Friday 21 December 2007

Football Field-Sized Kite Propels Latest Ocean Freighter

A 132-meter long vessel will soon be making its maiden voyage, but rather than using copious quantities of diesel while traversing the Atlantic, it'll be receiving a good bit of help from the computer guided kite attached to its bow. The $725,000 device (600 square metres of sail) will be tethered to a 15-meter high mast and will fly some 300 meters above the ship. The kite is constructed as a twinskin kite which keeps its airfoil shape due to internal air pressure: A set of small mesh openings in the leading edge allows air into the opening between the front and back side. This form of kite is an airfoil, not a spinnaker, the difference is huge: A spinnaker is effectively a large bag to catch the wind, while a kite works best by having air moving faster on one side than the other. Among other things, this means that a kite allows you to sail much faster at an angle to the wind instead of straight downwind.

According to the skysails website, and shown in a live action promo video,(requires fast broadband) the launch and retrieval of the sail is completely automated, as is the steering. a single person will be able to operate the whole thing by pressing the launch button in the control room to start it, and press the retrieval button when done. The control system acts like the autopitot systems on an aircraft, the company says. Autopilot software sends and receives data about the sail etc to make sure the sail is set at its optimal position.

The Beluga shipping company that owns the 460-foot Beluga said it expects the kites to decrease fuel consumption by up to 50% in optimal cases as well as a cutback of the emission of greenhouse gases on sea by 10 to 20%.

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