If you saw the Beluga SkySail gliding into port, you might be excused for thinking that someone on the multipurpose cargo vessel was trying to parasail. How else to explain the 1,700-square-foot kite billowing above the ship's bow? But the crescent-shaped fabric sail isn't there for recreational purposes. The ship's owners are taking advantage of the wind and using the no-cost, nonpolluting source of energy to provide auxiliary power.

A sophisticated computer system deploys and controls the sail while choosing routes that can make the best use of wind power. Because the sail allows the ship to use less fuel, the SkySail could cut its diesel usage by as much as 20 percent, say its backers.

Auxiliary wind power for commercial shipments is no pie-in-the-sky idea. The ship recently delivered 71 ocean containers and 91 crates of project cargo from Bremen, Germany, to the Port of Guanta, Venezuela, on behalf of DHL Global Forwarding. DHL, which tried out the windpowered ship as part of a carbon-reduction initiative, plans to continue the service and expand its use of alternative transportation services.