Energy Efficiency Ship Design

8/8/2019 Energy Efficiency Ship Design

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11 Wrtsil 3 February 2009 Energy Efficiency Catalogue / Ship Power R&D

SHIP DESIGN


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Efficiency of scale

A larger ship will in most cases offer greatertransport efficiency Efficiency of Scale effect.A larger ship can transport more cargo at the

same speed with less power per cargo unit.Limitations may be met in port handling.

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Regression analysis of recently built shipsshow that a 10% larger ship will give about4-5% higher transport efficiency.

< 4%


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Reduce ballast

Minimising the use of ballast (and other unnecessaryweight) results in lighter displacement and thus lowerresistance. The resistance is more or less directlyproportional to the displacement of the vessel. However

there must be enough ballast to immersethe propeller in the water, and provide sufficient stability(safety) and acceptable sea keeping behaviour (slamming).


< 7%

Removing 3000 tons of permanent ballast froma PCTC and increasing the beam by 0.25 metresto achieve the same stability will reduce thepropulsion power demand by 8.5%.


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Lightweight construction


< 7%

The use of lightweight structures can reduce the

ship weight. In structures that do not contribute toship global strength, the use of aluminium orsome other lightweight material may be anattractive solution.The weight of the steel structure can also bereduced. In a conventional ship, the steel weightcan be lowered by 5-20%, depending on theamount of high tensile steel already in use.

A 20% reduction in steel weight will givea reduction of ~9% in propulsion powerrequirements. However, a 5% saving is more

realistic, since high tensile steel has already beenused to some extent in many cases.


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Optimum main dimensions


< 9%

Finding the optimum length and hull fullness ratio

(Cb) has a big impact on ship resistance.A high L/B ratio means that the ship will havesmooth lines and low wave making resistance.On the other hand, increasing the length meansa larger wetted surface area, which can havea negative effect on total resistance.A too high block coefficient (Cb) makes the hulllines too blunt and leads to increased resistance.

Adding 10-15% extra length to a typical producttanker can reduce the power demand by morethan 10%.


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Interceptor trim planes


< 4%

The Interceptor is a metal plate that is fittedvertically to the transom of a ship, covering mostof the breadth of the transom. This plate bendsthe flow over the aft-body of the ship downwards,creating a similar lift effect as a conventional trimwedge due to the high pressure area behind thepropellers. The interceptor has proved to be moreeffective than a conventional trim wedge in somecases, but so far it has been used only in cruisevessels and RoRos. An interceptor is cheaper toretrofit than a trim wedge.

1-5% lower propulsion power demand.Corresponding improvement of up to 4%

in total energy demand for a typical ferry.


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Ducktail waterline extension


< 7%

A ducktail is basically a lengthening of the aftship. It is usually 3-6 meter long. The basic ideais to lengthen the effective waterline and makethe wetted transom smaller. This has a positiveeffect on the resistance of the ship. In somecases the best results are achieved whena ducktail is used together with an interceptor.

4-10% lower propulsion power demand.Corresponding improvement of 3-7% in totalenergy consumption for a typical ferry.


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Shaft line arrangement


< 2%

The shaft lines should be streamlined. Brackets

should have a streamlined shape. Otherwise thisincreases the resistance and disturbs the flowto the propeller.

Up to 3% difference in power demand between

poor and good design. A correspondingimprovement of up to 2% in total energyconsumption for a typical ferry.


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Skeg shape / trailing edge


< 2%

The skeg should be designed so that it directs theflow evenly to the propeller disk. At lower speeds itis usually beneficial to have more volume on thelower part of the skeg and as little as possibleabove the propeller shaftline. At the aft end of theskeg the flow should be attached to the skeg, butwith as low flow speeds as possible.

1.5%-2% lower propulsion power demand withgood design. A corresponding improvement ofup to 2% in total energy consumption for acontainer vessel.


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Minimising resistance of hull openings


< 5%

The water flow disturbance from openings to bowthruster tunnels and sea chests can be high. It istherefore beneficial to install a scallop behind eachopening. Alternatively a grid that is perpendicular

to the local flow direction can be installed. Thelocation of the opening is also important.

Designing all openings properly and locatingthem correctly can give up to 5% lower powerdemand than with poor designs. For a containervessel, the corresponding improvement in total

energy consumption is almost 5%.


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Air lubrication


< 15%

Compressed air is pumped into a recess in thebottom of the ships hull. The air builds up a carpetthat reduces the frictional resistance between thewater and the hull surface. This reduces thepropulsion power demand. The challenge is toensure that the air stays below the hull and does notescape. Some pumping power is needed.

Saving in fuel consumption:Tanker: ~15 %Container: ~7.5 %PCTC: ~8.5 %Ferry: ~3.5%


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Tailoring machinery concept for operation


< 35%

This OSV design combines the best of twoworlds. The low resistance and high propulsionefficiency of a single skeg hull form is combinedwith the manoeuvring performance of steerablethrusters. Singe screw propulsion is used for freerunning while retractable thrusters are used in DPmode when excellent manoeuvring is needed.The machinery also combines mechanicalpropulsion in free running mode with electric drivein DP mode. Low transmission losses withmechanical drive. Electric propulsion in DP modefor optimum engine load and variable speed FPpropellers give the best efficiency.

Diesel-electric machinery and twin steerablethrusters reduce the annual fuel consumptionof a typical supply vessel by 35% compared toa conventional vessel.

Energy Efficiency Ship Design

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