Commuting on a cushion of air

Numerous European cities exploit closed waterways and ferries to move passengers and goods within the local environment. Conventional ferries employ all-wet hulls in which the entire hull is in contact with the water. This, however, creates a large surface area for resistance and reduces efficiency and speed.

The EU-funded BB GREEN (Battery powered boats, providing greening, resistance reduction, electric, efficient and novelty) project was established to develop the next generation of fast, efficient and emission-free commuter ferries for operation in sheltered waters.

The ferries’ air-supported vessel (ASV) hull supports up to 85 % of full-load displacement on a cushion of pressurised air, which is created with a lift fan system. In addition the new ASV technology can reduce hull water resistance by 40 %.

To reduce the vessel’s weight and boost overall efficiency BB GREEN vessels were constructed from carbon fibre. In addition, diesel engines were replaced with battery electric drivelines for eco-friendly commuting.

The capacity of the lithium-titanate battery was 400 kilowatt-hours, sufficient to operate at design speeds of 30 knots for about 14 nautical miles between recharging. Efficient contra-rotating pod propulsion systems ensured high efficiency, excellent manoeuvrability and on-board safety.

A full-scale ASV prototype was constructed and tested as were battery operated electric drivelines and the lift fan system. The BB GREEN team then documented the vessel’s performance and capabilities under typical operational conditions.

The ASV concept clearly showed a motion damping effect with pitching and rolling greatly reduced compared to comparable vessels at the same high speed. Furthermore, the wash waves from the BB Green mono ASV resulted in a wave energy that was lower than for most of the reference ships.

The new transport system will contribute to reducing traffic congestion in cities with inland waterways, with considerable environmental benefits such as zero emissions and improved battery technology. Spin off solutions for the near future include fast work boats, as well as firefighting ambulance boats.