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Taking Flight: is Foiling now Mainstream?

Remember learning that the basic motions of a boat are roll, pitch and yaw? Now add “heave,” the nautical engineering term for the lift of a hydrofoil, or “foil,” as we seem destined to call them.

ZHIK NAUTICA 2012 Moth Worlds Week Review

Remember learning that the basic motions of a boat are roll, pitch and yaw? Now add “heave,” the nautical engineering term for the lift of a hydrofoil, or “foil,” as we seem destined to call them.

Foiling has been around for years, but the 2013 America’s Cup on San Francisco Bay turned up the spotlight dramatically on a phenomenon that has become exponentially more widespread of late—albeit beneath the radar of many sailors. In 2012, Oracle Team USA skipper Jimmy Spithill famously declared, “Foils are the future,” as we watched 72-foot catamarans begin flying at near-freeway speeds, and only two weeks after the Defender’s epic Cup comeback, an inaugural American foilboard event for kite sailors was launched on the same patch of water. At the same time, some 2,300 miles to the west, the Moth World Championship was underway on Kaneohe Bay, Hawaii, with 80 of the world’s best sailors competing in an 85-year-old dinghy class where the first world championship race win for a foiler only dates to 2001.

Bottom line: foiling may not be for you, but the awkward courtship is over. Foiling is the glamorous new in-law in our sailing family, so grab the smelling salts for Granny, and make room at the table.

What a poverty of language we’re exposing here, compared to Eskimo dialects and their umpteen different words for snow. A sail is a foil. So is a wing, a rudder or a keel. But it seems we’re stuck with the word. The essential feature of this foil is that it runs deep in the water, develops heave and lifts the hull(s) clear. There are immediate consequences for design, because hulls then become little more than foil delivery systems. The Moth being a development class, for example, designers are motivated to produce hulls that are fast up to takeoff speed. But above 7 knots, the hull is merely a place to sit, with windage minimized as much as possible. Foiling Moths double the speed of nonfoiling Moths—there’s a 30 Knot Club—and helmets are popular. You’re going fast enough to hurt yourself. We recall that, for the 11 men on an AC72, a helmet was only the beginning of the body armor. It’s a brave new world.

With the America’s Cup still underway, enthusiasts were also following the 2013 International C-Class Catamaran Championship in Falmouth, England. C-Cats have long been an exotic otherness as a development playground for hard wings and lifting foils. But with a record 11 entries in 2013, the leading boats struck the eye as miniature versions of AC72s: a role reversal for a group whose pioneers—Duncan MacLane and David Hubbard, for example—received offers as soon as the tipping point arrived for designing the giant catamaran and equally giant tri that took part in the 2010 Deed of Gift match. The circle is complete.

At Falmouth, Franck Cammas, who hopes to head a French campaign for America’s Cup 35, skippered Groupama C with Louis Viat and ran away with the races. The team’s design mantra was to maintain a stiff structure, thus maintaining precise angles for its S-shaped foils. Rudders were mounted inboard to contribute to stiffness, even though transom mounting would have offered more pitch-leverage, and hulls were angled out slightly so that when heeled the angle would be vertical.

In a week hampered by light air, Groupama C achieved 21 knots in just 7 knots of breeze. Do the math. Three times wind speed matches the performance of the AC72s. And you still struggle, explaining to nonsailors how a boat goes faster than the wind, right?

Oracle Team USA lead designer Dirk Kramers visited Falmouth and observed that only a minority of the boats were foiling well, and of the two finalists, “Groupama C was more benign. They would fix their settings and sail. The Swiss with Hydros were aggressively trimming the wing and the rake of the boards. They also had lower-drag boards, but, to talk development [even this many years on] these are the early days.”

The design rule for the AC72s attempted to prevent foiling by prohibiting trimmable winglets. It seemed like a good idea at the time, but the result was a complex workaround using fixed lifting foils on daggerboards that were then bodily raked and canted to control heave and pitch; for leverage there were winglets on the rudders that were fixed in place before each race. Kramers says, “The solution ended up being rather elegant, but you would never design an airplane that way.” And if a next-generation rule permits trimmable winglets? “The boats would go faster,” Kramers says, “and we’d reduce the risk of crashes.”

The man who probably did more than anyone to put the America’s Cup on foils is Pete Melvin of Morrelli and Melvin, who worked under contract with Oracle Racing to help write the design rule, and then worked for Emirates Team New Zealand to design the Kiwi raceboats. Testing 33-footers, he says, they really didn’t know where they were going to end up. The design team started with standard C-shapes capable of lifting 50 percent of displacement, followed by L-shapes to lift the hulls clear. The problem then was that with less board in the water, the increasing leeway would shift the flow over the horizontal portion of the foil and bring the boat crashing back down. “We got these speed bursts,” Melvin said, “so the question was, how do we bottle this? Then one of our clever engineers asked, what if we angle the foil up? That became the magic in a heave-stable foil.”

Kiteboarding in action

With that closed angle—to pass for an engineer, call it a dihedral—leeway causes moderate loss of lift instead of complete loss of lift, which in this environment translates to stability. From that discovery forward, the Kiwis and their catch-up competitors were on a quest for the foil that ideally balances stability vs. drag. The hunt was still on when it came time to start racing.

Everybody’s Doing It

In the 1990s, Hobie introduced a production foiling tri called the Trifoiler that was capable of 30 knots, but the market was narrow and the boat was ahead of its time. In 1994, Alain Thébault achieved flight on his first iteration of l’Hydroptere, but it took 15 years to set a nautical mile record of 50.17 knots. In 2012-13, l’Hydroptere made the 370-mile coastal trip from Los Angeles to San Francisco and back, but sponsorship shortfalls prevented a planned attempt at a record on the LA-to-Honolulu Transpac course. Compared to Thébault’s robust 60-footer, no AC72 belongs on the ocean, but Oracle skipper Spithill has allowed of his AC72, “If we had another 6 months we’d see 50 knots.”

Meanwhile, back in the world of monohulls, talk of foiling AC monohulls (had New Zealand won the Cup) can be matched against the highly publicized plans of Vlad Murnikov to foil-assist his planned SpeedDream monohull that he claims will reach 50 knots. Murnikov’s concept does not envision full flying; rather, his skimming design depends upon a keel that cants to a radical angle, its bulb clearing the surface, with foils that support 30-50 percent of displacement. But the principles remain much the same.

At the same time, around the smaller end of the LOA spectrum, Performance Sailcraft of Australia will now sell you a foiling kit for your Laser for about $5,500, and I recently overheard some high school kids on my dock planning to design some Laser foils their own. Even if they never do, you see what’s firing imaginations.

Back at the turn of the millennium the Moth community was still debating whether to allow foiling, but no longer: participation has exploded, rescuing a once dwindling class. The typical Moth setup employs a lifting foil plus an adjustable flap on the centerboard, with gross ride height controlled automatically by a bow-mounted “wand.” At low speed, when the hull is in the water, the pressure on the wand is transferred to the centerboard flap, angling it to lift the bow. Then, as the hull lifts above the surface, pressure decreases and so does the flap angle to prevent the boat from simply shooting up into the air and crashing. Once airborne, the skipper fine-tunes his flight angle via a flap on the rudder. Early foils were flexible and low-aspect, says class veteran Jonny Goldsberry: “Now they’re high-aspect, pre-preg and 10 times stiffer. That’s in only eight years. Think of riding a bike. Speed is stability.”

In 2009, at the first world championship for course racing with kites, prototype foilboards were fast upwind on San Francisco Bay, but slow downwind. Now the French—who began running separate foiling/nonfoiling divisions a year ago—are in the market with standardized high-aspect foils good for 30 knots, in the right hands, with a promise of 40-knot foils soon to come. As with many 2013 Moth foils, the tips are angled to maximize flow and lift. However, lacking a wand system, the entire board is adjusted to fine tune blade orientation. Both are sailed heeled to weather, with the lifting foils also working to resist leeway.

Two-time world champion and Rolex US Yachtsman of the Year Johnny “it must be yachting” Heineken won 10 of 12 races at the inaugural California Championship, with the French riders chasing hard. The mojo is all about riding aligned with the mast of the foil and managing the porpoise effect fore and aft. Keep the foil below the surface, keep the board above it, and believe. Think raceboard speeds plus 20 percent.

That is until Johnny gets an even faster foil.

AC34 Artemis skipper Nathan Outteridge compares on Moth and AC72 foiling



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