Wind propulsion for ships in 2010: why so few?

Etienne Gernez

Det Norske Veritas

etienne.gernez@dnv.com

September 13, 2010

Contents

1 Abstract 1

2 Show stopper 1: Investments VS savings 12.1 Performance prediction . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 There are fuel savings and fuel savings... . . . . . . . . . . . . . . . 22.3 Finding the most suitable trade . . . . . . . . . . . . . . . . . . . . 32.4 Optimizing savings . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.4.1 Weather routing . . . . . . . . . . . . . . . . . . . . . . . . . 52.4.2 Technology optimizing . . . . . . . . . . . . . . . . . . . . . 5

3 Show stopper 2: Reliability and Safety 63.1 Risk analysis for Structural integrity . . . . . . . . . . . . . . . . . 63.2 Schedule integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Show stopper 3: Operating a sailing, commercial ship 74.1 Propulsion analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.2 Crew and automation . . . . . . . . . . . . . . . . . . . . . . . . . . 74.3 Paper work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

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5 Show stopper 4: Who benefits from the savings? 8

6 Discussion 8

7 Conclusion 8

References 9

1 Abstract

This paper is asking: with more than 30 years of wind propulsion projects forcommercial shipping, why so few ships are actually sailing using wind energy?Four main industry show stoppers are examined, and some solutions presented inparallel, allowing to review existing research and reveal necessary developmentson the topic.

2 Show stopper 1: Investments VS savings

Investments in new technologies need to be paid off quickly (5 years pay backperiod max, 2-3 years is best) and surely (low but stable fuel savings are preferredto high yet unpredictable savings).

2.1 Performance prediction

Kites: math models [Wellicome and Wilkinson, 1984, Kherian, 2006, Naaijen, 2006],experimentation [Dadd, 2005, Gernez, 2006], validation [Dadd et al., 2010] (forZero mass model) [Schlaak et al., 2009] (for Skysails model).

Others: CFD and experimentation.Goal: polar diagram, showing pulling force VS a AWA

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2.2 There are fuel savings and fuel savings...

Expression of savings is always tricky...Resistance VS Sail force, Power compar-isons, Fuel consumption, Instantaneous VS Average...Need to find a commonground!

In Naaijen1 [Naaijen, 2006]:"4.3. Results and discussion The theoretical fuel saving that can be achieved inthe considered case is presented by the polar diagram in Fig. 14 for a towing linelength of 150 m. The angular axis represents the true wind direction from thebow. The radial distance from the origin represents the fuel consumption as apercentage of the fuel consumption as it would be without using the kite.

Figure 15 shows the force delivered by the kite in the direction of the forwardspeed as a percentage of the total resistance without kite for a towing line lengthof 150 m. One would expect this percentage to be higher than the relative fuelsaving: "....yet it is not - propeller efficiency...

In Naaijen2 "2.4(a) Applying constant RPM results in a relative fuel saving[tons / hour] of only 4.1 %, corresponding to 11.8 % in [tons / mile].

When the ship’s speed is kept constant by decreasing the RPM, a relative fuelsaving of 50.9 % can be achieved, as shown in Figure 15."

In Gernez[Gernez, 2009]: "The savings are always expressed as: % saving =(value without sail – value with sail) / value without sail The saving calculationis applied to the thrust and torque coefficients, the brake power, and the fuelconsumption. "

Fujiwara Thrust benefit (TB) introduced to measure the ability to reduce theengine delivered thrust at constant speed TB(%)= (Xp(nosail) - Xp (withsail)) /Xp(nosail) *100 Xp(nosail): mean value of the thrust force for the ship withoutthe sails for all wind directions Xp(withsail): mean value of the thrust force whenthe sails are in operation, and the ship velocity maintained TB is equivalent to amean reduction in effective horse power (EHP).

Shlaak paragraph 4. Direct measure of fuel consumption with and withoutkite at constant speed 12kn in liter/hour –> fuel reduction in l/h –> conversionto a "saving in useable machine power" by using the effective fuel consumption

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in liter/ kWh at same speed: DeltaPower= fuel reduction in l/h * (1/ effectivefuel consumption in l/kWh) = equivalent machine power in kW –> "The powersupplied by the kite is directly effective, without any energy conversion losses. Itis therefore not directly comparable to motor generated power." –> conversion ofkite force to kite power equivalent to motor power: kite force in N * wind speed inm/s * (1/ overall propulsive efficiency) = kite power equivalent to motor power.

2.3 Finding the most suitable trade

The most suitable trade for wind propulsion has to be carefully selected. Windatlases and performance predictions are here to help.

Article Fair trade winds 28/04/2009: "Cargo flows are matched where possiblewith wind potential, for example departing from Europe by plotting a course southof the Azores to the Americas and returning across the Atlantic on a nort-northeastroute." Route following "trade winds". Confirmed in Blackham in early days ofweather routing for wind assisted ships.

Simulation of ship performance with wind technology. Several levels: - full: ma-noeuvring (drift angle?), propulsion performance (propeller efficiency), resistance(in calm water, added in waves), wind statistics

Case studies: table withwind propulsion technologyship type, DWTroutewind stats databasesail prediction methodrange savingsreference paper

–> Gernez: 80m2 kite, 5820 DWT shuttle tanker , 500 nm between Corsica andMalta, ARGOSS database, static kite flying model [Wellicome and Wilkinson, 1984,Kherian, 2006]; 5-7%,[Gernez, 2009]

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–> Naaijen1: 500m2 kite, 50 000 DWT tanker, no specific trade, BF 4-7,quasi-static [Naaijen, 2006], up to 50%, [Naaijen, 2006]

–> Naaijen 2: 400m2 kite, 44579 Bulk Carrier, New york to English Channel,NOAA, quasi-static, up to 50%,5 % in average on 1 voyage, published article?

–> Allemands: Bermuda rig (classic), Dyna Rig (German), Generic producttanker and Generic Bulk Carrier, Le Havre Miami, San Francisco Yokohama, Val-paraiso Yokohama, ECMWF (which one?), wind tunnel testing (references given),up to 15%, article in german, not referenced...Try Google!!

–>Shlaak: Skysails 600m2, multipurpose freighter 10 000 DWT + Bulk Carrier48 000 DWT + Tanker 32 000 DWT, all at 13 and 15knots, 15 routes worldwide,ERA 40 ECMWF, experimental calibration of theoritical model (see ref 6 and 7),5% North Atlantic East-West 21% West-East.

–> Japonais: hybrid wing-sail, Bulk carrier, North Pacific, Ref 15 Watanabeet al, wind tunnel testing (references given), 10-15%,[Fujiwara et al., 2005]

–> Dadd: Nope! [Dadd et al., 2010]Conclusion: wide range of savings. Very dependant of sails characteristics

(mostly area, L/D ratio but also line length, flying pattern,..for kites), wind char-acteristics, Ship SPEED (shlaak: 15 to 13 knots = +10%.)

experimental or validated models available for kite static and dynamic, 3 ger-mans types of rig, 1 japanese hybrid rig. "fully" coupled simulations: wind - sail- engine - rudder

Only 1 study comparing different routes (Germans and Shlaak). Shlaak Figure7: 15 routes Out and Home with Kite power, compared to importance of the route(% goods passing through). Optimal sailing conditions for each tech: upwind 120deg (Kherian), slow ship (all!)!,

Further research: Mapping tool, inspired from wind turbine site selection in thewind energy industry. Schlaak using wind masts measurements for more accuratewind stats.

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2.4 Optimizing savings

2.4.1 Weather routing

Once the trade is selected, weather routing systems can help to use the availablewind as best as possible, the challenge being: how much the route can be changedto benefit from more wind?

Naaijen 2: isochrone method?? 3. Voyage simulation "Unfortunately theisochrone method appears to be not suitable for cases with no or very limitedspeed variation: all possible routes will diverge until the last isochrone resulting inan optimal route that is very unlikely to diverge from the minimum distance route.However, keeping in mind that the followed routes during the 30 simulations arepossibly not the optimal ones, the results for the situation with and without kiteand for constant speed and constant RPM are given in the next table."

Blackham: no specific method given. Just describing the idea. References:[Blackham, 1985, Hagiwara and Spaans, 1987] + Naaijen2 and Germans

Limitations: added safety concerns (more wind usually means more waves),added cost of routing services (weather forecasting service, data storage and trans-mission), and liability issues in case of incidents (what if the ship didn’t move awayfrom its normal route...?)

2.4.2 Technology optimizing

Another way to optimize the savings is to optimize the technology itself. For kitepropulsion, the kite flying patterns are an important component of the efficiencyof the overall system. The problem of finding kite trajectories maximizing the kitepulling force is a mathematical optimization and control problem studied for highaltitude wind energy generation [Ilzhöfer et al., 2007].

3 Show stopper 2: Reliability and Safety

What is the risk of using wind propulsion technologies?

• it is very much depending on the technology used

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• risk for who?

• what kind of risk?

3.1 Risk analysis for Structural integrity

What are the possible failure modes of the technology? The associated causes andconsequences? The available mitigation measures? Such an analysis is necessaryto have a better understanding of a technology and the operational risk.

The experience of Det Norske Veritas (DNV) in Risk Management has pro-duced early reports laying out principles of design for wind propulsion technology[Wagner, 1981, Brett, 1984] as well as detailed risk analysis, identifying and rank-ing more than 100 causes of failure, preparing a solid ground for discussions withthe technology supplier and vessel operator[Gernez, 2009].

3.2 Schedule integrity

As far as wind propulsion is only assistive, i.e not the main propulsion source,there is no reason not to maintain the contracted speed. At best, some fuel willbe saved, at worst, no fuel will be saved, but in both cases the ship will arrive ontime, once the structural integrity risk is cleared.

In the case of wind as main propulsion, safety margins have to be included inthe contracts. The French company Fair Trade Winds is chartering sailing vesselsto ship wine from France to the Northern Europe market, signing contracts withwine importers allowing a three days margin in the delivery date.Reference: personal communication with Fair Trade Winds CEO.

4 Show stopper 3: Operating a sailing, commercial ship

Using additional technologies gives an additional complexity to the operation ofthe ship, for instance in terms of:

• propulsion: how to run the engine and the propeller with the extra powergiven by the sail?

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• crew training: how automatic can the technology be and how much is left tothe crew?

• paper work: what kind of authorizations are required to sail?

4.1 Propulsion analysis

The extra power given by the sail is modifying the operating zone of the shippropeller. [Molland and Hawksley, 1985] is discussing wether to use a ControllablePitch Propeller or a Fixed Propeller with a gearbox in this case. The question ofdrift due to sail side forces is investigated in [Naaijen, 2006, Hudson et al., 2009].

4.2 Crew and automation

Automatization of sailing is one of the answers to the issues of added cost of extracrew and additional training required to operate a wind propulsion technology.Reference: personal communication with Associate Professor Jerome Jouffroy fromThe Mads Clausen Institute, University of Southern Danmark.

4.3 Paper work

The fact that a handful of ships are using wind propulsion technologies in theirdaily operation shows that paper work for insurance and ship classification can becarried out!Reference: the testimony of one ship operator using a wind propulsion technology.

5 Show stopper 4: Who benefits from the savings?

As fuel savings are the most important economic incentive to use wind propulsion,the questions of quantifying, documenting, reporting, and sharing the savings arise.

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6 Discussion

Extensive research and increasing feedback from experience reveals that most ofthe show stoppers described in this paper should not be seen as such! So whyso few wind propulsion ships in 2010? Going beyond the economic issue of oilprices variation, I would argue that it is more of a political issue in a contextof environmental regulation strengthening and increased consumer demand forenvironmentally-friendly operations.

In the cruising sector, environmental management policies are tighter thanin merchant shipping (for instance in waste management), and end-customers aredirectly in contact with the ship operations (again as opposed to the long and com-plex supply chains where the end-customer usually does not know which shippingcompany is contracted and how it is operating).

It is then probably not a surprise that some recent cruising projects are lookingagain into wind propulsion, for instance STX Europe and the EOSEAS project:wind propulsion here is not only seen as a mere fuel saving device, but is part ofa long list of solutions to reduce the environmental impact of the ship operations,from waste heat recovery to waste water management, innovative hull design,etc..., as well as a marketing operation built on the golden souvenirs of luxurious,glamour sailing cruises.

7 Conclusion

What could lead the shipping industry to select wind propulsion as a feasiblealternative?

• the entry into force of air emissions AND environmental management regu-lation. The IMO is working on it!

• the publication and sharing of existing experience in fuel savings from windpropulsion. But it in such an intense industry, would not that mean losinga competitive advantage?

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• the development of partnerships between industry and research to benefitfrom the experience and innovation gained in the last 30 years. Who isagainst that, at least in the research environment..?

References

[Blackham, 1985] Blackham, A. (1985). Weather routeing for wind assisted ships.Journal of Wind Engineering and Industrial Aerodynamics, 19(1-3):205 – 213.

[Brett, 1984] Brett, P. (1984). Principles of safe design of sail driven merchantvessels. Research Paper 81-P084, Det Norske Veritas.

[Dadd, 2005] Dadd, G. M. (2005). Development, validation and demonstrationof a test rig for kite performance. Master’s thesis, University of Southampton,Ship Science department.

[Dadd et al., 2010] Dadd, G. M., Hudson, D. A., and Shenoi, R. A. (2010). Com-parison of two kite force models with experiment. Journal of Aircraft, 47(1):212–224.

[Fujiwara et al., 2005] Fujiwara, T., Hearn, G. E., Kitamura, F., Ueno, M., andMinami, Y. (2005). Steady sailing performance of a hybrid-sail assisted bulkcarrier. Journal of Marine Science and Technology, 10:131–146.

[Gernez, 2006] Gernez, E. (2006). Experimental and numerical investigation ofthe performance of a kite. Master’s thesis, University of Southampton, ShipScience department.

[Gernez, 2009] Gernez, E. (2009). Risk, cost and benefit of wind assisted propul-sion for ship - the example of kite propulsion. Technical Report 2009-0634, DetNorske Veritas.

[Hagiwara and Spaans, 1987] Hagiwara, H. and Spaans, J. A. (1987). Practi-cal weather routing of sail-assisted motor vessels. The Journal of Navigation,40(01):96–119.

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[Hudson et al., 2009] Hudson, D. A., Shenoi, R. A., Hirdaris, S. E., Dadd, G. M.,and Chapman, T. (2009). Operational considerations of kite assisted merchantship propulsion. In 2nd Annual ME ShipTech 2009 Conference.

[Ilzhöfer et al., 2007] Ilzhöfer, A., Houska, B., and Diehl, M. (2007). Nonlin-ear mpc of kites under varying wind conditions for a new class of large-scalewindpower generators. International Journal of Robustand NonlinearControl,17:1590–1599.

[Kherian, 2006] Kherian, J. G. (2006). Kite force prediction for ship propulsion.Master’s thesis, University of Southampton, Ship Science department.

[Molland and Hawksley, 1985] Molland, A. and Hawksley, G. (1985). An inves-tigation of propeller performance and machinery applications in wind assistedships. Journal of Wind Engineering and Industrial Aerodynamics, 20(1-3):143– 168.

[Naaijen, 2006] Naaijen, P. (2006). On the power savings by an auxiliary kitepropulsion system. International Shipbuilding Progress, 53(4):255–279.

[Schlaak et al., 2009] Schlaak, M., Kreutzer, R., and Elsner, R. (2009). Simulatingpossible savings of the skysails-system on international merchant ship fleets.Trans RINA, International Journal of Maritime Engineering, 151(A4).

[Wagner, 1981] Wagner, H. G. (1981). Ships with main propulsion by sail: Generaland main requirement for reefing of sails and turning of masts. Technical Report81-0687, Det Norske Veritas.

[Wellicome and Wilkinson, 1984] Wellicome, J. and Wilkinson, S. (1984). ShipPropulsion Kites - An Initial Study. Technical Report SSSU19, University ofSouthampton, Ship Sciences Department.

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