531
1 INTRODUCTION
High speed vessels are primarily designed for short
distance services as public transport of passengers
and vehicles. The range of high speed, according to
the Code of high‐speed vessels begins at 20 knots,
which depends on the cruise speed you desire for
yourvessel;youwillhavetousethemosta
ppropriate
typeofpropellant.
In general in the past 20 years they have been
building high‐speed vessels with speeds above 33
Improving the Efficiency of a High Speed Catamaran
Through the Replacement of the Propulsion System
G.deMelo&I.Echevarrieta
PolytechnicUniversityofCatalonia,Barcelona,Spain
J
.M.Serra
TRASMAPI,ThecnicalManager,Ibiza,Spain
ABSTRACT:Thehighspeedvesselsareprimarilydesignedforshortdistancesservicesaspublictransportof
passengersand vehicles.The rangeof highspeed, accordingto theCode ofhigh‐speed vesselsbegins at20
knots,whichdependsonthecruisespeedyoudesireforyourvessel;youwillhavetousethemosta
ppropriate
typeofpropellant.
Ingeneral,inthepast20years,theyhavebeenbuildinghigh‐speedvesselswithspeeds above33knots,which
meantinstallingwaterjetpropellantscoupledtopowerfulenginesandthereforeofhighconsumptionoffuel,
increasingoperatingcostsandcausingincreasedairpollut
ion.
Althoughthepricesoffuelhavebeenreducedtohalf,duetothesharpfallinoil prices,theconsumptionof
fuelandtheairpollutionremainshighatthesespeedsandpowersused,inadditiontothatthereduction
ofthetimespentoneachtri
pisnotexcessive,mainlyinshortroutesthatarelessthananhour.
Thisarticleisaboutadaptingashipofhigh‐speedservice,withamaximumspeedintestsof34knotsandto
reduceitsoperatingcosts(fuel,maintenance,etc.)andmakeiteconomicallyviable;beforethetra
nsformation,
thisvesselwasoperatingwithaservicespeedof22knots,andwithaconsumptionpermileof135littersof
MGO.
Thetransformationprocesshasconsistedby:
– Replacementofthetwooriginalwaterjetwithfourshaftlineswithfixpitchpropeller.
– Replacement of thetwooriginalma
in engines (2x6500 kW = 13000 kW) by four engines (4x1380kW=
5.520kW).
– Changingtheunderwaterhullshapetofitthenewpropellersandmaximizeitsefficiency.
– Relocationofauxiliaryengines,toachievethemostefficienttrim.
– Installationoftwolateralpropellerstoimprovemaneuverabilit
yandshortenthetotaltimeofjourney.
Afterthereformandthereturntoserviceofthevesselwithaservicespeedofover22knots,ithasbeenverified
thattheconsumptionpermileisof45littersMGO,representingareductionof65%ofconsumptionandeven
morereductionofemissionsasthenewenginescomplywiththelat
estregulations.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 9
Number 4
December 2015
DOI:10.12716/1001.09.04.09
532
knots, which meant installing water jet propellants
coupled to powerful engines and therefore of high
consumption,increasingoperatingcostsandcausing
increasedairpollution.
Althoughthepricesoffuelhavebeenreducedto
half, due to the sharp fall in oil prices, the
consumptionoffuelandtheairpollution
remains
highatthesespeedsandpowersused,inadditionto
thatthereductionofthetimespentoneachtripisnot
excessive,mainlyinshortroutesthatarelessthanan
hour.
2 TRANSFORMATIONREQUIREMENTS
Trasmapi is a shipping company that has dedicated
morethanthirtyyearsto
thetransportofpassengers
between the islands of Ibiza and Formentera, with
high‐speed vessels. In 2013 it was decided to
incorporate to the service the transport of vehicles
thatiswhentheprocessoffindinga unitthat could
satisfytherequirementsbegan:
The journey between Ibiza and La
Savina (11
nauticalmiles)shouldbedoneinlessthan30min.
Thereforetheserviceofspeedwouldhavetobe22
knots.
Thefuelconsumptionshouldbelessthan50lper
milenavigatedandoperationshouldberespectful
withtheenvironment.
Thenavigabilityandmaneuverabilityskills
should
beappropriatetotheroute.
The High Speed Vessel Castaví Jet was found
togetherwithhertwin(hulls54and55)inthesecond
hand market,they were built in the shipyard
Austal Ships Pty Ltd in 1997. It was an aluminum
catamaran used for the transport of passenger and
vehicles.
These catamarans were purchased by the
municipal transport company Istanbul (IDO) and
operatedacrosstheSeaofMarmara,untiltheincrease
offuelmadetheoperationnotviableeconomically.
The original propulsive system consisted in two
diesel engines MTU 20V 1163 TB73L with a total
power capacity of 13,000
kW actuating through two
waterjet,withwhichtheyobtainedamaximumspeed
intestsof34knots,onthecommercialroutebetween
Yenikapi (Istambul) and Yolava it operated at a
servicespeedof22to23knots,wellbelowthedesign,
yet fuel consumption was excessive, as well as the
power
used, operating below 80% MCR, makes the
consumptionincreasessubstantially.
Figure1.Imageofthecatamaranstakenduringtheseatrial
doneinAustralia
3 ANALYSISANDSTUDYOFTHENEW
PROPULSIVESYSTEM
After a detailed technical study we came to the
conclusionthat thewayto meetthe requirementsof
theshippingcompanyTRASMAPIwastopurchase
thehigh‐speedvesseltypeCastavíJetandmakeitgo
throughatransformationthatbasicallyconsists
in:
Table1.PropulsionChange
_______________________________________________
ItemCurrentProposed
_______________________________________________
MainEngines2xMTU20V 4xMitsubishiS16R
1163engines MPTK
Gearbox 2xReintjes 4xZF5355
VLJ4431
Meansof 2xKaMeWa 4xFixedPitchpropeller
Propulsion 125SIIwaterjets 4xspaderudder
andsteering
_______________________________________________
The proposed conversion will be archived by
addressingthefollowingareas:
1 WeightAnalysis
2 Hullformdevelopment
3 Shaftlinearrangement
4 Regulatoryimpacts
Otheraspectsofthereconfigurationinvolve:
Removal of the existing ride control forward T‐
Foils,
Relocation of Auxiliary engines (generating sets)
fromauxiliaryengine
roomtomainengineroom
Addition of tunnel side thruster into the ride
controlroomofeachhull.
Replacement of the two original water jet with
fourshaftlineswithfixpitchpropeller.
Replacementofthetwooriginalmainengines(2x
6500 kW = 13000 kW)
with four engines (4 x
1380kW=5.520kW).
Changingtheunderwaterhullshapetofitthenew
propellersandmaximizeitsefficiency.
Relocation of auxiliary engines, to achieve the
mostefficienttrim.
Installation of two lateral propellers to improve
maneuverability and shorten the total time of
journey.
TheextensiveexperienceofTRASMAPI’stechnical
director and the people who design high‐speed
vessels have been the main basis for the creation of
thisreformproject.Thefactthattwinboatscouldbe
operated, as it occurs with the Fjellstrand 38.8
catamarans,equipped withwater jetpropulsion and
fix
pitchpropeller,hasallowedustogatherfirst‐hand
informationto beable todetermine the efficiencyof
the different propulsion systems in directly
comparablemodelsandatfull‐scale.
After studying the different propulsion systems,
the most effective for the new service speed of 22
knotswasshownwithfull
submergedpropellerswith
free actuation. For this reason it was decided to
replacetheoriginaljetpropulsionpropellerwiththe
conventionalformat.
533
Figure2. Image 3Dmodel of thecatamaran hullswith the
newpropulsiveandsteering.
Bymodifyingthepropulsionsysteminvestigations
havebeenmadetoimprovetheshipʹshull,soastudy
hasbeendonetocomparethenewhullwiththeold
one.Tominimizethehullresistance,itwasdecidedto
extendit to3600 mm,increasing thefloating length.
Asthereis
noneedtoprotecttheoriginalwaterjets,
whicharechangedbythenewsystemofconventional
propellers, it is possible the extension of the hull to
the transom (FR 50), this modification provides a
reductioninthehullresistanceof4,6%.
Figure3.Hullextensioncomparison
In the new aft blocks, the shaft brackets and the
steering system have been installed, this allows to
simplify the changing process, and that can be
developedinamodularway.In ordertoreduce the
maximum the hull resistance it is decided to install
singlearmsbracketsandsuspendedrudders.
According to calculations performed and
accordingtothe graphofFigure3, itwas estimated
that the propellers should provide approximately
350kN,tomakethefirstapproachtothe propellers,
twoalternativeswereevaluated:
Install two propellers, one in each hull, was the
most efficient solution. But this
option was
discarded,thesizeandtheweightofthepropeller
can generate excessive level of vibrations and
noise decreasing the comfort of passengers, and
increasingtheloadsoverthealuminumstructure.
And the hull depth was close to the maximum
depthintheroute.
Finally,fourpropellerswasinstalled,
twoineach
hull. Even it is not the optimal solution, is a
workableoptionand the numerical modelsshow
thatcomplywiththeprojectspecifications.
To calculate required power a conservative
propulsiveefficiencyof60%whichencompassesboth
propellerandmechanicallossesisuseduntilfurther
information is available
from the propeller
manufacturer.
Knowingthebrakepowerdelivered,theresistance
isinterpolatedtoobtainaspeedusingthefollowing
equation
Power(kW)=Resistance(kN)xVelocity(m/s)
ThenewmainpropulsionenginestobeMitsubishi
S16R‐MPTK producing 1380 kW at 1650 rpm to
archive the vessel speed requested
of 22 knots, four
offengineswillrequiredtodeliversufficientpower.
For full load condition a vessel speed of 22, 39
knotsispredictedat100%MCR(5520kW)inseastate
0atleveltrim.
Thefollowing appendageshavebeenincludedin
calculationoftotalresistance:
4
offrudder
4offshaft
4offshaftsupportbracketswithstrutboss
2offbowthruster
Figure4.Image3Dmodelofthe propulsive system layout
andsteering.
By installing two propellers per hull special
attention is required so no undesirable interactions
occur between them, decreasing their performance
and generating unwanted effects like noise or
vibrations.Itisdeterminedthattheoptimaldiameter
foreachpropelleris1575mmandtheminimumshaft
separationhastobeof2200
mm.
Asitisavesseldesignedtohaveasinglepropeller
perhull,theproblemthatarisesisthatthetwomotors
donotfitintheengineroomwithaseparationof2200
mm between crankshafts. In order to accommodate
theenginesisdecidedtoreducethedistance
between
themin 300mm by usinga driveshaftbetween the
gearboxandthemainengine.
Figure5.Originalgeneralarrangement
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Figure6.Finalgeneralarrangement
4 RESULTSOBTAINEDWITHTHE
TRANSFORMATION
The new propulsive system ( four fixed pitch
propellers ) two per hull, combined with the four
rudders and the side thrusters, gives the boat a
remarkable maneuverability, allowing it to perform
the docking and undocking maneuvers safely in
conditions with adverse weather, achieving that the
operation is done in a reduced ti
me. Keep in mind
thattheshipcancarryoutdailyabout20maneuvers
innarrowdocks,withcongestedtrafficandwithlittle
depth. Therefore in order to be able to perform
efficiently and safely the vessel requires to have a
greatmaneuverability.
Byreducingthepropulsionpowertherehasbeena
weightsaving withthefour newengines MHIS16R
with regards to the two existing motors MTU
20V1163,yetevenhavinganewequipment(engines
andsidethrusters,loadingfacilit
ies,etc.)areduction
in weight has been obtained in the light weigh of
around2%,leavingthelightdisplacementin490t.
Thesumofdifferentfact
orslike:
The installation of a propulsion system (FPP)
optimizedfortheservicespeed.
Theincreaseofthefloatinglengthandthereforeon
thenumberofFroude.
To improve the hull shape to maximize the
propellerperforma
nce.
Toreducethelightweight.
Optimizing the energy efficiency of high‐speed
craftcoveredbythisarticlehasbeenfeasible.
Thatvessel,initsoriginalconception,obtainedin
trials sea with maximum speed test of 34 knots,
although to contain its operating costs (fuel,
maintenance, etc.) and ma
ke it economically viable,
theirowneroperatedbyaservicespeedof22knots,
with a consumption of 135 l per mile of MGO, this
consumption comprising consumption of main and
auxiliaryengines.
After the return to service of the vessel after the
reformand withaservice speedofover22 knots,it
has verified tha
t the consumption per mile is 45 l
MGO,thisincludeconsumptionofmainenginesand
the auxiliary, which represents a 65% reduction in
fuelconsumptionandemissionsevenasnewengines
comply with the latest regulations of MARPOL
AnnexVI.
5 NEWEEIO
As regards the Energy Efficiency Operational Index
EEOItheshipbeforeandaft
ertransformationwould
be:
FC EF
EOI
GT D
where:
FC:Fuelconsumptionofma
inandauxiliaryengines
EF:EmissionfactorofthefuelusedinkgCO2/GT
xNM.
GT:Vesselʹstonnageintones.
D:Distanceinnauticalmiles.
EEOI for the ship before the transformation, for
fuel consumption of mainandauxiliary engines per
nauticalmile,givesava
lueof0.1381kgCO2/GTx
NM.
TheshipEEOIonce transformedand changedits
propulsion system for new fuel consumption of
enginesandauxiliary engines,givesavalueof0.0452
kgCO2/GTxNM.
This means that the transformed ship produces
threeti
meslessCO2perGRTandnauticalmilesailed
thantheshipwiththeoriginalpropulsionpower.
Giventhattheshiphasapproximately2,000hours
effective work with the new propulsion system, the
vessel would consume approximately 3406 t of fuel
less,whichforthepurposesofpollutiongreenhouse
gases such as CO2
, stop polluting the year about
10100tofCO
2.
6 CONCLUSIONS
1 The high‐speed vessels withwaterjetpropulsion
systems in order to maintain a high propulsive
efficiency have to navigate at speeds above 33
knots,makingunviableoperationatlowerspeeds
toreducefuelconsumption.
2 Thehighspeedforshortandmediumdistances is
insufficiently substantiated by the high level of
pollut
ionproducedandtheshorttimesavings.
3 High‐speedvesselsthatwerebuiltintimesoflow
fuel costcanbe converted to operate at a slower
speed,andkeepingtheclassificationofhigh‐speed
vessels,changingtheirpropulsivewaterjetsystem
bythetraditionalpropellerpitchfixedandwitha
highreductionoffuelconsumption.
4 Reducing the speed of high‐speed vessels
changing the propulsive system, allows a more
economicaloperation ofthevessel andmeetsthe
objective of the IMO to reduce the production of
greenhousegasesonships.
5 Maint
aining a minimum consumption of the
propulsion pla
nt and auxiliary engines, it allows
prolong the life period of high‐speed vessels,
535
without being affected, too much, due to the
increaseinfuelprices.
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