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VALENCIA, SPAIN — USA-17, the challenger for the America’s Cup, and Alinghi 5, the defender, may be stripped-down, lean racing machines, built purely for speed. But both are fully loaded.

Loaded, that is, with compressive and tensile stresses in an exquisitely choreographed dance of struts, spars and cables. Made almost entirely of carbon fiber, the enormous multihulls — USA-17 has three hulls, Alinghi 5 two — are about as delicate as a house of cards. If a big enough element were to break, the whole thing could fall apart.

That could be disastrous, considering that the boats, with masts that tower a couple of hundred feet above the water, are capable of speeds of 30 knots or more.

On Monday, however, the boats hardly moved at all, as inconsistent winds forced the postponement of the first race in the best-of-three series on the Mediterranean. The two teams will try again on Wednesday.

If the boats make it through the races relatively intact, it will be a testament to the skill of the sailors — and of the designers and engineers who spent several years building them, more or less on the fly as the two sides quarreled in court over the terms of the race.

“If we break it,” said Brad Butterworth, skipper of the Alinghi team (owned by the Swiss biotechnology mogul Ernesto Bertarelli), “it’ll be because of some failure of a fitting or a user mistake — something that we’ve done that’s put the boat in a compromising position where it couldn’t handle the loads.”

The America’s Cup has always been a showcase for innovation: the 1895 victor, Defender, for example, used aluminum, steel and bronze in the hull, an unheard-of combination at the time. And sailing in general, and high-level racing in particular, are no strangers to technology. But it has not been used at such an extreme scale before.

The most obvious advance can be seen rising above USA-17, which is owned by Lawrence J. Ellison, president of the software company Oracle. It looks as if someone wrenched a wing off a large jetliner and perched it, tip up, atop a trailer hitch on the boat’s middle hull.

Wing sails, as they are called, have been around for years, and one was even used to great advantage in the 1988 America’s Cup. But at 223 feet, this one is much bigger than others (and bigger, in fact, than any airplane wing) and more controllable, with nine adjustable flaps.

Like an airplane wing, it provides lift, although largely in a horizontal direction. And like an airplane wing, the slots between the main elements and the flaps add to the lifting power.

But the wing also solves a basic problem of sailing: how to take full advantage of the wind without overturning. The flaps can be adjusted to maximize lift on the wing’s lower end, generating a lot of power, and to reduce it up top, generating less heeling, or tipping, force.

“You can shift the center of the force up and down the wing very quickly,” said Russell Coutts, chief executive of BMW Oracle. “So when you’ve got too much power, then you can unload the top of the wing.”

The wing designers use the same principles, and much the same software, as airplane designers, said Mike Drummond, the team’s design director. (One member of the team also does work for Boeing, though not on wings.)

“You have to understand the aerodynamic principles well and how to apply them,” Drummond said. “If you have the skills to design an airplane, you have the skills to design a yacht. Now we could have a good crack at a windmill.”

Load-shifting can be done with more traditional sails, too, by changing their shape, which is accomplished in part by having a flexible mast. But even with technology, shape-changing is difficult. It is easier with a solid wing.