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The BB Green project set out in May 2011 to achieve an ambitious objective: the partners embarking on this four-year endeavour were determined to develop the world’s fastest battery-powered ferry. Mission accomplished, says coordinator Ulf Tudem of Surface Effect Ships Europe AS in Norway, reporting on the successful trials of a prototype constructed by the team.
“When the project applied for funding, typically the aim with regard to emissions would have been to achieve reductions of 10 to 20 %,” Tudem recalls. “But we decided to try for more, by developing and building a completely green and emission-free vessel. We have shown that the concept works.”
Forging ahead
The general opinion at the time, he notes, was that battery electric operation would only be possible for speeds of 5 to 7 nautical miles per hour (knots) – the equivalent of less than 13 kilometres per hour (kph). Here again, BB Green aimed higher. “We went for 30 knots, so nearly 56 kph,” says Tudem. “After all, if you build a boat today, you don’t want it to be outdated tomorrow.”
One of the project’s key activities thus involved selecting technologies that would help to keep their innovation afloat. “The battery was our main concern,” Tudem reports. Having considered a variety of options, the partners eventually opted for a battery based on a lithium ion titanate chemistry, with a life expectancy of some 20 000 charge cycles.
Fast-charging this battery for 20 minutes supports about 30 minutes of high-speed operation, Tudem notes. At a rate of 12 to 14 such charge cycles per day, he therefore expects it to last for four or five years. Batteries based on other types of chemistry would wear out in a matter of months, he adds.
The design of the hull was another key consideration. “We needed a hull concept with unique efficiency. A conventional hull would have limited the ferry’s range,” Tudem explains.
An air-supported vessel (ASV) concept patented by his company held the key: a lift fan system fills a cavity under the hull with pressurised air, lifting the boat up in the water. “This way,” says Tudem, “we have much less wetted surface area and resistance. These are key factors to take into account if you want to go fast.”
The ASV design has another important advantage, he notes. It reduces wake wash, the trail of turbulence a vessel leaves as it plows through the water. The waves that are stirred up carry a lot of energy, which can contribute to the erosion of shorelines and potentially put smaller vessels at risk, Tudem explains. Limiting this phenomenon adds to the BB Green concept’s green credentials.
Further attention focused on the choice of the propulsion system. “We wanted to make sure that we had the best in terms of efficiency,” says Tudem. The partners picked a concept involving forward-facing propellers that pull rather than push the boat through the water.
Initially designed for operation with a diesel engine, this prototype system was adapted for an electric set-up with pro-active support from manufacturer Volvo Penta, a company that specialises in power systems for the marine industry, Tudem notes.
The construction materials were also chosen with care. Instead of a conventional approach involving glass fiber wetted by resin and laid up by hand, the project opted for an alternative composed of two carbon layers enclosing a lightweight core.
The resin that holds this “carbon sandwich” together is injected under a vacuum, Tudem notes. This approach greatly reduces the health and environmental risks associated with the gases that are typically emitted during a conventional open construction approach.
Welcome aboard
The BB Green prototype passed all tests with flying colours, Tudem reports, and the partners are now developing the concept into a commercial product. Demonstration and dissemination activities are conducted as part of a follow-on project named Green Fast Ferry, launched with EU funding in September 2016 and in 2017 BB Green received the award of electric and hybrid propulsion system of the year.
Once all components have been approved for commercial use, a first order could be completed within a year, says Tudem. The prototype was sized for up to 100 passengers, he notes, but the concept itself could also be used to build larger vessels.
Potentially, BB Green ferries could reach up to 70 m in length and accommodate both passengers and cars, Tudem adds. They could also be designed as hybrids, running on batteries or with efficient diesel powertrains depending on the circumstances, he concludes – there are plenty of possibilities for clients keen to catch the tide.