367
1 INTRODUCTION
Many merchant ships moored at their berths were
severely damaged by the tsunami that hit
northeastern Japan following the March 11, 2011
earthquake.
Ingeneral,whenatsunami advisoryor warning
isissued,ashipmasterneedspreciseinformationto
decide whether to take countermeasures with the
shipmooredorto ta
kethe shipout oftheport and
then evacuate it. If evacuation is decided, it is
necessary to conduct unberthing without the
assistanceoftug‐boatsandlinehandlers.
We studied emergency unberthing without tug
assistance using numerical simulations with a
mathematical modeling group (MMG)‐type
mathematicalmodelandconductedfull‐missionship
maneuveringsimulator(SMS)experiments.
2 EXPERIMENTS
2.1 Unberthingsh
iphandlingwithouttugassistance
The test ships were a panama‐class medium‐sized
oceangoingmerchantshipanda6,000unitpurecar
carrier (PCC). For mooring conditions, we assumed
bow‐in port‐side mooring conditions because this
mooring‐type is common in most Japanese ports;
however, unberthing from thi
s mooring‐type is
difficultcomparedwiththatfromstern‐inmooring.
The unberthing of panamax class oceangoing
merchant ships is typically performed with tug
assistance; however, there are few reports on
unberthingof the aboveship‐typethat useonly the
ship’sengineandrudder,orbowthruster.Therefore,
weadop
tedthebackingunberthingmethodfromthe
bow‐in port‐side mooring, whichis widely usedby
smallmerchantships,inourexperiments.
Emergency Unberthing without Tug Assistance
Y.Kunieda,H.Yabuki,&T.Okazaki
TokyoUniversityofMarineScienceandTechnology,Tokyo,Japan
ABSTRACT:Shipmastersmayhavetoperformunberthingwithouttugboatassistancewhenatsunamiwarning
is issued. Keeping this in mind, we studied emergency unberthing without tug assistance by conducting
numerical simulations and full‐mission ship maneuvering simulator (SMS) experiments. A panamax class
medium‐sizedbulkerandapurecarcarrier(PCC)wereusedastestships.Intheexperiments,weest
ablished
thelimitationsofbasicshiphandlingtechniquessuchassternkickout,backing,andacceleratingturninwindy
conditionsusingamathematicalmodelinggroup(MMG)‐typemathematicalmaneuveringmodel.Onthebasis
oftheresults,weproducedashiphandlingscenarioandevaluateditusingSMSexperiments.Weconcluded
tha
tunberthingwithouttugassistancein5m/sonshorewindsispossible.Furthermore,theuseofthrusterscan
greatlyreducethetimerequiredforunberthing.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 9
Number 3
September 2015
DOI:10.12716/1001.09.03.09
368
2.2 Experimentalprocedure
The experiments were conducted according to the
procedurepresentedinFigure1.
First,wespecifiedtheshiptypeandtheberthing
and mooring conditions. We then decided the
shiphandlingprocedurebyconsideringshiphandling
waterconditionssuchasfairwayandturningbasin.
Forthewinddirection,weassumed
onshorewinds,
which make shiphandling difficult. Next, we
estimatedthelimitationsofbasicshiphandling,such
assternkickout,backing,acceleratingturnfromthe
sternway,andturningonthespot,usingtheMMG‐
typemathematicalmaneuveringmodel.
On the basis of the results, we produced a
shiphandling plan (scenario)and
evaluated it using
SMSexperiments.
Figure1.Experimentalprocedure
2.3 Shipmotionmodel
Wesimulatedtheshipmaneuveringmotionusingan
MMG‐type mathematical model (Kijima 1990). The
coordinate system is shown in Figure 2. The state
values were the ship’s position, heading, surge
speed,swayspeed,andyawrate.Thecontrolvalues
wererudderangleorder,propellerrevolutionorder,
andthrustorderofthesidethruster.
Figure2.Coordinatesystem
The equations for surge, sway, and yaw motion
are,
()()
x
yHPRW
mmu mmvr X X X X
(1)
()()
yxHRSW
mmv mmurY Y Y Y
(2)
()
Z
ZZZ H R S W
I
JrN NNN
(3)
where
m is the mass,
x
m
and
y
m
are the added
mass,
z
z
I
is the turning moment inertia, and
zz
J
istheaddedmomentofinertia.XandYrepresentthe
hydro‐dynamicforcesandNrepresentsthemoment.
Subscripts
H
,
P
,
R
,
S
and
W
denote the
hydrodynamic force induced by the hull, propeller,
rudder,sidethrusterandwindrespectively.
Wepredicteachofthehydrodynamicforcesusing
thefollowingmethods.
Added mass, moment of inertia: Motora’s chart
(Motora1959)
Hull: Kijima’s method (Kijima 1990), Hirano’s
method(Hirano1981)
Propeller:Yoshimura’smethod
(Yoshimura1995)
Rudder:Yoshimura’smethod(Yoshimura1978)
Bowthruster:Fujino’smethod(Fujino1978)
Wind:Yamano’smethod(Yamano1997)
3 RESULTS
3.1 Panamaxbulker
3.1.1 Testship featuresandshiphandlingcircumstances
Table 1 lists the principal characteristics of the
54,000DWTPanamaxbulker.
Weassumedthattheshipis
mooredbow‐inport‐
side to berth A at the K Port in Tokyo Bay. In the
experiments, starboard onshore winds without tide
effectswereassumed.
Specification
Shiptype,BerthingandMooring
conditions
Shiphandlingwaterconditions
Turningbasin,fairway
Roughshiphandling procedure
Estimationofthelimitationsofthebasic
shiphandlingtechniques
Shiphandlingplan
ValidationusingSMSexperiments
369
Table1.Principalfeatures(bulker)
_______________________________________________
Hull
_______________________________________________
G.T.(ton)43,000
LOA(m)209.00
Lpp(m)204.00
B(m)32.20
Cb0.8
Draft(forem)9.50
Draft(aftm)10.50
Trim(m)1.0B/S
Displacement(ton)52,931
Sailarea(transversem2)730
Sailarea(verticalm2)4490
_______________________________________________
Mainengine
_______________________________________________
MCO(kW)9,700
_______________________________________________
Rudder
_______________________________________________
Height(m)8.100
Breadth(m)4.600
Area(m2)37.260
AspectRatio1.7609
_______________________________________________
Propeller
_______________________________________________
Blade4
Dia.(Dpm)5.600
Pitchratioat0.7R0.702
_______________________________________________
3.1.2 Shiph andlingprocedureandlimitations
1 Shiphandlingprocedureandtechniques
The following undocking procedure was
conducted.
1 After heaving on the starboard‐side headline,
all shore lines except the head line and
forwardspringwereletgo.
2 The stern to starboard was kicked out by at
least two points
by heaving on the head line
while holding the spring and kicking the
engineaheadwiththerudderhardtoport.
3 Theshipwasbacked1L(L;Lpp)offtheberth
withtheenginedeadsloworslowasternand
the rudder hard to starboard. The sternway
was maintained
at approximately 2 knots for
backing.
4 An accelerating turn or turning on the spot
was made to keep the ship’s position at
approximately1Lfromtheberthandtheship
then proceeded toward the port entrance by
acceleratingimmediately.
Prior to the SMS experiment, it is necessary to
examine the
limitations of shiphandling techniques
such as stern kick out, backing, accelerating turn
fromthesternway,andturningonthespot.
2 Shiphandlinglimitations
Weestimatedthelimitationsofeachshiphandling
technique when the test ship is affected by 5, 8,
and10m/sonshorewindsusingthemathematical
maneuveringmodel.
1 Sternkickout
Figure 3 presentsthe stern kickout angle for
each wind velocity as a function of time. A
positivevalueoftheangleimpliesarightturn.
Thetestshiprequired3minfor2pointskick
outevenincalmconditionsandmoretimefor
the
kick out maneuver under windy
conditions. The calculation results suggest
that, although the stern kick out seems to be
possible even in the 10 m/s onshore wind,
substantialamountoftimewillbeneededfor
thismaneuver.
2 Backingfromtheberth
Figure 4 presents the estimated trajectories
whenthe
testshipbackswiththeenginedead
slowasternand the rudder hardto starboard
afterthesternkickoutmaneuver.InFigure4,
theunitsintheX‐andY‐axisareLpp.In5m/s
onshore winds, it was possible to back as
assumed. However, as winds increased to
8
m/s,thetestshipdrifted leeward at the early
stageofbackingwhenthesternwaywasslow.
Figure3.Timerelationofthesternkickoutangle(Bulker)
Figure4. Bulker’s trajectories of backing with the rudder
hardtostarboard
Figure5.Bulker’strajectoriesforacceleratingturn
370
Therefore, backing by the engine astern and the
rudder hard to starboard is difficult with 8 m/s
onshore wind. In addition, the leeward drift
increaseswhenthesternwayturnisslow.
1 Acceleratingturn
Figure 5 presents the trajectories when the test
ship accelerated windward to leeward. It seems
that
theturningmaneuverispossiblewith10m/s
winds.Duringtheleewardturningmaneuver,the
stronger the wind force is, the greater the drift
becomesafterturning90°.Thus,itisnecessaryto
make this turning maneuver in the direction of
thewind.
2 Turningonthespot
We examined
the turning‐on‐the‐spot maneuver
under windy conditions using the shiphandling
simulator. Figure 6 presents the trajectory when
thetestshipmadetheabovementionedsternway
maneuver at 2 knots in 8 m/s winds. As the
turning circle diameter is 1.8L and the turning
timeis18min,weinferthat
theturningmaneuver
canbeperformedin8m/swinds.
3.1.3 ResultsoftheSMSexperiments
Figure 7 presents the ship trajectory under calm
conditions. Both the trajectories of the center of
gravity and the ship’s shape at 3 min intervals are
displayed. The units of the X‐ and Y‐
axis are Lpp.
Figure 8 presents the time relation of the engine
operation and speed. In this case, although a
shiphandling procedure same as that described in
3.1.2 was conducted, the whole procedure took 27
min,probably,becauseoftheleftturning‐on‐the‐spot
andthelow‐poweroperationof
themainengine.
Figure6.Bulker’strajectoriesofturningonthespot
Figure7. Trajectory of the unberthing bulker in calm
conditions
The ship’s trajectory and time relation of the
engineoperationandspeedin5m/sonshorewinds
are presented in Figures 9 and 10, respectively. In
thiscase,thesternkickoutmaneuverwascompleted
within almost the same time as that in calm
conditions by applying rather strong ahead engine
motion.
Figure8. Time history of engine operation and speed in
calmconditions
Figure9. Trajectory of the unberthing bulker in 5 m/s
onshorewind
371
Figure10. Time history of engine operation and speed in
5m/sonshorewinds
Theshipcompletedtheturningonthespotinthe
directionofthewindinapproximately15minusing
rather strong engine operations, and the total
maneuvering time was approximately 27 min.
Although the test ship drifted leeward during
backing,theshipwasabletoproceedwindwardwith
thefullahead
engine.
3.1.4 Evaluationoftheshiphandlingmethod
From the results obtained by establishing the
shiphandling limitations and SMS experiments, we
consider that this ship‐type can unberth within a
relativelyshorttimewithouttugassistancein5m/s
onshorewinds.
When unberthing, it is necessary to mind the
following.
1
During the stern kick out maneuver, do not
slacken both the head line and forward spring,
anddo notapplyexcessivetensionto the spring
by properly operating the main engine. A
substantialamountoftimewillbeneededforthe
stern kick out maneuver when the beam wind
blowsto
theberth.
2 During the backing maneuver, back the ship as
soonaspossibleusingratherstrongasternengine
motions. It is recommended to keep the ship
sternwaywithin2knots.Notethattheresponseof
the bulker to the engine operation is relatively
slowduringacceleratingordecelerating.
3
Turningonthespotshouldbeinthedirectionof
thewindandtheship’sheadshouldbeturnedas
soonaspossibleusingratherstrongasternengine
motion.Itisrecommendedtokeepbothheadway
andsternway atamaximumof2knots. When a
shipdriftsleewardduringthe
turningmaneuver,
it quickly proceeds windward using the ahead
engineandtherudder.
3.2 6,000unitPCC
3.2.1 Testship characteristicsandshiphandling
circumstances
Table 2 lists the characteristics of the 6,000 unit
PCCwithabowthruster.
Table2.PCCcharacteristics
_______________________________________________
Hull
_______________________________________________
G.T.(ton)57,623
LOA(m)198.00
Lpp(m)190.00
B(m)32.26
Cb0.57637
Draft(forem)8.50
Draft(aftm)8.50
Trim(m)Nil
Displacement(ton)30,029
Sailarea(transversem2)1,224.26
Sailarea(verticalm2)4,554.69
_______________________________________________
Mainengine
_______________________________________________
MCO(kW)13,500
_______________________________________________
Rudder
_______________________________________________
Height(m)8.050
Breadth(m)4.900
Area(m2)39.445
Aspectratio1.6429
_______________________________________________
Propeller
_______________________________________________
Blade5
Dia.(Dpm)6.500
Pitchratioat0.7R0.925
_______________________________________________
Bowthruster
_______________________________________________
Thrust(ton)17.8
_______________________________________________
Weassumedthattheshipismooredbow‐instar‐
boardsidetoberthOatYPortinTokyoBay.Inthe
experiments,portonshorewindswithouttideeffects
were assumed. We examined the effect of the bow
thrusteronunberthingmaneuversbycomparingthe
handlingofashipwith
athrusterandthatwithouta
thruster.
3.2.2 Shiph andlingprocedureandlimitations
1 Shiphandling procedure and basic shiphandling
techniques
Wefollowedthefollowingunberthingprocedure.
1 Afterpreparingheavingontheport‐sidehead
line,allshorelinesexcepttheheadlineandthe
forwardspringwereletgo.
2
The stern to port was kicked out by at least
twopointsbyheavingontheheadlinewhile
holding the spring; the engine was kicked
ahead with the rudder hard to starboard. A
shipwithabowthrusterusesittostarboardto
hold her bow at a fixed position
by pressing
theship’sstarboardbowagainstthefender.
3 Theshipwasbacked1L(L;Lpp)offtheberth
withtheenginedeadsloworslowasternand
the rudder hard to port. The sternway was
maintained at approximately 2 knots during
backing.
4 Astherewassufficientspace
forturningonthe
port‐side of the ship, the ship completed an
accelerating turn, keeping her position
approximately 1L off from the berth, and
proceedingtowardtheportentrance.Theship
with a bow thruster can use it for assistance
during an accelerating turn. In this case, it is
necessary
to examine the limitations of the
followingmaneuverpriortoSMSexperiment:
stern kick out, backing, and accelerating turn
fromthesternway.
372
2 Shiphandlinglimitations
We estimated the shiphandling limitations for
each basic shiphandling technique when the test
shipexperiences5, 8, and 10 m/s onshorewinds
using the mathematical maneuvering model.We
performed the simulation calculations without a
bowthruster.
3 Sternkickout
Figure 11 presents the time relation of
the stern
kickoutangleforeachwindvelocity.Asthetime
required for stern kick out was approximately 2
minincalmconditionsand3minin10m/sport
onshore wind, we considered that the stern kick
out of PCC was easier than that of a bulker.
Therefore,
the stern kick out in relatively strong
onshorewinds wasfeasible withPCC,because a
PCC can produce strong kick ahead power with
thepropellerasitwasequippedwitha stronger
engine and a propeller larger than a bulker. In
addition, the PCC’s right‐hand turning moment,
which assists the
ship’s right turning, was
generated by the left beam wind, as shown in
Figure12.
Figure11.Timerelationofthesternkickoutangle(PCC)
Figure12. Coefficient of the yawing moment caused by
wind
Figure13.PCCtrajectoriesofbackingwiththerudderhard
port
Figure14.PCCtrajectoriesduringtheacceleratingturn
1 Backingfromtheberth
Figure13presentstheestimatedtrajectorieswhen
thetestshipbacks withenginedead slowastern
and the rudder hard to starboard after the stern
kickoutmaneuver;theunitsoftheX‐andY‐axis
areLpp.Itispossibletobackwith5m/s
onshore
winds;nonetheless,whenthewindincreasesto8
m/s,thetestshipdriftsleewardattheearlystage
ofbackingforslowsternway.Inthecaseof10m/s
left beam wind, the test ship strongly drifts
leeward and backing seems difficult using only
theengineandrudder.
2
Acceleratingturn
Figure 14 presents the trajectories when the test
ship made an accelerating turn windward at 2
knots of the sternway. A PCC can make an
accelerating turn in 10 m/s winds, but it is
necessary to conduct this maneuver in the
directionofthewind.
3.2.3 ResultsofSMS
experiments
Figure15 presents the shiptrajectoryandFigure
16 presents the engine operation and speed in the
experiment vs time under calm conditions. In this
case, the left accelerating turn is in the direction of
theberthbecausethereisnowindeffectonthehull.
The trajectory of
the test ship is similar to the
predictions in 3.2.2, and the ship completes the
unberthing maneuver as planned. In general, the
headwayofPCCsisstrongeveniftheengineisdead
373
slow ahead; therefore, it is necessary not to
excessivelystrainthespringduringthesternkickout
maneuverbyproperlyoperatingtheengineastern,as
showninFigure16.
Figure 17 shows the ship’s trajectory in the
experiment using only the engine and rudder in 5
m/s on‐shore winds.
The test ship completed the
unberthing maneuver in approximately 27 min
accordingtothescenario,andthetotalmaneuvering
time was 3 min longer than that of the experiment
under calm conditions. This is attributed to the
longer time required to complete the sternkick out
andacceleratingturnmaneuver
whenthebeamwind
isblowinginthedirectionoftheberth.
Figure18presentstheship’strajectoryandFigure
19 presents the time relation of the bow thruster
operation and heading in the experiment using the
PCCwithabowthrusterunder5m/sonshorewinds.
Inthiscase,the
totalmaneuveringtimewas21min.
Using the bow thruster for the stern kick out and
headingcontrolduringbackingandtheaccelerating
turn,thetestshipunberthedinarelativelyshorttime
compared with that without a thruster. Figure 20
presentsthesameunberthingmaneuverin8m/son‐
shore winds. Even through the onshore wind is
relatively strong, the ship completed unberthing
within22min.Fromtheaboveresults,weinferthat
theuseofabowthrusterforunberthingunderwindy
conditionsisveryeffective.
Figure15.PCCtrajectoryofunberthingincalmconditions
Figure16. Time history of engine operation and speed in
calmconditions
Figure17. Trajectory of unberthing PCC in 5 m/s onshore
wind
Figure19.TrajectoryoftheunberthingPCCusingthebow
thrusterin5m/sonshorewinds
Figure19.Bowthrusteroperation and headingvstime in
5m/sonshorewinds
374
Figure20.TrajectoryoftheunberthingPCCusingthebow
thrusterin8m/sonshorewinds
3.2.4 Evaluationofshiphandlingmethod
From the shiphandling limitations and SMS
experiments, we infer that ships of this type can
complete unberthing within a relatively short time
withouttugassistancein5m/sonshorewinds.When
theshipusesabowthruster,unberthingwithouttug
assistance is possible in relatively shorter
time in 8
m/sonshorewinds.
It is necessary to consider the following during
unberthingmaneuvers.
1 Duringthesternkickoutmaneuver,astheengine
output of PCC is relatively strong, the astern
propulsion should be appropriately used so that
excessive tension will not be applied to the
forward
spring.Asforshipswithabowthruster,
we recommend that the bows should be pressed
againstthefenderusingathruster.
2 Duringbackingunderwindyconditions,heading
controlusingabowthrusteriseffective.
3 Wind strongly affects this ship‐type; thus,
backing, accelerating turn, and turning on the
spot will have to be performed at slow speeds.
Therefore,itisnecessarytomindthedriftduring
theabovementionedmaneuvers.
4 SUMMARY
We studied emergency unberthing without tug
assistance using numerical simulations and SMS
experiments for emergency evacuation outside the
harbor because of a tsunami advisory or warning.
We
obtainedthefollowingresults.
1 Thebackingunberthingmethodfromthebow‐in
portside mooring commonlyconducted bysmall
merchantships can be usedtounberth panamax
class oceangoing merchant ships without tug
assistance.
2 It is possible to unberth using the ship’s engine
andrudderintheabovementionedmaneuver
in5
m/son‐shorewinds.
3 Ships can control their heading during backing
and easily turn using a bow thruster, thus
reducing the time required for shiphandling in
windyconditions.Unberthingofshipswithabow
thrusterwithouttugassistancemaybepossiblein
8m/sonshorewinds.
4 During
the stern kick out maneuver, it is
important not to slacken both the head line and
the forward spring. In addition, no excessive
tensionmustbeappliedtothespringbyproperly
controlling the ship’s headway using stop or
asternpropulsion.
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