Sailing skill is essential to winning an America's Cup. But so are physics and physique.The race that began with wood-and-canvas schooners in the 1850s has graduated to carbon-fiber hulls and Kevlar sails. Millions of dollars, and some of the best minds, go into developing the boats. The 1992 races again will show the heavy stamp of science. The French, for example, have been using artificial intelligence to pinpoint a boat's position relative to an opponent and help shape tactics. Powerful computers are augmenting the water tank and wind tunnel to design, test, and model boats. In this year's new class of yachts, which are nearly twice as fast as the 12-meter boats used for 30 years, hulls and masts are made of carbon-fiber composites. The material, a spinoff from the space program, is tough and lightweight, but not immortal: Four masts have snapped in trial runs. The wealthy Italian syndicate recently flew in a boat that its people assert has the "lightest hull yet." The New Zealanders supposedly have one with no rudder, twin keels, and a "revolutionary" bow. High-tech doesn't solve everything: Teams couldn't make lasers work to clear kelp off their keels so are resorting to "flossing pulling a rope under the hull. As for brawn, the 16-member crews follow Olympic-like training schedules. At least one has hired a former NFL conditioning coach, and most have their own cooks. Diets are regimented down the last Jenny Craig calorie. America3's crew starts its day at 6:45 a.m. with a two-hour strength-and-endurance workout. After a nutritionally correct breakfast, they hold meetings, sail for five to eight hours, and reconvene for more meetings.