05 MAR 2019

Norsepower Oy’s Rotor Sail solution has received the first-ever type approval design certificate granted to an auxiliary wind propulsion system on board a commercial ship.
The type approval from DNV GL was issued after a design assessment of Norsepower’s 30-meter by five-meter Rotor Sail, two of which have been installed on board the Maersk Pelican LR2 tanker. The certification means that vessels operating Norsepower’s Rotor Sails are technically capable of safely navigating “all operational and environmental situations.”

The system has already been installed on three vessels and has achieved over 35,000 hours in operation and has delivered independently verified fuel savings with potential of up to 20 percent. Last year, Viking Line installed an 80-foot Norsepower system on the cruise ferry Viking Grace.

The history of the Flettner rotor dates back to 1924, when engineer Anton Flettner installed two of his newly invented rotors on the converted schooner Buckau. Flettner rotors depend upon an aerodynamic phenomenon known as the Magnus effect. When wind contacts a rotating cylinder, it flows at different relative speeds as it passes on each side. That speed difference translates into a pressure difference, creating force at a right angle to the wind direction – an effect similar to that of a traditional cloth sail. Unlike a sail, though, the Flettner rotor needs no furling, reefing or line-tending. The Buckau’s performance also suggested that rotor-driven ships could sail closer to the wind than traditional sailing vessels.

The Norsepower rotor sail is an update on the original Flettner design, with several notable improvements. It is built of lightweight composite materials, and it is fully automated: its control equipment senses whenever the wind is strong enough to deliver fuel savings, at which point the rotor starts on its own (with full control available to the crew). It is suitable for vessels with high utilization, open deck space, and trading routes in areas with favorable wind conditions.

The E.U. forecasts that there could be up to 10,700 wind propulsion installations on bulkers and tankers by 2030. The International Windship Association notes that wind propulsion technologies are available in seven main categories:

  • Soft Sail – both traditional sail and new designs of dynarig etc.
    Hard Sail – wingsails, foils etc. Some rigs have solar panels for added ancillary power generation.
    • Flettner Rotor (Rotor Sail) – rotating cylinders operated by low power motors using the Magnus effect (difference in air pressure on different sides of a spinning object) to generate thrust
    Suction Wings (Ventifoil, Turbosail) – non-rotating wing with vents and internal fan (or other device) that use boundary layer suction for maximum effect.
    Kites – dynamic or passive kites off the bow of the vessel to assist propulsion or to generate a mixture of thrust and electrical energy.
    Turbines – using marine adapted wind turbines to either generate electrical energy or a combination of electrical energy and thrust.
    Hull Form – the redesign of ship’s hulls to capture the power of the wind to generate thrust.


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