401
1 INTRODUCTION
Itiswellknownthatashipmanoeuvringinshallow
water generally has a larger tactical diameter and
increased added mass compared to manoeuvring in
deep water. Tactical diameter tests, Z‐tests, etc., in
deepwaterareconductedbytheshipyardduringthe
ship’s construction; therefore, the manoeuvring
performa
nce and test results of such ships in deep
waterareavailable.Ontheotherhand,manoeuvring
performance tests of full‐scale ships are difficult to
carry out in shallow water, and performance is
usually estimated. Although the need for
manoeuvring performance criteria in shallow water
has been discussed, such criteria have not been
formulat
ed as international criteria. In recent years,
ship‐handling simulators are being extensively used
to study the number of tugs and total horsepower
required to prepare for and determine critical wind
speed when a ship enters port for the first time or
whenportfacilitiesarebeingnewlyconstructed.Ship
manoeuvringm
athematicalmodelstobepreparedfor
such studies are generally based on trial results in
deep water and the particulars submitted by the
shipyard.However,althoughthestudies mustfocus
onmanoeuvringwithin theport and almostentirely
inshallowwater,manoeuvringmathematicalmodels
available are mostly those tha
t consider general
shallow water effects estimated from trial results in
deep water given by the manufacturers of ship‐
handlingsimulators.Whileitiswellknownthatthe
studyofsafetyduringmanoeuvringwithinportusing
ship‐handling simulators is highly significant, the
author has pointed out the importance of the
followingtwotopi
cs:
Manoeuvring mathematical models in shallow
wateraregenerallyestimatedbymanufacturersof
simulator,theaccuracyofwhichisnotverifiedin
mostcases.
During the study of manoeuvring safety in port,
objective criteria for safety assessment are not
alwaysclear.
Study on Manoeuvring Criteria for Safety Assessment
in Shallow Water
S.Nakamura
J
apanMarineScienceInc.,Kawasaki,Japan
ABSTRACT:Thenecessityofverifyingmanoeuvringmathematicalmodelsinshallowwaterforstudyingthe
safetyofshipsusingaship‐handlingsimulatorispointedoutinthisreport.Severalinstancesofverificationof
mathematicalmodels inshallowwater areintroduced here based onmeasurementsof motion condit
ionsof
full‐scaleshipsandshallowwatertanktestsofmodels.Resultsofsafetyassessmenttestsoffivemanoeuvring
phases are given using the verified manoeuvring mathematical models to discuss manoeuvring criteria in
shallowwater.Objectivemanoeuvringcriteriaforsafetyassessmentinshallowwaterareproposedbasedon
subjectivejudgementrelated tocontrolma
rginassessedby more than 3,200 mastersand pilots forover 325
simulationtestsandbyanalysisofthestudyresultsof15full‐scaleships.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 11
Number 3
September 2017
DOI:10.12716/1001.11.03.01
402
The following items related to the two topics
mentionedabovearediscussedinthisstudy:
Free‐running tank tests (turning tests, Z‐tests)
were conducted in shallow water on models of
single‐screw and twin‐screw LNG carriers.
Reproducibility of manoeuvring mathematical
models in shallow water was verified and
adjusted.
Motionconditions whilemanoeuvring inshallow
waterwithinportofseveralLNGcarriersrecently
commissioned were measured on board.
Reproducibility of manoeuvring mathematical
models in shallow water were verified and
adjusted.
Theauthorconductedsafetyassessmenttestswith
full‐mission type ship‐handling simulator using
manoeuvring mathematical
model in shallow
wateronseveralLNGcarriersthereproducibility
of which was already verified. The test cases
amountedto325.
Objective manoeuvring criteria in shallow water
were determined from the response to subjective
judgementrelatedtocontrolmarginbymanyship
operators (masters, pilots, etc.) witnessing the
manoeuvring simulation
tests and motion
conditions for each of the following five phases:
course‐keeping phase, course‐altering phase,
speed‐reducing phase, lateral‐shifting phase, and
standstill‐turning phase. The results of one
simulation test case have been witnessed and
assessed by an average of 10 ship operators
(masters,pilots,etc.). Accordingly,
thenumberof
persons who have assessed the 325 tests exceeds
3.200persons.
Subjective judgements were acquired related to
control margin from masters and pilots who
boarded 15 LNG carriers that entered/departed
portaftermeasuringmotionconditionsforeachof
thefollowingfivephaseswhileberthing/sailingin
shallow water: course
‐keeping phase, course‐
altering phase, speed‐reducing phase, lateral‐
shiftingphase,andstandstill‐turningphase.
Based on the manoeuvring simulation tests in
shallow water using models for which
reproducibility had been verified, and based on
the study results of the 15 full‐scale ships, the
objective manoeuvring criteria below
were
formulated as acceptable motion conditions.
Results under comparatively calm weather
conditions included many from the study results
offull‐scaleships;however,findingsshowedthat
mostofthesimulatortestswereconductedunder
seaandweatherconditionsatacceptablelimitsof
controlmargin.
Acceptablemotionconditions
Course‐keepingphase:
Driftangleunder8degrees
inmainengineslowaheadcondition
Course‐altering phase: Turn rate greater than 8
degrees/min. in the main engine slow ahead
condition
Lateral‐shiftingphase:Lateral(shift)speedgreater
than20cm/sec.atstart
Speed‐reducingphase:Greaterthan0.2kts/min.
Standstill‐turningphase:Turnrategreaterthan10
degrees/min.
2 MATHEMATICALMODELINSHALLOW
WATER
2.1 Tanktestsinshallowwater
The general practice for ship manoeuvring
mathematicalmodelintheship‐handlingsimulatoris
totunethedynamicperformancebasedontheresults
ofdeep water trials.Turning tests of
full‐scale ships
are difficult to conduct in shallow water, and
manufacturers of simulators generally estimate the
manoeuvring performance in shallow water.
However,inmostcases,theship‐handlingsimulator
operationssidemaynotbeabletoconfirmadequately
the accuracy. In a project aimed at improving the
accuracy of
the ship manoeuvring mathematical
model of simulators in shallow water in which the
authorparticipatedasoneofthemainmembers,free‐
running tests were conducted in shallow water on
two kinds of LNG carriers (with models of 3‐m
overall length) with varying aft shapes: Ship A
(single‐screw)with
Lpp:275m,B:49mandL/B:5.6;
andShipB(twin‐screw)withLpp:293m,B:49mand
L/B: 6.0.A part of the tank tests results is shown in
Table1andTable2.
Comparing Ships A and B, the L/B of ship B is
slightlylarger,andtheaftshapeisdifferentbecause
ofthesingle‐screwand twin‐screwconfigurationsof
the two ships. Because of these differences, at the
same initial speed of 5 knots and a water depth to
draftratio(H/d)of1.2,thetacticaldiameterofShipB
was comparatively
much larger, and the overshoot
angleintheZ‐testwassmaller.
Thetestsconfirmedthatshallowwatereffectwas
not consistent, and the difference was large,
dependingonthehullshape.Careisnecessarywhen
settingthemanoeuvring performanceundershallow
water effects during safety assessment while
manoeuvring the
ship within port using the ship‐
handlingsimulator.
Table1.Tanktest(Tacticaldiameter)
Tacticaldia./Lpp
Starboard35degrees
ShipA;Lpp:275m,B:49m,draft:11.6m,Singlescrew
ShipB;Lpp:293m,B:49m,draft:11.5m,Twinscrew
_______________________________________________
H/d=1.2 H/d=1.5 H/d=∞
Tacticaldia./Lpp 5kts 5kts 19kts**
_______________________________________________
ShipA/Single‐screw 4.43.53.0
ShipB/Twin‐screw7.0* 4.53.6
_______________________________________________
* Duetoconstraintsinthewidthoftestingtankusedfor
thetests,someassumptionshavebeenincluded.
**Speedis19knotsatH/d=∞
Table2.Tanktest(Z‐testresults)
1
st
OvershootAngle
Starboard10degree
ShipA;Lpp:275m,B:49m,draft:11.6m,Singlescrew
ShipB;Lpp:293m,B:49m,draft:11.5m,Twinscrew
_______________________________________________
H/d=1.2 H/d=1.5 H/d=∞
1
st
OvershootAngle
(Degree)5kts 5kts 19kts**
_______________________________________________
ShipA/Single‐screw 2.94.36.3
ShipB/Twin‐screw1.24.66.3
_______________________________________________
**Speedis19knotsatH/d=∞
403
Fig. 1 shows the results of turning tests (deep
waterandshallowwaterwithinitialspeedof7knots
for both cases) by simulator of Ship B (twin‐screw),
basedontheresultsoftheabovetanktests.
Figure1.Resultsofturningtests(deepwaterandshallow
waterwithinitialspeedof7knotsforbothcases)by
simulatorofShipB;Lpp:293m,B:49m,draft:11.5m,Twin
screw.
2.2 Verificationofmanoeuvringmathematicalmodelin
shallowwaterbyonboardstudies
Theauthorandstudyteammembersboardedseveral
shipsinoperationfrom2007to2016fifteentimes,and
measured ship motions during berthing/sailing
manoeuvresinshallowwaterconditions.Signalssuch
asship’spositionandheadingwereacquiredbyGPS
from the AIS plug of the ships, and the steering
conditions,mainenginerpm,usageconditionsoftug
and thruster were also recorded in time series for
motionmeasurements.
Similar manoeuvring during measurements was
performed in the ship‐handling simulator. The
reproducibility of the ship manoeuvring
mathematical model was verified
in shallow water
conditionsbycomparingshipmotionconditions.
Fig.2showsthetrackchart(wind:WNW5.3m/s;
tidal current: ENE 0.1 knot) in the course‐altering
phasewhileberthinginJapanonDecember15,2014,
from the results of fifteen measurements. (Ship
particulars:LOA:288m,LPP:275m,
Moldedbreadth:
49 m, MOSS‐shape cargo tank capacity: 155,000 m
3
,
draft:11.8m)
Figure2. Track chart (wind: WNW 5.3 m/s; tidal current:
ENE 0.1 knot, H/d=1.5) in the course‐altering phase while
berthingonDecember15,2014).
Fig.3showsthechangedconditionsintimeseries
of turn rate for the same status. The changed
conditions in time series of the turn rate when the
samemanoeuvresofthestudiedfull‐scaleshipwere
implemented on the ship‐handling simulator under
thesamephase,aresuperimposedinFig.
3.
Figure3. Status ofdevelopmentof turn rate inthecourse‐
alteringphaseoffull‐scaleship(berthingonDecember15,
2014) and simulation (Wind: WNW 5.3 m/s; tidal current:
ENE0.1knots,H/d=1.5).
Althoughtheeffectivenessofrudderwasslightly
delayed with the main engine stopped in the
simulation model at conditions of H/d=1.5, water
depth approximately. 17.5 m, advance speed of 4.6
knots,rudderhardtostarboardat10:06hourswhen
course alteration started, the startup conditions of
turnrate,maximumturnrate,
etc.,werereproduced
togoodaccuracy.Full‐scaleshipdataareindicatedin
pulseform because the heading measured from AIS
data are integer values, and the turn rate is also an
integervalue.
3 SAFETYASSESSMENTTESTUSINGFULL‐
MISSIONTYPESHIP‐HANDLINGSIMULATOR
The manoeuvring mathematical model with
which
reproducibility of manoeuvring performance in
shallow water was verified in the previous section,
wasusedandseveraltestswereconductedtoverify
port/harbour implementation plan, and wind speed
criteriathatbecomelimitsforsafeoperation,number
of tugs, horsepower, etc. An overview of the safety
assessmenttestsconductedforLNG
carriersshownin
Table3isdiscussedhere.Thesearesafetyassessment
tests conducted with the purpose of formulating
operationalcriteriaforreceivingshipsorconstructing
berths.Theberthswere16inall:15withinJapan,and
1inAustralia.Thetestsconductedoverthepastfive
years were considered
for judgment; however,
combining berthing and sailing, the number of tests
finallyreached325.Sincestudiesaimingtodetermine
operational limits were many, the number of cases
implementedforwindspeedsbetween10m/sand15
m/s were numerous, including some cases with a
maximum wind speed of 20 m/s. Tests
were
conducted in shallow water with tidal current
between 0 to 0.5 knots, and ratio of water depth to
draft(H/d)between1.2to1.5.
Manoeuvringduringtestsusingfull‐missiontype
ship‐handlingsimulatorwastheresponsibilityofthe
pilotroutinelyperformingberthing/sailingoperations
atthe berth.The master
witnessedthe manoeuvring
404
test, and together with the pilot in charge of
manoeuvring, subjective judgements including
control margin for each manoeuvring phase were
obtained through questionnaire surveys. On an
average, about 10 masters witnessed one test. The
totaljudgementsfortheverificationtestswerebased
on assessments from over 3200 persons for each
manoeuvringphase.
Table3.Shipsforwhichtestwereconductedbyfull‐mission
typeship‐handlingsimulator
_______________________________________________
Tank Tank Loa Lpp B
2
Draft Draft Axis
4
Cap.
1
TypeLoad Ballst
3
_______________________________________________
147K
5
Moss 289m 277m4 9m 11.8m 9.4m 1
154K Moss 288m 277m 43m 11.5m 9.4m 1
155K CCM
6
288m 275m 49m 11.6m 9.5m 1
177K Moss 300m 287m 52m 11.5m 9.5m 1
170K Mem
7
291m 279m 45m 11.5m 9.7m 1
180K CCM 298m 293m 49m 11.5m 9.8m 2
217K Mem 315m 302m 50m 12.0m 9.5m 2
266K Mem 345m 332m 54m 12.0m 9.6m 2
_______________________________________________
1
Cap: Capacity
2
B: Breadth
3
Ballst:Ballast
4
Axis: NumberofPropellers
5
K:Thousand
6
CCM:ContinuousCoveredMoss
7
Mem:Membrane
Fig. 4 shows the full‐mission type ship‐handling
simulator used in the tests. Fig. 6 is the computer‐
graphicsgeneratedimageof atypicalshipsubjected
totests.
Figure4. JMS full‐mission type ship‐handling simulator
(360°‐screenwithvisibilityinthedownwarddirection)used
inthetests.
Figure5. Computer graphics‐generated image of LNG
carrier used in the manoeuvring simulation tests (217K
Membrane)
Berthing and sailing tests included manoeuvring
forapproach;thefivephasesshowninTable4were
consideredasthemanoeuvringphasesforthesurvey
questionnaire to be responded to by the masters
presentandtheshipoperators.
A five‐stage judgement was made with the
assessment divided into five judgement categories
shown in Table 5 for each of the five manoeuvring
phasesforwhichthequestionnairesurveywasgiven
to the pilots performing and the masters witnessing
themanoeuvres.
Table4.Manoeuvringphases
_______________________________________________
BerthingManoeuvre SailingManoeuvre
_______________________________________________
Course‐keepingphase Lateralshiftingphase
Course‐alteringphase Standstillturningphasere
Speed‐reducingphase Coursechangephase
Standstillturningphase Course‐keepingphase
Lateralshiftingphase
_______________________________________________
Table5 Control Margin level of subjective judgement on
manoeuvringsensedbytheshipoperatorsandthepersons
witnessingthemanoeuvres
_______________________________________________
Assessment ControlMarginlevelofsubjectivejudgement
category
_______________________________________________
5Adequatemarginremains Acceptable
4Marginexistsmarginlevel
3Allowablemarginlevel
2MargindoesnotexistUnacceptable
1Nomarginmarginlevel
_______________________________________________
4 OBJECTIVEMANOEUVRINGCRITERIAOF
SAFETYASESSMENTINSHALLOWWATER
Motion conditions of manoeuvring phases from the
simulation test results introduced in the previous
section and the responses of subjective judgement
from ship operators were analyzed. Not only
simulationtestresults,butalsointerviewswithpilots
andmasterswereconducted
duringthe15on‐board
studies introduced in “Sec. 2.2 Verification of
manoeuvring mathematical model in shallow water
byboardingandstudyingships”werealsoanalyzed.
405
Figure6.Exampleofsailingmanoeuvretrackchart
Figure7.Exampleofberthingmanoeuvretrackchart
Thecriteriaanalyzedherearebasedmainlyonthe
testresultsofLNGcarriersofoveralllengthof300m
approximately; however, the results may be applied
toothershiptypesofalmostequivalentclass.
Fig. 6 and Fig. 7 show the manoeuvring phases
and typical track charts according to the
ship‐
handlingsimulatortest.
4.1 Course‐keepingphase
Drift angle, lateral (shift) speed, deviation from
planned course may be considered as motion
conditions expressing the course‐keeping phase,
whilemainenginerpm,shipspeedandrudderangle
may be considered as control variables. Since it has
been reported that the
ease/difficulty of manoeuvre
feltby the shipoperator has a high correlation with
the drift angle, the drift angle in the slow ahead
condition(about8knotsspeedthroughthewater)is
considered the typical phase for course‐keeping
manoeuvre.
Fig. 8 shows the relationshipbetween drift angle
in the course
‐keeping phase and the subjective
judgmentoftheship operatorsfor LNGcarrier. The
subjectivejudgmenthasbeenplottedinthefigureas
theaveragevalueofabout10assessorsforeachtest.(
■ represent the results of interview related to the
degree of margin in on‐board studies of
full‐scale
ships)
As clarified in the tank test results (Table 2) in
Section 2, LNG ships show the trend of improved
course‐keeping ability in shallow water. Generally,
thewind‐receivingareaandwindeffectsarelargein
LNGcarriers; however, althoughthe course‐keeping
manoeuvring tests shown in
Fig. 8 include many
cases of wind speed exceeding 10 m/sec, there were
onlyafewassessedcasesinwhichthecontrolmargin
wassmall.
Figure8. Relationship between drift angle in the course‐
keeping phase and the subjective judgment of the ship
operatorsforLNGcarrier
From these results, it can be observed that the
averagevalueofsubjectivejudgementis2(marginis
small) when the drift angle exceeds 8 degrees. The
criterion for manoeuvrability in shallow water may
therefore be considered as acceptable within a drift
angleof8degreesintheslowaheadcondition
ofthe
mainengine.
4.2 Course‐alteringphase
Turnrateanddeviationfromplannedcoursemaybe
considered as motion conditions expressing the
course‐altering phase, while main engine rpm, ship
speedandrudderanglemaybeconsideredascontrol
variables. Among these variables, the ship operator
can sense the
rudder effect only from the turn rate.
Fig.9showstherelationshipbetweenturnrateinthe
course‐alteringphaseandthesubjectivejudgmentof
theshipoperatorsforLNGcarrier.
406
Figure9. Relationship between turn rate in the course‐
altering phase and the subjective judgment of the ship
operatorsforLNGcarrier
The subjective judgment has been plotted in the
figureastheaveragevalueofabout10assessors for
each test. At a turn rate of 5 degrees/minute, the
averagevalueofsubjectivejudgementislessthan2.5
(smallcontrolmargin).However,attheturnrateof8
degrees/minute, the average value
of subjective
judgementisgreaterthan3(acceptablemarginlevel).
The course‐altering phase mentioned here refers to
course‐altering manoeuvre using main engine and
rudderonlyofone’sownship.
4.3 Lateral‐shiftingphase
The lateral shift speed during sailing using tugboat,
etc.,istakenastheindexof
lateralshift manoeuvre.
For manoeuvring with the control target of lateral
shift speed as 10 m/sec. or less at the final stage of
berthing,itisdifficulttomakethislateralshiftspeed
the index of control margin. The method of
unberthingtoexpresscontrolmarginastheindexof
lateral
shift speed is appropriate. Fig. 10 shows the
relationship between maximum lateral shift speed
andthesubjectivejudgementvalueofcontrolmargin
in the lateral‐shift phase during unberthing. Fig. 11
showstherelationshipbetweenthelateralshiftspeed
and the subjective judgement value three minutes
afterthestartof
thelateralshift.Shipoperatorswho
performsailingmanoeuvresslowlyaremany,andso
are ship operators who feel that it may be allowed
evenif thelateralshiftspeeddoes notincreaseafter
threeminuteshaveelapsed.Finally,ifthelateralshift
speedreaches20cm/sec.,thestatewhenthe
allowable
control level is sensed can be understood. In other
words, to ensure control margin against external
forces such as wind and tidal current, provision of
tugsorthrustersmaybenecessaryifthelateralshift
speedincreasesabove20cm/sec.
Figure10. Relationship between maximum lateral shift
speedandthesubjectivejudgementvalueofcontrolmargin
Figure11.Relationshipbetweenthelateralshiftspeedand
the subjective judgement value of control margin three
minutesafterthestartofthelateralshift
4.4 Speed‐reducingphase
Fig. 12 shows the relationship between speed
reduction (knots/min.) during reduced speed
manoeuvringandsubjectivevalueofcontrolmargin.
Itcanbeobservedthatifthespeedcanbereducedby
morethan0.2knots/min.,theshipoperatorcansense
theacceptablemarginlevel.Forthesetests,
themain
engineoftheshipandtugswereusedasthespeed‐
reducingmeans.
Figure12. Relationship between the speed reduction
(knots/min.)andthesubjectivevalueofcontrolmargin
4.5 Standstill‐turningphase
Fig.13showstherelationshipbetweenturnrateand
subjective value of control margin in the standstill
turning phase using tugboat. In many of the tests
standstill turning occurred after un‐berthing, and
althoughmanytestcaseswereatwindspeedsbelow
407
15 m/sec., turning could be carried out within a
turning area of twice the overall length in all the
cases. Moreover, the turn rate was greater than 10
degrees/sec. and the subjective value of control
marginwasalsoattheacceptablelevel.
Figure13. Relationship between turn rate and subjective
valueofcontrolmargininthestandstillturningphaseusing
tugboat
5 CONCLUSIONS
Conclusionsofthisreportaresummarizedbelow.
1 The importance of verifying manoeuvring
mathematical models in shallow water was
pointed out for the safety assessment of
manoeuvring in port using ship‐handling
simulator.
2 Instances of verification of manoeuvring
mathematical models after conducting tank tests
were introduced for verifying
the manoeuvring
simulationmathematicalmodelsinshallowwater.
Measurements of motion conditions in shallow
water with full‐scale ships for fifteen times and
instancesofverificationofmathematicalmodelsof
simulatorwereintroduced.
Differing instances of manoeuvring performance
werefoundbecauseofthedifferences inL/Band
aft hull shapes
even for almost the same length
(Lpp) from the results of tank tests in shallow
water. For twin‐screw ships with the hull forms
introduced earlier, it was confirmed that when
H/d became 1.2, the tactical diameter increased
relativelyandcourse‐keepingabilityimproved.
3 Safetyassessmenttestswerecarriedout
withfull‐
mission type ship‐handling simulator using
manoeuvring mathematical model in shallow
wateronseveralLNGcarriers,thereproducibility
of which was already verified. The test cases
amountedto325.
4 Thefindingsofacceptablecriteriainshallowwater
obtained from the results of 325 cases of ship‐
handling
simulationtestsandtheresultsofmotion
conditionmeasurementsoffull‐scaleshipscarried
out 15 times are as given below. Assessment of
ship‐handlingsimulationtestswasmadefromthe
resultsassessedbyabout10mastersandpilotsper
case. Criteria have been formulated according to
theperceptions ofmore
than 3200masters, pilots
andshipoperators.
Acceptablemanoeuvringcriteria
Course‐keepingphase:
Drift angle under 8 degrees in the main engine
slowaheadcondition
Course‐alteringphase:
Turnrategreaterthan8degrees/min.inthemain
engineslowaheadcondition
Lateral‐shiftingphase:
Lateralshiftspeed
greaterthan20cm/sec.atstart
Speed‐reducingphase:
Greaterthan0.2knots/min.
Standstill‐turningphase:
Turnrategreaterthan10degrees/min.
ACKNOWLEFGMENTS
This research is a compilation of the findings of
studies and tests continuously implemented over
manyyearsbyateamconsisting oflargenumberof
staff
members led by the author in the company
presentlyemployed.
Theauthorisgratefultothecooperationgivenby
allconcernedpersonnel.
Theauthorwouldlike toexpresshisgratitude to
concernedstaffmembersandotherrelatedpersonnel.
REFERENCES
Andres, C. H. 2008. Manoeuvring Committee Report &
Recommendations International Towing Tank Conference,
Fukuoka
Eloot,K.Delefortrie,G.Vantorre,M.&Quadvlieg,F.2015.
Validation of ship manoeuvring in shallow water
throughfree‐runningtestsProceedingsof34
th
International
ConferenceonOcean,OffshoreandArcticEngineering
Nakamura,S.,FukuoY.&Hara,K.1989.Evaluationofthe
Difficulty of berthing Manoeuvre by Fuzzy Regression
Analysis, The Journal of Japan Institute of Navigation,
No.82,pp25‐31
Quadvlieg, F.H.H.A. & Coevorden, P. van. 2003.
Manoeuvring criteria: more than IMO A751
requirementsalone!.MARSIMInternationalconferenceon
marinesimulationandshipmanoeuvrability.
