Bridge Equipments handout.docx

8/15/2019 Bridge Equipments handout.docx

1/25

CMET LUCKNOW Made by Capt. P K Khare

BRIDGE EQUIPMENTSSEXTANT

A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is

to determine the angle between a celestial object and the horizon which is known as the object's altitude.

Using this measurement is known as taking a sight and it is an essential part of celestial navigation. Asextant can also be used to measure the angle between two terrestrial objects. he scale of a sextant has

a length of ! " # of a turn $#%&( hence the sextant's name $ sextāns, -antis is the )atin word for *one sixth*.

+eing of double reflection, the arc is divided into twice the number of degrees, which it actuallycontains, and angles up to !-% can be measured and read off from an arc of #%.

he arc is graduated to more than !-% at one end and a little beyond % at the other end.

/eadings taken from beyond the arc at % are said to be *off the arc.*A sextant measures angles in any plane, vertical, horizontal or obli0ue.

1back angle * or * back observation.*2 If the altitude of a celestial body is not too low and it is over the

land, or if for any other reason the horizon under it is not visible, back angle is taken by bringing the

reflected image of the body to the horizon farthest from it.

Errors of sextant

3 4rror of perpendicularity2 caused if the index glass were not perpendicular to the plane of theinstrument.

3 5ide error 2 caused if the horizon glass were not perpendicular to the plane of the instrument.

3 Index 4rror 3 his error results from the horizon glass not being parallel to the index mirror when the

sextant is set on zero.3 6ollimation 4rror 3 An error which results from the telescope not being parallel to the frame

hese errors may be corrected by the navigator using various adjustment points on the sextant.

he non3correctable errors on the sextant are2

3 7raduation 4rror 3 hese small errors are caused by imperfections in machining the arc, cutting thelimb gears, or marking the scale of the arc or micrometer drum.

3 8rismatic 4rror 3 his error is caused by the planes of a mirror not being exactly parallel.3 6entering 4rror 3 his error results when the index arm is not pivoted at the exact center of curvature

of the arc.

9f all these errors index error is the most important because it is an error which directly effects altitudemeasurements. +ecause sextant readings can be effected by changing temperatures, which tend to

expand or contract the metal parts of a sextant, the navigator should determine the amount of index error

at least once each day.Index error is determined by setting the sextant near zero, pointing it at the horizon and then turning the

micrometer drum slowly until the actual and reflected images of the horizon are aligned. If the sextantreads zero when the horizons are aligned, there is no error. If not, note the sextant reading when thehorizons are aligned. If the reading is a positive angle $greater than %&3%%.%' the error is said to be *on

the arc.* If the reading is less than zero, or a negative angle, it is aid to be *off the arc.* If the error

determined is on the arc it must be subtracted from sextant alt. If off the arc, it must be added to sextantalt.

:A7;4I6 69:8A55

4A/I4)?

1

http://en.wikipedia.org/wiki/Measuring_instrumenthttp://en.wikipedia.org/wiki/Anglehttp://en.wikipedia.org/wiki/Astronomical_objecthttp://en.wikipedia.org/wiki/Horizonhttp://en.wikipedia.org/wiki/Celestial_navigationhttp://en.wikipedia.org/wiki/Celestial_navigationhttp://en.wikipedia.org/wiki/Lunar_distance_(navigation)http://en.wikipedia.org/wiki/Turn_(geometry)http://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Anglehttp://en.wikipedia.org/wiki/Astronomical_objecthttp://en.wikipedia.org/wiki/Horizonhttp://en.wikipedia.org/wiki/Celestial_navigationhttp://en.wikipedia.org/wiki/Lunar_distance_(navigation)http://en.wikipedia.org/wiki/Turn_(geometry)http://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Measuring_instrument


2/25


9ur planet=s magnetic field is believed to be generated deep down in the 4arth=s core.

/ight at the heart of the 4arth is a solid inner core, two thirds of the size of the :oon and composed

primarily of iron. At approx. @,%%&6, this iron is as hot as the 5un=s surface, but the crushing pressure

caused by gravity prevents it from becoming li0uid.5urrounding this is the outer core, a -,%%% km thick layer of iron, nickel, and small 0uantities of other

metals. )ower pressure than the inner core means the metal here is fluid.

?ifferences in temperature, pressure and composition within the outer core cause convection currents inthe molten metal as cool, dense matter sinks whilst warm, less dense matter rises. he 6oriolis force,

resulting from the 4arth=s spin, also causes swirling whirlpools.

his flow of li0uid iron generates electric currents, which in turn produce magnetic fields. 6harged

metals passing through these fields go on to create electric currents of their own, and so the cycle

continues. his self3sustaining loop is known as the geodynamo.

he spiraling caused by the 6oriolis force means that separate magnetic fields created are roughly

aligned in the same direction, their combined effect adding up to produce one vast magnetic field

engulfing the planet

Above gives the illusion that a big magnet is in the 4arth in ;orth3 5outh direction with it=s poles closeto geographical 8oles of 4arth.

:agnetic variation is the angle on the horizontal plane between magnetic north $the direction in whichthe north end of a compass needle points, corresponding to the direction of the 4arth's magnetic field

lines and true north $the direction along a meridian towards the geographic ;orth 8ole. his angle

varies depending on one's position on the 4arth's surface, and over time.:agnetic deviation is the error induced in a compass by local magnetic fields, which must be allowed

for, along with :agnetic variation, if accurate bearings are to be calculated.

Magnetic deviation refers specifically to compass error caused by magnetized iron within a ship. his

iron has a mixture of permanent magnetization and an induced $temporary magnetization that isinduced by the 4arth's magnetic field. +ecause the latter depends on the orientation of the craft relative

to the 4arth's field, it can be difficult to analyze and correct for it.he sources of magnetic deviation vary from compass to compass or vessel to vessel.


3/25


navigation. It is like the ;orth 5tar, it is used as a marker to guide. )ater the cards were made of /ice

paper with brass ring at the outer circumference. >our magnetic needles were aligned in ;35 direction

and fixed to back of card.

Keepn! t"e card practca##$ "or%onta# n a## #att&des

; end of a free magnet points toward :agnetic ;orth and also dips towards horizon depending on

latitude.

he weight of the card and magnets is supported partly by the buoyancy and partly by an iridium pointfitting into a sapphire bearing.

he point of support is above the centre of gravity of the card, so that when the card dips, weight of

card acting at centre of gravity brings the card back to horizontal position and the card remainssubstantially horizontal in all latitudes.

T"e #'&d compass

4arly compasses did not have water or li0uid in them and were known as dry3card compasses. heir

readings were affected by shock and vibration. )i0uid3filled compasses were less effected by shock, butleaked and were difficult to repair. In !E#-, the first reliable li0uid compass was made with a float on the

card that took the weight of the needle. 6ompasses were later filled with alcohol because it could only

freeze at low temperatures. +ecause of these new improvements on li0uid compasses, they started to bemore popular than dry3card compasses by the end of the !Fth century.

he bowl is filled with a mixture of distilled water and pure ethyl alcohol thereby making the mixture to

have the following properties2G )ow freezing point about 3C%&6

G 5mall coefficient of expansion

G ?oes not discolour the cardG )ow relative density about %.FC

A #&((er #ne is a fixed line on a compass binnacle pointing towards the front of the ship and

corresponding to the ship=s centerline $being the customary direction of movement.

G$ro Compass

)ree G$roscope

A wheel at rest A wheel in motionA 7yroscope consists of a spinning wheel. If a spinning wheel is free to turn about two axes at right

angles to each other and to the spin axis, it is said to be a free gyroscope. he important properties of

>ree 7yroscope are its inherent gyroscopic inertia and precession.3

http://en.wikipedia.org/wiki/Compasshttp://en.wikipedia.org/wiki/Compasshttp://en.wikipedia.org/wiki/Binnaclehttp://en.wikipedia.org/wiki/Compasshttp://en.wikipedia.org/wiki/Binnacle


4/25


Inerta

A free gyroscope, when spinning rapidly, possesses considerable directional stability or inertia. hat is it

has a great resistance to any tendency to change the direction in which its spin axis lies.he earth too may be compared to a free gyroscope. he earth=s spin axis lies in the direction of the

Hpole star=.

Precesson

If a tor0ue a turning moment, in the plane of the spinning wheel is applied to a gyroscope axis, the

effect is only to increase or decrease the rate of spin. he direction in which the spin axis lies isunaffected.

If a tor0ue is applied to a gyroscope axis in a plane at right angles to the plane of spin, then the

gyroscope becomes unbalanced. And to restore the balance it moves in a direction at right angles both tothe plane of the spinning wheel and the plane in which the tor0ue is applied.

his movement at right angles to the tor0ue is known as precession.

or example, at night if the gyroscope is made to point in the direction of a star, then the gyroscope will

follow the star as the earth rotates and the star apparently moves in the sky.

he characteristics of 7yroscope are combined with 4arth=s /otation and >orce of 7ravity, with the

result that instrument aligns itself with geographic :eridian and provides a constant ;orth indicationregardless of rolling, pitching and yawing of the vessel

A free gyroscope may be made ;orth seeking by attaching a weight to the rotor

casing below the centre of gravity of the rotor. his so that when the axislies horizontal the weight is distributed e0ually between the two ends of

the axis but when the gyroscope is tilted the weight exerts more thrust on one end of the axis than on the other.

he control of a gyro by solid control weight is not used in practical compasses.

6ommonly used is a gravity control by a li0uid ballistic, which flows between the north and south sides of the rotor under the influence of gravity,

when the gyro axis tilts due to the earth turning.

he controlled gyro will never settle in the meridian. It will only oscillate about the meridian. 9nly in one position will the gyro axis remain pointing

in a constant direction, if initially set there, and that is pointing north with a tilt

such that the control precession is e0ual to the drifting.

Dampn!

?amping means the process by which these oscillations about the meridian will grow lesser and lesser

until the

4


5/25


axis is pointing along the meridian and even if destabilized will return to the meridian.

?amping may be achieved by the provision of2

JA precession in azimuth $towards the meridian, or casing

JA precession in tilt $towards the horizon.he 7yro 6ompass for ships use -nd :ethod

his is achieved by connecting the :ercury ballast slight to the east of

vertical centerline. Dith this arrangement the major effect of mercury stillacts about horizontal axis , causing 7yro to precess towards meridian.

+ut there now is a small additional effect about the vertical axis,

causing gyro to precess about


6/25


@ L cos. +

o compensate for steaming error, a speed rider is provided,

which in association with the latitude rider, shifts the lubber

line e0ual to steaming error in the appropriate direction.It can be calculated from formula, or can be read off from 5peed 6orrection able.

Ad,anta!es of G$ro a!anst Ma!netc Compass

J5eeks rue :eridian, hence no need to apply variation $which is not exactly knownJ It is not affected by ship=s magnetism. herefore if an error does exist in 7yro, it is same on all

headings

J 7yro heading can be transmitted electronically to other instruments.

*mtatons of G$ro

J;eeds constant power source, hence power failure will cause it to stop working.J If operation interrupted for long, as much as O hrs may be re0uired for it to settle.

J 7yro accuracy decreases drastically in latitudes above@ deg

J :aintenance and repairs are expensive

AUT- PI*-T


7/25


It determines amount of counter rudder to steady the ship on set course R Seeps over shoot to

minimum.

7reater the ship=s inertia, greater the setting re0uired. If ship has good dynamic stability, relatively small

settings of counter rudder will be sufficient. If the ship is unstable, higher settings will be re0uired.?epends on ship=s characteristics, loadedMballast conditions and rate of turn.

.0a1/ Contro# 2he yawing of a vessel causes elongation of the distance to go and the conse0uenthigher fre0uency of rudder movement produces drag which reduces the speed. )ow gain is re0uired to

reduce the fre0uency of the rudder movement. herefore proper setting of 1QawP 6ontrol is a veryimportant in any :arine Autopilot.

.-ff co&rse A#arm/ actuates an audible alarm to alert the navigator if the heading deviates outside the bandwidth of the setting.

2EAT3ER SETTING C-NTR-*2 Dhen steering in heavy weather with wind and sea at an angle to

the vessel=s heading, there is a tendency for the vessel=s head to be turned in a particular direction. heeffect of this can be offset by maintaining some permanent value of rudder angle( this angle is set using

Hweather helm= after a period of trial and error.

S0NC3R-NISATI-N C-NTR-*2 emporairly disconnects gyro repeater from main gyro for sync

of heading. /e0uired for sync and when gyro switched off and restarted.

C-URSE SE*ECT-R KN-B2 >or setting course to be steered.

?I::4/2 >or illumination of panel

AU9M>9))9D U8M ;9; >9))9D U8 2 >or choosing steering mode

C"an!n! o,er from 3and Steern! to A&to Steern! 2+efore changing over from hand steering to auto steering, the settings on the auto pilot panel must be

adjusted for weather and traffic conditions.

he vessel must be made steady on the course on which she has to be set on auto steering.

C"an!n! o,er to emer!enc$ steern! s$stem 2

Dhen the steering panel gives an alarm, it must be read carefully to see as to what has gone out of order,

operation must be changed3over to the otherM alterative steering gearM motor or transmission systemMtelemotor, engineroom must be informed immediately.

If the Auto3pilot gives an alarm or the off3course alarm goes off, adjust the settings on the Auto3pilot

panel accordingly.If the Auto3pilot fails, change3over to hand steering.

If the >ollow3up system doesn=t work $the feedback leg of the steering gears doesn=t function properly,

change3over to ;on3>ollow3Up mode.

If the steering transmission systems or telemotors stop working, emergency steering has to be performed by trick3wheel arrangement or solenoids after bringing the rudder mid3ships.

>urther, if the steering hydraulic or electric motors also stop working, rudder will have to turned by

some mechanical arrangement like chains and blocks, this is not possible in case of large rudders $largeships. As the last resort, Tury rudder is used, which means some arrangementM structural changes, which

7


8/25


overside work as an alternative rudder arrangement e.g. wooden planks on the stern turnedM rotated like a

rudder.

Use of t"e A&tomatc P#ot

$! he master shall ensure that an automatic pilot, where fitted, shall not be used in area of high

traffic density, in conditions of restricted visibility nor in any other hazardous navigationalsituation unless it is possible to establish manual control of the ship's steering within C% seconds.

$- +efore entering any area of high traffic density, and whenever visibility is likely to becomerestricted or some other hazardous navigational situation is likely to arise, the master shall

arrange, where practicable, for the officer of the watch to have available without delay the

services of a 0ualified helmsman who shall be ready at all times to take over the manual steering.$C he change3over form automatic to manual steering and vice versa shall be made by, or under

the supervision of, the officer of the watch, or, if there is no such officer, the master.

$O he master shall ensure that the manual steering gear is tested $a after continuous use of the

automatic pilot for -O hours and $b before entering any areas where navigation demands specialcaution.

$@ In areas where navigation demands special caution, the master shall ensure that the ship shallhave more than one steering gear power unit in operation when such units are available andcapable of simultaneous operation.

Steern! Gear 4 Testn! and Dr##s

he master shall, within !- hours before departure of the ship, cause the steering gear to be checked

and tested so as to ensure that it is working satisfactorily2

8rovided that in the case of ships regularly making more than one voyage a week to or from thesame port a check and test of the steering gear need only be made once in that week unless a part of

the steering gear or its control system has been dismantled or change since the last test.

he test procedure shall include, where applicable, the operation of the following2

$a the main steering gear(

$b the auxiliary steering gear($c the remote steering gear control systems

$d the steering positions located on the navigating bridge

$e the emergency power supply$f the rudder angle indicators in relation to the actual position of the rudder

$g the remote steering gear control system power failure alarms

$h the steering gear power unit failure alarms( and

$i the automatic isolating arrangements and other automatic e0uipment re0uired for steering gear.

T"e c"ec5s and tests s"a## nc#&de2

$a the full movement of the rudder according to the re0uired capabilities of the steering gear(

$b a visual inspection of the steering gear and its connecting linkage( and

$c the operation of the means of communication between the navigating bridge and the steering gearcompartment.

he owner shall provide simple operating instructions, with a block diagram showing the

8


9/25


changeover procedures, for the remote steering gear control systems and steering gear power units,

and the master shall ensure that they are permanently displayed on the navigating bridge and in the

steering gear compartment.

A person shall not supervise the operation or maintenance of the steering gear unless that person is

familiar with the operation of the steering systems fitted on the ship, and, where applicable, with the

procedures for changing form one system to the other.

In addition to the routine checks and tests prescribed in paragraphs $! and $- of this regulation, the

master shall ensure that emergency steering gear drills which practice emergency steering gear procedures take place at least once every three months. hese drills shall include, where applicable,

use of direct control form within the steering gear compartment, the communications procedure with

the navigating bridge and the operation of alternative power supplies.

he date time and place that the said routine checks and tests are carried out and the date and details

of emergency steering drills carried out shall be recorded by the master in the official logbook.

In ships not re0uired to keep an official logbook, a record of each check, test and drill shall be made

by the master and be retained on board for a period of six months and be available for inspection ondemand by a superintendent, proper officer or surveyor of ships.

*-GSIn the ancient times, the only way to measure ship speed was to throw a wood log into the water and

observe how fast it moves away from the ship. his approximate method of ship speed measurement

was called '


10/25


he 8ressure type log $8itot tube )og

E*ECTR- MAGNETIC *-GS

his type of log consist of

!. :aster Indicator

-. 8reamplifier C. 5ensor

-peratons

he sensing of speed makes use of law of electromagnetic inductionDhen the ship moves, the water passing through the hull acts as a conductor.

he magnetic field is produced by a solenoid, installed in such a way as to allow the field to extend into

water.his produces an 4:> $electromagnetic force, which is measured and converted into the speed ofvessel through the water.

Prncp#e

he electromagnetic log is based upon the >araday3:axwell induction law( Figure shows the principle

of the log.

he induced e.m.f. H4= is given by the following2 4 K > x ) x B

Dhere > K the magnetic field

) K the length of the conductor B K the velocity of the conductor through the magnetic field.

In the 4: log a direct current through the windings of a coil, generates a magnetic field. If the

conductors do not move relative to the coil they do not intersect the magnetic fines of force and novoltage is induced in them.

In the 4: log the H>= and H)= are maintained constants, therefore the induced e.m.f. is directly

proportional to the velocity HB=, which is the velocity of the vessel through the water.

he direction of the voltage 4 depends on the directions of the lines of force and the direction of thevelocity of the conductor water. According to the formula the induced voltage is proportional to the

velocity B.

5hould the velocity have the opposite direction, the direction of the voltage would change too.Alternating current through the coil

Instead of a direct current, suppose that we send an alternating current through the coil. hen the

induced voltage that we will have would be also an, alternating voltage with amplitude that is proportional to the velocity, B.

>or the electromagnetic log an alternating voltage is preferred to a direct voltage.

he speed out put from an 4: log depends upon the water flow by way of the sensors. hus siting of

the probe is critical. his is so since if too close to the hull then due to the non3linearity of the hull form

the speed of the water flow may give a wrong representation of the vessels speed. his is minimized bycareful siting of the sensor as well as by calibrating the instrument while installation.

8itch and roll also give rise to errors however these are reduced by having an electrical time constantthat is longer than a period of vessel motion.

A well3adjusted log can have an accuracy of better than %.! percent of the speed range

his type of log can give only speed through water and is greatly affected by the current flowing underthe ship.

In all the above logs the flow of water past and under the hull play a major part in the accuracy of the

readings.

1


11/25


D-PP*ER *-G

he ?oppler effect is a fre0uency shift that results from relative motion between a fre0uency source and

a listener.If both source and listener are not moving with respect to each other $although both may be moving at

the same speed in the same direction, no ?oppler shift will take place.

If the source and listener are moving closer to each other, the listener will perceive a higher fre0uency 3the faster the source or receiver is approaching the higher the ?oppler shift.

If the source and listener are getting farther apart, the listener will perceive a lower fre0uency 3 the faster

the source or receiver is moving away the lower the fre0uency.

T"e Dopp#er s"ft s drect#$ proportona# to speed (et1een so&rce and #stener+ fre'&enc$ of t"e

so&rce+ and t"e speed t"e 1a,e tra,e#s.

he ?oppler log is based on measurement of the ?oppler effect. It is seen that an observer, moving witha source of sound towards a reflecting plane, receives a fre0uency2

Dhere fv is the received fre0uency, f the transmitted fre0uency, c the speed of sound and v the speed of

the source of sound.+y measuring fv and knowing f and c, the speed of a ship with regard to the seabed can be determined.

Above can be simplified to( fd K -vft M c

where fd K ?oppler fre0uency shift in cycles per second, v K relative speed in the direction of the

transmitted wave, ft K transmitted fre0uency, and c K velocity of propagation of the radio wave.

Prncp#e

A transmitting transducer below the ship continuously emits a beam of sound vibrations in the water at

an angle $usually #%N to the keel in the forward direction.A second transducer aboard receives the echo caused by diffuse reflection from the seabed.

A ?oppler log uses a higher fre0uency than an echo sounder.

Ad,anta!es6

!.he resulting shorter wavelength leads to the more diffuse reflection desired( the echo from

a specular reflection would not be received, in view of the obli0ue incidence of the beam.

-.he shorter wavelength makes possible a smaller beam3angle and so avoids the dimensions of theradiating face of the transducer becoming too large.

C.he emitted power of the sound vibrations spreads less and thus the echo is stronger.

4very point of the seabed hit by the beam causes a stronger or weaker echo in the direction of the

receiving transducer.


12/25


>or that reason a thermistor is mounted near the transducers. $A thermistor is a resistance, the magnitude

of which depends on the, temperature. ?eviations of the sound speed Hc= from the normal value are

passed to the system computer for correction of its calculations.

he propagation time of the pulse and its echo plays no role.

Ref#ectons

+oth the echo sounder and the ?oppler log react to reflections of sound waves from the seabed( the

former measures the propagating time and the latter the difference of the two fre0uencies.If the beam is propagated from one water layer into a second one of different composition or

temperature, there will be reflection( there will also be a ?oppler effect if the second layer moves

relative to the first layer and if the beam hits this layer obli0uely.In that case the fre0uency of the sound vibrations penetrating the second layer will also change, if the

speed of the sound waves in the second layer is different from that in the first layer.

>or the echo, however, the reverse fre0uency change will occur and will cancel out the first change.A ?oppler log measures the algebraic sum of all ?oppler fre0uency shifts experienced by the sound on

its way to the bottom $or to a reflecting layer and back again.

o this fre0uency shift must be added the shift that arises at the transition of the transducer vibrations

between the ship and the water, and vice versa. If the beam hits the bottom $bottom lock the total

fre0uency shift is, proportional to the speed of the ship with regard to the bottom.If there is no bottom contact, but only reflection against a water layer, the measured ?oppler shift is

proportional to the speed of the ship relative to that water layer $water lock.

7an&s conf!&raton

7iven a propagation angle of #%&, cos #% K %.@

#s fd K-vft cos#%M$ K vft%$

It follows that if the angle changes, the speed calculated will be in error because the angle of

propagation has been applied to the speed calculation formula in this way. If the vessel is not in correcttrim $or pitching in heavy weather the longitudinal parameters will change and the speed indicated will

be in error. o counteract this effect to some extent, two acoustic beams are transmitted, one ahead andone astern. &he transducer asse!bly used for this type of trans!ission is called a 'anus) configurationafter the *o!an god who reputedly possessed two faces and was able to see into both the future (ahead

and the past (back"

A C& change of trim on a vessel in only forward pointing ?oppler system will produce a @ velocityerror. Dith a Tanus configuration transducer system, the error is reduced to %.- but is not fully

eliminated.

he addition of a second transducer assembly set at right angles to the first one, enables dual axis speed

to be indicated .he placing of the two transmitting transducers, to produce forward and backward beams is called

a Tanus configuration.

?ue to the Tanus configuration a linear relationship exists between the speed of the vessel and themeasured fre0uency shift.

A further advantage is that vertical movements of the ship cause e0ual changes to the ?oppler shifts in

the forward and backward beams, so the difference remains the same.+ertical !ove!ents of the ship do not therefore influence the Doppler shift"

>or measuring the athwart ship speed, a similar Tanus configuration is mounted at an angle of F% deg.with the along ships transducers(

Ptc"n! and ro##n!

12


13/25


the Doppler !easure!ent of the speed is not, in practice, influenced by pitching" he same applies to

the two athwartships beams during rolling.

6ontinuous3wave and pulse, systems


14/25


If the ?oppler log then loses bottom contact, the window is automatically shifted to occur immediately

after pulse transmission.

As a result, the receiver reacts only to reflections from the !%3C%3metre water layer.

Dhen this happens, 'bottom track' indicator is replaced by 'water track'.In some ?oppler log, it is possible to switch manually to the water track mode.

Uses of t"e Dopp#er #o!It is very useful during docking of )arge vessels as it also gives athward ship speed.

he ?oppler log can measure the speed to the nearest %.%! knot or @ mmMs( unfortunately, however, it

sometimes does not function correctly during docking if the screws of tugs cause air bubbles $whichreflect sound waves to pass through the beams $aeration.

It functions well for all speeds that modern vessels can attain and works from a minimum depth of about

!.@ feet to a maximum depth of about #%% feet. The !"pp#er $y$te% &a' be &"''e&ted ()th "ther e#e&tr"')& 'a*)+at)"' $y$te%$pr"*)d)'+ +e'era##y a&&,rate $peed )'p,t.ERRORS

here are primarily four errors to be aware of when using the ?oppler system with Tanus configuration2

!. ransducer orientation error caused when the pitching or rolling of the vessel becomes excessive-. Bessel motion error caused by excessive vibration of the vessel as it moves through the water

C. Belocity of sound errors due to changes in water temperature or density due to salinity and particle

contentO. 5ignal loss errors caused by attenuation of the vibrations during transit through the water or upon

reflection from the bottom

T"e na,!ator s"od (e ca&toned+ t"at precse speed s"od (e determned not on#$ ($ &sn! t"e

Dopp#er (&t a#so from caref ca#catons of dstances (e t1een acc&rate na,!atona# fxes8

AIS

he A&tomatc Identfcaton S$stem $AIS is an automatic tracking system used on ships and by vessel traffic services $B5 for identifying and locating vessels by electronically

exchanging data with other nearby ships,

Basc o,er,e1

AI5 transponders automatically broadcast information, such as their position, speed, and navigational

status, at regular intervals via a B transmitter built into the transponder. he information originates

from the ship's navigational sensors, typically its global navigation satellite system $7;55 receiver

and gyrocompass. 9ther information, such as the vessel name and B call sign, is programmed wheninstalling the e0uipment and is also transmitted regularly. he signals are received by AI5 transponders

fitted on other ships or on land based systems, such as B5 systems. he received information can bedisplayed on a screen or chart plotter, showing the other vessels' positions in much the same manner as a

radar display.

An AI5 transponder normally works in an autonomous and continuous mode, regardless of whether it isoperating in the open seas or coastal or inland areas. AI5 transponders use two different

fre0uencies, B maritime channels E+ $!#!.F@ :


15/25


In order to ensure that the B transmissions of different transponders do not occur at the same time,

the signals are time multiplexed using a technology called 5elf39rganized ime ?ivision :ultiple

Access $59?:A. In order to make the most efficient use of the bandwidth available, vessels that areanchored or moving slowly transmit less fre0uently than those that are moving faster or are

maneuvering. he update rate ranges from C minutes for anchored or moored vessels, to - seconds for

fast moving or maneuvering vessels. 4ach AI5 station determines its own transmission schedule $slot, based upon data link traffic history and an awareness of probable future actions by other stations. A

position report from one station fits into one of -,-@% time slots established every #% seconds on each

fre0uency. AI5 stations continuously synchronize themselves to each other, to avoid overlap of slottransmissions.

Broadcast nformaton

An AI5 transceiver sends the following data every - to !% seconds depending on a vessel's speed while

underway, and every C minutes while a vessel is at anchor2

:aritime :obile 5ervice Identity $::5I a uni0ue nine digit identification number.

;avigation status *at anchor*, *under way using engine$s*, *not under command*, etc.

/ate of turn right or left, from % to -% degrees per minutepeed over ground in knots

8ositional accuracy2)ongitude to %.%%%! minutes

)atitude to %.%%%! minutes

$ourse over ground relative to true northrue heading % to C@F degrees

rue bearing at own position. % to C@F degrees

U6 5econds he seconds field of the U6 time when these data were generated. A complete

timestamp is not present.

In addition, the following data are broadcast every # minutes2I:9 ship identification number /adio call sign

;ame -% characters to represent the name of the vessel

ype of shipMcargo?imensions of ship to nearest meter

)ocation of positioning system's $e.g., 785 antenna on board the vessel 3 in meters aft of bow and

meters port or starboard

ype of positioning system such as 785, ?785 or )9/A;36.?raught of ship %.! meter to -@.@ meters

?estination max. -% characters

4A at destination U6 monthMdate hour 2minuteoptional 2 high precision time re0uest, a vessel can re0uest other vessels provide a high precision U6

time and date stamp.

AD9ANTAGES -) AIS

+ecause B fre0uencies have a longer wavelength and better propagation, AI5 signals have an ability

to *see* behind islands or around bends in a river, where a radar cannot. his aspect of the AI5 signal

15

http://en.wikipedia.org/wiki/Self-Organized_Time_Division_Multiple_Accesshttp://en.wikipedia.org/wiki/Self-Organized_Time_Division_Multiple_Accesshttp://en.wikipedia.org/wiki/Self-Organized_Time_Division_Multiple_Accesshttp://en.wikipedia.org/wiki/Maritime_Mobile_Service_Identityhttp://en.wikipedia.org/wiki/IMO_ship_identification_numberhttp://en.wikipedia.org/wiki/Call_sign#Ships_and_boatshttp://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Differential_GPShttp://en.wikipedia.org/wiki/LORANhttp://en.wikipedia.org/wiki/Draft_(hull)http://en.wikipedia.org/wiki/Self-Organized_Time_Division_Multiple_Accesshttp://en.wikipedia.org/wiki/Self-Organized_Time_Division_Multiple_Accesshttp://en.wikipedia.org/wiki/Maritime_Mobile_Service_Identityhttp://en.wikipedia.org/wiki/IMO_ship_identification_numberhttp://en.wikipedia.org/wiki/Call_sign#Ships_and_boatshttp://en.wikipedia.org/wiki/Global_Positioning_Systemhttp://en.wikipedia.org/wiki/Differential_GPShttp://en.wikipedia.org/wiki/LORANhttp://en.wikipedia.org/wiki/Draft_(hull)


16/25


can add to safer navigation by detecting the whereabouts of a ship, even when it is out of sight behind a

headland or island.

Aids to navigation can be transmitted over AI5. hese can be physical aids like buoys or *virtual* onesto mark a new or transient danger such as a wreck. AI5 can also identify navigational aids that are not in

their charted position.

Additionally, safety messages can be issued from either a ship or shore3based stations. A ship that is

adrift may issue a broadcast warning *adrift with no engine*. 5afety messages also may include

meteorological broadcasts or search and rescue information.

AI5 does not replace standing a proper watch, but it can add improved situational awareness for the

watch3keeper and since the system constantly updates, real3time changes of another ship's movementsare immediately recognized.

argets $ships are easily identified because the name is broadcast to the receiving station. :aking

contact by actual ship name, instead of calling *ship off my port bow*, or *tanker at position latitude V,

longitude Q* increases the likelihood of a positive response to the call. Using your vessel=s digitalselective calling, you can punch in the ::5I number that AI5 provides to ring the bridge of the ship

directly. alse alarms are greatly reduced

by filtering out vessels or suppressing alarms for targets that are not moving, hence posing no collisionrisk, as one moves through the harbour.

It greatly reduces the /A?A/ errors of Hlost target= and Harget swapping=, Also the calculation time lostfrom Hac0uire target= till Htarget data= is available.

4rrors due to /adar limitations, miscalculations, and display malfunctions can be greatly reduced.

he data obtained can be integrated with a 46?I5 or a radar display, providing consolidated

navigational information on a single display.

6an send M receive short 5afety ext :essages

AI5 contributes to safety of navigation and has, in many respects, made it easier to navigate safely.here are, however, also some limitations to AI5 that it is important to take account of. If you trust your

AI5 data blindly, it can be extremely risky.

*IMITATI-NS AI5 uses B fre0uencies hence range is limited to )I;4 9> 5I7


17/25


and still discouraged. Identification of a target by AI5 does not remove the danger. ;ot all ships will be fitted with AI5, particularly small craft and fishing boats. 9ther floating

objects which may give a radar echo will not be detected by AI5.

AI5 positions are derived from the target=s 7;55 position. his may not coincide exactly with the

target.

>aulty data input to AI5 could lead to incorrect or misleading information being displayed on other

vessels. :ariners should remember that information derived from radar plots relies solely upon datameasured by the own3ship=s radar and provides an accurate measurement of the target=s relative course

and speed, which is the most important factor in deciding upon action to avoid collision.

he ability to provide synthetic AI5 targets and virtual navigation marks enable coastal authorities to

provide an AI5 symbol on the display in any position. :ariners should take particular care when an AI5target is not complemented by a radar target.

6ollision avoidance must be carried out in strict compliance with the 69)/47s. 5o far there is no provision in the 69)/47s for use of AI5 information therefore decisions should be taken based

primarily on visual and M or radar information.

*RIThe )ong3/ange Identification and racking $)/I system provides for the global identification andtracking of ships.

he obligations of ships to transmit )/I information and the rights and obligations of 59)A5

6ontracting 7overnments and of 5earch and rescue services to receive )/I information are establishedin regulation BM!F3! of the !FO 59)A5 6onvention.

he )/I system consists of the shipborne )/I information transmitting e0uipment, the6ommunication 5ervice 8rovider$s, the Application 5ervice 8rovider$s, the )/I ?ata 6entre$s,including any related Bessel :onitoring 5ystem$s, the )/I ?ata ?istribution 8lan and the

International )/I ?ata 4xchange. 6ertain aspects of the performance of the )/I system are reviewed

or audited by the )/I 6oordinator acting on behalf of all 59)A5 6ontracting 7overnments.

)/I information is provided to 6ontracting 7overnments to the !FO 59)A5 6onvention and 5earchand rescue services entitled to receive the information, upon re0uest, through a system of ;ational,

/egional and 6ooperative )/I ?ata 6entres using the International )/I ?ata 4xchange.

4ach Administration should provide to the )/I ?ata 6entre it has selected, a list of the ships entitledto fly its flag, which are re0uired to transmit )/I information, together with other salient details and

should update, without undue delay, such lists as and when changes occur. 5hips should only transmit

the )/I information to the )/I ?ata 6entre selected by their Administration. 5hips send automatic position reports every # hours, which are received by satellite, and securely

transferred to data centres which manage )/I information on behalf of flag 5tates.

4ach >lag state is obliged to establish a ;ational )/I Data Centre or to join

a /egional or 6ooperative ?ata 6entre. he >lag also has to formally appointan App#caton Ser,ce Pro,der :ASP;. his A58 manages the communications

between the ship, the 6ommunication 6entre provider $658 and the

?ata 6entre $?6.he DC collects all of the >lag=s )/I information $such as the ships=

17


18/25


positional data and their identities and is connected to the International

)/I system via the International ?ata 4xchange $I?4 using a specific

)/I communications protocol. In addition, these centres shall be capable of communicating amongst

themselves and exchanging position reports on re0uest. A ship having notified a port of impending entry$;9A can be tracked by that particular port thanks to this system.

;ext to that, it will be possible for 6ontracting 7overnments to track any ship within a


19/25


that sphere is yet unknown. If, at the same time, the distance from the person to a second satellite can be

discovered to be -%,%%% km, then a second sphere of radius -%,%%% km on which the person is positioned

can be determined. hus the person must be on the circle formed by the intersection of the two spheres

of position. A third satellite provides yet a third sphere, which narrows down the location of the personto exactly two points. 9ne of these points is often an impossible solution, fre0uently several thousand

kilometers off in space, thus three satellite ranges can determine the precise position of the person. hree

satellites provide enough information to find the x, y, and z coordinates $measured from the center ofmass of the earth. unctionhe 785 uses three elements to accomplish transmission, maintenance, and user interface. hese

segments are referred to as space, control, and user.

5pace 5egment

5atellites6urrently there are thirty one 785 satellites orbiting the earth in a 1constellationP. he constellation is

divided into six 1planesP. 4ach plane is tilted at a different angle relative to the e0uator and gives the

satellites different paths over the earth=s surface. 4ach of these planes has at least four satellites spacedalong its 1ringP. his allows the 785 to have four satellites in view at anytime from anywhere on the

earth. he satellites have a very precise clock on board and they transmit their clock signal continuously.

6ontrol 5egment

6ontrol of satellites and ground assets is accomplished with a three part control system.

:aster 6ontrol 5tationA master control station and backup control station monitor the condition of the satellites in orbit and

space weather in the vicinity of the satellites. he accuracy of a satellite=s orbit is monitored and

19


20/25


adjusted from these stations and the on board clocks are synchronized within nanoseconds of the control

clock.

?edicated 7round Antennas

hese assets are used to measure the accuracy of data transmitted from orbiting satellites. here are fourdedicated antennas with fixed, known positions. hey are used as references to calibrate instruments on

board satellites.

?edicated :onitoring 5tationshere are six dedicated monitoring stations around the globe. hese secondary stations are used to feed

data about performance to the master control station and assure the health of each satellite. :any

secondary stations are necessary because transmitted signals cannot penetrate the earth, so a singlestation is unable to monitor all satellites simultaneously.

User 5egmenthe user segment is what you encounter in you daily operations. A user segment consists of three

components.

Antenna

A 785 antenna may be a single, low profile unit or may be an array of several antennas. Dhether single

or multiple the antenna does the same job of receiving signals from satellites in orbit and transferringthose signals to the data processing unit they are connected to.

It is important to keep antennas free of obstruction or debris, most will still function but it is good practice to make sure all antennas have a good view of the sky.

?ata 8rocessing Unit

his device may be part of a display or it may be a separate device connected to a display. Incommercial marine applications the 785 data unit is often located remotely from the display to avoid

electrical interference, protect the unit from damage, or position the unit closer to antennas to avoid

signal loss from long antenna cables.

he unit receives data from the antenna and combines the signals using a mathematical formula todetermine the location of the receiver. his data is rendered into display format and sent to the display

unit. he controls on the display unit may re0uest additional information from the data processing unit.?isplayhe information from the data unit is combined with other information like maps or charts and is

displayed on a screen which may be a few inches across or very large and readable from several feet

away. )ocation data might also be displayed simply in a latitude and longitude format in a separate smalldisplay.

Using 785

Using 785 to navigate is very easy because most systems integrate the location data together with otherdata like electronic charts. he 785 places a vessel on the electronic chart for the viewer. 4ven a basic

785 provides latitude and longitude that can be recorded manually on a paper chart.

he amount of data needed to determine a 785 location is small and can be sent to parties who need toknow a ship=s position. 5hipping companies, traffic monitors, and law enforcement can be informed

about the location and course of a vessel for efficiency or safety reasons.

ime 5tandardization+ecause the 785 is based on time, every 785 unit has a very accurate synchronized clock as part of its

construction. his clock adjusts for time zones automatically and allows all vessels and ports to operate

on a time standard.)atitude and longitude are usually provided in the geodetic datum on which 785 is based $D753EO.

• /eceivers can often be set to convert to other user3re0uired datum.

2


21/25


• 8osition offsets of hundreds of meters can result from using the wrong datum.

GPS Errors

785 errors are a combination of noise, bias, and blunders.

8 Nose Errors

• ;oise errors are the combined effect of 8/; code noise $around ! meter and noise within the

receiver noise $around ! meter.

• ;oise and bias errors combine, resulting in typical ranging errors of around fifteen meters for

each satellite used in the position solution.

Bas Errors

• +ias errors result from 5elective Availability and other factors.

• 9ther +ias 4rror sources2

o S9 c#oc5 errors uncorrected by 6ontrol 5egment can result in one meter errors in

position.

o Troposp"erc de#a$s2 ! meter position error.

he troposphere is the lower part $ground level to from E to !C km of the

atmosphere that experiences the changes in temperature, pressure, and humidityassociated with weather changes.

o Unmode#ed onosp"ere de#a$s2 !% meters of position error.

he ionosphere is the layer of the atmosphere from @% to @%% km that consists of

ionized air.

o Mtpat"2 %.@ meters of position error.

:ultipath is caused by reflected signals from surfaces near the receiver that can

either interfere with or be mistaken for the signal that follows the straight line path from the satellite.

:ultipath is difficult to detect and sometimes hard to avoid. 6are in antenna

placement at fixed sites, special antenna configurations, and special tracking

techni0ues can help sometimes. B#&nders

• +lunders can result in errors of hundreds of kilometers.

o 6ontrol segment mistakes due to computer or human error can cause errors from one

meter to hundreds of kilometers.

o User mistakes, including incorrect geodetic datum selection, can cause errors from ! to

hundreds of meters.

o /eceiver errors from software or hardware failures can cause blunder errors of any size.

Geometrc D#&ton of Precson :GD-P;

• 785 ranging errors are magnified by the range vector differences between the receiver and the

5Bs.• 7?98 is computed from the geometric relationships between the receiver position and the

positions of the satellites the receiver is using for navigation.

• 7?98 6omponents2

o PD-P 3 8osition ?ilution of 8recision $C3?

o 3D-P 3


22/25


• Dhile each of these 7?98 terms can be individually computed, they are formed from

covariances and so are not independent of each other.

P-SITI-NS -BTAINED )R-M GPS MUST BE CR-SS C3ECKED USING -T3ER MEANS

-) P-SITI-N )IXING ESPECIA**0 23EN IN BU-0ED C3ANNE* AND DURING

C-ASTA* NA9IGATI-N8

ECDIS

46?I5 is a computer3based navigation information system compliant with International :aritime9rganization $I:9 regulations and can be used as an alternative to paper nautical charts. An 46?I5

system displays the information from electronic navigational charts $4;6

he main advantage of the 46?I5 is the integration and sharing of the radar image and other dataamongst workstations connected to the network, such as2

J 6harts and databases

J 6ontinuous monitoring of ships positionJ 5ensor data, /adar data

J /oute and Boyage plan dataJ Alarms and warningsJ +ridge ;avigation Datch Alarm 5ystem $+;DA5. $if provided by manufacturer

J rack history and electronic logbook.

46?I5 is most powerful charts management application, and also a set of databases, applications and

services intended for voyage planning.

It providesJ 8ort to port planning of a complete voyage plan

J A to + via 6 auto routing

J Under Seel and 9ver


23/25


69:8A/I59; 9> B469/ A;? /A54/ 6


24/25


4//9/5 9> 46?I52

4rrors of interpretation or human errors2

Ignoring scale of display ( Uncritical acceptance of own ship=s position( Ignoring difference between

rue ;orth and 7yro ;orth( 6onfusion of different type of vectorts, display mode andMor referencesystem.

4rrors of ?isplayed data2

5ource error( An electronic chart can be as good as the source of original data( 9bject size error( heitems on chart are not drawn to scale( 8osition shift $ due different datums between 785 and chart(

reference shift $ a difference in the matching during superimposing of the two displays.

9DR

9o$a!e data recorder, or B?/, is a data recording system designed for all vessels re0uired to complywith the I:9's International 6onvention 59)A5 /e0uirements $I:9 /es.A.E#!$-% in order to collect

data from various sensors on board the vessel. It then digitizes, compresses and stores this information in

an externally mounted protective storage unit. he protective storage unit is a tamper3proof unit

designed to withstand the extreme shock, impact, pressure and heat, which could be associated with a

marine incident $fire, explosion, collision, sinking, etc..he protective storage unit may be in a retrievable fixed unit or free float unit $or combined

with 48I/+ when the ship sinks in a marine accident he last -O hours of stored data in the protectedunit can be recovered and replayed by the authorities or ship owners for incident investigation. +eside

the protective storage unit, the B?/ system may consist of recording control unit and data ac0uisition

unit, which connected to various e0uipment and sensors on board a ship.Although the primary purpose of the B?/ is for accident investigation after the fact, there can be other

uses of recorded data for preventive maintenance, performance efficiency monitoring, heavy weather

damage analysis, accident avoidance and training purposes to improve safety and reduce running costs.

5implified voyage data recorder $53B?/, as defined by the re0uirements of I:9 8erformance 5tandard:56.!#C$E, is a lower cost simplified version B?/ for small ships with only basic ship's data

recorded.

he information recorded in the unit$s, sometimes also called lack box for ship, may include the

following information23

• 8osition, date, time using 785.

• 5peed log 5peed through water or speed over ground.

• 7yro compass


25/25


• Anemometer and weather vaneJ Dind speed and direction

?ata marked with J may not be recorded in 53B?/, except /adar and 4cho 5ounder if data R standard

interfaces available.

25
http://en.wikipedia.org/wiki/Anemometerhttp://en.wikipedia.org/wiki/Weather_vanehttp://en.wikipedia.org/wiki/Anemometerhttp://en.wikipedia.org/wiki/Weather_vane

Bridge Equipments handout.docx

Documents

Transcript of Bridge Equipments handout.docx