567

1 INTRODUCTION

Azimuth thrusters are widely used in the maritime

industry,specificallyontugs,offshoreandpassenger

vessels.Theyarerenownedforprovidingvesselswith

exceptionalmaneuverability.

Azimuth propulsion performs best in automated

low and zero‐speed tracking applications such as

auto‐trackinganddynamicpositioning,assystemcan

apply

 necessary steering forces at any speed in any

directions.

However, it also has some drawbacks. Higher

complexityleadstotwoapparentproblems:

 Vessel with azimuth thrusters is much more

complicatedinmanualhandling.

Higher propulsion system complexity leads to a

largerpossibilityfortechnicalproblems.

Many technical problems related to seals and

bearings cannotbe solvedin a day and, apparently,

do not appear in a day. They require correct

assessment of

visible symptoms, possible defects

locationandtimelycorrectivemaintenance.

Whenitcomeseithertosteeringsystemorpower

supplysystemfaults,itismoresituationalandoften

requires immediate actions from both bridge and

engineroomteams.

Therefore,simulatortrainingcanhelptobuildup

ahabitforspecificactionsand

acommunicationflow

betweenteamsincaseofsuchemergencies.

2 STEERINGMODESHIERARCHY

A typical azimuth thrusters system has a specific

proceduralflowgiveninfig.1.

Recommendations for Training of Crews Working on

Diesel-Electric Vessels Equipped with Azimuth

Thrusters

O.Pipchenko,M.Tsymbal&V.Shevchenko

NationalUniversity“OdessaMaritimeAcademy”,Odessa,Ukraine

ABSTRACT: This study addresses the problem of training the officers, which are assigned to an electrical‐

drivenvesselsequippedwithazimuththrusters.Apairofomnidirectionalthrustersincombinationwithpower

plant system containing several diesel generators imply a potential for a variety of

 different emergency

scenarios,whichalsoincludespartialorfulllossofcontrolorblackout.Thesefaultscenarioswereclassifiedin

thearticlewithpredefinedrisklevelsdependingonthearea,timelimitation,modeofoperationandfaultitself.

Mutualresponsibilitiesandactionalgorithmsforbridgeandengineteamsina

step‐by‐stepmannerhavebeen

developedforeachscenario.Personnelbehavioraldifferencesinbothexpectedandunexpectedemergencies

havealsobeenstudied.



http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 12

Number 3

September 2018

DOI:10.12716/1001.12.03.17

568

(1) DP / Track control: Synchronized steering

(2) Autopilot: Synchronized steering

(4) Follow-up (Tiller): Synchronized steering

(5) Follow-up: Independent steering

(6) Non follow-up (BRG): Independent steering

(3) Follow-up: Synchronized steering

(7) Non follow-up (ECR / SGR): Independent

steering

(8) Direct (SGR): Solenoid steering



Figure1.Steeringmodeshierarchy.

Modes (1) and (2) usually require routine

monitoring and minimum intervention from an

operator, except parameters adjustment, based on

shipbehavior.

However, simple things like steering angle

limitation along with reduced speed may lead to

temporarylossofsteeringinpoorweatherconditions.

Also in synchronous (both thrusters engaged in

steering)

 auto tracking mode vessel speed might be

unstable.Thisproblemcanbetreatedwithsettingthe

system into asynchronous mode, where one of the

thrusters is pushing only straight ahead. From the

other hand,on theminimum speed of 1.5‐2.5knots,

increase of rudder limit above conventional 35

 can

dramaticallyimprovetheship’sstabilityontrack.

Modes(3)and(4)arecommonlyusedathighand

moderatespeedstochangeheadingmanually.Inthis

case, rudder limits have to be checked prior to

maneuver to avoid abrupt turning, as all produced

thrustwillbedirectedtoagiven

angle.

Mode(5)isamaneuveringmode,whichrequires

specificskillsfromanoperator.Manualmaneuvering

technics and precautions on thrusters’ allocation is

discussed in several publications including

Kobylinski(2013),Ververk(2002)andNowicki(2014).

Thisstipulatesthefirststageofofficerstraining,dedicated

togainingamanualhandlingskillfor

thebridgestaff.

Non‐follow up (6) is the closest to emergency

mode, when a thruster does not respond to

manipulator. Generally, there are might be three

optionsavailablefortheoperator:

 NFUSteeringangle;

 NFURPM;

 NFUPitchangle.

Simply wrong sequence of actions during a

transferfromonecontrolsystemtoanother(i.e.from

DP to a conventional autopilot) may lead to a

situation when one of the thrusters is stuck on a

certainazimuthangle.

Thissituationhastobeassessedimmediatelyand

resolved

withuseofNFUcontrolbuttons.

Modes(6)‐(8)areemergencymodes,whichrequire

constant communication with an engine team. Non‐

followupanddirectsolenoidsteeringcanonlysavea 

vessel from imminent danger, after that a better

solutionhastobefoundinordertoregaincontrolof

the

vessel.

3 RISKBASEDAPPROACH

There is no danger in the loss of steering alone.

However,depending onthesituation,lossofsteering

may lead to a navigational incident such as

grounding, collision or various heavy weather

damage (i.e. loss of cargo due to heavy rolling

resultedfromvesselsinability

tokeepasafeheading).

Inrelationtogroundings andcollisions,intuitional

approachcanbeused.

AstheRISKisaproductofaLIKELIHOOD(LH)

and a SEVERITY (SV), we should define these two

componentsfirst.

Apparently, being closer to a hazard with no

steering means bigger likelihood of running

 across

thathazard.Thereareseveralfactorsinfluencingthe

LIKELIHOOD.

 Let’sname the firstfactorHAZARDS DENCITY

(HD).Evenifthe initialCPA (secondfactor) isnon‐

zerothereisstillarisktohitanobjectindensetraffic

ornarrowwaters.Although,ifitisaship,it

willmost

likelytrytodeviatefromourwaytogiveussearoom

asnecessary,whichsomewhatreducestheRISK.

However, the most critical is the time factor or

TCPA to the closest hazard, which almost

straightforwardly specifies how much time we have

tosolvetheproblemtoavoid

groundingorcollision.

In the most general cases, the SEVERITY of

collisionorgroundingcanberelatedstraittoaship’s

velocity. The higher the velocity the more damage

maybecaused.

InordertoobtaincorrectLHvalueHD,CPAand

TCPAshallbeinverselyproportional:

11 1

HST

DCPATCPA



 

, (1)

whereST–hazardmovabilityindex.

Basingonthekinematicenergyequation

0,5

mU

,

where m – ship’s  mass; U – ship’s speed, although

mass can be assumed as constant and thus will not

affecttheRISKforthepa rticularvessel,severitycan

begivenas

SV U

, (2)

In table 1 RISK level is given in each line for a

possiblecollisionwithastationaryobject.



569

Table1.Riskassessmentfactors

_______________________________________________

LikelihoodSeverity Risk

_______________________________________________

HD CPA TCPA Stationary Speed

nm nm hours

_______________________________________________

10  1  210.05

5  0.510.5‐NO  52 

2  0.25 0.51040 

0.50.10.25  1.0‐YES  201600 

_______________________________________________



These factors form multi‐dimensional RISK.

However, to get better visual representation lets

define HD = 1, CPA = 1 for a stationary target and

calculatetheRISKmatrix.

RISKlevelscanbedescribedasfollows:

BLACK(risk>400)–immediateactionsrequired

toavoidanaccidentortominimize

itsconsequences.

Speed has to be reduced in any possible way.

Assessment of possible catastrophic consequences to

bedone.

BLUE(risk>200)–immediateactionsrequiredto

avoid an accident or to minimize its consequences.

Speedhastobereducedinanypossibleway.

RED (risk > 100) –

Speed has to be reduced to a

levelwhereadditionalmeansofsteering(retractable

or side thrusters) can be utilized. As soon as safe

heading is achieved, assess options for emergency

anchorage. Try to regain the steering with main

meansofpropulsion.

YELLOW (risk < 100) – additional means of

steering

canbeutilized.Assessoptionsforemergency

anchorage. Try to regain the steering with main

meansofpropulsion.

Table2.Riskmatrix:lossofsteering

_______________________________________________

RiskTCPA,hours

1  0.75 0.50.25

_______________________________________________

Speed 1 1  1.33  2  4 

knots  5 25  33  50  100

10 100 133 200 400 

20 400 533 800 1600 

_______________________________________________

4 POWERMANAGEMENTANDBLACKOUT

PREVENTION

Thereisavarietyofpossiblefaultsthatmayhappen

tothesteerablethrusters(IMCA2011&2012),which

goesallthewayfrompowergenerationtoadirected

thrustdelivery.

Thisstipulatesthesecondstageofofficerstraining,

dedicated to gaining a power

 management skill for

the engine staff. This also includes changeover and

synchronization procedures between generators and

systemrestartafterblackout.

Generallyspeaking,ablackoutcanbeavoidedby

utilizingtwo different approaches(IMCA2000).The

first one is used on conventional DP II/III class

vessels, which usually have from four

to six

generators. During DP operations, a vessel usually

hasan open busbartie breaker,which splits power

delivery in two equal groups, feeding two separate

groupsofthrusters.

Suchapproachadvantagesareeliminationoftotal

blackoutincaseofanysingleelectricalormechanical

fault,greaterreliabilityandlessdiesel‐generator(DG)

restarting time in case of partial blackout.

Disadvantages are high fuel consumption at low

loads, low power plant flexibility, in addition

blackout on one side leads to inability to operate a

certaingroupofthrustersandapparentlyreducesthe

steeringability.

The second way of providing electrical

power

continuitywithoutsplittingbusbarsistheapplication

ofpowerplantadvancedprotectionsystem.

The primary function of protection schemesis to

isolatefaultycircuitsandlimitdamagetoequipment.

Thegreatestthreatto any systemisthe shortcircuit

fault, which can alter system operation in a sudden

and

 possibly violent manner. Electromagnetic forces

generated by large fault currents can cause

mechanical damage to transformer and machine

windingsandtheintenseheatassociatedwitharcing

has caused fire at fault locations. In DP and other

operations,evengreateremphasismustbeplacedon

the need to maintain supplies for

propulsion. The

arguments for and against operating with bus

sections connected have been discussed earlier and

arestillthesubjectofmuchdebate.Operationofthe

power system with bus sections connected offers

manyoperationaladvantageswithonlyslightriskof

complete blackout. The risk cannot be considered

negligible, however, and

 operators choosing to take

advantage of this mode of operation may wish to

considerinstallingoneofthehigherspecificationbus‐

bar protection methods. There are four types of

protectionthatperformthistask:

 zoneprotection;

 directionalprotection;

 protectionbytimediscrimination;

 opticalarcdetection.

Suchapproachallowsthepowerplanttobemore

flexibleinmostofknownships’operationmodesbut

requires more sophisticated and expensive power

management and protection equipment comparing

thesplitbusbarsoperation.

Engine team actions in case of full or partial

blackoutaregivenon

figure2.

5 EMERGENCYSTEERING

Inawiderscopeoftheproblemitisnotonlysolenoid

steering from the thrusters’ gear compartment, but

alsoallpossibleemergencyactionstakenbydeckand

engine departments, and communication between

them.Whichisthethirdstageoftraining.Thisincludes:

 control transfer from autopilot to feedback and

non‐followupmodesonthebridge;

 fullorpartialcontroltransferfromBridgetoECR

(onegroupofthrustersiscontrolledontheBridge,

another–inECR);

 troubleshootingandequipmentrestartontheECR

side;

 ensuring steerage and maneuverability or

emergencyanchoringontheBridgeside;

 transferringthecontrolbacktoEngine room.

570

Introducing realistic scenarios and time limits

related to existing navigational hazards helps to

improve deck and engine officers’ trouble shooting 

andcrisismanagementskills.

Ontheworkingvessel,thesescenariosusuallyare

onlylimitedtoatabletalk.Whichisunderstandable,

as the vessel schedule, mode or area of operation



mightnotallowtocarryoutapropertraining.

However, hands‐on experience is extremely

importantwhenitcomestoemergencies.Crewshall

notonlyknowwhattodo,butbeabletoactinaquick

andefficientmanner.Thiscanonlybeachievedwith

dedicatedsimulatortraining.

For

the purpose of simulator training vessel

specific action algorithms can be really useful as a

step‐by‐step to‐do list and communication protocol,

whichhastobediscussedandagreedwithinBridge

andEngineteams.

There are several events related to steering that

maysubstantiallyaffectvessel’scontrollability,which

also

havepreviouslyoccurredintheindustry:

 thrusterstartstorotatefreely;

 thrustergoestofullpowerloadunintentionally;

 thrusterfreezeoncertainazimuth;

 thrusterstopsduetofailure.

Apparently,ifathruster’spitchorRPMisatzero

or evenbelow some criticalvalue any steering with

suchthrusterwillbeineffective.

Blackoutdetected

(busbarsvoltage<20%

rated)

StarttwoDGswiththe

higheststandbypriority

DoesanyDG

work?

YES

CloserunningDGbreaker,

disableallotherDGbreakers

closing

Isthere oneDG

connectedto

busbars?

Closenextrunn ingD G

breaker,disable allotherDG

breakersclosing

Sta rtnextst andby DG

IsnextDG

connected?

YES

Sta rtnextst andby DG

DoesnextDG

work?

YES

Closerunning DGbreaker,

disableallotherDGbreakers

closing

Isthere oneDG

connectedto

busbars?

SynchronizesecondDGto

busbars

IssecondDG

connected?

YES

END

DoesnextDG

work?

Sta rtnextst andby

YES



Figure2.Flowchartonpowerrestoreafterfullblackout.

Get ready available

secondary means of control

Single thruster

steering fault

Consider choosing

comfortable heading

Follow emergency steering

procedure for a faulty

thruster, if necessary

End

Riskofcomplete

steeringlossexists?

Switch to: Follow-up

independent

Compensate with another

thruster

YES

Reduce the speed to

minimum

Use NFU controls to bring

azimuth to zero

Reduce speed on a faulty

thruster

Isazimuthatzero

setting?

Isazimuthatzero

setting?

Bring RPM /

Pitch to Zero

YES



Figure3.Actionsflowchartforasinglethrusterfailure

Thelatterhastwodifferentperspectives.Whenthe

steering mechanism works normally and thrust is

lost,headingcontrolwillbealsolost.

However, when thruster’s azimuth cannot be

controlled, the very first action required is to set

thrusttozero.

Actions flowchart for a single thruster fault is

shownonfigure

3.

Requiredactionsshallalsobechosenwithregard

to existing risk level. For instance, if a vessel is

steaming at 20 knots the very first action in case of

any serious steering fault is to slow down

appropriatelyinordertoreducepossibleharmandto

giveanengine

teammoretimefortroubleshooting.

Another consideration is that the vessel cannot

effectively use additional means of control such as

sidethrusters,retractablethrustersoranchorsathigh

speed.Ifthesteeringabilityisseriouslydegraded,the

deckofficerhastoensurethatthevesselisgoingslow

enoughinorder

todeployanadditionalthrusterorto

useanchorsasnecessary.

571

6 BEHAVIORALASPECTS

Team reaction on faults and communication in the

processoftrainingchangesdramatically.

There are several factors, which were observed

duringpracticalexercise.

Bridge and engine control room familiarization

obviously has the greatest effect on response time.

Thisalso includesknowledge of warningand alarm

sounds and

 indicators, and same important

knowledgeofhowtosilencethealarmbuzzers.This

recalls another important subject of alarms

standardization an ergonomics, but usually a team

hastodealwithwhateverisalreadyinstalled.

Secondly, communication in between bridge and

engine team has to be clear and precise in order

to

providethebestresponsetime.

Notonlylanguagebarriermaybeaproblem,but

isalsoawarenessonbothendsofthephoneline.

It is a good practice to have a toolbox meeting

(briefing) between deck and engine teams prior to

critical operations and practice emergency scenarios

asa

team,includingVHFandphonecommunication.

Also, it is recommended to five a training to the

sameteams thatwill actually worktogether. It does

helpthecrewtofeelmorecomfortableinthefuture,if

difficultiesoccur.

Finally, practicing all the stages of emergency

gives both teams (bridge and

engine) clear

understandingofwhatmayhappenandhowtodeal

with it. This builds up the operator’s ability to

recognizehowacriticalsituationdevelopsandwhat

arethebestwaystokeepitfromescalatingoratleast

tominimizetheharm.

7 CONCLUSIONS

A diesel‐electric vessel equipped

 with azimuth

thrusters have complicated steering and power

supply systems architecture, which stipulates many

possible faults, but also many troubleshooting

alternatives.Knowledgeofthesealternativescanhelp

toavoidincidentsrelatedtolossofsteeringorpower.

Asofferedinthearticle,thebestwaytogethands‐

onexperience

ondealingwitha steering  andpower

systemsfaultsistheMaritimeResourceManagement

training, which includes both bridge and engine

teams.

Suggested MRM training should consist of three

stages:

 azimuth thrusters manual handling training for

deckofficers;

 power management and troubleshooting for

engineers;

 emergency steering training for both teams

involvedinsamescenario.

Generic steering system failure risk assessment

method and emergency actions flowcharts are

providedinthisarticle.

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Freek Verkerk. 2002. Manoeuvring aspects of vessels

equipped with pods. Maritime & nautical permanent

education.

IMCA, 2000. Power Management System Study. IMCA M

154.

IMCA, 2011. Dynamic Positioning Station Keeping

Incidents:Incidentsreportedfor 2009(DPSI 20). IMCA

M211.

IMCA, 2012. Dynamic Positioning Station Keeping

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M218.

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politechnikiwarszawskiej,z.95.

Nowicki,J.2014.StoppingofShipsEquippedwithAzipods.

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Tom van Terwisga, Frans Quadvlieg, Henk

Valkhof. 2001.

Steerable propulsion units: hydrodynamic issues and

designconsequences.MARIN.