409

1 INTRODUCTIONTOPLANNED

MAINTENANCE

Commercialshippinginthemodernworldishighly

competitive, which coupled with high crewing and

fuelcosts,leadstohighoperationalcosts.Oneofthe

paramountfactorinvolvedinvessel operation is the

Maintenancecostandthereisadireneedtokeepthis

cost

 to a minimum. Fortunately the earlier policy of

repaironlymaintenanceincommercialshippinghas

beendoneawaywith,andwasreplacedbythepolicy

of preventive maintenance. Planned Maintenance

System was introduced by ship management

companiesintheearly90’s.

2 WHYCONDITIONBASEDMAINTENANCE

PlannedMaintenanceofferedbenefits

overtherepair

only policy, but has its own demerits. Many a time

machinery equipment is opened up for routine

maintenance after a specified time interval,

irrespectiveoftheneed. This could lead to potential

failures,whichisexplainedbythefactthatpreventive

Using Reliability Block Diagrams and Fault Tree

circuits, to develop a Condition Based Maintenance

Model for a Vessel’s Main Propulsion System and

Related Subsystems

M.Anantharaman

ustralianMaritimeCollege(Utas),Tasmania,Australia



ABSTRACT: Merchant shipping has undergone a great transformation over the past three decades. The

shipping market is highly competitive, which coupled with high crewing and fuel costs, leads to high

operationalcosts.OneoftheparamountfactorinvolvedinvesseloperationistheMaintenance

costandthereis

a dire need to keep this cost to a minimum. Fortunately the earlier policy of repair only maintenance in

commercialshipping has beendone away with,and was replacedby thepolicyof preventive maintenance.

Planned Maintenance System was introduced by ship management companies in the early

 90’s. Planned

Maintenanceofferedbenefitsover the repair only policy, buthasitsowndemerits. Many  a timemachinery

equipmentisopenedupforroutinemaintenanceafteraspecifiedtimeinterval,irrespectiveoftheneed.This

could lead to potential failures, which is explained by the fact that preventive maintenance

resulted in

meddlingofawellsetpieceofmachineryequipment,leadingtoitssubsequentfailure.Thisiswhere Condition

based maintenance or CBM steps into prominence. CBM monitors the health of the machinery equipment,

analysestheconditionandhelpsyouindecisionmaking. The Main Propulsion system forms theheart

ofa

vesselandweneedtoensureitsreliability,togetherwiththereliabilityofitsassociatedsub‐systems.Theentire

systemcanberepresentedbyreliabilityblockdiagrams,toshowtheinterdependence ofvariouscomponents

comprisingthesystem.ThishelpsinthedecisionmakingprocessofCBMwherebyship’s

engineermaydecide

tostoptherunningmachineryequipment, openandoverhaulthesame,elsepostponetheoverhaulforalater

safedate.



http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 7

Number 3

September 2013

DOI:10.12716/1001.07.03.13

410

maintenanceresultedinmeddlingofawellsetpiece

ofmachineryequipment,leadingtoits(Bhattacharjya

and Deleris, 2012)subsequent failure. The author

wouldliketociteanincidentexperiencedduring his

vastsailingcareer.Ageneralcargovesselwasonher

wayfromIndiatoEurope.Thispassageinvolvesthe



SuezCanaltransitwherelargenumbersofvesselsgo

on a convoy. A few days before transiting the Suez

canaltheNo.1Steeringgearmotorwasopenedupfor

routine overhaul, as specified in the Planned

MaintenanceScheduleforthevessel.Themotorwas

overhauledandreassembled.Thevesselthen

entered

theconvoyandallwent off well for an hour,under

theguidanceofthe Suez Canalpilotwhotravelson

board the ship during the transit. The pilot then

ordered a helm movement and the vessel failed to

steerasrequired.Thereasonwasoverloadtrippingof

the overhauled

 motor, and investigations revealed

errorsduringthereassemblyofthemotor.Thevessel

was then tied alongside the canal with the help of

tugs, the motor had to be reopened again, and new

bearingswere fitted.Motor tried out and finally the

vesselmanagedtotransittheSuezCanal,though

she

hadtobelastontheconvoy.resultinginconsiderable

losses in terms of thousands of dollars to the

company. This is where Condition Based

Maintenance or CBM steps into prominence. CBM

monitors the health of the machinery equipment,

analyses the condition and helps you in decision

making.Accordinglya

ship’sengineermaydecideto

stop the running machinery equipment, open and

overhaul the same, else postpone the overhaul for a

latersafedate.

3 ISMCODEANDMAINTENANCE

When it comes to operation of ships, all shipping

companies need to abide by the ISM Code which is

the International

Safety Management Code, the

purpose of this Code is to provide an international

standard for the safe management and operation of

ships and for pollution prevention. The above

research will also address section 10.3 of the code

which states that, ‘The Company should identify

equipment and technical systems the sudden

operational

failureofwhichmayresultinhazardous

situations. The safety management system should

provideforspecificmea s ures aimedatpromotingthe

reliability of such equipment or systems. These

measuresshouldincludetheregulartestingofstand‐

byarrangementsandequipmentortechnicalsystems

thatarenotincontinuoususe.’(ISM,2002)

4 DIAGNOSISANDPROGNOSIS

TheconceptofCBMforship’smachineryisstillinits

infancy. Reproducing a recent finding which says

‘However,accordingto class records,onlyabout2%

of thw world fleet is operating using

CBM’.(MER,2012).Effective application of CBM

techniques will result in large savings to the vessel

owner

/operator.Aship’smachineryspaceisalarge

mainpropulsionsystemwithseveralsubsystems.All

thesesystemshaveafairlyhighdegreeofcorrelation;

failureofanyonesubsystemcouldresultinstoppage

of the vessel, which is a highly undesirable event.

CBMisatwosidedcoinwith

diagnosisononeside

and prognosis being the other side. For an efficient

vesseloperationboththesidesofthecoinarevital.

Prognosis is an important element of the CBM

program as it deals with the predication of failure

faults.Theaboveresearchshouldbeuseful topredict

the occurrence

 and timing of a failure in a single

subsystem (example ship’s main propulsion and

power generation system) or in several different

subsystems (example ship’s main propulsion and

powergenerationsystemandcontrolairsystem)

5 GROSSMAINTENANCEDEFECIENCIES

A few instances of major shipping disasters on

accountofgrossmaintenance

deficiencieshave been

highlighted below. This information was gathered

fromleadingreputableMarineAccidentInvestigation

bodiesinthecommercialshippingworld.

‘The scavenge space inspection after the fire in

numberthreeunit,shortlyafterthefirstturbocharger

failure,apparentlyrevealeda high level ofscavenge

fouling.Similarlytheconditionofthe

scavengespaces

afterthesecondturbochargerfailurewaspooraround

number two cylinder, albeit as a result of piston

coolingoilleakingfromthedefectiveO‐ring.Whether

or not the condition of the scavenges led to a fire, 

which in turn caused the turbocharger failures,

cannotbeconcludedwith

anycertaintyhowevertheir

conditiondoesindicatethatthevessel’smainengine

maintenance regime in this respect may have been

deficient.’(ATSB,2006).



Figure1.Conditionofscavengeports onCylinderno.1of

MainpropulsionEngineSourcebasedonATSB(2006)



Figure2.Conditionofscavengeports onCylinderno.2of

MainpropulsionEngineSourcebasedonATSB(2006)



411



Figure3. Condition of damaged main propulsion

turbochargerrotor.SourcebasedonATSB(2006)



Figure4. Condition of damaged exhaust gas boiler tubes.

SourcebasedonMAIB(2007)

Apartfromthefailureoftheauxiliaryboiler,there

wereotherexampleswhereequipmentdidnotwork

properly that were attributable to ineffective

maintenanceorequipmentchecks:

 StandbyEGEcirculationpumpmechanicalseal

 Automaticoperationofsootblowers

 FueltankQuickClosureValves

 CO2drenchpilotoperating

system

 Emergencydieselgeneratoroverheating

 Emergencyfirepumpsuction

Themaintenancesystemrecordedthatchecksand

planned maintenance were complete on all these

items, and that there were no defects. While it is

always possible for equipment not to work in an

emergency,somanyseriousdefectsshould

notoccur

during the same incident. Neither the maintenance

systemnoranyofthetechnicalauditsdetectedthese

latent defects, so the effectiveness of these systems

mustbequestioned.’(MAIB,2007)

6 RELIABILITYCENTEREDMAINTENANCE

CBM leads to improved reliability of the machinery

equipmentandbetterinventorycontrolof spares on

board

 the vessel. This approach to maintenance has

beenadvisedtoshipownersbyleadingclassification

societies.’ By applying Reliability‐centered

maintenance (RCM) principles, maintenance is

evaluated and applied in a rational manner that

providesthemostvaluetoavessel’sowner/operator.

Accordingly improved equipment and system

reliabilityonboardships

andothermarinestructures

can be expected by applying this philosophy’.

(Robert,2004)



Figure5.P‐FDiagramSourceABSguidancenotes2004

ABS guidance notes on Reliability Centered

Maintenance‐ 2004 highlights the P‐F interval. ‘If a

potentialfailureisdetectedbetweenPointPandPoint

F, it may be possible to take action to prevent the

functionalfailure(oratleasttominimiseitseffects).

Tasksdesignedtodetectpotentialfailureare

known

ascondition‐monitoringtasks.SeeFigure5above.

7 RESEARCHPROPOSAL

Myresearchproposalistofocusonmainpropulsion

system and related subsystems (Figure 6) on

commercial bulk carriers and naval vessels, collect

dataforthesemainandsubsystemswhichwillthen

be processed for statistical analysis and

produce a

reliable maintenance model for the vessel. To begin

with, the research will be exploratory in nature,

collecting data pertaining to real life examples and

case studies published by reputed marine accident

investigation bodies in world shipping mentioned

above. I shall then start building up my theory

developing from the

 knowledge gained in the

exploratoryprocessstage.Thisshouldeventuallylead

todevelopmentofahypothesiswhichwillbetested

staticallyforalargesamplesize.

412



Figure6. Main propulsion system and related subsystems

forlargevessels.

8 FAULTTREEANALYSIS

I intend using FTA (Fault Tree Analysis) during 

development of the CBM (Condition based

maintenance) model. FTA is a  top down approach,

whichhelpstoidentifybasiceventwhichcanleadto

the top undesirable event. I have included a few

quotesfrommyearlierresearchwork

below:Looking

atthefaulttreeonecaneasilyrecognisethatabasic

eventof a distillatepumpfailure by itselfcan cause

thetopundesirableeventtohappen.Alsopastsailing

experience of the author provides ample cases of

FreshwaterGeneratorfailureonaccountoffailureof

the

distillatepump.Hencetheemphasisshouldbeto

avoidthisbasicevent.’(Anantharamman,2002)

‘Inconclusiontheauthorwouldliketoemphasise

that recognising a Fault Tree proves to be a very

reliable tool and healthy exercise for a Shipboard

Engineer responsible for Operation, Running &

Maintenanceofships.Thebenefitsto

costratiocould

be tremendous. Hence let us start planting thisTree

for all shipboard activities and reap the

benefits.’(Anantharaman,2003).

9 RELIABILITYBLOCKDIAGRAM

Another methodology which I find useful is

developing Reliability block diagrams (RBD), which

depict the functional relationships between

componentscomprisingasystem.Previousresearches

have

shown that RBD’s can be transformed to

Bayesian networks  (BNs) to represent probabilistic

relationships between uncertain variables. Previous

research has described how one can transform an

RBDintoaBN.Afaulttreecircuitcanbeconstructed

directly from an RBD and is more efficient than an

arithmetic circuit that is

 compiled from the BN

corresponding to that RBD. We develop several

methodsforfaulttreecircuits,highlightinghowthey

can aid the analyst in efficient diagnosis, sensitivity

analysis, and decision support for many typical

reliability problems. The circuit framework can

complement tools that are popular in the reliability

analysiscommunity.(Bhattacharjya

andDeleris,2012).

Figure7belowshowsa RBDforaLubricatingoil

systemforalargeMarineDieselEngine.

10 SUMMARYANDCONCLUSION

We have seen in this paper that at times, just

followingaPMSregimeonboardvesselscouldlead

tomachineryfailure,resultinginstoppageofa

vessel

at a critical juncture. (Anantharaman and Lawrence,

2013)In merchant shipping it is very important that

we make a shift from PMS (Planned Maintenance

System)toCBM(Conditionbasedmaintenance).The

mainpropulsionplantofavesselshouldbethefocal

point of CBM and we can work around the

related

subsystems.FaultTreeAnalysisisonesuchapproach

wherein we can identify the basic event, failure of

whichcouldleadtoapossiblecatastrophicfailureof

the plant. We need to look into the probability of

failureofthesystemcomponentusingstatisticaltools

foranalysis.

A neuro‐fuzzy modeling

 approach for CBM has

been effectively utilised by researchers in merchant

shipping and other shore based

industries.(Kothamasu & Huang, 2007), ( Xu et al,

2010).

Thistransformationcouldleadtoahugebenefits

to cost ratio at the same time ensuring safety and

reliability.



RBDRepresentationofSeriesandRedundant

FunctionsforMainEngineLubricatingOilsystem



 P1:MainLubOilPump,P2:StandbyLubOilPump

 BP;BypassfilterandTCV:TemperatureControlValve

Figure7.RBDforMainEngineLubricatingOilSystem

Strainer 

BP

Filter



Main

Filter

TCV

Lub Oil

Cooler

Engine

P1

P2

413

REFERENCES

ISM(2002) ‘International Safety Management (ISM) Code’.

InternationalMaritimeOrganisation(IMO).

MER, Operational  Obstacle, MER,IMAREST Publications,

November2012,page38.

ATSB, ( 2006).ATSB Transport Safety Investigation

Report. Marine Occurrence Investigation No. 186 and

191Final.

MAIB, (2007) Marine Accident Investigation Branch,

Southampton, United Kingdom, Report 15/2007, July

2007

Robert M. Conachey,

 American Bureau of Shipping, 

Houston,USA

Presented at 2

 International ASRANet Colloquium,

Barcelona,Spain,July5‐7,2004

Anantharaman,Mohan,A FaultTreeApproachtoPractical

Shipboard Problem on a Fresh Water Generator – a

SpecialSupplement,MaintenanceJournal,Vol.15,No.4,

pp.64‐65,2002

Anantharaman, Mohan, Fault Tree Analysis to Prepare

CargoHoldsforLoadingonBulkCarriers,Maintenance

Journal,Vol16,No.3,pp72–75,2003

Anantharaman, M.  & Lawrence, N. Develop a condition

basedmaintenancemodelforavesselʹsmainpropulsion

system and related subsystems.Marine Navigation

and SafetyofSeaTransportation: Maritime Transport

and Shipping,  2013 P.O. Box 447, 2300 AK Leiden,,

Netherlands.CRCpress/balkema,

235‐238.

RanganathKothamasu & Samuel H.Huang, Adaptive

Mamdanifuzzymodelforcondition‐basedmaintenance,

JournalFuzzySetaandSystems,Volume24,December

2007,Pages2715‐2733158Issue

Q.Xu,X.Meng&N.Wang,IntelligentEvaluationSystemof

Ship Management, TransNav International Journal on

Marine Navigation and Safety of Sea Transportation

Volume

4Number4December2010479

Bhattacharjya, D. & Deleris, L. A. 2012. From Reliability

BlockDiagramstoFaultTreeCircuits.DecisionAnalysis,

9,128‐137.

RanganathKothamasu & Samuel H.Huang, Adaptive

Mamdanifuzzymodelforcondition‐basedmaintenance,

JournalFuzzySetaandSystems,Volume24,December

2007,Pages2715‐2733

158Issue