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Stanford's composites bring high tech to the America's Cup
STANFORD - Once considered more art than science, yacht racing has gone high tech, depending on scientists as much as sailors.
The 28th Defense of the America's Cup will be the first in which all competing yachts are made of composite materials, according to the organizing committee.
The owners of four yachts competing for the right to defend the cup for the United States have called upon Stanford aeronautics and astronautics Research Prof. Stephen Tsai to choose their composite materials to mold into hydrodynamic designs.
Prized by the aerospace industry for their strength and light weight, composites are graphite fibers embedded in a resinous matrix that solidifies when heated. Composites give yachts light weight for speed and strength to withstand slamming waves.
Thanks to composites, the new, space-age yachts are 10 feet longer, 33 percent lighter and have 50 percent more sail area than the traditional 12-meter class boats used in Cup racing between 1958 and 1987. As a result, they are 25 percent faster.
"Traditionally, boat makers designed boats based on experience and intuition," Tsai said. "If you go to an uncharted area such as the use of composite materials for a big boat, you can't rely on art any more."
Tsai's engineering team picked and tested the composites used to build four high-tech yachts belonging to the America3 (A3 or America Cubed) Syndicate, which supports research at Stanford and MIT.
From January through April, the yachts are competing against Dennis Conner in Stars and Stripes for the right to defend the United States in the America's Cup races. In the last cup final, in 1988, Conner defeated New Zealand in 1988 with a catamaran (two-hulled vessel), also named Stars and Stripes.
The winner will meet the foreign challenger for a best-of-seven race off San Diego beginning May 9. Crews from Australia, New Zealand, France, Italy, Japan, Spain and Sweden are vying for the role of challenger in a separate series of trials.
In 1851, the New York Yacht Club's schooner, America, defeated 17 British opponents in a 58-mile race to win the Royal Yacht Squadron's Hundred Guinea Cup, which was renamed after the victorious boat. For the next 132 years, the world's best yachtsmen tried to wrest the trophy from American hands. In 1983 the Australians succeeded with a winged-keel boat, and the race was on to design high-tech boats.
All four A3 boats are made of the same composite materials, said Tsai, who first became involved with sailing as a composite materials specialist for the U.S. Air Force. He consulted on the production of the USA, a San Francisco yacht that reached the semi-finals in the 1986-87 America's Cup.
A3's boats differ only in design, Tsai said.
"You need to try different combinations of shapes, different weight distributions, different concepts," he said.
Design is so crucial that it inspires spying among yacht clubs. Helicopters with cameras buzz the competition's compound, and scuba divers try to photograph their keels. Yacht owners keep their boats' bottoms skirted until they are lowered into the water. Some even paint their keels to camouflage their true shape.
International yachting rules strictly govern the design and construction of America's Cup boats. Specific parameters such as hull thickness and cure temperature (the temperature required to solidify composite materials) insure the uniformity of the boats.
"You want some equity in terms of how the boats are built for the same reason Formula One race cars are restricted," Tsai said. "You cannot have a Mack truck and run it against a race car."
Keel design is especially critical, Tsai said. A bulb of lead at the bottom of the keel provides stability. A lighter boat can distribute more of its weight in the bulb, stabilizing the vessel and allowing it to sport bigger sails. Because the mast of A3's newest boat is more than 100 feet high, Tsai said, most of the boat's 20 to 30 tons of weight are in the keel for counterbalance.
. Tsai's Stanford team, in conjunction with John Hamilton of Lockheed, worked with blueprints provided by boat designers to determine the best way to build composite yachts within the manufacturing constraints of the America's Cup rules. The team included Tsai, aeronautics and astronautics department chair George Springer, visiting scientist Quiling Wang, postdoctoral scientist Sung-Kyu Ha, and graduate students R.J. Downs, Kuo-Shih Liu and Chris Dixon.
Based on such physical properties as stiffness, strength and density, they chose composite materials that would form the hull, deck, keel and mast of A3 boats.
In a Stanford laboratory, a machine bent and twisted a scale model of the keel to test its strength. Other models were subjected to wind tunnels or dragged though tanks to calculate the force necessary to propel them through water.
Computer simulations at Stanford allowed scientists to determine the boats' abilities to withstand wind and waves, which can buckle weak hulls to resemble folded beer cans. Computers calculated the stress borne by the keel, hull, mast and rigging as a boat slammed through simulated waves. Scientists tested thousands of design options with a few clicks of their keyboards.
Composites allow for cheap and easy construction of complex shapes, Tsai said. A composite boat can be built in only 60 days, he said.
Built with a sandwich technique used in aircraft construction, the hull is made of a man-made honeycomb core nestled between two skins of composite material.
The honeycomb minimizes the boat's weight while providing stiffness. The stiffer the boat's hull, the faster it glides through the water, he said.
Composite hulls are shaped in molds, which are either male (the composite is molded over a form), or female (the composite is placed inside the form). A female mold produces a smooth outer hull surface. A male mold creates an outer surface that needs smoothing but is easier to manufacture.
Hulls are built in sections that then are joined.
"You don't want too many parts because you pay a penalty at the joint," Tsai said. Materials overlap at joints, providing twice the thickness and therefore twice the weight.
How does all this science fare on the race course? After the second round robin of defenders' races, America3's yachts America3 and Defiant had impressive winning records, while Jayhawk was retired from competition after the first round. Conner's Stars and Stripes won less than half its races.
By the end of April, both the defender and the challenger of the America's Cup will be selected. They will meet in a best of seven match race starting May 9.
"A3 Syndicate, under the leadership of Bill Koch, probably places more emphasis on science and technology than all the other competitors combined," Tsai said. "An ultimate triumph (by A3) will not only reflect the work of a sports team but also that of high technology."
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