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6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 1/19
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ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
JANUARY28,2015BYSOUMYACHAKRABORTY
Mostofthepropellersthatareusedinshipsarefixedpitchpropellers(FPP).Whatdoesthispropellertermmeans?Letsunderstandthisfromabeginnerspointofview.
Ifyoulookatapropelleraxially,youwillnoticeatwistinthepropellerbladealongthelengthofthepropellerhub.Itisthistwistinthebladethatresultsintheforwardmotionofthepropellerwitheachrotation.
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6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 2/19
Partsofscrewpropeller
Itisprettymuchwhatyouseeonascrew.Theangleofthethreadisactuallywhatiscalledthepitchangle.Themorethepitchangle,themoredistanceistravelledbythescrewinonerotation,thatis,themoreisthepitch.Similarly,propellersactontheprincipleofscrew.Hencethetermscrewpropeller.
ButwhatisafixedpitchpropellerortheFPP?
Thepropellerisdesignedinawaysuchthat,ifyoucutthepropellerradiallyatanyrandomradiusfromitscentre,thenthecutsectionofthepropellerbladeswillhaveacertainpitch(magnitudedependsuponhowtwisteditisalongthelengthofthehub).Nowifyourotatethiscutsectioninwater,theaxialdistancetravelledinonerotationisthepitchofthissection.Ifyouvarytheradiusatwhichyoucutasection,thetwistofthebladealsovariesfromtheroottothetip.Thismakesitevidentthateachsectionofthepropellerhasaparticularpitch.
Therootofthepropellerwillhaveadifferentpitchfromthetipofthepropeller.SothepitchvariationfromtheroottothetipisasshowninFigure1.Thequestionnowis,ifeachsectionhasadifferentpitch,thenwhatistheresultantpitchofthepropeller?Answeristheresultantpitchistheaverageofallthepitchesofeachsectionofthepropeller.
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 3/19
Bladesectionandvariationofpitchwithsection
Noteverycarefully,thatthepitchvariesalongwiththebladesection(orincreasingdistancefromthepropellercentre),butthenetaverageorthenetpitchofthepropellerremainsconstant.Suchapropellerisafixedpitchpropeller.
Now,letsgobacktotheconceptofascrew.Whatifyoucouldsomehowchangetheangleofinclinationofthethreadsalongthescrew?
Ifyoucould,whatwouldyouactuallybedoingischangingthepitchangleandsubsequently,thepitchofthescrew.Thisisexactlywhythecontrollablepitchpropellerwasdevelopedbytheindustry.Wewillbedealingwiththeapplicationsindetailalittlelater.Butfornow,itisvitaltoknowthefundamentalworkingofaControllablePitchPropeller(CPP).
Thetwist(tobereferredaspitchfromnowon)oftherootsectionofthebladeisalwayswithrespecttotheangleitmakeswiththepropellerhub.Whatifwecanchangetheangleoforientationoftheroot?Andsincealltheotherbladesectionshadtheirpreviouspitchanglealready,theyattainanewpitchangle.Inotherwords,youareabletocontrolthepitchoftheentirepropeller,bychangingtheorientationoftherootsectiononthehub.Thisisdonebythemeansofahydrauliccylinder.
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 4/19
Whentherequiredorientationorpitchofthepropellerisobtained,thebladesarelockedinthatposition.Sothebladesarenotanintegralpartof(ornotcastedalongwith)thepropellerhub.Theyaremountedonspindlesthathaveaxesperpendiculartotheshaftaxis.
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 5/19
ImageCredits:Stahlkocher/Wikipedia
ThefollowingpointswilldiscusstheapplicationsandtheirrelationswiththeadvantagesanddisadvantagesofCPPandFPPsystems:
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 6/19
Thecontrollablepitchpropellerscanbeusedtoruntheshipinforwardandasterndirectionboth,withouttherequirementtochangethedirectionofrotationoftheengine.How?Well,thepropellerworksontheprincipleofliftgeneratedbyeachaerofoilsectionoftheblade.Whatifwecanchangetheorientationoftheblade,suchthatthedirectionoflifeforceisoppositetowhatitwasduringforwardrunningoftheship?Thatsexactlywhatisachievedbychangingthepitchangleoftheblades,asshowninFigure2.
Bladesectionsshowninvariouspitchorientations
Anonreversibleenginecanbeusedforbothforwardandasternoperationoftheship.Hence,theweightoftheengineandpropulsionmachineryisreducedconsiderablywhencomparedtowhatisrequiredinpropulsionsystemsequippedwithfixedpitchpropellers.
Sincethepitchofthepropellerdeterminestheamountofthrustgeneratedbythepropeller,achangeinthepitchanglecanbringaboutachangeinthespeedoftheship.So,acontrollablepitchpropellerisusefulinchangingthespeedoftheshipwithoutchangingthespeedorrpmofthemainengine.Butwhyarewefocusingonthisadvantage?Whathappensifweneedtoreducetheenginerpmtoreducetheshipsspeed?Well,manyshipshaveashaftdrivendieselalternatorsystem.Sotherpmofthemainengineshaftcontrolstheelectricpowerproductiononboard.Inthatcase,ifthespeedwastobereducedusingafixedpitchpropeller,itwouldrequireareductionintheshaftrpm,whichwouldresultinreductionofpowergenerated.
Duetotheabovereason,thespeedoftheshipcanbehandledfromthenavigationbridgedirectly.In
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 7/19
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caseoffixedpitchpropellers,themarineengineerneedstobeintimidatedinordertochangetheshipsspeed.ThereforeCPPtechnologyisusedforobtainingfasterresponseofspeedchange.
Theefficiencyofasternconditionincaseoffixedpitchpropellersislessthanthatofcontrollablepitchpropellerinasterncondition.
However,therearemanydisadvantagesofusingacontrollablepitchpropellertoafixedpitchpropeller.Itisimportanttoknowthemtoo.
Thepitchcontrolmechanisminstalledinthehubiscomplicatedenoughtodemandproperinspectionatregularintervals.Theinstallationprocessisalsomorecomplicatedascomparedtothatoffixedpitchpropellersystem.
Controllablepitchpropellershaveaveryhighinitialcost.Andthiscostincreasesrapidlywithincreasingdiameterofthepropeller.
Duetopitchcontrolmechanismshousedinsidethehub,thelengthandthediameterofthehubisalsohighascomparedtothefixedpitchpropellersystems.
Toconclude,itisvitaltoknowtheapplicationsofcontrollablepitchpropellers.Theseareusedinshipsthatarerequiredtooperateatvariablespeedsevenwhenoperatingatconstantpowerrequirements.Suchshipsaretugs,trawlers,ferries,icebreakers,andsmallscalewarshipsthatareequippedwithgasturbines.
Overtoyou..
WhataccordingtoyouarethemostimportantfeaturesofCPPandFPP?
Letsknowinthecommentsbelow.
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6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
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AboutSoumyaChakrabortySoumyaispursuingNavalArchitectureandOceanEngineeringatIMU,Visakhapatnam,India.Passionateaboutmarinedesign,hebelievesintheimportanceofsharingmaritimetechnicalknowhowamongindustrypersonnelandstudents.HeisalsotheCoFounderandEditorinChiefofLearnShipDesignAStudentInitiative.
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6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
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COMMENTS
AbhiVermasaysJanuary31,2015at7:14pm
beenadeckcadetforabout18monthsnow..sailedonbothtypeofpropulsionsystem..CPP.itsthebestformanoeuvring.beingonbridgewhenenteringportorchannel.whenthepilotseesaCPP.Youcanseethegrinonhisfacereducestensiononthebridgealot
FergusGloversaysMarch4,2015at6:12am
1.Whataretheadvantagesanddisadvantagesoffixedpropellerinship?2.whataretheadvantagesanddisadvantagesofcontrollablepitchproperller?
6/11/2015 ControllablePitchPropeller(CPP)VsFixedPitchPropeller(FPP)
http://www.marineinsight.com/marine/marinenews/headline/controllablepitchpropellercppvsfixedpitchpropellerfpp/ 10/19
POSTCOMMENT
TanvirBiswassaysApril4,2015at2:16pm
Canweusetheazipodinamerchantshipinsteadofcpporfpp?
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