward bearing will not take its designed load and the total stresses of the shaft will become high. In addition if other bearings are also worn out the shaft will start whirring, the misalignment and stresses will worsen further. To avoid this at times carefully bored slope bearings are used to enable the forward bearing to take its share of load as well.

*40)What is the purpose of thrust block ? *Ans:The thrust block transfers the thrust from the propeller to the hull of the ship It must therefore be solidly constructed and mounted onto a rigid seating or framework to perform its task. It may be an independent unit or an integral part of the main propulsion engine. Both ahead and astern thrusts must be catered for and the construction must be strong enough to withstand normal and shock loads.

41) a)Describe a full shell bearing suitable for use for main engine shafting. b)Explain how the bearing is lubricated. c)Explain how the bearing is cooled.

42)With reference to bearings for intermediate shafting: a)Describe with the aid of a sketch a tilting pad bearing . b)State the advantages & disadvantages of this type of bearing over normal full shell bearingans:- An intermediate tunnel bearing is shown in the figure, the usual journal bush is here replaced by pivoting pads. The tilting pad is better able to carry high overloads and retain a thick oil lubrication film. Lubrication is from a bath in the lower half of the casing, and an oil thrower ring dips into the oil and carries it round the shaft as it rotates. Cooling of the bearing is by water circulating through a tube cooler in the bottom of the casing.

advantages of using tilting pad bearings:- The three pressure wedges give a larger total support area than that obtained with a plain bearing. The tilt of the pads automatically adjusts to suit load, speed and oil viscosity. The wedge of oil gives a greater separation between shaft and bearing than does the oil film in a plain journal. The enhanced load capacity of a tilting pad design permits the use of shorter length or less bearings.

43)a)Sketch and describe a transmission shaft couplinhg (Muff coupling) which enables the propeller shaft to be removed outboard. b)State what safety precaution should be taken when dismantling the coupling

Ans-

This coupling is without flanges It is hydraulically connected and released Sleeves that make up the coupling to be accurately machined to a smooth finish There is an inner sleeve and an outer sleeve The inner sleeve is bored parallel to the shaft with sliding fit On its outer diameter is a slight taper,1:80, forming a cone The outer sleeve is bored with a similar taper and is parallel on its outer diameter The outer sleeve is thicker so providing elastic friction grip to allow the torque to be transmitted A nut and oil sealing arrangement is fitted at the smaller diameter end of the inner sleeve and screwed to it. To fit the coupling to the shafts hydraulic oil is injected at high pressure between the two sleeves forming a load bearing film As the pressure increases in the annular space between the oil seal and the outer sleeve an axial force pushes the outer up the taper and expands it The inner sleeve is compressed and grips the shafts creating the coupling Removing the pressure this grip is maintained. To remove the coupling the reverse procedure is followed Hydraulic oil is pressurized into annular space between the sleeves, relieves pressure from seal end and the outer end is driven off the taper and relaxes the friction grip of the inner sleeve, returning it to sliding fit.

Precautions to be taken when dismantling the coupling:- Outside dia's at end of outer muff measured before fitting After fitted, dia's should be approx. 0.5mm greater Restraining devices must be fitted to prevent the muffs separating too quickly

44) a)Sketch a line diagram of the lubricating system, for an oil filled stern tube, fitted in a large ship. b)What is the effect of sea water contamination with oil and how can contamination risk be reduced.

Ans-b)Sea water upon contamination with oil, leads to the formation of emulsion and oil looses its lubricating property which can have adverse effect on the stern tube bearing.

Risk of contamination is reduced by keeping aft seal in good condition.If at all any contamination happens, when the system is standstill, water can be drained out through drain valve.

45) a)Sketch & describe an oil seal suitable for oil filled stern tube, indicating the principal components. *b)Explain how the seal compensates for wear of the oil seal face and maintains oil tightness.*Ans- When the seal face wears out, it is compensated by the force applied by the garter spring circumferentially, keeping the seal face always in contact with the liner.

A very common arrangement for oil lubricated stern tube bearings is the Simplex Seal. A simplex seal arrangement is fitted to both inner and outer ends. The replaceable chrome liner prevents damage to the prop shaft which would be expensive to repair. Not shown is a rope guard bolted to the hull which prevents material from being 'wound' into the gap and damaging the seal Oil is fed to the area between the two opposite facing seals. The oil pressure in the stern tube is governed by the draught of the vessel and is often supplied via tanks situated at set heights. This pressure balances the sea water pressure on the seal and prevents sea water ingress. By opening the correct tank, the pressure exerted by the oil is insufficient to cause oil to leak out. Butadiene rubber is used for seal rings Stern tube seals, with oil lubrication have tended to use rubber rings increasingly. Fluoric rubber (Viton) with additives has been shown to be more effective than nitrile butadiene rubber for seal rings.

b) The inner sealing ring is fitted in the opposite fashion and prevents the oil in the stern tube leaking into the sea. The sealing rings are all held on the rotating chrome sleeve by a garter spring.46) How the forward seal of an oil cooled stern tube is lubricated & cooled ?*

Ans-The forward seal incorporates an oil circulator as a standard fitting. Oil from a 4 liter tank is circulated continuously through the annular chamber.This ensures effective cooling, as well as permanent lubrication with clean oil.

*46) How the forward seal of an oil cooled stern tube is lubricated & cooled ?*The forward seal assembly consists of two seal rings on a liner one to seal against high lubricating oil pressure arranged for the bearings and the other to seal any leakage in the engine room. The bearings, which work in conjunction with above assembly are normally made of white metal and are lubricated by oil, maintained at higher pressure by either a gravity tank or by oil pump. The life of bearings is ensured by the fact that lubricating oil is at higher pressure and if seals do not function efficiently the lubricating oil will be lost. The lubricating oil system may include an oil cooler if considered necessary. 47) a)Sketch a section through a propeller nut of the Pilgrim design, showing it in the propeller fitting mode: b)Give a brief explanation how the pilgrim nut is used to withdraw the propeller. a

b)REMOVAL: After removal of Fairwater cone, the pilgrim nut is taken off, reversed and screwed back on to the tail-shaft. A withdrawal plate is fitted and secured with studs to the propeller boss. Grease is now applied to the system which forces the withdrawal plate aft and this in turn draws the propeller down the tail-shaft taper*48) What is a Pilgrim Nut ?*Pilgrim is the trade name for a patented type of nut often used used for fastening a propeller on to a shaft.the landing face of the nut is bored out with a circumferential slot into which a steel ring like a short piece of tube is fitted

49) Sketch and describe the propeller mounting & dismounting by Oil Injection Method

Th Oil Injection method is used for mounting & dismounting of propellers, rudders & steering gear.Previosly propellers were driven up the tapered shaft end by means of a nut. The torque was transmitted as a result of the friction of the mating surfaces, the key performed a standby function if the friction proved insufficient. The grip achieved with the oil injection method is so powerful that the key can be dispensed with, without running any risk. Furthermore, the mounting operation is simplified.The propeller is driven a predetermined distance up the seating.This distance is selected so as to obtain a pressure, which can transmit the torque from the shaft with a wide safety margin. During the driving up operation, the friction is reduced by the oil being forced between the mating surfaces. When the propeller reaches the desired position, the injection pressure is released and the oil drains off, restoring the friction between the hub&the shaft. The drive up force is applied by means of a hydraulic tool, which is fitted on the shaft nut. When oil is pumped into the tool, an annular piston forces the propeller up on the seating.

1.Check that the mating surfaces of the propeller hub & shaft do not have any burrs or scratches & that they are thoroughly clean.Oil these surfaces & guide the propeller to the starting position on the shaft.2.Apply the nut, with the hydraulic tool, against the hub making sure that the piston is retracted as far as possible.(Oil supply hole & vent hole position to be adjusted).3)Remove the plugs from the three holes in the hub & attach nipples to the outer holes. Connect the pumps.4)Pump oil into the hyd. Tool until the pr. Gauge shows some reading. Apply a dial gauge to the forward end of the hub to measure the drive up.5)Pump oil into the hub until it flows out at the ends of the hub & plug the middle hole when oil begins to emerge. Then work the three pump & slowly increase the pressure.6)When the propeller has attained its predetermined position, release the oil pressure in the pumps for the hub, but maintain the pressure in the hydraulic tool. Disconnect the hub hoses, remove the adaptors & plug them. Let the oil drain away from the mating surfaces. Do not release the oil pressure in the hyd. tool, until two hours have elapsed. By that time the friction would have been reestablished & the propeller can not slide back.

50)What is drydocking ? Name the types of drydocks.*It is a technique used to remove a ship from the water so the under water portion may be inspected

TYPES OF DOCKS:1. FLOATING DOCK.

2. GRAVING DRY DOCK.

51)Sketch and describe a Floating Drydock.

Ans.

Floating dry dock as shown in figure above is U-Shaped and can be sunk to allow the vessel to enter and be positioned. The basin is first submerged and the ship is brought into position as before. Once the ship is in position, the basin is floated up, bring the ship above the water level. This is called a floating dock.When the ship is in position, the water in the ballast tanks of the dock is pumped out and the dock rises to meet the ship.Then the ship is lifted out of the water by the upward motion of the dock. This type of dock typically can lift heavier ships but not as heavy as a graving dock.The benefits of this dock are that it can be towed anywhere in the world and that it can be ballasted to lift a damaged ship with an excessive list or trim.

52)Sketch and describe a Graving drydock.

Ans. A graving dock is a channel cut out of a basin or river in which a closable gate is placed in front of the opening and water is pumped out. As the water is pumped out the ship is lowered on to the blocks. This type of dock can handle the largest of vessels.53)What are the routine jobs done in drydock ?

Ans. For a routine dry-docking, the usual work to be done are: 1.Hull cleaned of marine growth. Painting with anti-corrosive and anti-fouling paints. Sacrificial anodes renewed. Hull inspection and repairs. 2.Shipside gratings cleaned and repaired. 3.All overboard and sea suction valves overhauled. 4.Cleaning and surveying of tanks done. 5.Rudder, rudder carrier ring, rudder pintles clearances examined. 6.Propeller damage, nut looseness checked. Blade polishing done. 7.Tail shaft bearing wear down checked. Tail shaft removed and inspected. Coupling bolts and holes checked for deformation. 8.Anchor chain examined, cleaned and re-marked. All underwater stuffing boxes repacked

54)What preparations are made for drydocking a ship ?

Ans.Prior to vessels entry into the dry dock, its condition to be ascertained for satisfying the requirements while being dry docked, such as proper draft, trim & head, its tank conditions, de-ballasting of tanks for lightening & trimming, and vessels docking plan.Following work should be accomplished: When the vessel has entered the dock, ensure that it is held in position for draining the dock water. Ensure that the shore power is connected and tested. Ensure water availability on the fire main. Ensure that the ship is grounded to earth. Impressed current to be switched off. Ships power to be put off.>Ensure all sea valves are kept open to drain lines to dock. Ensure that all gas-free and work permits certificates are posted at the gangway. Along with the second engineer, inspect hull, including plating for erosion, damage etc., plugs and their condition, condition of anodes, sea chest grids, tail shaft aft seal condition After removal of rope guard, check propeller boss and blades surface condition, rudder condition. Check sea water leaks from welds, bearing bushes, striking pad etc.

55)What precautions are taken before and after flooding the docks ? Ans. Before flooding the docks, the dock floor must be cleared of all debris, so that no floating debris are found on the water. Otherwise these floating debris will find their way into sea chests and obstruct the free flow of sea water. Before flooding, the sea chest air vents must be open. All sea suction and over board valves must also be open.

After flooding the docks, the Engine room and the cargo holds must be checked for any sea water leaks and the same must be rectified. Especially in the engine room, all the sea suction valves & overboard valves must be checked for leakages from glands, joints etc. and the same rectified.

When the water level in the dock reaches the sea chest level, start the auxiliary engines one by one and vent the complete sea water system, starting from the sea water pump, fresh water cooler, lub. oil cooler and air cooler .

56.What is rudder drop & propeller drop ? Name the tools used to measure them? When the rudder carrier bearing wears down, rudder stock and hence the rudder also drops by that amount. This is called rudder drop. When the stern tube bearing wears down, the propeller shaft and hence the propeller also drops by that amount. This is called propeller drop. Rudder drop is measured by Trommel gauge & Propeller drop is measured by Depth gauge.

57.Name the different types of thrusters The different types of thrusters are:a) Controllable pitch thrusters andb) Water jet thrusters.c) Azimuthing thrustersd) Pump jet thrusterse) Vertical axis thruster

58)Describe a transverse bow thruster unit using a controllable pitch propeller.

The bow thruster is an auxiliary propulsion device used to provide lateral thrust to improve a ship's maneuverability. By varying the pitch of the propeller blades, a vessel may be thrusted, port or starboard at any desired rate from full to dead slow, or brought to a quick stop and reversed in direction, all without changing direction or speed of the prime mover. Varying propeller blade pitch assures maximum efficiency under all load and operating conditions and provides bow control with either headway or sternway on the vessel, the efficiency dependent upon vessel speed, with the greatest efficiency obtained at zero speed. The bow thruster assembly consists of a tunnel, which is welded athwart-ships into the hull of the vessel, well forward and as low as possible in the bow. Three stays attached to the tunnel wall support a pod, which houses the hydraulically operated mechanisms. The bow thruster is driven by an electric motor, diesel engine or steam turbine. The oil in the bow thruster system functions as both a lubricant for the gears and bearings, and as a hydraulic medium to operate the pitch changing mechanism. Good anti-wear, rust and oxidation inhibited hydraulic oils have provided satisfactory lubrication for these unitsined at zero speed. *59)What is water jet propulsion ?*

Ans. The water jet propulsion is essentially a water pump, draws water in through a cavity (usually located in the base near the rear of the craft) using what is termed an impeller where a mesh is used to stop large objects from being sucked up.The water is then forced out of a nozzle (located at the very rear) at high pressure. The force pushing the water out of the rear of the boat is mirrored by an equal and opposite force, accelerating the craft forward. Water is expelled at 15 degrees through outlet nozzles in the water jet propulsion engine. Since the nozzles can turn a full 360 degrees it is possible to achieve maximum thrust in all directions.60)Sketch and describe a controllable pitch propeller

Controllable pitch propellers can be divided into 2 main types:

The mechanism for the propeller consists of 4 main parts: 1) Propeller hub incorporating servo, crank ring for turning blades and necessary seals. 2) Oil distribution box (transfer box), which in mounted at the forward end of the hollow tail-shaft and controls the oil flow to the hub servo through a valve rod.3)Control system, which may be either pneumatic or electric.4) Hydraulic system, consisting of motor or shaft driven pumps, cooler, filters, tanks etc The pitch of the CPP blades is controlled hydraulically through a system consisting of a pump, piston, crosshead, and blade crank rings. The piston, crosshead, and crank rings are located in the propeller hub. High pressure hydraulic oil, acting on either side of the piston, moves the piston axially within the propeller hub.The piston is attached to a piston rod that connects to the crosshead that moves axially with the piston. Sliding blocks fit in machined slots on the crosshead and these sliding blocks fit over eccentrically-located pins mounted on the crank pin rings. As the crosshead moves forward and backwards within the hub, the sliding blocks move in an arc that also moves the eccentric pin and rotates the crank pin rings to which the CPP blades are bolted.

Safety Springs fitted in the propeller hub: These are fitted to allow the propeller pitch to move to a full ahead position in event of failure of the hydraulic system. The springs are mounted in the astern portion of the servo and so push the servo piston forward to bring the blades into ahead position. The springs are powerful enough to overcome friction but not the full hydrodynamic torque on the propellers when full rpm is used. 61). Sketch & describe a Chemical Sewage Treatment Plant.

Ans)

Chemical Sewage Treatment Plant minimizes the collected sewage, treats it and retains it until it can be discharged in a de-controlled area, usually well out at sea. Shore receiving facility may be available to take this retained sewage. Working: A perforated rubber belt is used to separate liquid from solids in a separating tank. The liquid is then passed through treatment tanks to a prepress arrangement (compressed air pressure tank) for use as a flushing fluid at the toilets. SolidTreatment by chlorine and caustic based compound makes the liquid acceptable for the purpose. s are inerted by a caustic compound and delivered via a grinder to the holding tank. Capacity of tank is 2 litres per person per day. It is important to maintain the correct chemical dosage rates. 62). a) Sketch & describe a biological sewage treatmet plant. b) What are the IMO Standards for the Effluent discharge from the Sewage Treatment Plant.

Ans) a) Biological Sewage Treatment ,utilizes bacteria to completely break down the sewage into an acceptable substance for discharge into any waters. The extended aeration process provides a climate in which oxygen loving bacteria multiply and digest the sewage, converting it into a harmless sludge. These bacteria are known as aerobic bacteria The treatment plant uses a tank which is divided into three watertight compartments; an aeration compartment, a settling compartment & a chlorine contact compartment The sewage enters the aeration compartment where it is digested by aerobic bacteria and micro-organism, whose existence is aided by atmospheric oxygen which is pumped in. The sewage then flows into the settling compartment, where the activated sludge is settled out. The clear liquid flows to the chlorinator and after treatment to kill any remaining bacteria, it is discharged. Tablets are placed in the chlorinator and require replacement when used up. The activated sludge in the settling tank is continuously recycled and consequently it builds up, so that every two to three months it must be partially removed. This sludge must be discharged only in decontrolled areas ie. in the open sea. B) IMO STANDARDS FOR EFFLUENT DISCHARGE 1.The geometric mean faecal coliform bacteria count of the sample should not exceed 250 /100 ml. 2)The geometric mean suspended solids should not exceed 100mg/litre, above the suspended solids content of the water used for flushing purposes. 3)The geometric mean of the 5-day biological oxygen demand (BOD-5) should not exceed 50 mg/litre. (What is BOD ? - Quantity of oxygen in mg/litre required by bacteria to stabilise or oxidise the sewage within a given period of time and at a particular temperature.) 4) If chlorine is used as a disinfectant, the residual chlorine should not exceed 5mg/litre as free available chlorine. 63). a)Sketch and describe an Incinerator Plant fitted to a large vessel. *b) Name the safety devices fitted to the Incinerator Plant. *

Ans)a)

Annex V of MARPOL 73/78 gives guidelines with regard to waste material storage and disposal at sea. Ships generated garbage are 1.Galley waste including food scraps, bones, cans,2.Accommodation wastes such as paper, cardboard, cans, textiles, 3.Oil waste such as oil sludge including bilge, oil purifier, lubricating oils etc; 4.Sewage sludges) Incineration of various waste materials, is without doubt the most effective means of dealing with the storage problems of them, because the residuals are extremely small in volume and easily disposed off.Marine Incinerator. It is a vertical, cyclone type, with a rotating arm device to improve combustion and remove ash and other non combustibles from the furnace.Sludge burning is carried out with burner. Combustion air is supplied by forced draught fan. The loading door is pneumatic and is inter-locked with the burner and forced draught fan Solid waste is fed in standard plastic bags. Liquid waste may be introduced through the liquid waste burner when refractory is hot. Control is covered by all safety measures, applicable to boiler burner.

(b)1.GARBAGE FEEDING DOOR INTERLOCK WITH THE BURNER2.FLAME FAILURE TRIP OF BURNER3. LOW AIR PRESSURE TRIP OF BURNER4.HIGH FLUE GAS TEMPERATURE TRIP OF BURNER*64) What arrangements are provided to protect ships hull from corrosion?*

Ans) Methods of External Hull Protection: 1.Anticorrosion Paints2.Cathodic Protection of Underwater Hull: a) Inorganic Zinc Coatings: b) Use of Sacrificial Anodes: 3.Attachment of Anodes 4.I.C.System

65) a)Sketch & describe an Impressed Current System as fitted to a large ship. b)How the rudder & shafting system is protected by the above system? Give a line sketch for any one of them.

In the impressed current system, the current is fed to permanent (inert) anodes, which emit the current through seawater, to be received by the hull of the ship. The low-volt D.C. supply generated in the ship is connected across the inert anodes (positive) and the hull (negative) and the circuit completes through the seawater. The anodes are completely insulated from the hull (by glass fibre mould etc.). The direction of this protective current will be opposite to that of all local corrosion currents. An impressed current system consists of: A controller unit. Step-down transformer and rectifier units. Permanent (inert) anodes. Reference electrodes Current required: 1mA/m2 for newly painted steel, 100 mA/m2 for clean bare steel. From the above, it should be understood that effective corrosion control depends upon the successful combination of cathodic protection and paint coating which are complementary. Permanent anodes are made of TITANIUM, PLATINIZED NIOBIUM and LEAD/SILVER ALLOYS, which are capable of giving about 20 years of uninterrupted service. These anodes produce chlorine at their face, which keeps them free from marine growth/fouling. Hull Potential (Ref. to Ag/ Ag Cl) Level of Protection

Less than 0.6V Under protected.

Between 0.61 to 0.89V Protected.

Above 0.9V Over protected.

The main controller unit compares the level of protection, read by reference electrodes, with the desired or set value and accordingly regulates current output through the permanent anodes. Since the anode to seawater interface drop is about 2.5 volts, the actual D.C supply voltage will be in the order of 3.4 to 4.0 volts, to maintain hull potential at 0.85 V. With cathodic protection, it is recommended to paint the hull with alkali- resistant paint such as coal tar epoxy paint to withstand temporary over-protection effect. (Alkali-attack). Impressed current system also incorporates: Propeller shaft slip-ring assembly. Rudder grounding arrangement. Since under normal operational conditions, both the propeller/shaft and rudder are electrically isolated from the hull due to the lubricants in the bearings, proper grounding arrangements are fitted to include these components also in the protectionB) Propeller shaft grounding system.

Rudder Grounding System