3 Important Calculations Every Marine
3 Important Calculations Every Marine
Engineer Must Know On Ships
Engineer Must Know On Ships
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APRIL 21, 2014 BY
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Bunkertermstofueloilinmaritime industry.Bunkerquantitycalculationisthemostimportantcalculationwhichevery marineengineershouldbefamiliarwiththroughouthiscareer.Bunkerfuel,beinga highvaluedproduct,hastobeverycarefullyandaccuratelycalculated for
determiningthequantity.
Thevolumeofdefinitequantityofbunkerincreaseswithincreaseintemperature whereasitsweightremainsthesame.Forthisreason,bunkerisalwaysorderedand measured in weight and not by volume.
Alsoalltheenergyandefficiencycalculationsoffuelonboardshipsarecalculatedin termsofmassofthefuelratherthanitsvolume.(Calculationofbunkerfuelquantity inweightinvolvesmanyfactorstobeconsideredmakingitmorecomplex.)
Mostly,thefourthengineerwillbethedeputyoftheChiefengineerfor receiving bunker & measuringthebunkerquantityformaintainingrecords.
Mentionedbelow istheprocedureformeasuringandcalculatingthebunkerquantity: -> Oncethetotalquantity(tonnes)ofbunkerfueltobereceivedisconfirmed,take soundingofship’sbunkertanks&calculatetheavailablequantityoffueloilonboard toformulateabunkeringplandenotinghowmuchtonnesoffueltobebunkeredon eachtank & thetank sequence ofbunkering.
-> Beforecommencingofbunkeroperations,confirm thetemperatureatwhichthe bunkeristobereceivedandnotedownthestandarddensityofthefueloil.Withthis parameterscalculatethevolumeofbunkertobereceivedineachtankasper
bunkeringplanandnotedownthefinalsoundinglevelofeachtankafterbunkering usingcapacitytablefortheeaseofstopping&changeovertonexttank.
Thebasicformulausedforcalculatingthebunkerquantityinweightis:
Mass = Volume x Density
-> Itistobenotedthatintheaboveformula,thedensityandvolumeofbunkerfuel
should be known at same temperature.
-> Afterreceivingthebunker,takesounding/ullageofallthebunkertanksusing soundingtapeandnotedownthetanktemperature.Usesoundingpasteinthetape whilemeasuringdistillatefuelsuchasMDO foreasyreading.
-> Shipalwaysdoesnotfloatwithevenkeelsothefloatingconditionsoftheship suchastrim andlistshouldbewellnotedwhiletakingthesoundingofbunkertanks. -> Everyshipisprovidedwithatankcapacitytableinwhicheachtankcapacityin volumeismarkedagainstthesuccessivelevelsofsounding/ullagewithcorrection factorsundervarioustrim andheelconditionsoftheship.Thevolumeoffueloilat tanktemperatureforthecorrespondingtanksoundingisthusmeasuredusingtank capacitytable,whichgivestheactualsoundedvolume.
-> Thedensityoffueloil(inkg/m3)atstandardreferencetemperatureof15⁰C is
alwaysprovidedbythesupplierinBunkerDeliveryNote.Withthisthedensityoffuel oilattanktemperaturecanbedeterminedusingASTM tableorusingsoftwaremost commonlyinstalledonallship’scomputer.
TheformulausedtocalculatetheTemperatureCorrectedDensityis: =(DensityofFuelOil@ 15⁰C)x[1-{(T-15)x0.00064}]
Where:
T=temperatureofoilinbunkertanksindegreecelcius, 0.00064=Correctionfactor
Sincethebunkeroilisnormallysuppliedtothevesselattemperaturehigher then15⁰C,theformulausedforcalculatingthebunkerquantityinweightwill
be-MetricTonnes= (ActualSounderVolume)X(TemperatureCorrectedDensity) -> Thecorrespondingvaluesofeachtankaretabulatedforeasyreadingandthe totalweightofbunkerquantityiscalculated.
2. Specific Fuel Oil Consumption (SFOC):
Specificfueloilconsumptionisthemeasureofmassoffuelconsumedperunittime toproduceperKW.Themarineengineefficiencyisusuallydeterminedusingthe SFOC.
Inordertoachieveaccuracy,thefuelconsumptionandpowerdevelopedisalways measuredoverasuitabletimeperiodonagoodweather.Theformulausedfor calculatingSFOC is:
SFOC (g/kwh) = Mass of fuel consumed per hour / Power developed in KW
-> Thereadingsofflow metertomainengineshouldbenotedoverthespecifiedtime intervalsay1hour.Withthedifferenceinreadingsthevolumeoffuelconsumedis obtained.ItcanalsobemeasuredbynotingdowntheHFO servicetankreading providedtheoilisbeingsuppliedonlytomainengine.
-> Themass of observed volume of fuel consumedcan bedetermined by following theabovesaidbunkercalculationprocedure.
-> Thehorsepowercan bemeasuredusingdynamometerif fittedontheshaft ofthe enginewhichwillindicatetheBHPindigitalindicator.Ifnot,thehorsepowercan alsobecalculatedusingenginerpm andaveragepumpfuelindexwiththeaidof enginecharacteristiccurveofvariousseatrialswhichissuppliedbythe
hencecompensationfactorhastobedeterminedtoobtaintheaccuracyin calculation.
Slipisconsideredas
thedifferencebetweenthespeedoftheengineandactualspeedoftheship.Itis alwayscalculatedinpercentage.Positiveslipisinfluencedbyvariousreasonssuch asfouledbottom orhullpartwhichoffersresistancetothemovementofship,
environmentalfactorssuchaswatercurrentandwindagainsttheshipdirection.Slip maybenegativeiftheshipspeedisinfluencedbyfollowingseaorwind.Engineslip iscalculateddailyonboardthevesselandrecordedinlogbook.
Enginedistance–Observeddistance
Percentage of Slip = ————————————————– X 100%
Enginedistance
• Theactualdistance(nauticalmile)coveredbytheshipfrom noontonoonis
measuredusingship’slog.
• Thetotalrevolutionsofthepropellerfrom noontonoonisobtainedusing
revolutioncounter.Theenginedistancecanbecalculatedusingthepitchof thepropellerprovidedbythemanufacturer.Caremustbetakeninunit
conversionofpitchfrom metertonauticalmile(ingeneral1NM =1800m). Enginedistanceinnauticalmile=(Pitchxrevolutionsperday)
Obtainingtheaccuracyofvalueinalltheabovecalculationsarealwayschallenging onboardastheparametersrecordedaremoresensitivetodynamicconditionsofthe shipandalsodependsonvariousenvironmentalfactors.
Over to you…
Doyouknow anyotherimportantcalculationthatcanbeaddedtothislist?
Let us know in the comments below.
References & Image Credits:
M.V.JagRahul–Ship’stankcapacityplanmanual.
M.T. Jag Preeti – MITSUI B&W – Operation & Data Manual ReedsNavalArchitectureforMarineengineers.
