Steering Gear

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SteeringGearRuddersArudderallowstheshiptoturn,simpleplateshavebeensupersededbyplatesweldedtocastorfabricatedframe.Ruddersarehollowandsoprovideforsomebuoyancy.Inordertominimisetheriskofcorrosioninternalsurfacesareprovidedwithaprotectivecoatingandsomeareevenfilledwithfoam.Adrainplugisprovidedtoallowforthedrainageofwater,enableinternalinspectiontobemadeusingfiberopticdeviceandevenallowforthelimitedapplicationofaprotectivecoating.Platesareweldedtotheframesinternallyinordertoprovideflushfitting,thefinalclosingplatemustbeweldedexternally.Ameansofliftingisprovidedtakingtheformofatubeasclosetothecenterofgravityaspossible.Ruddersaretestedtoapressurehead2.4mabovethetopoftherudder.

Iftherudderhasitsentireareaaftoftherudderstockthenitisunbalanced.Arudderwithbetween20and40%ofitsareaforwardofthestockisbalancedsincetherewillbesomeangleatwhichtheresultantmomentonthestockduetothewaterforcewillbezero.Mostmodernruddersareofthesemibalanceddesign.Thismeansthatthatacertainproportionofthewaterforceactingontheafterpartoftherudderiscounteractedbytheforceactingonthefor'dhalfoftherudderhence,thesteeringgearcanbelighterandsmaller.Aruddermayliftduetothebuoyancyeffect,theamountofliftislimitedbythejumperbarfittedtothesternframe.Thejumper/rudderclearancemustbelessthanthesteeringgearcrossheadclearancetopreventdamage.Arudderissupportedbymeansofabearingpintleoralowerbearingdependinguponthedesign.Wherealowerbearingisemployedtherudderisactuallysupportedonsplitbearingringsfittedonthelowerfaceoftherudderandtheupperfaceofthesolepiece(theextendedlowersectionofthesternframeuponwhichtheruddersits)

SEMIBALANCEDRUDDERSemibalancedrudderwithrudderhorn



FullybalancedrudderToreducetheamountoftorquerequiredtoturnarudderthepivotpointismovedbackfromtheleadingedge.Theamountoftorquethenvariesdependingontheangleofattack.Zerotorqueleadstoinstabilitywithruddermovingwithinitsclearances.



SpadeRudder

Thereduceddiameterattheupperpartispurelytotransmittorque.Thelowersectionmustalsosupportbendingmomentsandhenceincreaseddiameter.Withtwinruddershipstheinnerruddermustturnthroughagreateranglethantheouter.Thisisachievedbyhavingthetillerarmatanangletothecentrelineoftherudder.Itispossibletohavethebladesangledinoroutwhenthewheelisamidshipsto



increasepropulsiveefficiency.SPECIALSTEERINGDEVICES

THEKORTNOZZLE

Adequateclearanceisessentialbetweenpropellerbladetipsandsternframeinordertominimisetheriskofvibration.Asbladesrotatewaterimmediatelyaheadofthebladesiscompressedandatthebladetipsthiscompressioncanbetransmittedtothehullintheformofaseriesofpulseswhichsetupvibration.Adequateclearanceisnecessaryoralternativelyconstantclearance,thisbeingprovidedwithductedpropellerssuchastheKortnozzleOriginallydesignedtoreduceerosiononriverbanksthenozzlehasproveditselfalsoabletoincreasethrustwithoutincreaseofappliedpower.Thenozzleconsistsofaringofaerofoilsectionwhichformsanozzlesurroundingthepropeller.Thesuctionofthepropellercausesanaccelerationofflowinthemouthofthenozzleandhenceadropofpressureinthisregion.Sincethepressureontheouterpartofthenozzleremainsrelativelyunchanged,thereisaresultingdifferentialinpressure,whichactingontheprojectedannulusofthenozzle,givestheadditionalforwardthrust.Thisadditionalthrustistransmitteddirectfromthekortnozzletothehullviathenozzlesupports,sothatnoadditionalforceactsonthepropellerandshaftthrustblock.TherearetwotypesofKortnozzles.Thefixedtypehasaconventionalrudderbehindit,whereaswiththeswivellingruddertype,thewholeassemblyissupportedbyacarrierattachedtotherudderstockandactuatedbythesteeringgear.



Inthecaseofnozzlerudders,whenhelmisapplied,theincreasedthrusthasanathwartshipcomponentwhichhaspowerfulsteeringeffect,sothathardoveranglesof25'(or30'inspecialcases)aresufficienttoprovideeffectivesteeringaheadduringacrashstopand,providedthehullisareasonabledesign,astern.Thisdeviceisespeciallyvaluablefortugs,trawlers,specialvesselsandmorerecently,VLCC,whicharerequiredtomanoeuvrewell,particularlyatslowspeed,andhavethebestpropulsiveefficiency.

Bollardpullgainsbetween30and50%,equivalenttoreenginingupto13/4timestheoriginalpower,havebeenobtainedintugsandtrawlersandinVLCCgainsinpropulsiveefficiencybetween6to13%canbeexpected.Thenormalmethodofcalculatingruddertorque'scanbeappliedtonozzlerudders.Themaximumsteeringeffortisrequiredtoreturntheruddertowardsmidshipsandnottomovetherudderoverfromamidships.Thus,thesteeringgearmustbedesignedtokeepcontroloftherudderundertheseconditions.Fordiagramandadditionalnotessee'methodofreducingvibration'and'increasingpropulsiveefficiency'

PLEUGERRUDDER

Anormalruddercanonlybeeffectivewhentheshipismoving,andthetorqueitexertsvarieswiththesquareofthespeed,sothatatverylowspeedsitcanbeveryineffective.Apleugerrudderincorporatesasubmersibleelectricallydrivenpropellerwhichcanberunwhenthemainpropulsionisatrest.Inordertoattainmaximumeffectandmanoeuvretheshipatresttherudderisabletoturnto90',owingtothisnormalfloatinglinkagehuntinggearcannotbeused,andaspecialcamhuntinggearused.Fornormalcoursekeepingtheangleislimitedto35',andawarningsignalinitiatedifexceeded.

THEVOITHSCHNEIDERPROPELLER



Thispropellerconsistsofaseriesofbladesofaerofoilsectionwhichprojectverticallydownwardsfromtheship'shullandrotateaboutaverticalaxis.Thebladesaremountedonaxesonacirclearoundthecentralaxisandarelinkedtogetherwithamechanismwhichcancausethemtooscillatesoastoprovidethrustinanydirection.Theamountofthrustcanbevariedbyvaryingthedegreeofoscillation,thuswiththebladeassemblyrotatinginthesamedirection,manipulationofthebladescangiveaheadorasternthrust,orportandstarboardthrustwithoutanaheadorasternthrustcomponent,oranyangleofportorstarboardthrustwithaheadorasternthrust.Thecycloidmotionofthebladescanbemadetoproducethrustinanydirectionroundthecircleofrotation.Thismeansthatthepropellerinadditiontoprovidingthemaindriveforashipprovidesfullmanoeuvrabilitywithouttheneedtoprovidearudderandsteeringgear.Thisunusualdegreeofcontrolisofparticularvalueforspecialcraftorfloatingequipmentsuchasfloatingcranesordrillingshipswhichmustbekeptinposition.

Thelocationofthepropellerdependsupontheparticularapplicationanditcanbeplacedwherethemaximumdesiredeffectcanbeachieved.

JETFLAPRUDDER



AnotherdevicewhichisbeinginvestigatedattheN.P.L.isthejetflaprudder.Inthetrailingedgeofanotherwiseconventionalrudder,afluidicswitchisfitted,whichcandirectajetofwatertoportorstarboard.Thewaterispumpedintothehollowrudderthroughahollowrudderstock.

Considerableincreaseinmanoeuvrabilityisclaimed,especiallyatlowspeeds.

ROTATINGCYLINDERRUDDERS



ThisisadevicetomakeashipequallymanoeuvrableatallspeedsandwasdevelopedintheU.KbytheShipDivisionoftheNationalPhysicalLaboratory(N.P.L.).

Anormalrudderiseffectiveuptoanglesofabout35',afterwhichtheflowovertherudderstallsinamannersimilartothatoveranaeroplanewingathighanglesofincidence.Therearevariousmethodsofpreventingthisfromoccurringandtheyallinvolvefeedingenergyintothestreamoffluidadjacenttotherudderoraerofoilsurface.Thisiscalledboundarylayercontrol.Onesuchmethodistorotateacylinderattheleadingedgeofthesectionatsuchaspeedthattheruddercanbeputoverto90'withoutstall,andthisisthebasicprincipleofoperationoftherotatingcylinderrudder.Itis,ofcourse,necessarytoreversethedirectionofrotationofthecylinderdependingonwhethertherudderisputtoportorstarboard,andsuchasystemcanbefittedtoalmostanytypeofrudder,balancedorunbalanced.

Themajoradvantageofputtingarudderovertosuchahighangleisthattheflowfromthemainenginesmaybedeflectedthroughamuchlargeranglethanwithaconventionalrudder,andstaticsidethrustsofover50percentofthebollardpullhavebeenmeasured.Anothermainadvantageisthatitseffectisindependentofforwardspeedanditworksaseffectivelyatzeroasatfullspeed.

SchillingRudder

Beckerflap



Theflapisattachedtothehull.Astherudderrotatestheflapisturnedinansamedirectionincreasingtheaerofoilshapeandtherebyincreasinglift.Thissystemcanbeusedatverylargerudderanglesgivingsidethrustcapabilities

Thisdesignallowsforlargerturningforcesforthesamesizedrudderorreducedsize



requirementscomparedtoothersizes

Anotherformatallowstheflaptobesteeredindependently.Thisagainallowsincreasesinthrustaswellasimprovingsteeringwiththevesselunderwayasonlytheflaphastobeturnedtocausesmallcorrectionstobecarriedout

MANOEUVRABILITYANDSTOPPINGTheproblemsofimprovingthemanoeuvrabilityandbrakingofshipsisofincreasingimportanceastheyincreaseinsize.Onedevicewhichisbeingtriedouttoimprovestoppingpoweristoarrangethecontroloftwinrudderssothattheymoveoutboardsimultaneously.Thisinvolvestwoseparatesteeringgears,oneforeachrudder,themovementofwhichmustbesynchronisedfornormalsteering.Withtwinruddershipstheinnerrudderonaturnmustturnthroughagreateranglethantheouter.Thisisachievedbyhavingthetillerarmatanangletothecenterlineoftherudder.Itisalsopossibletoslightlyangletherudderseitherinorouttoincreasepropulsiveefficiency.

PumpssuitableforsteeringgearsystemsPumpsusedforsupplyingtheworkingfluidtothemainsteeringgearcanbeofeitherthevariablecapacityreversibledeliverytypeorthefixeddeliverynonreversibletype.Forlargecapacityoutputswithhighratesofchangeindemand,thevariablecapacitypumpsarenormallyfitted.Theseareoftwomaintypes,theHeleShawvariablestrokepumphavingradialcylindersandtheswashplatevariablestrokepumphavingaxialcylinders.HeleShawPump



Leftshowstheconstructionandoperationofthistypeofpumpwhichisnormallydrivenbyaconstantspeedelectricmotor.Thepistonsarefittedinarowofradialcylindersandthroughtheouterendofeachpistonisagudgeonpin,whichattachestheslipperstothepiston.Theslippersarefreetooscillateontheirgudgeonpinsandfitintocirculargroovesinthecircularfloatingring.Thisringisfreetorotatebeingmountedonballbearings,whicharehousedinguideblocks,thisreducesoilchurningandfrictionlosses.Thelatterbearontracksarecontrolledbytheactuatingspindles,whichpassesthroughthepumpcasing.Themovementofthefloatingringbytheactuatingcontrolspindle(operatedby,say,thetelemotorreceiver)fromthecentralpositioncausespistonstoreciprocateintheradialcylinderssothatapumpingactiontakesplace.Thedirectionofthepumpingdependsuponwhetherthemovementistotheleftorrightofthecentralorneutralposition.



Theactionofthepumpisshownabove.Itshouldbenotedthatanadvantagewiththissystemisthatinreversingthedirectionoftheflowoffluid,thepumpmovesfrommaximumdeliveryinonedirectionacrosstozerodeliverythenthroughzerodeliverytomaximumdeliveryintheoppositedirection.Thebuildupinfluidpressuretakingplacewithoutshockloadingofpipelinessupplyingfluidtothemainsteeringunit.

Thepumpisusuallyprovidedwithanoddnumberofcylinders,usuallysevenornine,whichproducesmoreevenhydraulicflowandabetterbalancedpump.

VariableStrokeReversibleSwashplatePump

Thispumpissometimescalledthevariablestrokegearpump(V.S.G),itrunsinthefloodedcondition,themakeuptankbeingabovethelevelofthepumpsothatalltheworkingpartsareimmersedinoil.Itisdrivenbyaconstantspeedelectricmotorthevolumeanddirectionoftheoilflowbeingcontrolledbymeansofastrokecontrollever.



TheVSGpumpisstatedtohavesomeadvantagesovertheHeleShaw,thisisduetothefactthatthecofgoftheHeleShawplungersisarelativelylargedistancefromthecentreofrotationoperatingrelativelylargecentrifugalforces.TheVSGplungeshaveacofgclosetothecentreofrotationcreatingrelativelysmallcentrifugalforces,thismeansthattheVSGsystemcanberunatmuchhigherspeedsandthereforecanbemuchsmallerwhilstdoingthesameworkastheHeleShaw.Duetocentrifugalforcesacting,thewearontheV.S.G.pumppistonscanbegreaterthanthatfortheradialtypepistonsThereisasmallclearancebetweenthevalveandcylinderblockswhenrunningoffload.Whentheunitcomesonstrokethehydraulicpressureforcesthetwofacestogether.Externalpipesconnectportstosteeringgear.VSGpumpsandHeleShawpumpshaveanoddnumberofcylinderssincecalculationshowsthatthisgivesbetterhydrodynamicbalancing(andabetterstartingtorquewhenusedinapumpdrivinghydraulicmotor).AuxiliaryPumpSomemanufacturerssupplyanauxiliarypumpdrivenfromthemainpumpshaft,whichdrawsoilfromthereplenishmenttank,deliveringthroughnonreturnvalvestoeachsideofthemainhydraulicsystem.Alowpressurereliefvalveopenstoreturntheauxiliarypumpdeliverybacktothereplenishmenttankifthemainsystemisfull,atthesametimekeepingequivalentinitialpressureonthewholesystem.Thisensuresthelubricationofthemainpumpswhenatnostrokeandresiststheingressofairintothesystem.Pressurefromthispumpcanalsobeusedtopowertheautomatichelmsmancontrol,tooperatechangeovervalves,ortopowerservocontrolunitswhichinlargeinstallationsmaybeusedtooperatepumpstrokemechanismsandsoreducetheforcerequiredfromthetelemotor.ConstantPressurePumpsTheconstantpressuredeliverypumpisastandardproductionline,cheappumpitrunsconstantlydeliveringasetvolumeofliquidwhosepressuremustberegulated.Recirculatingv/v'sallowoiltobypassramswhenstationary,anoilcoolermayhavetobeincorporated.Valvesmustbeincorporatedtodiverttheflowofoiltoonesideortheother.Thesenormallytaketheformofelectricallyoperatedsolenoidvalveswhicharesubjecttowear,aswellasdamagetoseatsandsolenoidcoils.Shockloadingtoramsandpipeworkcausingnoiseandvibrationaswellasdamage.



RudderCarrierbearings

Theruddercarrierbearingtakestheweightoftherudderonagreaselubricatedthrustface.Therudderstockislocatedbythejournal,alsogreaselubricated.Supportforthebearingisprovidedbyadoublerplateandsteelchock.Thebaseofthecarrierbearingislocatedbywsdgetypesidechocks,weldedtothedeckstiffening.Thecarrierisofmeehanitewithagunmetalthrustringandbush.Carrierbearingcomponentsaresplitasnecessaryforremovalorreplacement.Screwdownlubricatorsarefitted,andthegreaseusedforlubricationisofawaterresistanttype(calciumsoapbasedwithgraphite).WeardownAsmallallowanceismadeforweardown,whichmustbeperiodicallychecked.Thismaybemeasuredeitherbetweenpadsweldedontopoftherudderandontotherudderhorn,orbetweenthetopoftherudderstockandafixedmarkontheinnerstructureofthesteeringgearflat.Thelattergenerallyinvolvestheuseofa'Trammelgauge'whichtakestheformofa'L'shapedrodadetofitthenewconditionofthegear.Asweardownoccursitcaneasilybecheckedwiththisgauge.Therudderispreventedfromjumpingbyrudderstopsweldedontothesternframe.

RuddermovementstopsRudderstopsarearrangedasfollowsAnglefromcentrelinePositionofstopNote35oOntelemotorsystemNormallimit37oOnsteeringgearPreventsrudderstrikingexternalstops39oExternal,onsternframeemergencystoptoprotectpropeller

Theselimitsrefertoruddersoftraditionaldesignandisgovernedbyboththe



physicallayoutoftherudderandactuatorbutalsoduetothestallanglesoftherudder.i.e.theangleatwhichlift(turningmoment)isreducedorlostwithincreasingangleofattack.Therearedesignsofruddersuchasbeckerflapwhichhaveincreasedstallanglesupto45o

Criticalprofilingofcarrierbearing

Reasonsforcriticalcontouringofthrustface1. forlubrication2. conicalinordertopreventsideslipandcentraliserudder3. projectedareagivesgreaterbearingareaallowingsmallerdiameter

bearing

Steeringgear



Ahydraulicsteeringgearconsistsofabridgecontrolwhichapplieshelm,anenginecontrolwhichisoperatedjointlybythehelmandhuntinggear(whenfitted)andapowerpumpandrudderactuatorwhichconstitutesthesteeringengine.TelemotorsystemsThetelemotorsystemconsistsofatransmitteronthebridgeandareceiverfittedonthesteeringgearformingapartofthehuntinggear.Thesystemmaybeelectricalorhydraulicoracombinationofthetwo.Mostmodernvesselsarefittedwithelectricorelectrohydraulicsystems.Duetotheincreasingsizeofvesselspiperunshavelengthencausinglagsintheoperationofthereceiverinhydraulicsystems.Inadditionhydrauliconlysystemsgenerallyrequiremoremaintenance.Hydraulictransmitter

Shownaboveisatypicalhydraulictransmitterunit.Thepiniondrivingthepistonsisturnedbythebridgewheel.Thecasingisusuallygunmetal,withbronzerams,andcopperpipesareledinbyfrilledleadsonthecasting.Totestthesystem,withthesteeringgearactuatingpumpsstopped,thewheelmaybelashedathardoverandthepressurerecorded.ItshouldmaintainthispressureforsometimeToallowforexpansioninthesystemandtoallowtoppingupa'bypassvalve'isfitted.Itwillalsoactasasafetyvalve.Authornote:Themainproblemappearstobetheeffectofairentrainedwithinit.Thusregularventingofthesystemisrequired.

Bypassvalve



Theoperatingrodispusheddownmakingbothlinecommonwheneverthewheelisatmidships,generallybyacamfittedtothepinion.Thisensurestheysystemisalwaysbalanced

Thechargingvalvesareopenedonlywhenfillingorflushing.

Themovingcylinderisattachedtothehuntinggear.Whenthebridgewheelisturnedhydraulicpressureactsonthecylindercausingittomove.Thisinturnmovesthehuntinggear.Thesteeringgearisthenmovedtocompensateuntilthehuntinggearismovedbacktotheneutralposition.Thetotalmovementofthereceiverislimitedbystops.



Electrohydraulictypetelemotorsystem

Shownisaverysimplesystemcapableofoperatingasteeringhuntinggear.Apressurereliefvalvewouldnormallybefittedafterthevalveandacrossthepumptopreventoverpressurisationofthesystem.Thesignalisderivedfromtheactiononthesteeringwheel,createdbytheautopilotordirectlyfromthenonfollowupcontrollevers.Telemotorfluid

shouldbeagoodqualitymineraloilwiththefollowingproperties1. lowpourpoint2. nonsludgeforming3. noncorrosive4. goodlubricatingproperties5. highflashpoint6. lowviscosity

HuntingGear



Thesteeringgearsystemaboveconsistsofthetelemotorwhichreceivesasignalfromthebridgewheel.Thisactsonthehuntinggear.

Thehuntinggearmovesdisplacingacontrolrod,thisrodactsonthepumpdisplacementcontrolgeartoalterthedeliveryfromthepump.Thedeliveryfromthepumpcausestheramtomoverotatingtherudderstockandhencetherudder.Theotherendofthehuntinggearismountedontherudderstock.

Therotationoftherudderstockmovesthehuntinggearreturningtheoperatingrodforthepumptotheneutralpositiononcetherudderhasreachedthecorrectangle.

RudderActuators



Therearemanydifferentmechanismsbymeansofwhichhydraulicpowercanbeconvertedintotorqueattherudderstocksomeofwhichareasfollows

RapsonSlideActuatorsRamtype

Steeringgearincorporatingtherapsonslideprinciplearethemostcommoninuseonheavydutyapplications.

Therapsonslideactingoneitheraforktillerorthemorecommonroundarm.Thetillerdrivestherudderstockbymeansofakeyorkeys.Thecrossheadisfreetoslidealongthecirculararmofthetillersothatthestraightlineeffortoftheramsisappliedtotheangularmovingtiller.Eachsetoftwocylindersinlineareconnectedbyastrongsteelgirderusuallycalleda"Joist"whichstiffensthesystemandformsa"guidebar"forthecrossheadguideslipperstoslidealong.Thejoistisoftendesignedtoincorporatethesteeringenginestops.

Animportantconsiderationinallsteeringgearsisthe"weardown"oftheruddercarryingbearing,thisbearingtakesalltheweightoftherudder.

Thereforetheremustbeadequateclearancebetweenthebottomofthetillerandthecrossheadbearing,soastherudderbearingwearsdowninservicethetillerandcrossheadbearingdonottouch,clearancewhennewcanbe22mmatbottomand12mmattopthetopclearanceisaprecautiontostopthetillerbumpingupthesteeringramsintheunlikelyeventoftherudderliftinginheavyweather.Shouldthebottomofthetillerandthecrossheadbearingtouch,thentheweightoftherudderwillbetransferredfromtherudderbearingtothesteeringramswithdisastrousresultssuchasleakingofworkingfluidfromthecylindersandshearingoftherams.

Inthecaseofforkedtillerdesign,thethrustfromtheramsistransmittedtothetillerthroughswivelblocks.Oneadvantageofthisarrangementisthattheoveralllengthofpairsoframsisreducedcomparedtotheroundarmtillerdesignandthiscanbeanimportantconsiderationinsomecases.Adisadvantageisthatwhereasanyslightmisalignmentinthecaseoftheroundarmtillerisnotvitallyimportant,itcouldleadtounevenloadingoftheswivelblocksintheforkedtillerdesignanditisessentialthatthelineoftheramsbeexactlyatrightanglestothe



rudderstockcentrelineifthisistobeavoided.WiththeRapsonSlidethetorquereactionfromtherudderistakenonthetillerbyaforcewhichisbalancedbyanequalandoppositeforcehavingtwocomponentsoneofwhichisproducedbytheramandactsinthelineoftheram,whilsttheotherisatrightanglestothelineoftheramandisproducedbytheguidereaction.

Whereguidesarenotfittedasissometimesthecasewithsmallersteeringgearsthentheguidereactionforcemustbecarriedbybearingsortheglandsofthecylinders.a=actuatorareap=Workingfluidpressuren=Numberofeffectiverams(1for2ram,2for4ram)q=rudderangler=tillerradiusatamidshipsr'=tillerradiusatqooftillerhelms=guidereactionforcef=forceonramwithtilleramidships(=pxa)f'=effectiveforceactingat90ototiller

r'=r/cos.qalsof'=f/cos.q=pxa/cos.qt=torqueavailable=f'xr'xn=((pxa)/cosq).(r/cos.q).nt=(pxaxnxr).(1/cos.2q)ShowingthattherapsonslideeffectwhichgivesincreaseofavailabletorquewithincreasesofrudderangleThetorquedemandedfromthesteeringgearincreasesandisatamaximumatmaximumrudderanglewhenthemechanicaladvantageoftheRapsonSlidegearisatamaximum.Ramtypegearsarealsowelladaptedtotakeadvantageofthehighpressureswhicharecurrentlyavailable,sinceramdiametersandcasingarerelativelysmallandleakagepathsaresmallornonexistent.

OscillatingCylinderActuatorsTheuseofoscillatingcylindersorpinnedactuatorsisarecentdevelopment.Theycanbeusedassinglecylinderunitsforhandonlysteeringortwocylinderunitsfor



handandpowersteering.Whilefourdoubleactingcylinderscancopewithlargertorquedemands.Theseunitsaredoubleactingbecausepistonsworkinthecylindersandpressurecanbeappliedtoeithersideascomparedwithramgearswhicharesingleacting.Inthesecases,thetorqueTappliedtotherudderstockvarieswiththerudderdeflectionangleandonthelocationoftheactuator.Ingeneralthetorquedevelopedwillbelessatthemaximumrudderanglethanthemaximumpossiblefromtheactuator.Maximumtorquefromactuator=p.a.n.r.Torqueat35o=p.a.n.r.cos(35=o)whereo=angletracedoutbytheactuatorbetweeno=0oando=35oMechanicaladvantageat35o=Cos35o=0.82sincetheactuatorsarepivotingabouttheirpincentre,theyusuallyhavetheirworkingfluidtankandpumpmountedontheactuatorcylinder,ortheyareconnectedtotankandpumpbyaflexiblepipeline.RamsConnectedToCrossheadsByLinksThistypeofgearisusediftheathwartshipsspaceislimited,ortheheadroomattherudderheadisrestricted,asforexample,inthecaseofavehicleferryhavingaslipwayaft.Thedesignenablesthesteeringgeartobemovedforwardwherethereisreasonableheadroomforaccess.AsinthecaseoftheoscillatingcylinderdesigntheMechanicalAdvantageoftheRapsonSlidegearislostinthelinksandthetorqueoutputofthegearisataminimumathardoverwhenthetorquedemandcreatedbytherudderhydrodynamicforcesisatamaximum.RotaryVaneGear

Theseconsistoftwoelements:acylindricalstaticcasing(stator)withusuallythreeinternalvaneswhich

projectradiallyinwardsarotorkeyedtoandconcentricwiththerudderstock,therotorhasrotor

vaneswhichprojectradiallyoutwardsintothespacesformedbythestatorvanes.

Thespacesformedbetweenthestatorandrotorvanesareusedashighandlowpressurechambers.Themainadvantageofthesystemisthatitiscompact,occupyingabout1/10thespaceofaramsystem.Thedisadvantagesare

ithasalongoilsealingpathitisaconstanttorquemachineatallanglesofhelmcomparedtotheram

systemwhereduetotheRapsonslideeffect,thetorqueavailableincreaseswithincreasinghelm.

Where100%redundancyisrequiredtworotaryvanesinpiggybackareused.Allvanesarespheroidalgraphitecastironsecuredtothecastironrotorandstatorbyhightensilesteeldowelpinsandcapscrews.Rotorstrengthismaintainedbykeysfittedfulllengthoftherotaryvane.Steelsealingstripsarefittedalongtheworkingfaces,backedbysyntheticrubberingroovesalongtheworkingfaceswhichareelasticallyloaded,soastoensurethatcontactwiththematingsurfacesismaintainedinordertoholdthehydraulicpressures.



Thechambersarealternatelyconnectedtothesuctionanddeliveryfromthehydraulicpumpsothattheycanbeusedtoproducetherudderactuatingtorque.Becausethedistributionofthepressurechambersisbalancedaroundtherudderstock,onlypuretorqueistransmittedtothestockandnosideloadingareimposedbythegear.

Therearetwomaintypesofrotaryvanesteeringgearinusetoday.Onehasitsstatorfirmlyfixedtothesteeringflatdeckandthestatorhousingandcoverareprovidedwithsuitablebearingstoenabletheunittoactasacombinedruddercarrierandrudderstockbearingsupport.Theothertypeofvanegearissupportedwherethestatorisonlyanchoredtotheshipsstructuretoresisttorquebutisfreetomoveverticallywithintheconstraintsoftheseparaterudderheadbearingandcarrierwhichissimilartothebearingprovidedforramtypesteeringgears.Theruddercarrierringbearing(PallisterBearing)istakingtheweightoftherotaryvanesteeringgearandtherudderandstock.



Rotationofthestatorispreventedbymeansoftwoanchorbracketsandtwoanchorbolts.TheanchorbracketsaresecurelyboltedtothestoolandverticalclearanceisarrangedbetweentheinsideoftheStatorflangesandthetopandbottomoftheanchorbracketstoallowforverticalmovementoftherudderstock.Thisclearancevarieswitheachsizeofrotaryunitbutcouldbeabout40mmtotal.Itisessentialthattheruddercarriershouldbecapableofrestrictingtheverticalmovementsoftherudderstocktolessthanthisamount.Theanchorboltsarefittedwithspecialbushesinhalves,shapedexternallyinordertopreloadthesyntheticrubbershockabsorbers,whicharefittedbetweenthemandtheanchorbrackets.Themaximumdeflectionoftheshockabsorbersunderfullloadisapproximately1mm.Theworkingangleofthegearisgovernedbythenumberofvanesandtheirthickness.Vanesactasrudderstopswhenamovingvanecontactsafixedvane.Valvesatinlettothechambersmaybeshutcausingahydrauliclock.IntherotaryvaneunitstheMechanicalAdvantageisunityatallanglesandhencetorqueisconstantTorque=p.a.n.r.wheren=numberofrotatingvanes

TendfjordRotaryPistonGearActuatorThisgearconsistsofacasingaroundtherudderstockwhichcontainspistonsofrectangularsectionslidinginangularcompartmentsconcentricwiththerudderstock.Thetillerprojectsintoagapbetweenthecylinder,thepistonendsabuttingontothetillerbutnotbeingattachedtoitsothataxialmovementsoftherudder



cannotbetransmittedtothepistons.Steeringgearsofthistypeoperateathydraulicpressuresupto41bar(600lbf/in2)andareingeneralrestrictedtolowpowerapplication.AswiththerotaryvanesteeringgearstheMechanicalAdvantageisunityatallanglesandhencethetorqueisconstant.Torque=p.a.n.r.whereninthiscaseisunity.

Components

ReliefIsolatingAndBypassValvesHydraulicactuatorsareprovidedwithreliefandbypassvalvesbetweencomplementarypairsofcylindersorchambersofvanegears.Thereliefvalvesaresettoliftatpressuresabovethenormalmaximum.Thebypassvalvesarenormallyclosedbutcanbeopenedonatwocylindergeartoenableemergencysteeringtobeused.Onafourcylindergearonepairofcylinderscanbebypassedwhiletheotherpairprovideemergencysteeringatareducedtorque,aninstructionplateisfittedoverthecontrolsvalveblockgivingacombinationoffailuresandwhichvalveshavetobeopenorshuttocopewiththeemergencyetc.Itshouldbenotedthatifoneramorcylinderinafourramsystembreaksdown,thenneverisolatethecylinderdiagonallyoppositethedamagedunit,sincethesteeringgearwillnotoperateduetothefactthattheremainingtwocylinderswillbeeitheronallpressureoronallsuctionatthesametime.Isolatingvalvesareprovidedateachcylinderorrotaryvanechamberwhichwhenclosedwillholdtherudderbytrappingtheoilinthechambers.Isolatingvalvesarealsofittedtopumpssothatapumpcanbecompletelyshutofffromthecircuitandremovedforservicingwhilesteeringiscontinuedwiththeotherpump.Inthecaseofgearswithduplicatedvariablestrokepumps,inordertobeabletobringastandbyunitquicklyintooperation,thepumpstrokemechanismsarepermanentlycoupledtogetherandbothpumpsareleftopentothehydrauliccircuit.Thusitisonlynecessarytostartupamotorforthestandbypumptobeoperative.Itisusualtorunbothpumpsinrestrictednavigationwaters.Asavariablestrokepumpcanoperateasamotorifpressureoilisappliedtoonesidewhileitisonstroke,itisnecessarytopreventwindmillingorrotationofthepumpwhichisonstandbyduty.Otherwise,theoutputoftheoperationpump,insteadofmovingthesteeringgearwouldbeusedupinrotatingthestandbypump.Onemethodtopreventthis,isusingafixedratchetisprovidedconcentricwiththepumpdrivingshaft.Pawlsthatcanengagethisratchetarecarriedinthedrivecoupling.Whenthepumpisonstandbythepawlsengagewiththeratchetandpreventrotationwhenoilonthedeliverysideoftheoperatingpumpisonpressure.Inthisconditionthetendencytomotorthestandbypumpwillalwaysbeagainstitsnormaldirectionofrotation.Assoonasthepumpisstarted,rotationbeingintheoppositedirection,thepawlsdisengageandbycentrifugalactionflingoutagainsttheinnerflangeofthecouplingcompletelyclearoftheratchet.Whenapumpisonstandbyandtherudderisbeingdrivenbywaterpressureinthedirectioninwhichitisbeingmovedsoastogeneratepressureonwhatisnormallythesuctionsideoftheoperatingpump,thiswillcausethestandbypumptorotateinitsnormalrunningdirection.Thismeansthatthepawlswilldisengageandthepumpwillbemotoredround,allowingtheruddertomovemorequicklytoanewsteeringpositionthanthesingleoperatingpumpwillallow.AnothermethodofprotectionagainstrotationofthestandbypumpistofitServopressureoperatedautomaticchangeovervalvesinthepipelinestheseensurethatthepumpcanonlybestartedintheunloadedcondition(neutral)andinadditionpreventsthestandbypumpfrombeingmotoredbythepumpinservice.Onsomeshipsithasbeendiscoveredthattheballbearingracesonthestandby



pumphavebeenfailingduetobrinellingoftheballbearings,causedbyshipvibrations,andinthesecasesitisusualtofitdeviceswhichallowsthestandbypumptobemotoredslowly.Whenfixeddeliverypumpsareduplicatedinsupplyingoiltoacommonhydraulicallyoperatedcontrolvalve,anautomaticchangeovervalvecanbefittedwhichwillisolatethestandbypumpwhenitisatrest,butwillconnectittotheactuatorwhenthepumpisstartedup.StopsAndLimitSwitchesExternalorsternpostsstopsaresetattheabsolutelimittohardovermovementoftherudder,protectspropellerandshipsternintheeventofmetalorotherfailurewhichallowsruddertoswinginanuncontrolledmanner.Mechanicalstopsontherudderactuatoroperatebeforetheexternalstoparereached.thesetaketheformoftravellimits.Stopsonthebridgecontroloperatebeforemechanicalstops.localcontrolsaresetmidway.autopilotcontrolsaresetfirst.Itshouldbenotedthatthevanesactasstopsonrotaryvanegears.DriveBackDueToHeavySea'sHeavyseasactingontheruddercanforcetheactuatoragainstthehydraulicssufficienttoliftthereliefv/v,inwhichcasetherudderwillmove.Huntinggearwilltendtoreturnthegeartoitscorrectposition.HandAndPowerHydraulicSteeringGearsForsmallshipsduringnavigationalcoursekeepinghandsteeringcanbeused,whistduringmanoeuvringpowersteeringcanbeused.Thesemaytaketheformofchainsorsimplehydraulicsoperatedbyafixeddeliverypumpattachedtothesteeringgears."FollowUp"SteeringThisisthenormalmethodofsteeringandinvolvesthefeedbackofsteeringangletothehelm.Thisissuitedtobothmanualandautomaticoperation.Theshipsheadingmaybesetintotheautopilotwhichcanthencomparetheactualtodesiredheadingandadjusttherudderangletosuit"NonfollowUp"SteeringNormallyusedforbackuppurposesonly.Consistsofasingleleverpersteeringgearunit,bymovingtheleverinondirectiontherudderwillbegintoturn,therudderwillcontinuetoturnuntiltheleverisreleasedoritreachesthelimitofitsoperationChargingASystemWithFluid.Inallcaseshighqualityhydraulicoilshouldbeused,containinginhibitorsagainstoxidation,foaming,rustandwearandemulsification.Inordertokeepthetransmissionloadaslowaspossiblewhenhandsteering,handpowersystemsmusthaveoiloflowviscosity.Theconditionoftheoilshouldbemonitoredandensuredatleastcleanandfreeofmoisture.SteeringgearfailureAstudyofsteeringgeardefectsdemonstratesthatthemostcommonarerelatedtovibrationandtheworkinglooseofcomponents.Themostcommonsourceoffailurearethepumpandthehydraulicsystemassociatedwithit.



RuddertorquecalculationsFormulaeforassessingruddertorque'sarebasedupontheexpressionTaACpV2Sinqwhere:T=ruddertorqueC=rudderareaCp=centreofpressuredistancefromcentrelineofrudderstockV=velocityofshipq=rudderanglemeasuredfrommidshippositionInpracticedifferentconstantsobtainedempiricallyareusedwiththisexpressionandtakeintoaccountsuchfactorsaspropellerslipandwakespeedasappropriatedependingupontherelationoftherudderandpropellerpositions.ThepositionofthecentreofpressurehasasignificanteffectuponruddertorqueandhencethesizeofthesteeringgearrequiredthegreaterthedistanceoftheCofPfromthecentrelineoftherudderstock,thelargerthetorquerequiredthereforedesignersattempttobringtheCofPasneartothecentrelineaspossible.Withthesimple"barndoor"typerudderonsomesinglescrewships,noadjustmentcanbemade,butthesemibalancedandbalancedtyperudderscanbedesignedtoreducethetorquerequiredforinstance,withthespadetyperuddersuchasfittedtotwinscrewferries,thepositioncanbeadjustedbythedesignertogiveoptimumposition.Thisliesbetween30and32percentabafttheleadingedgeofthemeanchordoftherudder.SucharudderwouldhaveitsCofPforwardofthestockpositionatlowanglesofhelm,wouldbalancearound10oto15oanddriftaftofthestockathigherrudderangles.

Ingraphaboveisshownatypicaltorquecharacteristicsforaspadetypebalancedrudderanda"barndoor"orunbalancedplaterudder.Theasterntorque'sshouldalsobecalculatedsincethisissometimeshigherthantheaheadtorque,thisistrueforspaderudders.

POWER



Thepeakpowerthatasteeringgearmustdevelopistheproductofthemaximumtorque(T)usuallyathardoverwiththeshiptravellingatfullspeed,andthemaximumspeed(S)ofruddermovementi.e.Power(max)aTxS.

Thecombinationofmaximumpowerandspeedonlyexistsfor2or3secondsduringeachmanoeuvresoclearlytheaveragepowerrequiredtooperatethesteeringgearisconsiderablybelowthepeak.Becausethesteeringgearmusthavesufficientpowertoovercomefrictionandstillhaveamplereserveofpower,thevalueforusedintheforegoingexpressionissignificantlyhigherthanthatusedintheexpressionforruddertorque.Whenconsideringthediameteroftherudderstock,bendingandshearstressesmustbetakenintoaccount.

RudderWearDownThisreferstothemeasurementstakengenerallyduringadockingperiodtoindicateexcessivewearinthesteeringgearsystemparticularlytheruddercarrier.Thesignificanceofthisisthatforramsystemsexcessivewearcanleadtobendingmomentsontherams.Forrotaryvanesystemsitcanleadtovaneedgeloading.Thereadingstakenareofferedforrecordingbytheclassificationsociety.

TrammelThistakestheformofan'L'shapebarofsuitableconstruction.Whenthevesselisbuiltadistinctcentrepunchmarkisplacedontotheruderstockandontoasuitablelocationonthevesselsstructure,heregivenasagirderwhichistypical.ThetrammelismanufacturedtosuitthesemarksAsthecarrierwearstheupperpointerwillfallbelowthecentrepunchmarkbyanamountequaltotheweardown.



RudderClearancePadsareweldedtothehullandrudder.Aclearanceisgiven(sometimesreferredtoasthejumpingclearance).Asthecarrierwearsthisclearancewillincrease

SteeringgearClearanceDirectmeasurementcanbetakenfromthesteeringgearassembly.Shownbelowisoneexample,heretheclearancewillbeseentoreduceasthecarrierwearsandimpacthishasonthesystemcanbedirectlyjudged

RulesDesignofsteeringgearshavebeeninfluencedovertheyearsbytherulesandregulationsofnationalauthoritiesandclassificationsubjects.Anychangesofreal



substancetendnowadaystooriginatefromtheinternationalMaritimeOrganisations(I.M.O.)conventionsandregulations.Classificationsocietyrequirementsareasfollows

1. Allshipstohavepoweroperatedmaingearcapableofdisplacingtherudderfrom35oportto35ostarboardatthedeepestdraughtandatmaximumservicespeed.Mustalsobecapableofdisplacingtherudderfrom35oportto30ostarboardin28secondsandviceversa.

2. Theauxiliarygearmustbepoweroperatedandcapableofbeingbroughtrapidlyintoaction.Theauxiliarygearisonlyrequiredtosteertheshipateither7knotsorhalfservicespeed

3. Ifthemaingearcomprisestwoormoreidenticalpowerunits,thenasinglefailureofeitherpowerunitorpipingmustnotimpairtheintegrityoftheremainingpartofthesteeringgear

4. Eachpowerunitmustbeservedbyatleasttwoelectricalcircuitsfromthemainswitchboard.Onecircuitmaypassthroughtheemergencyswitchboard.Allcircuitstobeseparatedaswidelyaspossiblethroughouttheirlength.

5. Allpoweroperatedgearstobefittedwithshockrelievingarrangementstoprotectagainsttheactionofheavyseas.

6. Anefficientbrakeorlockingarrangementtobefittedtoenabletheruddertobemaintainedstationary

7. themaximumpowerdevelopedbythegearisproportionaltoTxSwhereT=ruddertorqueS=Speedofruddermovement

alsoT=AxPxsinqxV2whereA=rudderareaP=centreofpressureq=rudderangleV=velocityoftheship

SpecialrequirementsOwnersmayspecifyadditionalrequirementssuchasfasterhardovertohardovertime,strengthofcomponentsabovethatrequiredbytheRules,additionalcontrolpointsandadditionalduplication,Newtankersof100000dwtandaboveshallcomplywiththefollowing

Themainsteeringgearshallcompriseofeithertwoindependentandseparatepoweractuatingsystemseachcapableofmeetingthehardoverportto30ostarboardin28secrequirements,oratleasttwoidenticalpoweractuatingsystemswhichactingsimultaneouslyinnormaloperation,shallbecapableofmeetingthehardoverrequirements.Wherenecessarytocomplywiththisrequirementinterconnectionofhydraulicpowersystemsshallbeprovided.Lossofhydraulicfluidfromonesystemshallbecapableofbeingdetectedandthedefectivesystemisolatedsothattheothersystemshallremainfullyoperational

Intheeventoflossofsteeringcapabilityduetoasinglefailureotherthanthetiller,quadrantorcomponentsservingthesamepurpose(theseareexcludedfromsinglefailureconcepts),orseizureoftherudderactuators.Thesteeringcapabilityshallberegainedinnotlessthan45secondsafterthelossofonepoweractuatingsystem.Steeringgearotherthanhydraulicshouldmeetthesamestandards.

Exampleofsuitablesystempermissibleforallships



Thesystemshownconsistsoftwosetsoframsbutcouldequallybetworotaryvaneunits.Withnopoweronthesolenoidsareinbypassmodewithoilbeingallowedtopassfreelyfromonesidetotheother.Whenanelectricmotorisstartedthecontrolpumpsuppliesoiltothesolenoidshuttingit.Highpressureoilfromthemainunitisnowfedtotheramsasrequired.Theotherunitremainsinbypassuntiltheelectricmotorisstarted.

Lowlevelalarmsarefittedtothetanks.Lowlowchangeoversmayalsobefittedsothatintheeventofoillossfromonesystem,theothersystemisstarted.

Newtankersbetween10000gtupwardsto100000tdwt



Forthesetankersthesinglefailurecriterionneednotapplytotherudderactuatororactuatorssubjecttocertainrequirementsbeingfulfilled.Theseincludearequirementthatsteeringberegainedwithin45secondsfollowingfailureofanypartofthepipingsystemorpowerunitsandaspecialstressanalysisofnonduplicatedrudderactuators.Thelefthandunitisshowninoperation.Forthisbasicarrangementthepowerunitsmustbeidentical

Newships70000gtandupwardssystemsuitableforallshipsexcepttankersof10000gtandabove



Themainsteeringshallcomprisetwoormorepowerunitsandthatthemainsteeringgearissoarrangedthat,afterasinglefailureinitspipingsystemorinoneofthepowerunitsthedefectcanbeisolatedsothatsteeringcanbespeedilyregained.'Speedily'isintendedtomeantheprovisionofduplicatehydrauliccircuitsor,forexample,aconventionalfourramsteeringgearwithacommonhydrauliccircuitwithappropriateisolatingvalves

Newshipsoflessthan70000gtandtankerslessthan10000gtsuitablesystem

Singlefailureisnotapplicableasarule,however,attentionisdrawntotherequirementthatauxiliarysteeringgearbeindependentofanypartofthemaingearexceptthetiller.Thereisnorequirementthatmainandauxiliarypowerunitsbeidentical.Theauxiliarysteeringgearmustbecapableofputtingtherudderoverfrom15o



fromonesidetotheotherinnotmorethan60secondswiththeshipatitsdeepestdraughtandrunningaheadathalfmaximumspeedor7knots.Existingtankersof40000gtandupwards

Thesteeringgearshallbearrangessothatintheeventofsinglefailureofthepipingoroneofthepowerunits,steeringcapabilitycanbemaintainedortheruddermovementcanbelimitedsothatsteeringcapabilitycanbespeedilyregainedby

AnindependentmeansofrestrainingtherudderorfastactingvalvestoisolatetheactuatororactuatorsfromtheexternalhydraulicpipingtogetherwithameansofdirectlyrefillingtheactuatorsbyafixedindependentpowerpumpandpipingsystemorAnarrangementsothat,wherehydraulicpowersystemsareinterconnectedanylossofhydraulicfluidfromonesystemshallbedetectedandthedefectivesystemshutoffeitherautomaticallyorremotelyfromthebridgesothattheothersystemremainsintact

RequirementsforallnewshipsAdministrationsmustbesatisfiedinrespecttothemainandauxiliarysteeringgearprovidedforeveryshipthatallcomponentsandtherudderstockareofsoundconstructionEverycomponent,whereappropriate,utiliseantifrictionbearingswhichwillbepermanentlylubricatedorprovidedwithlubricantfittingsPartssubjectedtohydraulicpressuresshouldbedesignedtocopewith1.25maximumworkingpressurewhentherudderishardoveratmaximumdraughtandservicespeedspecialrequirementsforfatigueresistance(duetopulsatinghydraulicpressure),reliefvalvesandoilcleanlinessLowlevelalarmtobefittedtoeachhydraulicreservoir.Fixedstoragecapacitysufficienttorechargeonsystem

AuxiliarysteeringgearTheothersetofsteering(auxiliary)maybeanarrangementsofblocksandtacklesorsomeotherapprovedalternativemethod.Theauxiliarysteeringgearneedonlybecapableofsteeringtheshipatnavigablespeed,butitmustbecapableofbeingbroughtspeedilyintoactioninanemergency.Navigablespeedisonehalfofmaximumservicespeedaheador7knotswhicheveristhegreater.Theauxiliarysteeringgearmustbeapoweroperatedtypeiftherudderstockexceeds230mmforpassengershipsand250mmforcargovessels.Noadditionalmeansofsteeringisrequiredwhenelectricorelectrohydraulicsteeringgearisfittedhavingtwoindependentmotorsortwosetsofpumpsandmotors.ElectricalSupplyShortcircuitprotectionandoverloadalarmaretobeprovidedinsteeringgearcircuits.Indicatorsforrunningindicationofsteeringgearmotorsaretobeinstalledonthenavigationbridgeandatasuitablemachinerycontrolposition.Eachelectricorelectrohydraulicsteeringgearshallbeservedbyatleasttwoindependentcircuitsfedfromthemainswitchboard.Cablesforeachcircuitledthroughaseparaterouteasfarapartaspossiblesothatdamagetoonecabledoesnotinvolvedamagetotheother.Achangeoverswitchisfittedinanapprovedpositiontoenablepowersuppliestobeinterchanged.Onecircuitmaypassthroughanemergencyswitchboard.RuddersInpassengershipswheretherudderstockexceeds230mm,analternativesteeringpositionremotefromthemainpositionistobeprovided.Failureofonesystemmustnotrendertheothersysteminoperable.Provisionmadetotransmitorders



frombridgetoalternativeposition.Theexactpositionoftheruddermustbeindicatedatprincipalsteeringpositions.Anefficientbrakingorlockingdevicemustbefittedtothesteeringgeartoenabletheruddertobeheldstationaryifnecessary.Springorhydraulicbufferreliefvalvesfittedinsteeringgearsystemtoprotecttherudderandsteeringgearagainstshockloadingduetoheavyseasstrikingtherudder.Suitablestoppingarrangementsaretobeprovidedsoastorestrictthetotaltraveloftherudder.Stopsorcutoutsonthesteeringgeararearrangedsothatitoperatesonasmallerangleofhelmthantherudderstops.RudderrestraintSincefailureofasinglehydrauliccircuitcanleadtounrestrictedmovementoftherudder,tillerandrams,repairandrechargingmaynotbepossible.Difficultyariseswithwhichthespeedarestraintwhetherintheformofamechanicalorhydraulicbrakecanbebroughtintouse.Duetothepossibilityofconsiderabledamageoccurringbeforeitcould,regulationshaveconcentratedoncontinuityofsteeringratherthanashutdownandrepairsolutionTestinganddrills

Within12hbeforedeparture,theship'ssteeringgearshallbecheckedandtestedbytheship'screw.Thetestprocedureshallinclude,whereapplicable,theoperationofthefollowing:

themainsteeringgeartheauxiliarysteeringgeartheremotesteeringgearcontrolsystemsthesteeringpositionslocatedonthenavigationbridgetheemergencypowersupplytherudderangleindicatorsinrelationtotheactualpositionoftheruddertheremotesteeringgearcontrolsystempowerfailurealarmsthesteeringgearpowerunitfailurealarmsandautomaticisolatingarrangementsandotherautomaticequipment.

Thechecksandtestsshallinclude:thefullmovementoftherudderaccordingtotherequiredcapabilitiesof

thesteeringgearavisualinspectionofthesteeringgearanditsconnectinglinkageandtheoperationofthemeansofcommunicationbetweenthenavigation

bridgeandsteeringgearcompartment.Simpleoperatinginstructionswithablockdiagramshowingthechange

overproceduresforremotesteeringgearcontrolsystemsandsteeringgearpowerunitsshallbepermanentlydisplayedonthenavigationbridgeandinthesteeringgearcompartment.

Allships'officersconcernedwiththeoperationormaintenanceofsteeringgearshallbefamiliarwiththeoperationofthesteeringsystemsfittedontheshipandwiththeproceduresforchangingfromonesystemtoanother.

Inadditiontotheroutinechecksandtestsprescribedinparagraphs(a)and(b),emergencysteeringdrillsshalltakeplaceatleastonceeverythreemonthsinordertopractiseemergencysteeringprocedures.Thesedrillsshallincludedirectcontrolfromwithinthesteeringgearcompartment,thecommunicationsprocedurewiththenavigationbridgeand,whereapplicable,theoperationofalternativepowersupplies.

TheAdministrationmaywaivetherequirementtocarryoutthechecksandtestsprescribedinparagraphs(a)and(b)forshipswhichregularlyengageonvoyagesofshortduration.Suchshipsshallcarryoutthesechecksandtestsatleastonceeveryweek.

Thedateuponwhichthechecksandtestsprescribedinparagraphs(a)and(b)arecarriedoutandthedateanddetailsofemergencysteeringdrillscarriedoutunderparagraph(d),shallberecordedinthelogbookasmaybeprescribedbytheAdministration.

Steering Gear

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