Kongsberg rim-drive thrusters chosen for Norwegian vessel

OV Bøkfjord, a Norwegian Coastal Administration (NCA) vessel, will be retrofitted with Kongsberg Maritime electric rim-drive azimuth thrusters, and the battery capacity increased by four times, allowing it to make better use of locally available electric power from Norway’s almost entirely renewable energy grid.

“To maximise emission reductions, changing propulsion technology to our rim-drive azimuth thrusters allows the vessel to operate for much longer periods on full electric, emission-free clean energy,” said Eivind Midtlid, Kongsberg sales manager Offshore Integration and Energy.

Propellers, fans and rotors generate the most significant noise at their blade tips, which generate vortices – and below the waterline, cavitation. These phenomena are also understood to increase corrosion in ship propellers.

Rim-drive thrusters sidestep this problem by distributing vortices along the blade length, leading to lower noise emissions. This alone is also responsible for a potential increase in efficiency, but more still is possible thanks to the rim-drive’s lack of shaft and gearbox. A smaller hub, too, means a larger blade area.

In general, battery-hybrid operation can be responsible for around a 15% improvement in the efficiency of smaller vessels such as ferries and workboats. Batteries and electric propulsion are better at ramping up and down to match variances in load, allowing gensets to run continuously within their most efficient load range. “This project proved that the hybrid technology has developed significantly over the last ten years since the OV Bøkfjord was first introduced,” said Midtlid. “Through our detailed analysis we have been able to expand the battery capacity by four times compared to the original design.”