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Winging It

Just for a little while, in the second race of the America’s Cup regatta last February in Valencia, Spain, the defending champions thought they had it made. Two days earlier, the Swiss Société Nautique de Genève’s Alinghi 5 yacht had started the first race with a substantial lead, but the challenger, the USA-17 had come from behind to win. Now, midway through the first leg of the course, Alinghi 5 was again ahead. If it could hold on, it would even the score of the best-of-three contest and force a third and decisive race for the cup.

But Alinghi 5’s advantage proved as elusive as the shifting winds, and USA-17 soon overtook it just as before, “blowing the sails off” the Swiss boat in a decisive victory for the series and the cup. America’s BMW Oracle team, led by Oracle software mogul Larry Ellison, brought the cup back to the United States after an absence of 15 years.

Not so unusual—after all, most of the champions in the 159-year history of the competition have been American. Both craft were sleek, 90-foot-long carbon-composite multihulls, both cost millions of dollars to build, both were sailed by expert crews, both were among the fastest things on sails. So what gave USA-17 its winning edge?

That becomes clear when comparing the craft side by side. Alinghi 5 is still obviously a sailboat, with big, soft sails. USA-17 has a giant airplane wing sticking out of it, as though someone had broken it off an airliner and attached it end-on upon the comparatively tiny hull, towering taller than a 20-story building above the water. This “wing sail” works just like an airplane wing—only horizontally rather than vertically. It harnesses the cutting edge of wind power over the water.

USA-17’s wing sail is the most sophisticated and largest yet built. Even a 747 wing is only slightly more than 100 feet in length, whereas the object rising out of USA-17 is over twice that. “It’s hard to describe how big it actually is until you stand alongside it,” says Mike Drummond, design director for the BMW Oracle team. “If we’d thought about it at the start, we might have been scared off.”

It may sound futuristic, but the basic concept has been around about as long as that of the aircraft wing. “Wings on sailboats go back 100 years,” notes David Hubbard, who led the design effort for USA-17’s wing sail and has created them for many other craft, including the 1988 America’s Cup champion, Stars and Stripes.

The precise origins of the idea, however, remain somewhat hazy. “The concept of something rigid [as a sail] goes back at least to a guy named Flettner,” notes Mark Maughmer, an aeronautics professor at Pennsylvania State University. Anton Flettner was a German engineer who exploited the Magnus effect, the generation of lift by a spinning cylinder. In the 1920s he designed and built a number of craft leveraging this phenomenon, including the Baden-Baden, which used two large spinning rotors to propel itself across the Atlantic in 1926. While Flettner’s applications worked, they proved inefficient when compared to other propulsion methods and were eventually abandoned.

Whoever first conceived the idea of wing sails, sailors looking to outrun their soft-sail competitors have been experimenting with them for years. Maughmer participated in substantial research on the concept at Princeton University in the 1970s under aerodynamicist Tom Sweeney. “He was an avid sailor and got the idea of sort of creating a hybrid sailboat sail and airplane wing,” Maughmer recalls. “It used a rigid leading edge like a mast, and it had a rigid tip rib and a root rib, and cable that ran between those along the trailing edge, and it had background sail cloth that wrapped around it.” The Princeton sail wing eventually found use on wind turbines and windmills after testing in NASA’s wind tunnels.

The Princeton work proved highly influential, and semirigid wing sails gradually began appearing on small boats. “They were quite good,” says Maughmer. “The only reason they didn’t show up on America’s Cup and racing is because it was illegal.”

By 1988, however, the game had changed. “For the first 100 years, it was 12-meter-yacht rules, which are very specific,” explains Maughmer. Then challengers and defenders alike began tweaking the rules of the race and the types of boats allowed. In the 1988 race, New Zealand’s Mercury Bay Boating Club challenged the San Diego Yacht Club amid a storm of controversy. The American defenders wanted to stick to a 12-meter boat, but the Kiwi team was able to get their much larger and more imposing yacht approved by the race administrators. That forced the San Diego sailors to quickly develop a new design.

“They decided that the best way to do it, given the time available and the speed potential, was to use a catamaran, which would be faster than the monohull,” says Hubbard. “Then to further improve their chances, they decided to use a wing.” Hubbard and another noted designer, Duncan MacLane, were brought in to design a wing sail for the American contender Stars and Stripes. Two identical catamaran hulls were built and tested, one with a conventional soft sail, the other with the wing sail. The latter proved to be faster and was adopted for the final model.