Super fast and always just a mistake away from mayhem, the boats will be the stars when the 34th America's Cup starts today in the rough and cold waters of San Francisco Bay.
The defending champions Oracle Team USA will confront the challengers Emirates Team New Zealand in a best-of-17-race chase for the oldest trophy in international sports.
The 72-foot catamarans are powered by 131-foot mainsails that look and perform like airplane wings.
When the boats reach "take-off speed", both hulls pop out of the water on hydrofoils and fly across the tops of the waves. "When you're foiling, the sensation is just like a turbo boost," the Oracle skipper Jimmy Spithill said.
His rival, New Zealand's Dean Barker, calls it "an amazing sensation" to be speeding over the water on the seven-ton boat, sometimes faster than 50mph (80kph), supported only by winglets on the bottom of the two rudders and a hydrofoil on the bottom of a daggerboard on the bottom of the leeward hull.
The wing mainsails are not new in the America's Cup, but foiling is.
The Kiwis were the first to do it and the American syndicate was quick to learn how to get the hulls out of the water to reduce drag and increase speed.
Given the right conditions, the boats should be foiling on today's first leg, a reach across the wind to the first mark, where the boats will turn downwind. Whichever boat is first to the first mark may very well win the race, because passing lanes will be scarce on the five-leg course.
"It's a really cool sensation," Barker said. "The boat, as it comes up out of the water, it accelerates and you gain three, four, five knots of boat speed just as the hull actually pops clear and you take off. Everything sort of lightens up, the loads decrease and you go faster and faster."
The Kiwis set the race record of 54mph during the Louis Vuitton Cup final against Italy.
This regatta has been marred by the death of the British sailor Andrew "Bart" Simpson when Artemis Racing capsized on a training run on May 9, and by a scandal in which the Oracle team illegally modified prototype boats in warm-up regattas. Oracle was docked two points in the America's Cup match - meaning the holders must win 11 races to retain the trophy - and Dirk de Ridder, who trimmed the wing sail, was disqualified from the competition.
If anything can save the regatta, it will be the boats.
This America's Cup is all about trying to make the staid old competition more accessible to fans and television. For the first time in its 162-year history, the sailing will be inshore on a short course.
A bonus is the backdrop.
The starting line is parallel to San Francisco's Golden Gate Bridge, and the course stretches just past Alcatraz Island. The finish line is just off Piers 27-29, with the Transamerica pyramid and Coit Tower in the background.
"You can take the people to the sailing out on the ocean or you can bring the sailing to the people," said Tom Speer, a retired US Air Force officer who is Oracle's aero and sail design leader.
"If you want the people to be able to see the sailing up close and really feel like they're part of the event, then I think you need the kind of short-course sailing we're doing in this edition of the America's Cup.
"Then you need a boat that's exciting to watch and is manoeuvrable."
The foils on the bottom of the rudders are like the horizontal stabilisers on the tail of an airplane.
The foil on the daggerboard, often shaped like a J, is like the upturned winglets on the ends of jetliners' wings. The daggerboards, made of carbon fibre, weigh about 180kg. Not only do they lift the boat out of the water, but they must resist about four tons of side load, said Pete Melvin, a designer with Emirates Team New Zealand.
A key element of racing is mastering the foiling gybe, when the boat changes course while zigzagging downwind.
The crew must lower the daggerboard on one hull while raising the other daggerboard. The goal is to keep the boat on the foils and not let the hulls touch the water, which can slow the boats.
Mastering foiling gybes throughout a race can be worth a total of several hundred metres, Barker said. Keeping control, though, is key. Spithill was at the helm when Oracle's first boat capsized, during training last autumn.
In the opening race of the Louis Vuitton Cup final, the Kiwi boat took a nosedive after being hit from behind by a strong gust of wind, tossing two crewmen overboard.
Spithill, who got his pilot's license before the 2010 America's Cup to better understand the wing sail, said riding above the waves on foils has brought a whole new sensation to racing.
"You're so used to feeling the bumps in the waves, and then when you go through them and nothing happens, it's eerie," he said.
