Rotor Sail puts new spin on Flettner rotor

Norsepower said savings of 2.6% were made in a six-month trial using one of its 18m rotor sails on a route in the North Sea.

“It is the first-ever modern auxiliary wind propulsion system that has this kind of proof of concept,” Norsepower CEO Tuomas Riski told The Engineer.

The Rotor Sail Solution is a modernised version of the Flettner rotor – a spinning cylinder that uses the Magnus effect to harness wind power.

When wind meets the spinning rotor sail, the airflow is accelerated on one side of the equipment and restricted on the other.

The resulting pressure difference creates a force perpendicular to the wind flow direction – a lift force.

An electric drive system powered by the auxiliary grid in the vessel is used to rotate the rotor sails.

When wind conditions are favourable, the rotor sails allow the main engines to be throttled back, saving fuel and reducing emissions.

Compared with other methods aimed at improving vessel fuel efficiency, such as air bubble systems, the Norsepower solution was the only one bringing renewable energy to the board, Riski said.