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The benefits of fitting wingsails to a commercial ship are primarily financial. Modern wingsails can reduce the running costs of the vessel by 20% to 40% in an existing vessel, and by 50% to 70% in a brand new ship designed to obtain the best results from wingsail assistance.
The easiest vessels to equip are vehicle carriers, with their long, flat upper deck and forward positioned bridge, closely followed by cruise liners and tankers. In the case of retrofitting wingsails on to a tanker, four-legged support structures mounted to the edges of the deck will be needed to position the wingsails above the forward sightlines from the bridge. The economics of fitting wingsails to tankers are likely to be relatively attractive, because of the comparatively slow passage speeds employed, usually of no more than 8 to 10 knots.
In the case of retrofitting wingsails to existing ships and arranging the specification of brand new ships to include wingsails it is important that voyage speeds above around 16 to 18 knots are avoided, since higher speeds will result in the frequent occurrence of wind on bow conditions, with consequent reductions in thrust availability from the wingsail equipment.
In the case of fully optimised new wing-assisted ships, the naval architects will specify smaller and cheaper main propulsion engines, capable of maintaining the full service speed at 100% of rated power, rather than the 75% - 80% of power normally specified, to allow a margin for adverse conditions. The smaller engine and proportionately reduced stern gear will occupy a smaller volume of the ship's structure and this allows for increased cargo carrying content. The smaller engines and stern gear will offer a capital cost saving which could pay for all or most of the cost of the wingsail installation. A logical extension of this optimised auxiliary ship will introduce the fully optimised wingship, where the wingsails are the main propulsion system and a comparatively small diesel installation is the auxiliary. Such a wingship could operate at exactly the same service speeds (and with slightly more cargo carrying capacity) at something like 5-10% of the fuel consumption of an existing non-wingsail vessel, and could well cost less to buy. Her operating economics would therefore be very attractive to ship owners.
Wingsails in all cases will stabilise the vessel, offering increased comfort for passengers and crew, and eliminating or reducing the need for costly fin stabilisers. In the event of main engine failure a modern wingsail installation will provide propulsion and steering to avoid dangerous shoals, and its solar energy can provide emergency lighting as well as powering vital instruments.
The picture above shows the 6500dwt mv Ashington, fitted with the first of a planned pair of Walker wingsails. Because of the oil price crash of 1986 the second, bow, wingsail was never fitted. The single aft unit was successful, and by itself could save 15-20% of her fuel.
A most interesting initiative by Wallenius Wilhelmsen in Sweden has developed the car carrier "Orcelle" concept, which includes, among a host of interesting new approaches, a full set of wingsails. Details of the "Orcelle" project can be found at www.2wglobal.com
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