Conventional fabric sails are unreliable. "Wind speed and direction change by the second," says Mike Drummond, the design director for the BMW Oracle Racing team. "The crew must constantly maneuver the mainsail to maintain maximum speed." A sail's leading edge often ripples, particularly when tacking into the wind, increasing drag and causing the sail to lose the airfoil shape that helps propel the boat. In contrast, it takes just one sailor a few clicks on a computer to immediately swing the 190-foot-tall carbon-fiber-and-Kevlar wing into position, where it will hold its shape regardless of conditions. With the wing, Drummond says the 90-foot trimaran can sail up to 5 percent, or about one knot, faster.