Wavefoil’s fibreglass retractable bow foil solution was retrofitted to MF Teistin in September 2019. (Picture courtesy of Wavefoil A/S)
Wavefoil, the Norwegian bow foil technology company, said its retractable bow foil solution had significant fuel savings after analysis of six months of performance of its first installation aboard a Faroe Islands based ferry.
Wavefoil’s retractable bow foils were installed on board MF Teistin in September 2019. Fuel consumption on board the ferry declined by 9% after the installation, Wavefoil chief executive Eirik Bøckmann said.
Bøckmann added that the economics of the solution were dependent upon the ship’s size, speed, route and the price of its fuel.
Larger vessels could achieve fuel savings of between 5-15%, while most vessels could achieve savings of between 5 and 10%. Some larger vessels could achieve a payback period of just 3 years, although typical payback periods are between 4 and 8 years, Bøckmann added.
However, the benefits of the solution extended to reduced movement in waves, which offered improved comfort for passengers and crew. “Healthy and happy passengers on a passenger vessel spend more money in restaurants, bars and shops than seasick passengers,” Bøckmann said.
How the foil works
The foils function by lowering the added resistance in waves and by providing auxiliary forward thrust in all wave angles. Both head and bow seas give large pitch motions and added resistance, which the bow foils reduce.
One of the obstacles to bow foil installations has been their variable effect on thrust. In other words, in calm water, the foils can exert additional backward drag, rather than providing forward thrust.
Wavefoil’s bow foils can be managed tactically to ensure that a ship operates optimally.
“Typically, the ship master will deploy the foils once the wave height exceeds 0.5-1 m. The foils are retractable to avoid giving extra drag in calm water, to protect the foils in extreme waves, and to avoid objects in the water, such as ice, timber, fish nets etc,” Bøckmann said.
The management of the bow foil is also relatively straightforward. It takes about three minutes to deploy or retract the foils for Wavefoil’s three largest foil modules (for ships between 40 and 200 m long). The foils are made from an especially strong type of fiberglass.
The fibreglass ensures flexibility, which is important for reducing the slamming load if the foils come out of water, while maintaining the required strength.
“Installations on larger vessels will impose enormous loads on the foils, but our calculations show that the foils will have sufficient strength, with a reassuring safety margin,” Bøckmann added.
The company also offers a smaller foil module tailored to high-speed catamarans between 20 and 40m long. That solution is cast from bronze and has a shorter retraction/deployment period of about a minute.