Flettner Rotor Sail Technology Becomes Modern Reality in Fuel Efficient Passenger Ferry

FINLAND – Viking Line has installed a rotor sail on the LNG-fuelled passenger ferry, the Viking Grace, and is accurately describing her as the first passenger ship in the world equipped with a rotor sail for the utilisation of wind power. This however is a technology dating back to 1924 and the launch of the experimental cargo vessel Buckau, and based on the Flettner system, in turn developed from the discovery of the hitherto unrecognised Magnus force revealed in 1851 by German physicist Heinrich Gustav Magnus. This latest rotor sail, developed by Finnish company Norsepower, is expected to cut fuel consumption and reduce emissions by up to 900 tonnes CO₂annually. The Viking Grace is already operating on wind assisted voyages between Turku, Finland and Stockholm, Sweden.

Lloyd’s Register (LR) approved the structure and the risk-assessment related to the installation of the sail in line with its Guidance Notes for Flettner Rotor Approval. The approvals were conducted to ensure that the Flettner rotor would not adversely affect the safe operation of the ship or the safety of the crew. Finland has taken something of a lead with the modern development of this technology as it was maritime engineering company Wärtsilä which proposed a concept cruise ferry in 2009, leading to this latest vessel's construction.

The LNG-fuelled ferry has been in operation since 2013, less the rotor sail system, when LR helped Viking Line handle the complexities of accommodating the LNG tanks on the stern deck as well as its regulatory, class and operational requirements. LR’s Jane Jenkins, Lead Specialist, Passenger Ship Support Centre, commented:

“A few years ago LR developed an animation called ‘The Ferry - a story of innovation’, which at one point shows a ferry with wind rotors and kite sails sailing across the screen at breakneck speed. At the time rotor sail technology was clear but not immediately contemplated in the context of a ferry. It is wonderful to see what seemed like an idea at the time become a reality. We are immensely proud to have been part of the journey.”

The cylindrical rotor sail installed on Viking Grace is 24 metres high and 4 metres in diameter and uses the Magnus effect for propulsion. As the rotor is spinning, the passing air will flow with a lower pressure on one side than the opposite side. The propulsion force created by this pressure difference drives the vessel forward. The modern rotor sail operation is automated, and the system will shut down in response to any disadvantageous changes in the direction or force of the wind. Jan Hanses, CEO of Viking Line, said:

“The use of wind power reflects Viking Line’s green values and we want to pioneer the use of solutions that reduce impact on the environment. Based in Finland, Norsepower has developed a world-class mechanical rotor sail solution that will reduce fuel consumption. We are proud of the fact that Viking Grace will be the first passenger ship in the world to benefit from this innovative solution.”

In addition to the rotor sail solution installed on board Viking Grace, Viking Line plans to use wind propulsion in the company’s new vessel, due to be operational in 2020. Built in China, the passenger ship will be equipped with two mechanical rotor sails supplied by Norsepower, doubling the wind power potential. Maersk Tankers and Shell have also been experimenting with Flettner rotors as a source of power in the past year or so.

Photo: The Viking Grace