Sailing ships with a new twist

The Economist (Paid subscription required) ^ | Sep 15th 2005

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Giant kites that act like sails could bring wind propulsion back to ocean-going ships, reducing emissions and saving on fuel costs

IN THE first half of the 19th century, ships began to adopt steam engines, first alongside and then instead of sails.

{snip} ... the high price of oil and stricter pollution regulations are strong forces working to turn back the clock. Wind propulsion is coming back in a new form: kites, not sails. Next year, SkySails, a German firm based in Hamburg, will begin outfitting cargo ships with massive kites designed to tug vessels and reduce their diesel consumption. The firm estimates that these kites will reduce fuel consumption by about one-third—a big saving, given that fuel accounts for about 60% of shipping costs. {Snip}

But the SkySails approach does away with masts and is much cheaper. The firm says it can outfit a ship with a kite system for between €400,000 and €2.5m, depending on the vessel's size. Stephan Wrage, the boss of SkySails, says fuel savings will recoup these costs in just four or five years, assuming oil prices of $50 a barrel.

SkySails' kites are made of a type of nylon similar to that used in the sails of modern windjammers, but they fly between 100 and 300 metres above sea level, where winds are less turbulent and, on average, more than 50% stronger than the winds that sails capture. An autopilot computer adjusts the height and angle of the kite, the surface area of which can range from 760 to 5,000 square metres. When the wind blows too strongly, one end of the rectangular kite is released so that the kite flaps like a flag. A powerful winch retrieves the kite when necessary.

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Here's an update following the test of the prototype kite (now called a "traction kite")

"Earlier this year SkySails trailed a kite on an 800-ton former buoy tender in the Baltic Sea. Using a towing kite of only 80-square-meters the Beufort reached five knots in low winds.

While this doesn't sound very impressive, add to it engine propulsion and Wrage and his team believe that a saving of between ten and 35 percent could be made on fuel costs and in better wind conditions, perhaps even 50 percent."

More at this site:

http://edition.cnn.com/2006/TECH/science/10/27/ft.kiteships/