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1
MooringSystemIntegrity
InExposedLocations
AndNarrowChannels
JohnFlory,TTILLC
SteveBenfield,
TTI
Ltd.
Presentedat
3rd ASME/USCG
Workshop
OnMarineTechnologyandStandards
July,2013
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Introduction
TensionTechnologyInternational
Largervesselsarenowbeingmooredatterminals
exposedtohighwaves
andsubjectedtopassingshipforces.
Thistalk
discusses
someoftheproblems
and
someofthesolutions.
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Introduction
TensionTechnologyInternational
FiveTopicswillbediscussed:
WaveInduced
Vessel
Motions
and
Tails
HighPerformanceFiberRopeMooringLines
LowFriction,
Low
Abrasion
Fairlead
Liners
PassingShipSituations
MooringArrangementComputerAnalysis
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4MooringSystemIntegrity
WaveInducedVesselMotions
TensionTechnologyInternational
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WaveInducedVesselMotions
Ajettylocatedoffshore,exposedtowavesandswell
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WaveInducedVesselMotionsandTails
Syntheticfiberropetailsareemployed
ontheendsofmooringlines
toreduce
wave
motion
induced
forces.
11m(36ft)longnylontailsweresuggestedby
theOil
Companys
International
Marine
Forum
(OCIMF)MooringEquipmentGuidelines(MEG).
Thissuggestion
was
taken
as
obligatory
by
manyterminalsandports.
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WaveInducedVesselMotionsandTails
Onvessels
moored
in
high
waves,
using
short
nylontailsonwireandHMPEmooringlines,
themooringlinesandthetailswerefailing
duetohightensions.
ATTIstudyrecommendedtheuseoflonger
tails,either
polyester
or
nylon.
ThenewMEG3rd editionnowstates
Longer tails may be required
for exposed berths
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WaveInducedVesselMotionsandTails
Polyesterropes
are
much
more
durable
than
nylonropesinwetcondition.
Butpolyester
tails
are
also
stiffer.
Longerpolyestertailscanprovidethesame
stretchcharacteristics
as
short
nylon
tails.
Newlyintroducednylonropedesigns
have
good
durability
and
may
be
preferred.
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Polyestertail
replaced
by
nylon
tail
at
about
0700
hrs.
TensionTechnologyInternational MooringSystemIntegrity
WaveInducedVesselMotionsandTails
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HighPerformanceFiberRopeMooringLines
HighPerformance
Fibers
are
usually
called
HighModulus,buttheyarealsostronger.
Theyinclude:
Aramid (Kevlar*, Twaron*, Technora*)
HMPE(HighModulusPolyethylene)
(Spectra*, Dyneema*)
LCAP(LiquidCrystalAromaticPolyester)
(Vectran*)* Trademarks
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HighPerformanceFiberRopeMooringLines
Highperformance
fiber
rope
has
about
the
samestrengthaswireropeofthesamesize.
Ithas
more
than
twice
the
stretch
of
wire
rope.
Itweighsmuchlessandismuchmoreflexible.
Itdoes
not
have
protruding
broken
wires.
Itismucheasierandsafertohandle.
Itcan
be
handled
by
fewer
people.
Itreducesaccidentsandinjuries.
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HighPerformanceFiberRopeMooringLines
Becausehigh
performance
fiber
rope
hasmorestretchthanwire,
itsusereducespeakmooringloads.
Butthisalsoincreasesmotionthroughfairlead.
Fiber
rope
is
also
more
vulnerable
toabrasiondamageonthefairlead.
Alowfriction,lowabrasionnylon
fairleadlinerhasbeendeveloped
tosolvethisproblem
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WaveInducedVesselMotions
Fiberropemooringlinewearingonsteelfairlead.
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NylonFairleadLiner
TTIdeveloped
anylon
fairlead
liner
to
overcometheproblemoffairleadabrasion.
TTIhad
been
successfully
used
the
nylon
materialtoeliminateabrasionproblems
inoffshore
netting
systems.
TTIthenconductedropeabrasiontests
over
new
and
corroded
steel
fairleadsandoverthenylonmaterial.
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ResidualStrength
After
1500
cycles
between
10
and
30%
of
new
strength.
NylonFairleadLiner
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NylonFairleadLiner
Thenylon
fairlead
liner
is
molded
in
two
parts
whichcanbefittedinexistingfairleadsonships.
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NylonFairleadLiner
Thelowfriction,lowabrasionnylon
fairleadlinerinstalledonboardaship.
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PassingShipProblems
Therisk
of
passing
ship
problems
increases
aslargershipsenterintoand
mooralongside
confined
channels.
Paststudiesofpassingshipforcesmodeled
onlythe
open
water
case.
TTIandCoastal&HarborEngineering
have
now
conducted
computer
modelingofalongsidequayandconfinedchannelcases.
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PassingShipinNarrowChannel
FXmax FYmax MXYmax
OpenWater 59t 363t 57tm
Narrow Channel 452t 140t 18tm
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PassingShipProblems
Comparedto
the
open
water
case:
Surgeforcesessentiallydouble
alongsideasolid
quay
wall.
Surgeforcesagainessentiallydouble
alongsideaquay
wall
in
anarrow
channel,
Resultinginessentiallyquadruplingof
surgeforces
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MooringArrangementComputerAnalysis
Theeffects
of
waves
and
passing
ships
can
be
determinedbydynamiccomputeranalysis.
OCIMFand
SITTGO
mooring
guidelines
nowrecommendcomputeranalysisof
tankerand
gas
carrier
terminal.
Somegascarrierterminalsnowrequirethat
each
vessels
mooring
arrangement
be
vettedbycomputeranalysis.