619
1 INTRODUCTION
Nowadays tanker’s STS operations consist an
essential part of the oil supply chain, in many cases
alsosecurityoftheoilsupplyforexampleiftheport
infrastructureisdamagedorstillnotexisted.TheSTS
operation is cost effective way of oil supply and
greater trading flexibility to compare with the
t
raditionalwayoftheoiltransferbetweentankerand
oil terminal. There are many solutions to perform
suchoiltransferbetweentwotankers:
atanchor,
inadrift,
andunderway.
Themostpopular methodtoperformoil transfer
between two tankers is STS operation when both
ta
nker aftermooringoperationsstayadrift.TheSTS
in adrift to compare with others method always
requiredmorespacearound.Thispapershouldgive
the answer, what is the speed and direction of the
drift and drift pattern for both tankers perform STS
operation.
Figure1.Exampleofsimulationofthetankers involved in
STSoperation.
Determination of the Tankers’ Drift During STS
Operation - Simulation Study
K.Formela,M.Gil&P.Wilczyński
GdyniaMaritimeUniversity,Gdynia,Poland
ABSTRACT:ThesafetyofthetankersduringtheShip‐to‐Shipoperationscarriedoutinshallowwatercloseto
portlimitisinfluencedbymanyfactors.BasedontheexperienceofshipcrewinvolvedinSTSoperationitwas
foundthatareaforsuchoperationandweatheranalysesisthemostimport
antfactorsaffectingthesafetyofthe
tankers.Windspeedandaccompanyingwavesveryoftendetermineifsuchoperationcouldbecommenced.
Forthearticlesimulationswerecarriedoutwithmaximumallowablewindspeedandwavesforsuchoperation
toobtainthedriftofbothtankersandcapacityofareaforSTSoperation.
The results obtained from simulations allowed to assess the required space for tankers involved in STS
operation.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 10
Number 4
December 2016
DOI:10.12716/1001.10.04.11
620
2 CHARACTERISTICSOFTHERESEARCHAREA
Transferareasshouldbeselectedinsafeseaareas.In
coastalareas,theseSTStransferareaswillbeagreed
to by nearby coastal authorities and, as appropriate,
in accordance with specific port or national
regulations[1,4,5].
Variousenvironmentalconditionsprevalentinthe
transfer location may impose restrictions on the STS
operation. Some coastal state authorities may have
regulations that would limit STS operations under
adverseweatherconditions[3].
On the grounds of the fact, that the research
objectivewastodeterminatetotaldistanceofthedrift,
forthebothvessels,theirloading
conditionsdidnot
changeduringthesimulation.MotherVessel(MV)in
the beginning of each scenario was in the position:
φ=55°27.382’N,λ=018°10.796’E. For each of the
analysed directions of the hydrometeorological
conditions, receiving vessel position and orientation
waschanged.Shewasplacedbothonthelee
sideand
onthewindwardsideoftheMV.
Comparison of all conducted scenarios of the
simulationwaspresentedintable1.
Table1.Detailedlistoftheconductedscenarios.
_______________________________________________
Scenario Truewind Current Positionof
dir.[°] dir.[°] ReceivingVessel(RV)
_______________________________________________
001 000180 StarboardsideofMV
(windwardside)
002 000180 PortsideofMV(lee
sideofMV)
003 238058 StarboardsideofMV
(leeside)
004 238058 PortsideofMV
(windwardside)
005 058238 StarboardsideofMV
(windwardside)
006
058238 PortsideofMV(lee
side)
007 328148 StarboardsideofMV
008 328148 PortsideofMV
009 148328 StarboardsideofMV
010 148328 PortsideofMV
_______________________________________________
According to the requirements [4], atmospheric
condition during STS transfer operation reached
maximumBeaufortforce4[2].Thisvaluerepresents
windspeedsfrom11to16knots[8].
For that reason, as the speed limit of constant
wind, average number was 13 knots. Changing
hydrometeorological conditions followed regardless
oftheselected
scenario.Foreachsimulation,research
was carried out based on the following procedure
(table2).
Wind wave direction consistent with the
aggregateddirectionofthewindandcurrent.Height
of wind wave changed automatically for specified
parameters of wind, according to Phillips Spectrum.
Maximalrecordedvalueofwindwave:height
1.1m,
length 20.4m, period 3.6s at medium‐development
stage.
Table2.Detailedprocedureofconductingsimulations.
_______________________________________________
SimulationWind Gusts[dir. CurrentAction
time speeddeviation, speed taken
[hh:mm] [kn]speed, [kn]
period]
_______________________________________________
00:00 0.0 n/a 0.0Beginningofthe
simulation,
sendingand
heavingup
mooringlines.
_______________________________________________
00:20 1.0±10°, 0.0Linearincreasingof
00:30 2.00.5kn,windspeed(1kn
00:40 3.010sper10minutes).
00:50 4.0Increasingofwind
speedingusts.
_______________________________
01:00 5.0±10°, 0.0
01:10 6.01.0kn,
01:20 7.010s
01:30 8.0
01:40 9.0
01:50 10.0
02:00 11.0
_______________________________
02:10 12.0
02:20 13.0 ±10°,
02:30
1.5kn, 0.1Linearincreasingof
02:4010s 0.2currentspeed(0.1
02:500.3knper10minutes).
03:000.4
03:100.5
03:30
±15°, Increasingofgusts
5.0kn,parameters.
20s
08:00
Endofthesimulation.
_______________________________________________
3 MODELOFOILTANKERINVOLVEDINSTS
OPERATION
Conducted research contained ten simulations,
realized according to project assumptions. Further
scenariosdifferedfromeachotherbythedirectionof
the true wind, sea current and wind wave. Two
tankers – represented as a Mother Vessel (MV) and
Receiving Vessel (RV)
– were used during all the
simulations.
VLCC05L (MV) is powered by one diesel engine
rating19280kWat80rpmandpropelledbyonefixed
pitch propeller (FPP). Direction of propulsory
revolutionisright.
Model TANK16B (RV) is ballasted 115000DWT
tanker, based on Americas Spirit vessel. She is
powered by one diesel engine rating 12711kW at
105rpm and propelled by one fixed pitch propeller.
Directionofpropulsorrevolutionisright.
Characteristic and basic operating parameters of
bothmodelsarepresentedinthetable3 and4.
621
Table3.Characteristicandthebasicoperatingparametersof
themodelVLCC05L.[9]
_______________________________________________
_______________________________________________
ModelVLCC05L
Lengthoverall[m] 315.0
Breadth[m]47.2
Draftforward/aft[m] 18.45
Displacement[t]226000
TypeofEngineDiesel19280kW
PropellerFPP
_______________________________________________
Table4.Characteristicandthebasicoperatingparametersof
themodelTANK16B.[10]
_______________________________________________
_______________________________________________
ModelTANK16B
Lengthoverall[m] 249.9
Breadth[m]43.8
Draftforward/aft[m] 5.97/8.58
Displacement[t]61320
TypeofEngineDiesel12711kW
PropellerFPP
_______________________________________________
4 REQUIREMENTS&RECOMMENDATION
Theoiltransferfromonetankertoanotherisasubject
to a strict regime of environmental and safety
regulation, both though as international conventions
MARPOL 73/78 and industry guidelines and
requirementsprovidedbytheOCIMF(OilCompanies
International Marine Forum). In the area where an
STSoperationisplannedalsothelocalregulationand
requirementsshouldbefulfilled.
The areas for STS transfer operations may be
defined by the appropriate coastal State authorities.
Thesizeoftransferareasselectedvariesconsiderably
andthespaceavailableforthetransferwouldhavea
directrelationtothe
typeofmanoeuvrethatwouldbe
usedfortheSTSoperation.Ifbothshipsareintended
tobeunderway,arelativelylargetransferareawould
be required. Whereas if one ship is required to
approach the other ship at anchor a much smaller
overallareawouldberequired[3].
Inselecting
theareaforSTStransfer,thefollowing
shouldbeconsidered,intheabsenceofanyapplicable
nationallegislation:
thetrafficdensityinthegivenarea;
the needforsufficientsearoom andwaterdepth
required for manoeuvring during mooring and
unmooring;
the availability of safe anchorage with
good
holdingground;
presentandforecastedweatherconditions;
availabilityofweatherreportsfortheareas;
distancefromshorelogisticalsupport;
proximitytoenvironmentallysensitiveareas;and
securitythreat[3].
Regulation 41 of the MARPOL convention
required that any oil tanker involved in STS
operations shall carry
on board a Plan prescribing
howtoconductSTSoperations.Eachoiltanker’sSTS
operations Plan shall be approved by the
Administration[1].
TheSTSoperationsPlanshallbedevelopedtaking
into account the information contained in the best
practice guidelines for STS operations identified by
the Organization. The STS
operations Plan may be
incorporated into an existing Safety Management
System required by chapter IX of the International
Convention for the Safety of Life at Sea, 1974, as
amended[1].
And additional any oil tanker subject to this
chapterandengagedinSTS operationsshallcomply
withitsSTSoperationsPlan
[1].
Thetankerscompatibilityistheessentialfactorto
conductanSTStransferoperation.ToensureanSTS
transfer operation is conducted safely, reliably and
efficiently, it is necessary to choose in proper way
parameters of the tankers. All necessary ship’s
parameters, system, equipment with all limitations
are presented in
Q.88 form. This form is exchanged
between tanker’s operators on the first phase of
plannedoperation.
Generally, tanker’s operator for STS operation
choicetheshipswiththedifferentlength,onelarge
tanker called mother vessel or STBL ship to be
lighteredandthesmalltankercalledreceivingshipor
daughter vessel.
In many cases STS operation is
performedbyshipswiththesameorwithalmostthe
samelength.Thesevesselsofsimilarlengthsinvolved
inSTSoperationsmayrequireadditionaladjustment
of the fore and aft positions of the ships for the
purposeofoffsettingthebridgewings.
To protect
sides of the both vessel appropriate
mooring equipment should be used, the most
important is to use primary fenders, capable of
absorbing the impact energy of berthing and wide
622
enoughto prevent contactbetweentheshipsshould
theyrollwhilealongsideoneanother.[2,3,4,5]
Figure3.Typicalmooringarrangementforthedifferent size
tankersinSTSoperation.
5 RESEARCHSTUDIES
Main part of the conducted research depended on
performing several simulations with the use of the
representativevesselmodels,todeterminedistanceof
their drift during Ship‐to‐ship (STS) underway
operation.
To carry out the research studies Kongsberg
Navigational Manoeuvring Simulator Polaris was
used. Devices selected to
analyse apply complex
mathematical models. As a result, it is possible to
perform the detailed mapping of reaction and
behaviouroftheshipanditssurroundingsaccording
tothephenomenaobservedinrealconditions.
The Polaris simulator was repeatedly used in
numerous scientific studies, research work and
expertise. Besides the
objectives of researches, the
deviceswereusedatregularlyconductedspecialized
coursesanddidacticclassesforfuturewatch‐keeping
officers,senior merchantnavy officersandDeep‐Sea
captains. The simulator is accredited by the
classification society DNV (DetNorskeVeritas) and
has certificates confirming its ability to perform
certified specialist courses
in accordance with the
requirements of the International Maritime
Organization–IMO.
Accordingtotheresearchassumptions,eachofthe
simulation in this study held with the use of
equivalenttankermodels.Seaarea,onwhichresearch
was conducted, was excluded of vesselʹs traffic, as
well as free of
any aids of navigation and
hydrotechnical structures. Each of the simulation
depended on the orientation of the vessels on the
sameinitialcourse,sendingandheavingupmooring
lines, Afterwards, gradual deterioration of the
hydrometeorological conditions as per simulation
scheme.Eachofthescenariosassumedequalresearch
duration totalled 8 hours,
which represents average
STScargotransferoperation[2,4].
6 SIMULATIONDATAPROCESSING
Thedatarecordedbythesimulatorduringexecuting
research,wasstoredinintervalsfrom2to12seconds,
depending on the dynamic changes of ship’s
parameters.Duringsimulation,followingparameters
forbothvessels(RVandMV)and
environmentwere
recorded:
Simulationtime,
Latitude,
Longitude,
Heading,
Coursethruwater,
Course,
Speed,
Rateofturn,
Roll,
Surge,
Surgethruwater,
Sway,
Swaythruwater,
Driftanglethruwater.
To presentdriftdistancefor both vessels as
two‐
dimensional chart, it was necessary to convert
geographiccoordinatesintogridcoordinates.Tothat
end, Gauss–Krüger projection was used for the
referenceellipsoidWGS‐84,asperfollowingformulas
[6,7]:
24
3224
6
5242224
sin cos sin cos 5 9 4
224
sin cos 61 58 270 330 445
720
SB L L
xkR B B B B t
R
L
BB tt t
(1)
35
3224
524222
ΔΔ
Δcos cos 1 )
6 120
cos 5 18 14 58 13
LL
yR L B B t
Btt t
(2)
where:
B,L–measuredellipsoidalcoordinates,
R–radiusofcurvate,
S(B) –distance from equator to the point at the
specifiedcoordinates[m],
L∆–distanceofpointfromcentralmeridian[m],
k=999923,0–scalefactor.
Calculations for the central meridian 018° was
performed pursuant
to the Polish National Geodetic
Coordinate System 2000 (PL‐2000). Total drift of
vessels was calculated through determination
distancebetweenintermediate,followingcoordinates
of ships. Remaining projection parameters for grid
coordinatesinPL‐2000systemwere[6,7]:
,ttanB
(3)
22
2
,
1
ecosB
e
(4)
where:
e–eccentricityofellipsoid,
η–orientationangleofellipsedistortion.
623
Figure4.PresentationofMVandRVpositionsafter3.5hof
simulation.
7 SUMMARY
Thesimulationresearchallowedtoassessparameters
of tanker’s drift during STS operation and required
seaspacetofulfilallthesafetyrequirements.
Results of simulation show the tanker’s drift
pattern due to different weather condition are
presentedintable5.
Table5. Drift parameters of MV in relation to scenario
number.
_______________________________________________
time total wind position profit profit profit
[hh:mm] drift dir.ofRV [m] [NM] [%]
scenario [NM] [°]
no.
_______________________________________________
001 7.87 000 windward 0.00.00 0.00
002 6.17leeward 3143.5 1.70 21.58
003 5.90 238 leeward 3483.2 1.88 24.19
004 7.78windward 0.00.00 0.00
005 7.46 058 windward 0.00.00 0.00
006 6.05leeward 2619.1 1.41 18.95
007 6.65 328 frombow 0.00.00 0.00
008 6.22frombow
798.6 0.43 6.49
009 5.76 148 fromstern 0.00.00 0.00
010 5.49fromstern 499.1 0.27 4.68
_______________________________________________
Figure5.TotaldriftofMVinrelationtoscenarionumber.
Driftpatterns(001,004and005),whereReceiving
Vessel isonthewindwardsideinrealconditions is
up to 25% greater than, when the RV is on the lee
side. That is why, during STS operation, Mother
Vessel(MV)shouldprotectandgiveashelterforRV
–especially,
oninitialstage,whenshehasmaximum
freeboard. In simulations 001, 004 and 005 observed
driftdistances,wererelevant(from1.41to1.88NM)
greaterthan,whenRVwasonleeside.
Additional, it should be mentioned about the
disadvantages of simulation research that tanker’s
modelsduringallsimulationsdidn’tchange
loading
condition.Thisfactcausedthattotaldriftsduringreal
conditions will be greater than these during
simulation’s research. The dynamic changing
(increased) freeboard from windward side of the
Mother Vessel for sure increased drifting speed of
bothtankersandchangethefinalpatternofthedrift
inrealcondition.
Thesimulationresearchmaybeused asaone of
thetoolsforplanningprocessoftheSTSoperationsin
the defined sea area, taking in to account tanker’s
parameters.
Inordertoobtainfulloverview,itisnecessaryto
carried out in the same hydrometeorological
conditionsadditionalsimulations,takinginto
account
anotherloadingconditionofReceivingVessel.
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[1]IMO,MARPOL73/78AnnexI,Chapter8:“Preventionof
Pollution during Transfer of Oil Cargo between Oil
TankersatSea”,Regulations40,41and42,London2014
[2]Wilczyński P., STS transfer plan for m/t ICARUS III,
Gdansk2014
[3]ABS, STS Transfer operations Plan for compliance
with
MARPOLAnnexI,Chapter8revision3.
[4]CDI,ICS,OCIMF&SIGTTO,ShiptoShipTransferGuide
first edition, Edinburgh: Whitersby Publishing Group
Ltd.,2013.
[5]ICS,OCIMFandIAPH,International SafetyGuidefor Oil
Tankers and Terminals, ISGOTT 5th Edition., London:
Withersby,2006.
[6]Deakin
R.E., Hunter M.N., Karney C.F.F., The Gauss‐
Krüger Projection, Proceedings of the 23
rd
Victorian
RegionalSurveyConference,Warrnambool2010.
[7]SpechtC.,SzotT.,iSpechtM.,TheResearchofAccuracyof
the Personal GPS Receivers in Dynamic Measurements,
Technika Transportu Szynowego, no. 10, p. 2547–2555,
2013(inPolish).
[8]Cornish M., Ives E., Reeds Maritime Meteorology, 3
rd
Edition,AdlardColesNautical,London2014.
[9]Kongsberg Maritime, Description of Ship Model
TANK16B Version 3, Doc.No.TANK16B ver.3 / 24‐Jul‐
2015,2015.
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VLCC05LVersion15,Doc.No.VLCC05Lver.15/24‐Jul‐
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