wartsila sp a id ferry b

7/29/2019 Wartsila SP a Id Ferry b.

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K_\i\`jXe eZi\Xjèê\\[]fi]\ii`\jkfèZi\Xj\k_\ìZfdg\k`k`m\e\jj% 8b\pXjg\Zkf]Zfjki\[lZk`fej`jkf `dgifm\\e\i^p\]Z`\eZpXe[e\n[\j`êjZXe_\cgèi\XZ_è^k_`jkXi^\k%This article will look at two different ferrytypes representing opposite ends of thesize spectrum, and compare how energyefficiency has been tackled in each case.One of the ferries is a short route ferry forday crossings, while the other is a largecruise ferry providing attractive onboardfacilities for overnight passengers.

The smaller ferry represents a low costsolution, featuring an innovative hull form

design and novel propulsion machinery.

Nevertheless, the systems are all simple andhave few components. The larger cruiseferry, on the other hand, is equipped withmany new features representing the mostadvanced technology available today.

J`q\dXkk\ijSize has a big impact on the transportefficiency of a ship. The larger thevessel, the more efficient it is. Low speedmeans low energy consumption. Thesemaxims apply also to ferries. However,

when it comes to evaluating transportefficiency, ferries are somewhat trickierthan pure cargo vessels and there aredifferent opinions on how it should bedone. In a tanker or container vessel, thepayload is rather obvious. But a cruise

ferry, for instance, carries not only ro-ro

cargo, but also a complete hotel for thepassengers. Should only the weight of thepassengers be considered as payload? Orshould it include the entire superstructureand all the various hotel functions?

In resolving this issue, many suggest thatit is better to use the volume (gross tonnage)of the ships as the measurement, rather thanpayload weight or deadweight. The IMO(International Maritime Organization) hasalso considered this principle in its proposalfor a CO2 index. This index, and its rathercomplicated formulas, is still underdiscussion, but the main principle can besimplified by including only a few mainparameters - installed power divided bygross tonnage and speed. This gives a unitof energy per transported ship size and

distance [kWh / (GT * nm)].

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important. In order to reach the lowestpossible resistance, the block (and prismatic)

coefficient of such vessels should be low.Careful optimization of the maindimensions is of the utmost importanceduring the initial stages of ferry design.Lengthening the hull gives a lower blockcoefficient and Froude number andthereby reduced wave resistance. Addedbeam and draft can also result in a lowerblock coefficient and produce positiveeffects in some cases. Too low L/B ratiosshould, however, be avoided.

The effective length can also beincreased by adding a ducktail, which

is quite popular in ferries. Other sternfeatures, such as trim wedges andinterceptors, can also yield good results,especially at high Froude numbers.

The two ferry designs developed havehull forms where the waterline length hasbeen maximized within the overall length

of the vessel. They are also longer thancompeting vessel designs. For example, the

length of the short route ferry is stretched510 m compared to a conventional ferryof the same size. Already a 5 m lengthincrease, gives a 14% effective power (hullresistance) saving at service speed and20% saving at trial speed. Furthermore,in order to offer very low added resistancein heavy seas, the bow has been designedto have a fine waterline entry angle and avertical stem profile with low flare angles.

Even though added length is easy tojustify from a power saving point of view,it is sometimes difficult to realize in practice.

There are restrictions on the size of vesselsin many ports, and ships should be ableto turn in the port basin and fit alongsidethe quay. Draft is sometimes limited bythe fairways leading into port. However,since the benefits of longer vessels are soclear, naval architects should ask if these

limits are carved in stone or if they canbe changed. Investing in improved port

facilities could perhaps be more lucrativethan investing in too much engine power.

Klie$Xifle[k`d\`egfikIt is not only investments in bigger portsthat can be interesting; development of theport infrastructure can also pay itself backquite quickly. Speeding up port time isalmost always beneficial, and the shorterthe turnaround time in port is, the slowerthe ship can sail while still maintaining thesame departure frequency. A 10 minutesaving can, for example, produce annual

fuel savings of 3% for a typical ferry.A bigger time saving of half an hour canresult in 10% savings.

Both ferry concepts aim at achievinggood cargo handling. The cruise ferry isdesigned to have a dedicated shore basedlink span also for the upper car deck, which

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;lXc$]l\cThe cruise ferry is designed for operation on

LNG with marine diesel as back-up. Themachinery is based on six Wrtsil 50DFdual-fuel engines, of which two are drivingthe centre propeller via a twin-in single-outreduction gear. The remaining four enginesare driving the generators. The engines aredivided into two separate compartmentsto comply with safe return to portrequirements.

The use of LNG significantly reducesthe vessels emissions, with CO2 cut by~25% and NOXemissions by 85%.In addition, there are virtually no SOX

emissions and the particle levels arereduced significantly as well. But loweremissions are not the only advantages ofLNG. Energy demand is also reduced, andthe low temperature of LNG can be usedfor cooling in the air-conditioning (AC)systems, thus reducing the need to run

AC compressors. The savings potential isestimated at ~1.1 MW of cooling power,

which corresponds to ~275 kW in electricpower assuming a COP (coefficient ofperformance) factor of 4. Furthermore,there is no need for an HFO tank or trace

heating, thereby reducing the use of the oilfired boiler.

N`e[gfn\iWhen trying to improve energy efficiencyin ships, thoughts soon turn to harnessingsome of the free energy from thesurrounding elements. Wind is the mostfeasible of these options and there aremany means of using wind power, theoldest, but still relevant method, being touse sails. Flettner rotors and kites have alsoemerged as potential options for creating

forward thrust from wind. Anotherapproach is to use some kind of windturbine to produce electric energy. Thebenefit of the latter is that it also works

when the ship is standing still in port, butis perhaps less ideal in head winds.

A ferry is a rather challenging ship typefor wind power. The speed of the vessel isusually high, which means that headwindsbecome the apparent wind direction. Thesail device must, therefore, work wellat small angles of attack. A slower vessel

will have more side and downwind

encounters. The other typical feature ofa ferry is that the legs are short, and theremight be many turns and changes in theheading. This means that the sail devicemust be adjusted frequently.

Taking these special requirements intoaccount, the Flettner rotor seems to be the

most promising sail device. The Flettnerrotor, named after its inventor AntonFlettner, is a vertical cylinder that is rotatedaround its axis by a motor. As the windblows past the rotating cylinder, highpressure on one side is formed with acorresponding low pressure area on theopposite side. This pressure difference willgenerate a thrust force perpendicular to the

winds direction. There is also a drag force.The forward components of these forces

will result in thrust to drive the ship ahead.The advantage of the Flettner rotor,

compared to a sail or kite, is that the rotorworks at rather small angles of attack andis simple to turn on and off. The rotor isalso more efficient than a sail. A Flettnerrotor can have a lift coefficient (CL) ofaround 10, while normal sails are justabove 1. This means that the rotor cangenerate about ten times more thrust withthe same sail area. The speed of the rotoris adjusted by controlling the electric motordriving it, and when the wind speed ordirection changes, the rotational speed anddirection is adjusted automatically to give

optimal thrust. If the wind power is nolonger needed, the rotor is simply stopped.No need to lower any sails. It is a verysimple and easily adjusted device needingno additional crew.

The Flettner rotor was first applied in aship in the 1920s. It was tried a few timesin different ships, but no big breakthroughoccurred since the era of sailing ships wascoming to its end at that time. Now, onceagain, it is becoming a hot topic as energycosts are rising, and there is a need toreduce the CO2 footprint.

The cruise ferry concept features fourFlettner rotors to produce extra thrust.Three of the rotors are integrated intothe funnel and one is part of the forwardmast structure. The exhaust pipes are fedthrough two of the aft rotors. The idea hasbeen to introduce rotors without changingthe side profile of the vessel too much. Therotors are relatively small in comparison tothe overall ship size. However, according toan assumed operating profile and actual

wind data for the route, they are estimatedto produce an average thrust gain of 10%.

Their contribution is larger at lower speeds,while at high speeds it is correspondinglyreduced.

The wind power suggested forthese ferries is not intended for primary

propulsion, as it was for old sailing ships,but rather as a means of reducing fuel

consumption.

JfcXigfn\iThe cruise ferry design also features solarpanels to produce electric energy fromsunlight. About 800 m2 of panels havebeen located on the sloped sides of the ACrooms on the top deck. Unfortunately,todays solar panels will not produce verymuch power in a ship operating in northernEurope, and an annual average power of11 kW was calculated for the ferry. Thisis not very much for this type of ship, but

in the future when solar panel technologybecomes more efficient and cheaper, it canbecome more interesting, especially forships operating in sunnier climates.

NXjk\_\Xki\Zfm\ipOne potential area for improving theenergy balance in a ship is to apply wasteheat recovery (WHR) systems for themachinery. This has been done successfullyin container vessels, and is now also beingconsidered for a wider range of ship types,ferries being one. In ferries, surplus energy

is available in the exhaust and enginecooling water when operating at highpower. Unlike cruise ships, ferries bunkerfresh water in port and seldom produce

water onboard, so the waste heat is notneeded for these systems. The waste energyshould ideally be converted into electricpower to give more flexible use.

Large container vessels use a WHRsystem that combines exhaust powerturbines and steam cycles. This might notbe as well suited for ferries.

The cruise ferry is designed to use a

WHR system based on an Organic RankingCycle (ORC). This system has not yet beenapplied in ships, but there is somedevelopment work being carried out. Theidea is to achieve good efficiency already atpart load, and to be able to use low gradeheat from the cooling water. The systemin the cruise ferry is designed to utilize theheat from two engines, as all engines areused only for short periods of time in theassumed operating profile. It is estimatedthat the WHR system will be able torecover about 1 MW of energy from two

engines at high load. The drawback withthe ORC is the large volume of spaceneeded for the equipment. This also limitsthe feasibility of this system for very largepower plants.

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