Ship & Boat International: November/December 2016
The construction of the novel, 40m carbon fibre hybrid catamaran Vision of the Fjords, which will carry sightseers around Norway’s Nærøyfjord, presented a few challenges – especially since “nothing like this has ever been built before” explains Torstein Aa of builder and designer Brødrene Aa. Based on the group’s Seasight design, Vision of the Fjords has brought the company a great deal of attention, including the Ship of the Year award at 2016’s SMM fair in Hamburg.
Following the tradition of many innovative Norwegian firms, Brødrene (literally 'Brothers') Aa was founded by Olav and Bertel in 1947 and remains a family business to this day. However, it thoroughly embraced composite design during the 1970s and took to building first glass fibre, then carbon fibre vessels at its Hyen shipyard.
So, it's perhaps not surprising that the design is a synthesis of the company's materials expertise and Norway’s inspiring geography. No less than 150m² of windows and two decks of gently sloping walkways, modelled on winding hill paths, combine to give each of the 400 passengers 'a front-row view' of their surroundings.
There are very good reasons to consider a carbon fibre design in a sensitive environment, says Aa, as the light weight directly translates to fuel savings and lower emissions – especially when compared to the existing sightseeing ferries servicing Nærøyfjord, some of which are more than 50 years old. However, Aa emphasises that although the company has constructed larger yachts of the same material, Vision of the Fjords is “the biggest ever commercial passenger boat to be built in carbon fibre”. Moreover, while the company has completed over 50 vessels in the same material, a sightseeing ferry presents rather different structural challenges. The main challenge is that there is “a very big open area and large windows in the front,” Aa explains, adding that 80% of the deck has been made accessible to passengers. Therefore "a lot of finite element analysis" was necessary to make sure the superstructure would support itself.
The second challenge is that this vessel is a hybrid. The twin 1,500 kW MAN D2862 LE422 engines have been configured by Norwegian company MANCraft to run a parallel hybrid system using a CENTA electro-magnetic clutch, driving the shaft-mounted propeller via a ZF gearbox and a pair of Oswald, permanent-magnet synchronous motors. These also act as alternators to charge the batteries with any spare capacity.
As a result, the diesel and electric elements can power the propellers together or independently of each other with a seamless transition between modes. During electric-only operation, the vessel can glide along for between 2.5 to 3 hours of near silent running at Nærøyfjord’s 8knot speed limit. On the other hand, full diesel power can be directed through the electric engine to the ZF gearbox and the controllable pitch propeller – even then, separate damping and insulation of all the individual components of the drive system limits noise and vibration levels.
The 576kWh battery system from ZEM is stored below deck and is managed by a lightweight version of ABB’s Onboard DC Grid. However, Aa explains, another challenge presented itself at the beginning of the service. “When the boat started operating there was no shore charging [station] for the batteries, so we needed to recharge them from the diesel for the two first months,” he says. Happily, the configuration proved flexible enough to adapt itself to the changed circumstances.
All in all, Vision of the Fjords represents an important first for commercial sightseeing ferries. With greater implementation of developing green technologies, the hope is that more people will have a chance to experience the world's natural beauty – without destroying it in the process.
