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 compression
a.)
Compressor work for various vario us types of compression indicated indicat ed in a P- V diagram : b.) . ISOT!"#$% CO#P"!SSIO&'
It is the compression at constant temperature. In practice, it means that the temperature by of gas (air) remains constant throughout the compression. compression. It means that heat of compression is immediately taken away. This would necessitate innitely slow compressor. This type of compression theoretically is most ecient compression, but
dicult to achie!e. "ery slow mo!ing piston in a well#cooled small#bore cylinder can approach Isothermal compression.
$. $(I$$TIC *IS!&T"OPIC) CO#P"!SSIO& :
It is the compression under constant enthalpy conditions, i.e. no heat is gi!en to or taken from the gas through the cylinder walls and all the work done in compressing the gas is stored within it. %uring this compression the temperature raises progressi!ely progressi!ely causing increase in rate of pressure rise, which calls for increased power input to piston. This gi!es it poor eciency. eciency. & !ery fast mo!ing piston in totally insulated cylinder will gi!e adiabatic compression.
PO%+T"OPIC CO#P"!SSIO&' '. PO%+T"OPIC
It is the compression compression process which lies#in between two etremes of isothermal and adiabatic compression. ere, ere, some parts of heat of compression is usually etracted by *acket cooling cooling and multi#staging with inter cooling cooling is used to reduce work work of compression.
,)y mu/tistage compression is used on air compressors01 compressors01 #2%TIST$3! CO#P"!SSIO&' If we had an a n innite number of stages of compression with coolers in between each stage returning returning the air to ambient temperature, temperature, then we would be able to compress compress o!er the desired range under near isothermal conditions. This of course is impracticable so two or three stage compression with inter#stage inter#stage and cylinder cooling is generally used when relati!ely high pressures ha!e to be reached. *)a)!hy intercooling is use" in multistage air compressors# * *b)!hat are the a"vantages of intercooling# *
a.) $nter-cooling%
To To a!oid ecessi!e ecessi!e temperature temperature rise associated with higher higher compression ratios, ratios, and to approach isothermal compression, compression, inter#cooling inter#cooling is adopted after each stage of compression in a multistage compression. +sually, deli!ery temperature from nal stage is limited to '- (Lloyd/s 0ules).
b.) $dvantages of Inter-coo/ing' Inter-coo/ing' 1. ompressio ompression n work work is reduced. reduced. $. "olumetric eciency and hence compressor compressor capacity is increased. '. It approi approimate mates s isothermal isothermal compre compression. ssion.
2. The !olume of air deli!ered deli!ered is reduced, reduced, re3uiring re3uiring reduced si4es si4es of cylinder, cylinder, piston and deli!ery pipes. 5. The temperature temperature of air deli!ered deli!ered is is reduced, which which gi!es less less thermal loading onto material and better lubrication of piston and cylinder. cylinder. 6. %ue to less less temperature temperature suction and deli!ery !al!es remain remain cleaner without being fouled with carboni4ed oil. 7. 8oisture 8oisture separatio separation n is easier through through intercoole intercoolerr drains. 9. +se of after after cooler cooler allows allows smaller smaller recei! recei!ers. ers. &)Explain
i) a) clearance volume b)Vo b)Volumetric lumetric efficiency c)compressor capacity' ii)Enumerate the factors affecting volumetric efficiency'
iii)(raw a simp/e sketc 4 sowing te e5ects of c/earance vo/ume a) C%!$"$&C! VO%2#!' To To pro!ide for thermal thermal epansion and for machining machining tolerances, a small clearance, clearance, called, ;umping clearance<, is left between cylinder head and the piston. This clearance must be as small as possible, as its increase will reduce the !olumetric eciency and hence capacity of the compressor. b)
VO%2#!T"IC !66ICI!&C+ !66ICI !&C+'' "olumetric eciency is the ratio of the actual !olume of air drawn in each suction stroke to the stroke !olume. 0eferring to the gure:
Pressure Vo/ume (iagram of a Compressor wit c/earance *witout 7ow resistance). = v s/ v p Volumetric efciency = ηv = s/ v
c.) CO#P"!SSO" C$P$CIT+ :
ompressor capacity is determined as !olume of the free air actually discharged by compressor in one hour. It is termed as =.&.%. (free air deli!ery) in m ,>hour.
ii) 6actors $5ecting vo/umetric !8ciency'
1. learance !olume !olume (;umping clearance) clearance) ad!ersely ad!ersely a?ects !olumetric !olumetric eciency eciency.. igh#pressure igh#pressure air remaining remaining in the cylinder after compression and deli!ery will epand on the return stroke stroke of the piston. This epanding air must fall to a pressure pressure below that in the suction manifold before a fresh air charge can be drawn in. ence, part of the return return or suction stroke of the piston is non#e?ecti!e. This non#e?ecti!e part of the suction stroke must be kept as small as possible in order to keep capacity to a maimum. $. @luggish @luggish opening opening and and closing closing of !al!es. !al!es.
'. Leaka Leakage ge past past pisto piston n rings. rings. 2. Insucient Insucient cooling cooling water. water. 5. ooling ooling water water temperatu temperature re high. 6. &ir inlet inlet tempe temperatur rature e high. high. 7. Throttling of air air intake. intake. (%ue to dirty intake lter, lter, insucient or ecess ecess suction !al!e lift, suction !al!e spring too strong).
iii)
!5ects Of Increasing C/earance vo/ume.
6) a) What are the statutory requirements requirements for Air Air Compressors
A!" C#$%"&''#" "&(!"&$&*+' 1- +wo +wo starting starting compressors compressors must be fitted, fitted, of sufficient sufficient total total capacity capacity to meet the engine requireme requirementsnts&ach compressor must be able to press up Air recei.er from 1/ bar to 0 / bar in thirty minutes- +wo +wo air recei.ers must to be pro.ided- +otal +otal air recei.er capacity is to be sufficient for +wel.e +wel.e 10) starts of "e.ersible engines and si2 6) starts for non3re.ersible engines0- Additional Additional one Diesel Diesel dri.en dri.en or hand operated operated or if possibl possible, e, both) emergency emergency air air compressor compressor must must be fitted to start au2iliary engines of a 4Dead 'h ip5- 'afety .al.es .al.es or preferabl preferably y bursting bursting discs must must be fitted fitted on the cooling cooling water casing casing to gi.e ample ample relief of pressure, should an air3cooling tube burst7- 7-&ach compress compressor or must ha.e ha.e a safety .al.e .al.e designed so that that the accumulated accumulated pressur pressure, e, with the outlet outlet .al.e closed will not e2ceed 189 of the ma2imum working pressure/- /-+he air compresso compressorr cylinders, cylinders, co.ers, co.ers, intercoolers intercoolers and after3co after3coolers olers,, are tested by hydraulic hydraulic pressure pressure to twice their working pressure-
6- 6-+he casing casing of the inter3cooler inter3cooler and after3c after3cooler ooler is hydraulical hydraulically ly tested to 1-/ times times cooling water water pressure- +hus, for 7 bar cooling water pressure, the the casing will be tested at 6 bar pressure:- :- A water separato separatorr or drain should be fitted fitted on the airside of each intercool intercoolerer- +he drain cock should should be used at regular inter.als to pre.ent water from one stage being carried into the following stage b) ;ow are compressors classified
C
et Compressors !n which a dri.ing .apour attains a high supersonic .elocity in in a
$odern practice is to use a synthetic oil for lubrication-
y using intercooling and cylinder cooling usually BAir or BWater with air compressors) the oil is kept in a fluid condition i-e- it does not .aporise or carbon ise) so it may lubricate properly-
#peration
#n the downward stroke of the piston in a single cylinder compressor, air is drawn in through the suction filter and the suction .al.e, to fill the cylinder- +he downward motion of the piston causes a partial .acuum in the cylinder so the atmospheric pressure of the outside air pushes the suction .al.e open against the light force of the spring that holds it closed when the machine is stoppedAs the piston begins its upward stroke the suction .al.e is pressed shut as the air pressure inside the cylinder rises- Continued upward motion further raises the pressure until at a designed pressure the discharge .al.e is pushed open against the larger spring force that holds it closed when the machine is stopped, and the compressed air will then pass through an intercooler to a second stage-
+he piston3reciprocating compressor has a more positi.e sealing arrangement rings) than any other type of compressor and consequently it can achie.e higher compression ratios than any other form of compressor+he two3stage compressor arrangements below show the single acting pistons acting in con@unction with an intercooler
y using intercooling and cylinder cooling usually BAir or BWater with air compressors) the oil is kept in a fluid condition i-e- it does not .aporise or carbon ise) so it may lubricate properly$ulti3stage air compression ha.e the following ad.antages 1- +hey can maintai maintain n a moderate moderate range of air air temperature temperature by cooling cooling the the air between between stagesstagesCylinder cooling also assists this to a smaller e2tent0- y cooling between stages and cylinder cooling), less work input i-e- less electric motor or diesel power) is required to compress a gi.en quantity of o f air to a specific pressure-
b) 'tate the typical air pressures E temperatures for for each stagestages
Deli.ery
Air- temperature temper ature
%ressure
efo efore re the the cool cooler erss
Afte Afterr the the coo coole lers rs
=irst stage
7-: bar
18C
/C
'econd stage
06-: bar
18C
/C
F) a)*ame the main components of a reciprocating air compressor E the materials they are made of+he main components of a reciprocating air
compressorG are
a) edplate 3 cast iron b) Crankcase 3 cast iron c) Cylinder block block 3 cast iron d) Cylinder co.er 3 cast iron e) %iston 3 cast iron or alurninium alloyalloyf) piston rings rings 3 cast iron iron wet wet liner) liner) and bron?e or phenolic plastics plastics dry liner) liner)
g)connecting rod 3 forge
steel or alurninium alloy h) crankshaft 3 forge steeli) top ends bearing 3 brass bush @) bottom ends bearing 3 thin shell white metal lined k) gudgeon pins 3 case hardened steel steel 1) suction and deli.ery .al.es33 .al.e seat 3 carbon hardened steel, hardened and polished working surfaceschrome .anadium or stainless steel, hardened and
.al.e 3 nickel steel,
polished.al.e spring 3 hardened spring tempered) c) Enumer Enumerate ate the various mountin mountings gs fitte" fitte" to the air compre compressor ssor''
+he following mountings are fitted to the air compressors to ensure safe and efficient operations 1) Air =ilters 0) !ntercoolers 3) Drain Hal.es 7) "elief Hal.es /) urs ursti ting ng Dis Discs cs 6) =usi =usibl blee %lu %lug g ()a)!hat are the conseuences of unfiltere" unfiltere" air getting into the compressor suction si"e
Air contains suspended foreign matter, much of which is abrasi.e- !f this is allowed to enter the compressor it will combine with the lubricating oil to form an abrasi.e3like3paste which increases wear on piston rings liners and .al.es !t can adhere to the .al.es and pre.ent 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 .al.es, .a l.es, etc 'trictly, the apparent carbon deposit on .al.es contains .ery little carbon from the oilI it is mainly solid matter from the atmosphere +his carbon like deposits can become e2tremely hot on .al.es which are not closing correctly and could act as igniti ignition on points points for air3oil air3oil .apor mi2tur mi2tures, es, leadin leading g 3to 3to possib possible le fires fires and e2plosi e2plosions ons in the compressor ;ence air filters are e2tremely important, they must be regularly cleaned and where necessary renewed and the compressor must ne.er he run with the air intake filter remo.edb) Describe the effect of a "irty air filter in a multistage air compressor' * •
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%irty lter causes pressure drop in air intake, which causes higher compression ratios resulting in higher deli!ery temperature, which can cause re and eplosion.
A chok choked ed filt filter er caus causes es a .acu .acuum um on the the comp compre ress ssor or inle inlet, t, whic which h redu reduces ces the the out put, put, rais raises es air air temperature and may cause filter element sucked in cylinder with inherent dangers-
c)Explain why the air inlet filter nee" to be maintaine" in goo" woring or"er' •
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!t 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!f clean, imposes .ery little resistance to airflow- With most types, regular cleaning or renewing filter elements is necessary- A choked filter causes a .acuum on the compressor inlet, which reduces the output, raises air temperature and may cause filter element sucked in cylinder with inherent dangers-
+)a)etch an automatic valve for .ir "elivery an" .ir suction
.ir "elivery
.ir suction b) /ame the materials use" in their construction' Va/ve seat: A.2B carbon steel hardened and polished working surfaces. Va/ve: Cickel steel, chrome !anadium steel or stainless steel, hardened and ground, then nally polished to a mirror nish. Spring' ardened steel (C.;. all hardened steel would be tempered).
++) Describe the principle of operation of an automatic "rain trap , fitte" to air compressors an" air receivers with a setch'
Drinciple of Eperation : Fith water under pressure pressure at the inlet the disc will lift, allowing the water to Gow radially across the disc from & to the outlet ; when the water is discharged and air now Gows radially outwards from & across the disc, the air a ir epands increasing in !elocity ramming air into and the space abo!e the disc, causing the disc to close on the inlet. ;ecause of the build#up of static pressure in the space abo!e the disc in this way, and the di?erential area area on which the pressures pressures are acting, the disc is held rmly closed. It will remain so unless the pressure in the space abo!e the disc falls. In order that this pressure can fall, and the trap re#open, a small groo!e is cut across the face of the disc communicating ; and through which the air slowly leaks to outlet. Eb!iously this gi!es an operational fre3uency to the opening and a nd closing of the disc which is a function of !arious factors, e.g. si4e of groo!e, disc thickness, !olume of space abo!e the disc, etc. It is therefore essenti essential al that the correct correct trap be tted to the drainage system to ensure ecient and e?ecti!e operation.
+2)!hat are the safety "evices fitte" to an air compressor# 0ention their reuirements'
Safety devices "e/ief va/ve =itted to each stages on air side and set to lift at pressure 1AB more than stage pressure.
ursting disc 9 ursting Va/ve
=itted to water side on coolers, will relie!e ecess pressure in the water casing in the e!ent of failure of an air tube. Eil relief relief !al!e (Inside rankcase) rankcase) =itted in the oil system to relie!e pr. more than $5B of normal working pr. to protect oil pump from o!erloading, during cold start up. =usible plug En air deli!ery pipe or on air reser!oir a fusible plug is also tted which melts at 1$1-c, this ensures the safety of after machine system against temperature temperature rise. L.E.Dr.cut out switches H Drotects Drotects the compressor machine from damage due to loss of lubrication oil. &ir high temperature cut out switches Drotects compressor and air system from damages due to high temperature air. +1) Enumerate the various metho"s use" for unloa"ing the air compressor cylin"ers'
&ns. +nloader : & compressor, during starting and stopping must be in unloaded condition. This reduces starting tor3ue (current (current for motor)for the machine, also it clears out any accumulated moisture. If the compressor is re3uired to be running continuously, it has to be unloaded after the reser!oir is lled to full pressure.
#etods of un/oading Compressor 1.Throttling of suction $)@peed !ariation ')%epressors ')%epressors to hold suction !al!e plates on their seats. 2);y#pass, discharge to suction 5)hanges in !olumetric clearances of the cylinders 6)@tep unloading of cylinders in a multi cylinder machine
+) etch "escribe the unloa"ing metho", by throttling the suction si"e'
2n/oading by Trott/ing te Suction Side
Operation' The compressor compressor discharge at maimum pressure pressure will will mo!e the !al!e to the left, stopping the air intake. @o no air is deli!ered.
:;)ow is te running gear of reciprocati reciprocating ng air compressors /ubricated0 @ome air compressor piston are a re connected to the connecting#rod through a gudgeon pin and are similar to trunk pistons. Fith 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. compressor. Fhen air compressors 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 tted on crosshead engines for cylinder lubrication .the oil is passed through a 3uill tting to the cylinder liner. liner.
+3)!hat are the two basic "esigns of rotary compressors# 4riefly "escribe a sli"ing vane compressor with a setch'
1.positi!e displacement type in which power is con!erted directly into pressure energy. $.%ynamic type in in which a fast mo!ing impeller causes the air to mo!e at a high !elocity and the kinetic energy energy so created is subse3uently subse3uently con!erted into pressure pressure energy by the di?user.eg:centrifugal blowers. @LI%IC "&CJ E8D0J@@E0:
In tis design a s/otted rotor carries a number of b/ades4 wic maintain contact wit te bore of te casing by s/iding in and out as te rotor turns wit te e/p of springs backup. Inspection of te diagram wi// make te operation c/ear. c/ear. (uring te ero at te point were rotor and casing are in c/ose contact. (uring te
+5)!hat are the effects of leaing suction "elivery valves of first secon" stage, in a two stage air compressor'
Va/ves can /eak and
!5ects of va/ves /eaking' J
6irst stage suction' "educed air de/ivery4 increased running time and reduced pressure in te suction to te second stage. If te suction va/ve /eaks bad/y it may comp/ete/y un/oad te compressor.
J
6irst stage de/ivery' it ig-pressure air /eaking back into te cy/inder /ess air can be drawn in. Tis means reduced de/ivery and increased discarge temperature.
J
Second stage suction' ig pressure and temperature in te second stage suction /ine. "educed de/ivery and increased running time.
Second stage de/ivery' Increased suction pressure in second stage4 reduced air suction and de/ivery in second stage. (e/ivery pressure from
+6)etch a line "iagram for 0ain air bottle, in"icating all the mountings their wel"ing arrangements' b)!hat are compensation rings why are they necessary# !henever a hole is cut
(b)The mountings of the air bottle are tted 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 tted whene!er a hole is cut to regain the reduced strength due to drilled hole. +()a)!hat are the basic reuirements for steering gear# b)7epresent the steering gear system of a ship, by by a bloc "iagram'
T! $SIC "!?2I"!#!&TS 6O" ST!!"I&3 3!$"S' In brief, a steering gear is re3uired re3uired to: a) ;e continu continuous ously ly a!aila a!ailable bleKK b) 8o!e the rudder rudder rapidly to any position in response response to the orders orders from the bridge during manoeu!ring, and hold it in the re3uired positionK c) a!e arrangements arrangements for relie!ing relie!ing abnormal abnormal stress stress and returning returning the rudder to to its re3uired re3uired position, d) 8aintain 8aintain the ship on course course regardl regardless ess of wind and wa!es. wa!es. The rst three points are now go!erned go!erned by complicated statutory re3uirements re3uirements and the last is of particular interest for economic reasons. & steering gear is pro!ided for steering a ship s hip and therefore its perfect ness of design is of utmost importance. J!en a small fault cannot be o!erlooked as this may subse3uently result in failure of the system, which in turn would result in collision or grounding g rounding of the ship.
8b)
2)Explain the 9elemotor hy"raulic transmitter with a setch' $n"icate the materials of the components'
#ateria/' Casing @ 3unmeta/. "ams @ ron>e. Pipes @ Copper. Copper. Cups *o/d type) @ %eater. In te new Transmitters te rams are /apped to te cy/inders. Te transmitter transmitter consists of two two rams ending in racks4 wic mes wit a primary pinion attaced to te steering wee/ saft and oused in a casing.
Te unit consists of two parts' Te top wic ouses te racks and te pinion and serves as te rep/enising or make up tank4 te racks and pinion being /ubricated by tis 7uid. Te bottom a/f wic is made of two cy/inders in wic reciprocate te rams passing troug sea/ing g/ands.
2+)Explain the construction woring of the :4ypass valve; of the
Te/emotor transmitter. y it is provided0
Since te cy/inders are a/ways fu// of te ydrau/ic 7uid a device as to be ed. Tis eAua/ising connection is a/so connected to te rep/enising tank at te top of te te/emotor te/emotor transmitter transmitter as sown sown in te attaced diagram.
22)Explain the 9elemotor hy"raulic receiver with a setch' $n"icate the materials of the components'
$t consists of two hollow rams in line, fitte" to two fixe" crosshea"s' . cylin"er close" at mi" length an" open at each en", fits over an" floats between the rams' ealing glan"s 8construction "escribe" later) are fitte" at each en" of the cylin"er an" air cocs cocs provi"e" provi"e" on both si"es' 9he crosshea" crosshea" an" the rams are ept fixe" an" aligne" by two parallel ro"s' 9he ro"s have two sleeves each fitte" over them an" sli"ing through the cylin"er casing' 9he stopper nuts as shown restrict the movement' Each set of sleeves carry a strong spring between them' 9he crosshea"s are connecte" by supply
21) !hat are the "esirable properties of 9elemotor hy"raulic oil# 9he =y"raulic oil shoul" have the following properties% properties% >ow pour point aroun" -&*?' >ow viscosity 81 7e"woo" sec' at 3*?)' =igh viscosity in"ex 8++)' =igh flash point 8close" flash point +&*?)' /on-slu"ge forming' /on-corrosive' @oo" lubricating properties but not too thin that will mae glan" sealing "ifficult' Density about 66 g
Aperating Principle
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•
•
•
•
•
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Tis pump consists of a saft wic is stationary and a cy/inder body wic rotates around tis saft. Cy/inder body is provided wit odd number of cy/inders spread around it !ac cy/inder as a p/unger4 connected to s/ippers4 wic in turn run in annu/ar grooves inside two circu/ar rings on eiter side of te p/ungers. On/y one cy/inder of te cy/inder p/unger assemb/y at four di5erent positions during one rotation is sown. P/unger4 in addition to rotating a/ong wit te cy/inder4 may a/so ave in and out movement4 depending upon te position of te circu/ar ring. If center of te circu/ar ring is concentric wit center of stationary saftD as sown by O4 te p/ungers wi// ave no in and out movement. Tus p/unger wi// act /ike a pump sucking in oi/ from camber at top *T) and pumping into te oi/ camber at te bottom *) of te stationary saft. $s te stroke of te p/ungers can be varied wit te cange in eccentricity of te circu/ar ring4 te pump terefore is a variab/e de/ivery pump. Cy/inder body is rotated at constant speed and direction by an e/ectric motor. Odd number of cy/inders4 usua//y seven or nine are provided4 to produce more ydrau/ic 7ow and to give better pump ba/ance.
E;)a)#ake a /abe/ed sketc of a two ram steering gear.
b)State te purpose of unting gear The tiller arm arm is connected to the bottom portion portion of the Goating Goating le!er by a bu?er bu?er spring and link. This is called called the hunting hunting gear. gear. unting gear gear acts as a feedback feedback system of rudder mo!ement to to the control system.
23)Discuss the mechanical stops limits in a teering @ear system'
&. mechanical stops limits in a @teering ear system: system: &s per regulations a steering gear system should be capable of putting the rudder from an angle of '5- on one side to '5- on the other side (statutory re3uirement re3uirement is to put rudder from '5- on one to 'A- of the other side) in $9 seconds. seconds . To ensure that these limits are maintained there are are a number of stops and limit switches. the mechanical stops that are pro!ided are in the following actuating order:
:. $uto pi/ot mecanica/ stop. E. %oca/ contro/ mecanica/ stop4 were /oca/ contro/ provided. ,. $ctuating system mecanica/ stops tat /imits on te ram trave/4 provided as stops against ti//er arm movement or some ting simi/ar. F. ridge Te/emotor transmitter mecanica/ stop *"ack trave/ /imited).
;. 6ina//y4 stern- post mecanica/ stop. !=tra movement of te rudder due to eavy seas or some oter reasons is
25)Describe 25)Desc ribe the con constru structio ction n of cro crosshe sshea" a" arr arrange angement ment of a ram type steering steering gea gear, r, with a se setch, tch, labeling all parts clearances' .'
Te ram ends are usua//y forked and eac pair of rams are bo/ted togeter at tese ends forming bearing a/ves as sown. Tese are bused to form te top and bottom vertica/ bearings4 wic take or c/amp te pins or trunnion arms of te swive/ b/ock. Te swive/ b/ock and te pins togeter are ca//ed te crossead . Te swive/ b/ock as a ori>onta/ gunmeta/ bus troug wic passes te ti//er arm. Provision is made by te way of c/earances as sown between te swive/ b/ock and te ram fork ends for wear-down of te rudder and ti//er arm and a/so to accommodate te vertica/ movement of te rudder.
Tese two c/earances are of utmost importance importance for te safe working of te cy/inders and rams.
$ny vertica/ movement of te rudder sou/d not re7ect by te virtue of forces on te crossead.
To ensure tis *ie. &o force coming on te crossead) it is important to make sure'
:) ear down c/earance as sown above4 sou/d be at a// times4 more tan any pint/e wear down provided4 in te "udder. E) Humping c/earance as sown above sou/d be at a// times4 more tan te a//owab/e vertica/ p/ay c/earance permitted by te rudder4 tat is c/earances at te striking pad or c/earance at te pa//ester bearing.
If striking pads are
It is of utmost importance tat a// te c/earances are measured and recorded wit date4 during te vesse/s routine dry-docking
EJ)at are te regu/ations for Steering gear on Tankers K %P3 3as carriers01 $. Oi/ tankers4 gas tankers K cemica/ tankers are reAuired to ave a safematic design of steering system i.e. no sing/e fai/ure on a steering sou/d make te steering of te sip inoperative and tus give te rudder a cance to become free. 2()Explain the 7otary vane teering gear system, with a line "iagram, labeling all the parts' .'
It consists of a rotor wic is a taper
$ variab/e de/ivery pump de/ivers into one side and receives from te oter side4 ti// te rudder is at te reAuired position. $t tis point te feed back /ever %, brings te pump to neutra/ *>ero pumping position) and te rudder gets ydrau/ica//y /ocked. Compared wit te F ram ydrau/ic steering gear4 te cost of te rotary vane type to produce te same torAue on te rudder stock is genera//y /ess. It is /igter in weigt4 takes up /ess space and reAuires /ess maintenance.
1)$n electrical steering gear system, show with a setch, how the power is transmitte" '
1+)a)!hat is follow up an" non follow up steering system#* b)!hat is the function of .uto Pilot # * c)!hat is a gyrocompass#*
&) .M=ollow .M=ollow +pN steering system system the angle or amount through through which the rudder turns is dependent on the amount of turn of the steering s teering wheel.
In a MCon#=ollow +pN steering system, the steering gear and a nd hence the rudder will mo!e as long as the control is held in an actuating position, and will only stop when it is mo!ed back to an ME==N position or until the gear has reached the hard# o!er position.Thus in a non#follow up system the amount of rudder mo!ement depends upon how long the control is held in the operating position and therefore this system can also be termed as OThe time dependent steering system.O
b)The function of an &utomatic &utomatic elmsman elmsman or &uto Dilot Dilot is to steer a ship on a preset course (aided by a gyrocompass), with a minimum of de!iation, which could be caused by hea!y seas or bad weather. weather. The maimum de!iation de!iation allowed is '- on either side. c)& yrocompass is a compass tted on a yroscope, which consists of hea!y swiftly rotating wheels wheels so mounted that its ais can turn freely in all directions and the compass would still maintain maintain its position with reference reference to the true north.
,E)!=p/ain ,E)!=p/ai n te non fo//ow up system wit a /ine sketc4 /abe/ing /abe/ing a// parts.
Te above es one of te two so/enoids4 depending upon te direction of movement reAuired. Tese so/enoids operate a pi/ot va/ve wic causes te main contro/ va/ve to move so as to divert oi/ pressure from a continuous/y running <=ed de/ivery pump to te steering gear in order to give te desired direction of rudder movement.
en te switc is re/eased4 it springs back to te centra/ position4 te contro/ va/ve moves to a position were it bypasses te pump de/ivery4 and te steering gear stops. $t te same time4 te contro/ va/ve sea/s o5 te pipes to te main cy/inders so as to o/d te rudder. If te system is on autopi/ot contro/ ten te /ever is e/d over by te autopi/ot and springs back to Bo5 position as soon as it stops acting. Tus te autopi/ot acts as te unting gear4 stopping rudder movement as soon as it as reaced te desired ang/e as signa/ed by te rudder indicator
11)Describe the Electro 0echanical .uto Pilot, with a setch'
It is a separate unit to the hydraulic telemotor and tted in the steering Gat. The bridge console has a switch or control le!er with three positionsK E?, and and yro. In the ME?N position the autopilot is out of action and operation can be done using the hydraulic telemotor. In the MandN position the control le!er or push buttons of the non#follow up system can be used and in the
MyroN position, the automatic steering is engaged. In both MandN and MyroN positions the bypass !al!e of the telemotor transmitter is opened so that the recei!er can mo!e freely. The auto pilot pilot unit is linked linked to the the steering gear control and consists consists of a dri!e motor motor (ser!o 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 re!ersible type and to ensure 3uick stopping #dynamic braking is used. The motor dri!es dri!es the rack through through gearing gearing and an electro electro magnetic clutch, the rack rack being coupled to the telemator recei!er actuating or mo!ing cylinder. The clutch is necessary so that the motor and rack will be disconnected disconnected when the gyro pilot is not in use and it also acts as a safety de!ice, designed to stop under ecessi!e tor3ue tor3ue load. (The coil of the electro magnetic clutch in connected through a control switch, operated by the control le!er, the circuit being completed only when the control le!er is in the MandN or MyroN positions. The limit switches switches are are cam operated, turned turned through through gearing by the mo!ement of the rack and are set to trip in the hard#o!er positions, inside the stops on the telemotor recei!er. They are so arranged that when one has tripped in one direction, no further mo!ement can be made in that direction but the unit would respond to a re!erse signal. The auto pilot pilot ser!omotor has has a feed from from the yrocompass. yrocompass. Ence the the course is set, set, and de!iation of more than three degrees ('-) makes a contact in the compass which actuator, the ser!omotor and hence results in the rudder mo!ement. The operation between the rack and the rudder has been eplained earlier on, under the non#follow up steering system.
1)Enumerate the rules governing teering @ears' •
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All .essels must be pro.ided with efficient main main and au2iliary steering gear of power operated type- An au2iliary gear is not required if the main gear is pro.ided with duplicate power units and duplicate connections up to the rudder stock+he main steering gear must be able to steer the ship at ma2imum ahead se.ice speed and be capable at this speed, and at the ships deepest draught, of putting the rudder from / degree on one side to 8 degree on the other side in no more than 0F seconds+he .essel must ha.e means pro.ided to allow steering from a position aft+wo +wo tillers, or their equi.alent, are required unless the working tiller is of special d esign and strength%ower operated gears must be fitted with a de.ice to relie.e shockAny lead lead connectio connections, ns, steam, steam, hydraulic hydraulic or electric electric should should be independent independent to the the gear gear onlyonly- &lectri &lectricc leads and fuses are to allow 1889 o.erload$o.ing parts of steering gears should be guarded to a.oid in@ury to personnel;ydraulic systems should employ non3free?ing fluid- 'teering room floors should ha.e wooden gratings to pro.ide for easy mo.ement of personnel p ersonnel in case of ol spillA clear .iew from the steering position is required and the wheel, tell3tale indicators, and rudder mo.ement must correspond in the correct amount and in the correct direction for the ships head#perating trials should be carried out on steering gears to ascertain degree of action, time of operation, angle of heel at .arious speeds, etc-
1&)Describe a steering system for a 9aner ship, with automatic changeover within & secon"s, with a line setch'
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'afematic 'afematic Design Design $ethod $ethod *o-1 *o-1 Also Also called 1889 redundancy redundancy method), method), refer refer figure figure
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All .al.e .al.ess are automa automatic tically ally cont control rolled led and elect electric ricall ally y operate operated d .al.es.al.es-
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!n this this arrangement arrangement 'ystem ! supplies supplies to to ram *o*o- ! E0 - 'ystem 'ystem 0 supplie suppliess to ram ram *o- E7 E7 - ;owe.er, ;owe.er, as it is not practical to ha.e both bo th systems work simultaneously, and therefore the only combination of operations a.ailable are
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Combination Combination *o- 1 !solating !solating .al.e .al.e ! E 0 open, open, y pass .al.e / shutI system system *o- ! !n operationoperation-
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!solat !solating ing .al.e .al.e E 7 shut, shut, y y pass pass .al.e .al.e 6 openI openI syste system m *o*o- 0 stopp stopped ed
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+op +op two rams are in in operation, operation, working working on system system *o- ! and are are pro.iding pro.iding 1889 1889 torquetorque-
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ott ottom om two two ram ramss E syst system em *o*o- 0 is is shut shut--
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Combi ombina nattion *o-0
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!solat !solating ing .al. .al.ee E 7 open, open, y pass pass .al.e .al.e 6 shut, shut, syste system m *o- 0 in in operati operationon-
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!solat !solating ing .al.e .al.e 1 E 0 shut, shut, y y pass pass .al.e .al.e / open, open, syste system m *o- stopped stopped
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ottom ottom two rams are in in operation, operation, working working on system system *o*o- 0 and and are pro.id pro.iding ing 1889 1889 torquetorque-
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+op two two rams rams E sys syste tem m *o*o- l is is shu shutt
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*ow the logic circui circuitt of safemat safematic ic design design in this this method method will will cause the the condition condition of operation operation to change change from Combination *o- ! to Combination *o-0 or
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Combi Combinat natio ion n *o-0 *o-0 to Comb Combin inat atio ion n *o*o- 1
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depending depending on which Combination Combination was in in operation operation when the the hea.y loss of oil oil <<<
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&2ample
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!f Combina Combination tion *o-1 is in in operatio operation, n, i-ei-e- system system *o-1 E rams rams *o- 1E *o- 0 are in operati operation) on) E <<
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+his alarm alarm takes takes care care of normal normal leakage leakage E can can be set right right by filling filling in some some oil in the tank tank during during the watch-
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;owe.er, ;owe.er, if if <<<
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!t may be noted that as said earlie earlierr e.en though though we ha.e ha.e 7 rams, rams, only 0 rams are are in operati operations ons at any any gi.en time- +hus each set of 0 rams should pro.ide 1889 torque-
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$ost ships ships will will not employ this this method method to take care care of 4single 4single failur failuree criteria, criteria, as as this method method means a 1889 duplication and a costly one*13)Explain the test proce"ure that shoul" be carrie" out on an electrohy"raulic steering gear a)before leaving port * b)before arriving port'
Drior %eparture: 1. $. '. 2.
@teering gear should be checked checked at least one hour prior departure from a port. The duty ocer and the senior duty engineer should carry carry out the tests together. together. Telemotor transmitter transmitter oil le!el to be checked. checked. Eil le!el of the actuating actuating system tank should be checked and replenished replenished if necessary. 5. Dallester allester bearing bearing and bottom sea sea gland checked checked and greased greased.. 6. &ll links links on the steering steering gear checked checked to be in order order.. 7. =irst one pump is is started from from the bridge and the wheel turned turned from port to starboard to check the telemotor response. 9. Cet with with both the ocers in the steering steering Gat the wheel is turned from from hard#a#port to hard#a#starboard and the running checked. . heck heck made to see if the the helm angle angle indicator indicator on the the bridge bridge and the local local mechanical one correspond correctly correctly to each other for all positions. 1A.. 1A The The rs rstt pump pump is sh shut ut o? and and the the seco second nd one one sta start rted ed and and che cheek eks s 9 and and repeated. 11.. 11 Then Then both both the the pump pumps s ar are put put in para parall llel el oper operat atio ion n and and chec checks ks 9 and and repeated. 1$.. 1$ &fter ter tes testi ting ng is sati satisf sfac acto tory ry one one pum pump p iis s shu shutt o?. o?. Fit Fith h one one pump pump runn runnin ing g and and if it is of the ele @haw type it should be ensured that the wheel is actuated e!ery 15 minutes, so that the pump parts get properly lubricated. 1'.. 1' Eper Eperat atio ion n of of the the aui auili liar ary ys ste teer erin ing gg gea earr or or use use of the the sec secon ond dp pum ump, p, whic which h acts as the auiliary. 12.. 12 Eper Eperat atio ion n of the the rem remot ote e cont contrrol (tel (telem emot otor or)) syst system em or sys syste tems ms from from the the main bridge steering positions. 15.. 15 Eper Eperat atio ion n of of the the stee steeri ring ng gear gear us usin ing g tthe he emer emerge genc ncy yp pow ower er su supp pply ly. 16.. 16 The The alar alarms ms tte tted d to to the the remot emote e con contr trol ol sy syst stem em and and the the ste steer erin ing g gear gear powe powerr units should he checked for correct correct operation. 17.. 17 %uri %uring ng the these se test tests s th the e rud rudde derr sho shoul uld d he he mo! mo!ed ed thr through ough its its full full tra! tra!el el in both both directions and the !arious e3uipment items, linkages, etc., !isually inspected for damage or wear.
19.. 19 The The com commu muni nica cati tion on sy syst stem em betw betwee een n tthe he brid bridge ge and and tthe he stee steeri ring ng gear gear compartment should also be operated. ;efore &rri!ing Dort: 1. Ene hour before before picking picking up the pilot, pilot, the speed should should be reduced reduced and engine engine maneu!ers and astern running checked. &lso steering gear actuation checked. $. ;oth pumps pumps are put on and and the mo!ement mo!ements s on either side side checked checked.. '. elm angle indicator and local indicator in the steering steering gear compartment checked for correct and matching response on either side.
13)Explain the test proce"ure that shoul" be carrie" out on an electrohy"raulic steering gear a)before leaving port * b)before arriving port' .ns%
T!STI&3 O6 ST!!"I&3 3!$" P"IO" (!P$"T2"! $&( !6O"! $""IVI&3 PO"T'
Drior %eparture: 1.@teering gear should be checked at least one hour prior departure from a port. $.The duty ocer and the senior duty engineer should carry out the tests together. '.Telemotor transmitter oil le!el to be checked. 2.Eil le!el of the actuating system tank should be checked and replenished if necessary. 5.Dallester 5.D allester bearing and bottom sea gland checked and greased. 6.&ll links on the steering gear checked to be in order. order. 9.=irst 9.=irst one pump is started s tarted from the bridge and the wheel turned from port to starboard to check the telemotor response. .Cet with both the ocers in the steering s teering Gat the wheel is turned from hard#a#port to hard#a#starboard and the running checked. 1A.heck made to see if the helm angle indicator on the bridge and the local mechanical one correspond correctly correctly to each other for all positions. 11.The rst pump is shut o? and the second one started and cheeks 9 and repeated. 1$.Then both the pumps are a re put in parallel operation and checks 9 and repeated. 1'.&fter 1'.&fter testing is satisfactory one pump is shut o?. Fith one pump running and if it is of the ele @haw type it should be ensured that the wheel is actuated e!ery 15 minutes, so that the pump parts get properly lubricated. 12.Eperation of the auiliary steering gear or use of the second pump, which acts as the auiliary auilia ry.. 15.Eperation of the remote control (telemotor) system or systems from the main bridge steering positions. 16.Eperation of the steering gear using the emergency power supply. 17.The alarms tted to the remote control system and the steering gear power units should he checked for correct correct operation.
19.%uring these tests the rudder should he mo!ed through its full tra!el in both directions and the !arious e3uipment items, linkages, etc., !isually inspected for damage or wear. 1.The communication system between the bridge and the steering gear compartment should also be operated. ;efore &rri!ing Dort: 1.Ene hour before picking up the pilot, the speed should be reduced and engine maneu!ers and astern running checked. checked. &lso steering gear actuation checked. $.;oth pumps are put on and the mo!ements on either side checked. =elm angle in"icator an" local in"icator in the steering gear compartment chece" for correct an" matching response on either si"e' *15) !hat are the obBectives of shaft alignment# *
&ns:
Saft a/ignment obLective 1. To transmits the power output from from the 8ain Jngine to the propeller propeller in most ecient way. $. To pre!ent pre!ent undue stresses stresses and !ibratio !ibrations ns '. To transmits transmits the thrust thrust de!eloped de!eloped by the propeller to the ship
16) etch an" "escribe a metho" a"opte" for shaft alignment on boar" ship' .ns% During the construction of the ship, the main shafting is aligne" an" mostly remains unchange" till the life of the ship, unless affecte" by any acci"ent or wear' 9here are various external factors which can alter the alignment even "uring the construction an" the entire operating perio" of the vessel' During buil"ing, the common causes are, stern tube aperture incorrectly machine", .ny contractionexpansion of hull owing to temperature variation along with changes cause" by wel"ing' hafting .lignment in hip 7eference "atums here are the height of the shaft above the eel aft, an" the height of the cranshaft centre above above the eel exten"e" to the forwar" forwar" machinery space space bulhea" 8also centre centre athwartships) athwartships) forwar"' 9hese two "atas are taen from the shipCs "rawings 9he rough bore of the stern frame is fitte" with a plate flange, this flange has a small hole 8say + mm) "rille" at the correct height above the eel' !ith this centre the reference circle can be "rawn for the setting up of the exact boring of the frame' imilarly at the engine room forwar" bulhea" a small flange in the bulhea" has the small hole "rille" at the correct engine height above the eel an" at the mi"ship point athwartships
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.n electric light is sighte" behin" the hole in the forwar" machinery space bulhea" an" by looing from outsi"e through stern frame this light can be seen through the two sight holes' /ow
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at the aft pea bulhea" an" the aft machinery space bulhea" an" any water-tight bulhea" through which the shaft passes, sighting plates are use" ' .t these points the horiontal plate is move" vertically up until the light line of sight is mase", a horiontal reference mar is now ma"e across the bulhea"' 9he plate is move" vertically "own until the light is mase" an" another horiontal reference mar ma"e, bisection of these two lines gives the horiontal centre '
9he same same proce" proce"ure ure is now rep repeate eate" " using using vertical vertical boar"s, boar"s, move" move" horion horiontall tally y port port to starboar starboar", ", bisection bisection of these two lines gives the vertical centre' centre' 7ough bores are now bri"ge", bri"ge", the centre is fixe" temporarily with a tin plate an" a small hole is centre"' /ow from aft to forwar" a continuous light shoul" be visibe through all bulhea"s, the reference circles can now be "rawn for exact boring' 9he exact borings are now ma"e
*1()!hat are the stresses in a tail en" shaft#* shaft# *
$ns' ST"!SS!S' Steady Stresses' @tresses due to thrust and shear stress due to tor3ue (continuous), radial loads due to the weight of the propeller such as centrifugal force etc. form the maPor part. entrifugal force on the coupling bolts although relati!ely relati!ely smaller creates steady stresses on the shafting.
$/ternating Stresses'
<ernating stresses are due to bending and torsional !ibrations. <ernate bending stress is !ery pronounced in the propeller shaft due to weight of propeller and is in maimum intensity at a point forward of the propeller. Dortion 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 fre3uency of !ibration Induced by the blades with respect to resonance. resonance. It should be noted here that aft bearing of stern tube is subPected to more load due to tipping moment of propeller and if it wears out ecessi!ely ecessi!ely 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 sha ft will start whirring, the misalignment and stresses will worsen further. To a!oid this at times carefully bored slope bearings< are used to enable the forward bearing to take its share of load as well.
*)!hat is the purpose of thrust bloc # *
&ns: The thrust block transfers the thrust thrust from the propeller propeller to the hull of the ship It must must therefore therefore be solidly constructed and mounted onto a rigid seating or framework to perform its task. It may be an a n independent unit or an integral part of the main propulsion engine. ;oth ahead and astern thrusts must be catered for and the construction must be strong enough to withstand normal and shock loads.
+) a)Describe a full shell bearing suitable for use for main engine shafting' b)Explain how the bearing is lubricate"' c)Explain how the bearing is coole"'
2)!ith reference to bearings for interme"iate shafting% a)Describe with the ai" of a setch a tilting pa" bearing ' b)tate the a"vantages "isa"vantages of this type of bearing over normal full shell bearing
ans:# &n intermediate tunnel bearing is shown in the gure, the usual Pournal bush is here replaced by pi!oting pads. The tilting pad is better able to carry high o!erloads and retain a thick oil lubrication lm. 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. ooling of the bearing is by water circulating through a tube cooler in the bottom of the casing.
ad!antages of using tilting pad bearings:# •
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Te tree pressure wedges give a /arger tota/ support area tan tat obtained wit a p/ain bearing. Te ti/t of te pads automatica//y automatica//y adLusts to suit /oad4 speed and oi/ viscosity. Te wedge of oi/ gives a greater separation between saft and bearing tan does te oi/
1)a)etch an" "escribe a transmission shaft couplinhg 80uff coupling) which enables the propeller shaft to be remove" outboar"' b)tate what safety precaution shoul" be taen when "ismantling the coupling .ns3
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+his coupling is without flanges !t is hydraulically connected and released 'lee.es that make up the coupling to be accurately machined to a smooth finish +here is an inner slee.e and an outer slee.e +he inner slee.e is bored parallel to the shaft with sliding fit #n its outer diameter is a slight taper,1F8, forming a cone +he outer slee.e is bored with a similar taper and is parallel on its outer diameter +he outer slee.e is thicker so pro.iding 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 slee.e and screwed to it+o fit the coupling to the shafts hydraulic oil is in@ected at high pressure between the two slee.es forming a load bearing film As the pressure increases in the annular space between the oil seal and the outer slee.e an a2ial force pushes the outer up the taper and e2pands it +he inner slee.e is compressed and grips the shafts creating the coupling "emo.ing the pressure this grip is maintained+o remo.e remo.e the coupling the re.erse procedure is followed ;ydraulic oil is pressuri?ed into annular space between the slee.es, relie.es pressure from seal end and the outer end is dri.en off the taper and rela2es the friction grip of the inner slee.e, returning it to sliding fit-
%recautions to be taken when dismantling the coupling3 #utside diaKs at end of outer muff measured before fitting • After fitted, diaKs should be appro2- 8-/mm 8-/ mm greater • "estraining de.ices must be fitted to pre.ent the muffs separating too quickly •
) a)etch a line "iagram of the lubricating system, for an oil fille" stern tube, fitte" in a large ship' b)!hat is the effect of sea water contamination with oil an" how can contamination ris be re"uce"'
&ns# b)@ea water upon contamination with oil, leads to the formation of emulsion and oil looses its lubricating property which can ha!e ad!erse e?ect on the stern tube bearing.
0isk 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 !al!e.
&) a)etch "escribe an oil seal suitable for oil fille" stern tube, in"icating the principal components' *b)Explain how the seal compensates for wear of the oil seal face an" maintains oil tightness'* tightness '* Ans3 Ans3 When When the the seal seal face face wear wearss out, out, it is comp compen ensa sate ted d by the the forc forcee appl applie ied d by the the gart garter er sprin pring g circumferentially, circumferentially, keeping the seal face always in contact con tact with the liner-
& !ery common arrangement for oil lubricated stern tube bearings is the M@imple @ealN.
& simple seal arrangement is tted to both inner and outer ends.
The replaceable chrome liner liner pre!ents pre!ents damage to the prop shaft which which would be epensi!e to repair.
Cot shown is a rope guard bolted to the hull which pre!ents material from being /wound/ into the gap and damaging the seal
Eil is fed to the area between the two opposite facing seals.
The oil pressure pressure in the stern tube is is go!erned by the draught of of the !essel and is often supplied !ia tanks situated at set heights.
This pressure pressure balances the sea water pressure pressure on the seal and pre!ents pre!ents sea water ingress. ;y opening the correct correct tank, the pressure eerted eerted by the oil is insucient to cause oil to leak out.
;utadiene rubber rubber is used for seal rings
@tern tube seals, with oil lubrication ha!e tended to use rubber rings increasingly. increasingly.
=luoric rubber ("iton) with additi!es has been shown to be more e?ecti!e than nitrile butadiene rubber for seal rings.
b) The inner sealing ring is tted in the opposite fashion and pre!ents the oil in the stern tube leaking into the sea. The sealing rings are all held on the rotating chrome slee!e by a garter spring. 3) =ow the forwar" seal of an oil coole" stern tube is lubricate" coole" # *
Ans3 +he forward seal incorporates an oil circulator as a standard fitting- #il from a 7 liter tank is circulated continuously through the annular chamber+his ensures effecti.e cooling, as well as permanent lubrication with clean oil-
*3) =ow the forwar" seal of an oil coole" stern tube is lubricate" coole" # *
The forward seal assembly assembly consists of two seal rings on a liner one one to seal against high lubricating oil pressure arranged arranged for the bearings and the other to seal any leakage in the engine room. The bearings, which work in conPunction conPunction with abo!e assembly are are normally made made of white metal and are lubricated by oil, maintained at higher pressure pressure by either a gra!ity tank or by oil pump. The life of bearings is ensured by the fact that lubricating oil is at higher pressure pressure and if seals do not function eciently the lubricating oil will be lost. The lubricating oil system may include an oil cooler if considered necessary. necessary. 5) a)etch a section through a propeller nut of the Pilgrim "esign, showing it in the propeller fitting mo"e% b)@ive a brief explanation how the pilgrim nut is use" to with"raw the propeller'
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b)"!#OV$%' &fter remo!al of =airwater cone, the pilgrim nut is taken o?, re!ersed and screwed back on to the tail#shaft. & withdrawal plate is tted and secured with studs to the propeller
boss. rease is now applied to the system which forces the withdrawal plate aft and this in turn draws the propeller down the tail#shaft taper *6) !hat is a Pilgrim /ut #* #* Pilgrim is the tra"e name for a patente" type of nut often use" use" for fastening a propeller on to a shaft'the lan"ing face of the nut is bore" out with a circumferential slot into which a steel ring lie a short piece of tube is fitte"
() etch an" "escribe the propeller mounting "ismounting by Ail $nBection 0etho"C
9h Ail Ail $nBec $nBectio tion n meth metho" o" is use" use" for mounti mounting ng "ismo "ismount unting ing of prop propel eller lers, s, ru""e ru""ers rs steer steerin ing g gear'Previosly propellers were "riven up the tapere" shaft en" by means of a nut' 9he torue was transmitte" as a result of the friction of the mating surfaces, the ey performe" a stan"by function if the friction prove" insufficient' 9he grip achieve" with the oil inBection metho" is so powerful that the ey can be "ispense" with, without running any ris' Furthermore, the mounting operation is simplifie"' 9he propeller is "riven a pre"etermine" "istance up the seating'9his "istance is selecte" so as to obtain a pressure, which can transmit the torue from the shaft with a wi"e safety margin' During the "riving up operation, the friction is re"uce" by the oil being force" between the mating surfaces' !hen the propeller reaches the "esire" position, the inBection pressure is release" an" the oil "rains off, restoring the friction between the hubthe shaft' 9he "rive up force is applie" by means of a hy"raulic tool, which is fitte" on the shaft nut' !hen oil is pumpe" into the tool, an annular piston forces the propeller up on the seating'
+'?hec that the mating surfaces of the propeller hub shaft "o not have any burrs or scratches that they are thoroughly clean'Ail these surfaces gui"e the propeller to the starting position on the shaft' 2'.pply the nut, with the hy"raulic tool, against the hub maing sure that the piston is retracte" as far as possible'8Ail supply hole vent hole position to be a"Buste")' 1)7emove 1)7emove the plugs from the three three holes in the hub attach nipples nipples to the outer holes' holes' ?onnect the pumps' )Pump oil into the hy"' 9ool 9ool until the pr' @auge shows some rea"ing' .pply .pply a "ial gauge to the forwar" en" of the hub to measure the "rive up' &)Pump oil into the hub until it flows out at the en"s of the hub plug the mi""le hole when oil begins to emerge' 9hen wor the three pump slowly increase the pressure' 3)!hen the propeller has attaine" its pre"etermine" position, release the oil pressure in the pumps for the hub, but maintain the pressure in the hy"raulic tool' Disconnect the hub hoses, remove the a"aptors plug them' >et the oil "rain away from the mating surfaces' Do not release the oil pressure in the hy"' tool, until two hours have elapse"' 4y that time the friction woul" have been reestablishe" reestablishe" the propeller can not sli"e bac'
&)!hat is "ry"ocing # /ame the types of "ry"ocs' * $t is a techniue use" to remove a ship from the water so the un"er water portion may be inspecte"
T+P!S O6 (OCMS' :. 6%O$TI&3 6%O$TI &3 (OCM (OCM.. E. 3"$VI&3 3" $VI&3 ("+ (OCM. (OC M.
&+)etch an" "escribe a Floating Dry"ocC'
&ns.
6/oating dry dock as sown in
&2)etch an" "escribe a @raving "ry"ocC'
&ns.
& gra!ing dock is a channel cut out of a basin or ri!er in which a closable gate is placed in front of the opening and water is pumped out. &s the water is pumped out the ship is lowered on to the blocks. This type of dock can handle the largest largest of !essels. &1)!hat are the routine Bobs "one in "ry"oc #
Ans-
For a routine "ry-"ocing, the usual wor to be "one are% +'=ull cleane" of marine growth' Painting with anti-corrosive an" anti-fouling paints' acrificial ano"es renewe"' =ull inspection an" repairs' 2'hipsi"e gratings cleane" an" repaire"' 1'.ll overboar" an" sea suction valves overhaule"' '?leaning an" surveying of tans "one' /-7u""er, ru""er carrier ring, ru""er pintleCs clearances examine"' 3'%ropeller damage, nut looseness checked- lade polishing done5'9ail shaft bearing wear "own chece"' 9ail shaft remove" an" inspecte"' ?oupling bolts an" holes chece" for "eformation' 6'.nchor chain examine", cleane" an" re-mare"' .ll un"erwater stuffing boxes repace"
&)!hat preparations are ma"e for "ry"ocing a ship #
Ans-Prior to vessels entry into the "ry "oc, its con"ition to be ascertaine" for satisfying the reuirements while being "ry "oce", such as proper "raft, trim hea", its tan con"itions, con"itions, "e-ballasting of tans for lightening trimming, an" vessels "ocing plan' Following wor shoul" be accomplishe"% !hen the vessel has entere" the "oc, ensure that it is hel" in position for "raining the "oc water' Ensure that the shore power is connecte" an" teste"' Ensure water availability on the fire main'
Ensure that the ship is groun"e" to earth' $mpresse" current to be switche" off' hips power to be put off' GEnsure all sea valves are ept open to "rain lines to "oc' Ensure that all gas-free an" wor permits certificates are poste" at the gangway' .long with the secon" engineer, inspect hull, inclu"ing plating for erosion, "amage etc', plugs an" their con"ition, con"ition of ano"es, sea chest gri"s, tail shaft aft seal con"ition .fter removal of rope guar", chec propeller boss an" bla"es surface con"ition, ru""er con"ition' ?hec sea water leas from wel"s, bearing bushes, striing pa" etc'
&&)!hat precautions are taen before an" after floo"ing the "ocs #
de bris, so that no floating debris .ns' efore flooding the docks, the dock floor must be cleared of all debris, are found on the water- #therwise these floating debris will find their way into sea chests and obstruct the free flow of sea water- efore flooding, the sea chest air .ents must be open- All sea suction and o.er board .al.es must also be openAfter flooding the docks, the &ngine room and the cargo holds must be checked for any sea water leaks and the same must be rectifiedrectified- &specially &specially in the engine room, all the sea suction suction .al.es E o.erboard o.erboard .al.es must be checked for leakages from glands, @oints etc- and the same rectifiedWhen the water le.el in the dock reaches the sea chest le.el, start the au2iliary engines one by one and .ent the complete sea water system, starting from the sea water pump, fresh water cooler, lub- oil cooler and air cooler -
&3'!hat is ru""er "rop propeller "rop # /ame the tools use" to measure them# !hen the ru""er carrier bearing wears "own, ru""er stoc an" hence the ru""er also "rops by that amount' 9his is calle" ru""er "rop' !hen the stern tube bearing wears "own, the propeller shaft an" hence the propeller also "rops by that amount' 9his is calle" propeller "rop' 7u""er "rop is measure" by 9r 9rommel ommel gaugeC Propeller "rop is measure" by Depth gauge' &5'/ame the "ifferent types of thrusters 9he "ifferent types of thrusters are% a) ?ontro ?ontrolla llable ble pitch pitch thrus thrusters ters an" b) !ater Bet thrusters' c) .imuthing thrusters ") Pu Pump mp Bet thr thrust uster erss e) Verti rtical cal ax axis is thr thrust uster er &6)Describe a transverse bow thruster unit using a controllable pitch propeller'
The bow thruster is an auiliary auiliary propulsion de!ice de!ice used to pro!ide lateral lateral thrust to impro!e a ship/s maneu!erability. y .arying the pitch of the propeller blades, a .essel may be thrusted, port or starboard at any desired rate from full to dead slow, or brought to a quick stop and re.ersed in direction, all without changing direction or speed of the prime mo.er- Hary Harying ing propeller blade pitch assures ma2imum efficiency under all load and operating conditions and pro.ides bow control with either headway or sternway on the .essel, the efficiency dependent upon .essel speed, with the greatest efficiency obtained at
4ero speed. +he bow thruster assembly consists of a tunnel, which is welded athwart3ships into the hull of the .essel, well forward and as low as possible in the bow- +hree stays attached to the tunnel wall suppo rt a pod, which houses the hydraulically operated mechanisms- +he bow thruster is dri.en b y an electric motor, diesel engine or steam turbine+he 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 chang ing mechanism- Lood anti3wear, rust and o2idation inhibited hydraulic oils ha.e pro.ided satisfactory lubrication for these unitsined at ?ero speed*&()!hat is water Bet propulsion #* #*
&ns. The water Pet propulsion is essentially a water pump, draws water in through a ca!ity (usually located in the base near the rear of the craft) using what is termed termed an impeller where where a mesh is used to stop large obPects from being sucked up. The water is then forced forced out of a no44le (located at the !ery !ery rear) rear) at high pressure. pressure. The force pushing the water water out of the rear of of the boat is mirrored mirrored by an e3ual and opposite force, accelerating the craft forward. Fater is epelled at 15 degrees through
outlet no44les in the water Pet propulsion engine. @ince the no44les can turn a full '6A degrees it is possible to achie!e maimum thrust in all directions. 6A)@ketch 6A)@ke tch and describe a controllable pitch propeller
?ontrollable pitch propellers can be "ivi"e" into 2 main types
The mechanism for the propeller propeller consists of 2 main main parts: 1) Dropeller Dropeller hub incorporating incorporating ser!o, ser!o, crank ring for turning turning blades and necessary seals. $) Eil distribution bo bo (transfer bo), bo), which in mounted mounted at the forward forward end of the hollow tail#shaft and controls the oil Gow to the hub ser!o through a !al!e rod. ')ontrol system, which may be either pneumatic or electric. 2) ydraulic system, consisting of motor or shaft dri!en pumps, cooler, lters, tanks etc The pitch of the DD blades is controlled controlled hydraulically hydraulically through a system consisting of a pump, piston, crosshead, and blade crank rings. The piston, crosshead, and crank crank rings are located in the propeller propeller hub.
igh pressure hydraulic hydraulic oil, acting on either side of the piston, mo!es the piston aially within the propeller hub.The piston is attached to a piston rod that connects to the crosshead that mo!es aially with the piston. @liding blocks t in machined slots on the crosshead and these sliding blocks t o!er eccentrically#located eccentrically#located pins mounted on the crank pin rings. &s the crosshead mo!es forward and backwards within the hub, the sliding blocks mo!e in an arc that also mo!es the eccentric pin and rotates the crank pin rings to which the DD blades are bolted.
Safety Springs
.ns)
Cemica/ Sewage Treatment Treatment P/ant minimi>es te co//ected sewage4 treats it and retains it unti/ it can be discarged in a de-contro//ed area4 usua//y we// out at sea.
Sore receiving faci/ity may be avai/ab/e to take tis retained sewage.
orking' $ perforated rubber be/t is used to separate /iAuid from so/ids in a separating tank.
Te /iAuid is ten passed troug treatment tanks to a prepress arrangement *compressed *compressed air pressure tank) for use as a 7using 7uid at te toi/ets.
So/idTreatment by c/orine and caustic based compound makes te /iAuid acceptab/e for te purpose.
s are inerted by a caustic compound and de/ivered via a grinder to te o/ding tank.
Capacity of tank is E /itres per person per day. It is important to maintain te correct cemica/ dosage rates.
32)' a) etch "escribe a biological sewage treatmet plant' b) !hat are the $0A tan"ar"s for the Effluent "ischarge from the ewage 9r 9reatment eatment Plant'
$ns) a) io/ogica/ Sewage Treatment 4uti/i>es bacteria to comp/ete/y break down te sewage into an acceptab/e substance for discarge into any waters. Te e=tended aeration process provides a c/imate in wic o=ygen /oving bacteria mu/tip/y and digest te sewage4 converting it into a arm/ess s/udge. Tese bacteria are known as aerobic bacteria
Te treatment p/ant uses a tank wic is divided into tree watertigt compartmentsD an aeration compartment4 compartment4 a sett/ing compartment K a c/orine contact compartment Te sewage enters te aeration compartment were it is digested by aerobic bacteria and micro-organism4 wose e=istence is aided by atmosperic o=ygen wic is pumped in. Te sewage ten 7ows into te sett/ing compartment4 compartment4 were te activated s/udge is sett/ed out. Te c/ear /iAuid 7ows to te c/orinator and after treatment to ki// any remaining bacteria4 it is discarged. Tab/ets are p/aced in te c/orinator and reAuire rep/acement rep/aceme nt wen used up. Te activated s/udge in te sett/ing tank is continuous/y recyc/ed and conseAuent/y it bui/ds up4 so tat every two to tree monts it must be partia//y removed.
Tis s/udge must be discarged on/y in decontro//ed areas ie. in te open sea. ) I#O ST$&($"(S 6O" !66%2!&T (ISC$"3! :.Te geometric mean faeca/ co/iform bacteria count of te samp/e sou/d not e=ceed E;N 9:NN m/. E)Te geometric mean suspended so/ids sou/d not e=ceed :NNmg9/itre4 above te suspended so/ids content of te water used for 7using purposes.
,)Te geometric mean of te ;-day bio/ogica/ o=ygen demand *O(-;) sou/d not e=ceed ;N mg9/itre.
*at is O( 0 - ?uantity of o=ygen in mg9/itre reAuired by bacteria to stabi/ise or o=idise te sewage witin a given period of time and at a particu/ar temperature.)
F) If c/orine is used as a disinfectant4 disinfectant4 te te residua/ c/orine sou/d not e=ceed ;mg9/itre as free avai/ab/e c/orine.
31)' a)etch an" "escribe an $ncinerator Plant fitte" to a large vessel' *b) /ame the safety "evices fitte" to the $ncinerator Plant' *
$ns)a)
$nne= V of #$"PO% ,9J gives guide/ines wit regard to waste materia/ storage and disposa/ at sea. Sips generated garbage are :.3a//ey waste inc/uding food scraps4 bones4 cans4 E.$ccommodation wastes suc as paper4 cardboard4 cans4 te=ti/es4 ,.Oi/ waste suc as oi/ s/udge inc/uding bi/ge4 oi/ puri
b) 1-LA"AL& =&&D!*L D##" !*+&"<#CM W!+; +;& "*&" 0-=
$ns) #etods of !=terna/ u// Protection' 1.&nticorrosion Daints $.athodic Drotection of +nderwater ull:
a) Inorganic Qinc oatings:
b) +se of @acricial &nodes:
'.&ttachment of &nodes 2.I..@ystem 3&) a)etch "escribe an $mpresse" ?urrent ystem as fitte" to a large ship' b)=ow the ru""er shafting system is protecte" by the above system# @ive a line setch for any one of them'
In te impressed current system4 te current is fed to permanent *inert) anodes4 wic emit te current troug seawater4 to be received by te u// of te sip.
Te /ow-vo/t (.C. supp/y generated in te sip is connected across te inert anodes *positive) and te u// *negative) and te circuit comp/etes troug te seawater. Te anodes are comp/ete/y insu/ated from te u// *by g/ass
$ contro//er unit. Step-down transformer and recti
>evel of Protection
>ess than '3V
Hn"er protecte"'
4etween '3+ to '6(V
Protecte"'
.bove '(V
Aver protecte"'
Te main contro//er unit compares te /eve/ of protection4 read by reference e/ectrodes4 wit te desired or set va/ue and according/y regu/ates current output troug te permanent anodes.
Since te anode to seawater interface drop is about E.; vo/ts4 te actua/ (.C supp/y vo/tage wi// be in te order of ,.F to F.N vo/ts4 to maintain u// potentia/ at N.J; V. it catodic protection4 protection4 it is recommended to paint te u// wit a/ka/iresistant paint suc as coa/ tar epo=y paint to witstand temporary temporary overprotection e5ect. *$/ka/i-attack). *$/ka/i-attack). Impressed current system a/so incorporates' Prope//er saft s/ip-ring assemb/y. "udder grounding arrangement.
Since under norma/ operationa/ conditions4 bot te prope//er9saft prope//er9saft and rudder are e/ectrica//y iso/ated from te u// due to te /ubricants in te bearings4 proper grounding arrangements are
"udder 3rounding System
