Ferry uses electric power and air support

Investigations into efficient and environmental friendly waterborne transport solutions, to ease traffic congestion in and around cities and densely populated coastal areas, have lately become increasingly more common around Europe and beyond. Under the EU 7th Framework R&D programme, the three-year €3.2 million BB Green maritime innovation project applies and combines technologies and solutions to design and demonstrate a novel fast ferry solution.

To succeed with the innovative approach the team is starting out with a new hull concept. Norwegian company Effect Ships International provides air supported vessel technology; its subsidiary SES Europe is responsible for the hull form developments. Tank testing has taken place on two ASV hulls designs, corresponding to ferries of length 20m and beam 6m, at SSPA in Gothenburg, Sweden. With a design speed of between 25 and 35 knots these two concepts, one a catamaran and one a monohull, are being extensively tested in calm waters and waves that represent conditions that might be experienced on the planned routes. The ASV hull designs have been compared with modern planing hull designs to evaluate hull resistance and onboard motion data.

The favoured ASV Mono design demonstrated a reduction in hull resistance of around 50 % over a wide range of speeds. The fan power needed to obtain these significant benefits in calm waters was low as 3% to 6 % of total power consumed. Another discovery was that the efficiency improvement extends down to low speeds – even at 10 – 15 knots hull resistance is much reduced. A signigicant reduction in wetted surface area, and efficient planning surfaces, both contribute to the low resistance.

The vessels are intended for commuter operations, with frequent stops. Therefore fast and efficient acceleration from stand still to cruisespeed will be important, not only for the time table, but also to optimise overall energy consumption and wake wash generation. The reduced hull resistance at ‘hump’ speed for the ASVs enables a fast transit to cruising speed with less power consumed and less wash generated.

Typical routes for the BB Green ferries will be in relatively sheltered waters, such as in and out of Rotterdam and surrounding suburbs. Here relatively low and short waves are dominant, and onboard comfort is essential. The air cushion typically supports up to 80 – 85% of the total operational displacement, and this air cushion contributes to motion reduction and motion damping. Now that the hull form has been developed, attention is turning to detail design of the ferry and the electric propulsion system.