Wind-Assisted Propulsion for Commercial Ships. Wind Energy as a Possible Solution to Reduce Emissions and Fuel Cost

Date 2014

Author

Markey, D J . and G. Bordogna

Address

Delft University of Technology [

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Ship Hydromechanics and Structures Laboratory

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Mekelweg 2, 2628 CD Delft

Delft University of Tectinology

Wind-Assisted Propulsion for Commercial S h i p s .

by

D J . M a r k e y and G. Bordogna

Report No. 1 9 0 4 - P 2014

S W Z I M A R I T I M E , Maritiem T e c h n i s c h v a k b l a d . J a a r g a n g

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Voortstuwing

Door D.J. Markey PhD en G. Bordogna PhD

for Commercial Ships

Wind E n e r g y a s a P o s s i b l e Solution to R e d u c e

E m i s s i o n s and Fuel C o s t

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In rccent years, the possibility to employ wind energy as an auxiliary form of propulsion for

commorcial ships has again become of great Interest among ship owners and government

instltutions alike. It is now time to develop a tool which allows the users to properly

theDynarig,

evaluato tho actual possible benefits of wind-assisted propulsion attuned to their needs.

Dylistra Naval Architects

The shipping industry is highly influencad by the omnipresent rise of oil prices and an increasing awareness of environmental issues. Due to ships' high fuel consumption and accompanying emissions, innovative solutions need to be found. The maritime sector puts a big emphasis on reducing fuel consumption and this is usually done fay employing already existing standard practices such as hull/ propeller optimisation and engine improvements. However, in more recent years, also due to the ever stricter regulations regarding emissions, major improvements towards sustainable ships are sought. The possibility to employ wind energy as an auxiliary form of propulsion for commercial ships has again become of great interest and might be a viable alternative in the near future. Wind-Assisted Ship Propulsion (WASP) refers to every kind of auxiliary unit meant to assist the propulsion of a ship by making use of wind energy. This is in fact not a new concept as it was already a populartopic of discussion in the eighties.

History

Until the twentieth century, wind energy was the only form of propul-sion until it was completely replaced fay steam engines. It was only with the oil crisis of 1973, caused by the war inthe Middle East, that the idea of wind propulsion was reintroduced. During those days, oil costs rapidly increased, forcing ship owners and the whole maritime sector to evaluate alternative types of energy, which could fae suita-ble to reduce, or even fully replace, the need for oil as fuel for ships. This has led to many inventors and scientists alike to propose several new concepts mainly focused towards v\/ind-assisted ship propulsion. Some of these concepts are actually still considered as viable solutions today Academically, the increasing interest on the matter resulted in several symposia on wind-assisted propulsion in the eighties. Here several old and new types of wind propulsors were evaluated on the basis of practical, economical and scientific reasons.

Ship H y d r o m e c h a n i c s & S t r u c t u r e s van de TU Delft I w w w . O a v i d J M a r k e y . c o m ) . Giovanni Bordogna is joint PhD R e s e a r c h e r bij de afdeling Ship H y d r o m e c h a n i c s & S t r u c t u r e s v a n de TU Delft en de University P o l i t e c n i c o di M i l a n o (g.bordogna@tudelft.nl).

However, as quickly as it arose, the interest on the subject faded due to the sudden oil price drop, the discovered complexity of the subject and the lack of a strong focus on the environment.

R e s e a r c h P r o j e c t

The development of practical and commercially viable wind propul-sion systems to partially or fully propel a ship is nowadays ham-pered by the difficulties of modelling the sophisticated aerodynamic and hydromechanic aspects involved. Therefore, a Performance Prediction Programme (PPP) needs to be created to evaluate the behaviour of a wind-assisted ship and which can be used as a relia-ble design tool.

Two PhD researchers have started the Sail Assist project atthe Ship Hydromechanics and Structures department of Delft University of Technology to develop such a PPR The project is conducted in cooperation with Damen, Marin, Dykstra Naval Architects and the University Politecnico di Milano as well as the University of South-ampton f o r t h e aerodynamic part.

The aim o f t h e project is to study the aerodynamic and hydro-mechanic aspects of wind-assisted propulsion in much greater de-tail than presently available. The practicalities and possible regula-tions involved are outside o f t h e scope. They are taken into account,

however, to set the boundaries and limitations o f t h e PPP.

A e r o d y n a m i c A s p e c t s

The challenge of developing a useful PPP as a design tool is to make it as generic as possible, that is, give the users the possibility to explore several different designs, but yet make it able to provide accurate, and thus reliable, results. The first step to make the pro-gramme generic is to present the users with the possibility to evalu-ate designs that employ different types of wind propulsors. The most common ones are the Dynarig, the Flettner rotor, the Turbosail, the Aerorig, the Kite, the Wing Sail and the Wind Turbine. This last one, which is different from the others, mechanically drives the pro-peller o f t h e ship ratherthan generating an aerodynamic thrust.

"E'Ship V'ofEnercon equipped witti Flettner rotors (picture b/Carschten}

An initial study has shown that the Dynarig and the Flettner rotor look like very promising solutions due to their aerodynamic proper-ties as well as their relatively easy operation. They will, therefore, certainly be included in the PPP Regarding the other types of pro-pulsors, an in-depth study is currently being carried out to evaluate their aerodynamic qualities and, at least as important, to study whetherthey are suitable to be employed on board a commercial ship from a practical point of view.

The other aspect which is fundamental to make the programme ge-neric, is to have it be able to deal with different types of ships and, within a type of ship, to deal with possible different layouts (for in-stance, the superstructure atthe aft or atthe bow of the ship). From an aerodynamic perspective, one o f t h e largest challenges of the research is to properly take into account all the complicated in-teractions between the wind propulsors and the various parts of the ship (the superstructure, the cargo, et cetera) as well as the inter-action between multiple propulsors. Intact,these interinter-actions have a substantial influence on the aerodynamic forces, which, in turn, will affect the aero/hydro equilibrium and eventually the output of the performance prediction. The arrangement of the various parts of a ship and the wind propulsors may vary considerably depending on the needs o f t h e ship owner. This results in an extremely large num-ber of possible interactions that need to be taken into account.

IWV BBC Skysails equipped with a kite sail (picture by SkySails)

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These aerodynamic interactions can only be studied by means of expensive and time-consuming procedures such as wind-tunnel experiments or CFD simulations. Therefore, a method to reduce the number of experiments/simulations will be developed such, that the generality ofthe programme will not be compromised.

H y d r o m e c h a n i c A s p e c t s

Sailing with an auxiliary wind propulsion system on board certainly has a major impact on the behaviour of a ship. The aerodynamic forces acting on the ship need to be balanced by the hydrodynamic forces to obtain an equilibrium that results in a steady forward speed.

It is known from sailing yacht theory that, to obtain this balance, the ship will undergo a constant heel and leeway angle. This is a whole new area for commercial ships and it needs to be carefully studied as it also affects the behaviour of resistance, yaw balance, propel-ler efficiency, stability, manoeuvrability and seakeeping.

As the hull of a commercial ship differs significantly from that of a sailing yacht, one major focus o f t h e research is to find a hull form that is able to effectively and efficiently counterbalance the forces generated by the wind propulsor. Moreover, due to the auxiliary thrust generated by the wind propulsor, the existing engine and pro-peller operating conditions will change. Not only will the propro-peller

mainly operate in a light load condition, it will also no longer operate in an upright, optimised flow.

It can be observed that every aspect has a large influence on the others and to arrive at the equilibrium all these phenomena need to be properly combined by using an iterative optimisation procedure.

Potential U s e r s

An initial study has shown that Wind-Assisted Ship Propulsion is a viable solution in many different applications. In terms of size, it is believed that, f o r t h e time being, the small-medium ship-length range (that is, 20 to 200 metres) is of particular interest. Larger ships are probably less likely to gain substantial advantages by using auxiliary wind propulsion.

Several different types of ships appearto be suited for wind-assisted propulsion. Certainly all kinds of freighters such as general cargo vessels, multipurpose vessels, tankers and dry-bulk carriers are suitable. Smaller cruising ships, both for adventure (Arctic exploration for instance) and other types, as well as small fishing vessels have potential too. Lastly, patrol and guarding vessels are also suited for wind-assisted propulsion as they have to spend long periods of time away from the coast sailing at low speeds, during which fuel replenishment is difficult and expensive.

Alcyone olCousteau equipped with Turbosails (picture by Entomolo) 10 SWZIMARiTiME