"Wind power makes another comeback" Topic

"OLD technologies can return with a twist, just as airships keep threatening to and windmills and electric cars have already. Fitting ships with sails to assist with propulsion, thus saving fuel and reducing emissions, is an idea that has been around for decades. It has now gained renewed interest with a search by the Energy Technologies Institute (ETI), a British public–private partnership that promotes low-carbon uses, for suppliers and a shipowner prepared to undertake a trial of wind-driven rotors on a large cargo vessel. The plan is to gather operating data on whether rotor sails are a worthwhile investment. Depending on the routes, suitably equipped vessels could reduce fuel consumption by 5-12%. As some 90% of the world's trade travels by sea, such savings would soon add up.

The type of sail the ETI is interested in is the Flettner rotor. These were demonstrated by Anton Flettner, a German aerospace engineer, in the 1920s. When placed on a ship the giant rotating cylinders extract energy from the wind using the Magnus effect, a force acting on a spinning body in an airstream to create a pressure difference on either side—the same effect that causes a spinning ball to curve through the air. This force can be used to help push the ship along.

Rotor sails are most suitable for ships that sail below 15 knots (28kph) on trade routes where the apparent wind (that experienced by an observer in motion) is blowing sideways across the vessel, reckons the ETI. For a rotor sail the higher the ratio of wind speed to ship speed the better. In general, the rotors produce more thrust the windier it is and the slower the ship steams…"
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Amicalement
Armand

The problem with wind is lack of when needed and too much when not needed. Ships need to keep to schedules and with the wind it may or may not be blowing when needed. Then when a ship gets into gale force winds will the sail still be there after the storm ends.

I think that they tried these sails on The Undersea World of Jacques Cousteau.

Sails for commercial vessels, yes.

Adding sails to a military craft? Can anyone say "radar signature"?

Harpoon magnets.