boosting ferry efficiency article

8/8/2019 Boosting Ferry Efficiency Article

1/5

40 Twentyfour7. 2.09

in-depth


2/5

Twentyfour7. 2.09 41

in-depth

While the efciency o ships in

general terms has become a hot

topic in recent years, the need

to reduce uel costs is perhapsmost urgent in the erry sector

o the marine industry.

TexT: Oskar Levander, Head O COnCepTuaL design, WrTsiL sHip design


3/5


in-depth

interest

in saving

fuel

remains.

LeveLs of instaLLed power are oten relatively highin erries and it is this segment that competes most clearly withother orms o transport such as road, rail and air. Higher uelcosts thereore have a big impact on the bottom line and canencourage a modal shit away rom sea transportation. Tis wouldbe undesirable, since there is a common need to transer both peopleand goods rom overloaded road and rail networks to more ecientsea transportation routes.

Even though current oil prices are lower than the levels achieved

last year, expectations are that prices will move back to high levels inthe uture. Interest in saving uel thereore remains - and exploitingevery possible method o reducing costs is o course essential orsurvival in this ercely competitive sector.

Another important actor is pollution. Ferries that operate closeto shore, oten berthing in densely populated areas, are undersignicant public pressure to reduce their exhaust emissions. Tisurther increases the need to cut power demands.

Multiple specifcations. Ferries transport a mix o wheel-basedcargo, cars and passengers. Ferry types in use today cover everythingrom high-speed crat and small double-enders to large RoPax vesselsand luxury cruise erries.

Ferries usually operate on short routes with a xed itinerary andregular schedules. Teir speed is tailored to suit each route so thatthe desired departure and arrival times can be oered. Speed anddisplacement are the two dominating actors aecting the power

demand o a ship. Conventionalerries oten operate at Froudenumbers between 0.25 and 0.35.Te relatively high hull speeds odisplacement-type vessels makehydrodynamic optimizationparticularly important. Teblock coecient o such vesselsshould be kept low so that their

resistance to moving through the water is as small as possible.Using low-weight structures is thereore benecial, especially asthe ships lightship weight (LW) represents a big proportion othe total displacement in a erry. Careul optimization o the maindimensions is o the utmost importance during the initial stage inerry design. Lengthening the hull oten reduces power demandsignicantly. Tis can be seen rom the benet a erry can achieveby adding a ducktail to give a longer efective waterline. Other sterneatures such as trim wedges and interceptors can also yield verygood results. As ast monohulls and catamarans operate in the semi-displacement mode, saving weight becomes even more important.

Reducing appendage drag. Ferries oten have a low drat and twin-screw propulsion is very common. As the two shat lines result inrelatively large drag, appendage design can have a major impacton power demand. Alternative congurations include combininga shat line in the centre skeg with either a single pulling thruster


4/5


5/5


in-depth

definitions

froude number. Th o mb mol

mb ct th ltoh btw l lth

t .

bLock coefficient cb. Th to o th wt olm

o h to th olm o ctl bloc wth th m

lth, bth t th h hll. ll om ch

ol t h hh Cb, whl h ch lbot

h low Cb.

ducktaiL. a ttch to th tom o l

to lth t t cto, m th ct wtl

lo.

trim wedGe. a w-h om to h t

blow th wtl whch c c th l fow

tc. alo ow t w.

interceptor. a mtl lt to th t o h

tcl otto co th m bth o th tom.

Th low o th lt ot blow th tom,

ct tl tm w. itcto c b ch to

tot th tm w.

appendaGe. i th cott o h , tm tht

ttch to, o ot thoh, th tl c o

l hll (, ht l, ht l ot, bo, tbl, bl l, bow tht tl, tc.).

skeG. a , tcl -l ojcto o th bottom o

l th t, tll to o co tblty,

ot th l y oc , l-cw l,

ho th oll ht.

anGLe of attack. Th l btw l l th

cto o th w.

Te need or speed alsoinfuences the decision onwhether a vessel should havea lower RoRo hold. Althoughthis eature increases a erryspayload capacity, operationsin port will be slower. Inmany cases, investmentin port inrastructure canbe more benecial. Cargooperations carried out usingtwo-level link spans canbe completed much morerapidly than when single-

level ramps are employed.High-power tunnel thrusters oer good manoeuvringcharacteristics, reducing port time. In many cases they are alsoinstalled in the vessels stern to provide additional side thrust. I aCRP or Wing Truster concept is applied, it will not only improvepropulsion eciency but also enhance manoeuvring and give shorterturnaround times.

Reducing the hotel load.A errys payload unctions can be dividedinto two distinct categories: passenger acilities and RoRo spaces.Te split between passenger and cargo unctions aects the way avessel is designed and optimized. As large passenger areas give rise tohigh hotel loads, all means o reducing power consumption by usingenergy-ecient lighting, smart HVAC systems and well designedgalley operations can result in large energy savings.

Te large variations in demand or propulsionpower during a voyage also mean that requency-

a ferrys

payloadfunctions can

be divided into

passenger

facilities and

roro spaces.

controlled pumps are an attractive option or manyauxiliary systems. Tis is particularly true or erriesoperating in climates that are signicantly cooler thanthe maximum temperatures used when dimensioningthe vessels systems.

Since erries operate on widely varying routes withdiferent cargo mixes and have to meet a range opassenger expectations, they are tailored to meet specicoperator demands. A good ship designer should tailorthe whole ship concept to achieve the best possibleeciency as it carries out its dened mission.

boosting ferry efficiency article

Documents