Super fast and always just a mistake away from mayhem, the boats will be the stars when the 34th America's Cup starts Saturday between defending champion Oracle Team USA and challenger Emirates Team New Zealand.
The 72-foot catamarans are powered by 131-foot mainsails that look and perform like jetliner wings. When the boats reach "takeoff speed,'' both hulls pop out of the water on hydrofoils and fly across the tops of the waves on San Francisco Bay.
"When you're foiling, the sensation is just like a turbo boost,'' Oracle Team USA skipper Jimmy Spithill said.
His rival, ETNZ's Dean Barker, calls it "an amazing sensation'' to be speeding over the water on the seven-ton boat, sometimes faster than 50 mph, 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.
This America's Cup is Popular Mechanics meets Wired meets Star Wars down at the boat basin.
While wing mainsails aren't new in the America's Cup, 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 the first leg Saturday, 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 since 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 54 mph during the Louis Vuitton Cup final against Italy.
This regatta has been marred by the death of British sailor Andrew "Bart'' Simpson when Artemis Racing capsized on a training run on May 9, and by a scandal in which Oracle Team USA illegally modified prototype boats in warmup regattas last year and earlier this year. Oracle was docked two points in the best-of-17 America's Cup match - meaning it must win 11 races to retain the trophy - and Dirk de Ridder, who trimmed the wing sail, was booted from the competition.
If anything can save the regatta, it'll be the boats.
This America's Cup is all about trying to make the staid old competition more TV- and fan-friendly. For the first time in its 162-year history, the sailing will be inshore on a short course. A bonus, of course, is the backdrop. The starting line is parallel to the 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.
The 2010 America's Cup brought the event into the 21st century, with Oracle's monster trimaran, powered by a radical 223-foot wing sail, beating an equally immense catamaran sailed by Alinghi of Switzerland.
This regatta is now fully in the space age, with aeronautical engineers and retired U.S. Air Force officers holding key positions on design teams.
"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 lieutenant colonel who is Oracle Team USA'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. If that's the kind of sailing we're going to do, then you need a boat that's exciting to watch and is maneuverable.''
Adam May, who was in charge of Artemis Racing's performance and analysis, is both a sailor and an aeronautical engineer.
"Ultimately, these things fly like an aircraft in terms of wings,'' May said. ``Water is so much denser than air that you can do that with very small wings. The lift and how it's generated is like an aircraft. The takeoff part is the easier part. If you've got enough power from the sail, your engine, effectively, you can get the boat to enough speed to take off. The hard part is how you fly it through a very narrow height range, how you keep it at a certain height.''
That's accomplished through a number of factors, including how the wing sail is trimmed and the helmsman's ability to change the angle of the foils with controls on the steering wheel.
"The helmsman is flying the boat by doing that,'' May said.
The foils on the bottom of the rudders are like the horizontal stabilizers 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 daggerboads, made of carbon fiber, weigh about 400 pounds. Not only do they lift the seven-ton boat out of the water, but they must resist about four tons of side load, said Pete Melvin, a designer with 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 keep the boat on the foils and not let the hulls touch the water, which can slow it down.
Mastering foiling gybes throughout a race can be worth a total of several hundred meters, Barker said.
The wing sails have a main element and trailing edge with flaps, just like a jetliner's wing.
Add it all together, and Oracle Team USA's catamaran has been known to pull away from chase boats with twin 375-horsepower engines.
Keeping control, though, is key. Spithill was at the helm when Oracle's first boat capsized during training last fall.
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 in order 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.