Have Wingsails Gone Mainstream?
Now that Beneteau is experimenting with wingsails, is this proven concept about to take flight?
Has the wingsail finally come of age? After last year’s breathtaking America’s Cup series, and the news from boatbuilding giant Beneteau that it is experimenting with wings as an alternative to the traditional Bermudian sailplan on its production boats, it certainly looks that way. Where one leads, others follow, and if Beneteau’s trials go the way the factory expects, then cruising boats sporting one or two elliptical wings will be a common sight in years to come.
It took the Cup to put the spotlight back on the wingsail, but it has been around for decades in various iterations. Dennis Conner sailed the catamaran Stars & Stripes, sporting a hard wingsail, to victory in the 1988 mismatch against Sir Michael Fay’s Kiwi challenger. Back in the early 1990s Walker Wingsail Systems also designed and built a handful of cruising trimarans equipped with computer-controlled hard wingsails, before technical and legal problems—not mention a distinct lack of enthusiasm from the sailing community—eventually ended the company’s attempts to make an impact on the market. The execution may have been flawed, but for many designers, engineers and sailors, the Walker Wingsail was at least a brave attempt to answer one question: why do sailboats have rigs and sails that are inherently inefficient?
BECAUSE A MAST is supported by wires fore and aft, which make two triangles, its sails must also be triangular in shape; and the triangle is the worst possible planform for a sail that must propel a boat to windward, thanks to a phenomenon called induced drag, which comes as a product of any surface generating lift. You don’t see many birds or insects with triangular wings, nor aircraft, except very high-speed fighter planes aboard which the triangle planform actually comes into its own at supersonic speeds.
Worse yet, these inefficient triangles are held aloft by a rig that’s trying to push the mast through the bottom of the hull while pulling the ends of the boat up like a banana: a highly tensioned assemblage of wires, turnbuckles and myriad other small fittings, even the smallest and cheapest of which could cause the whole lot to crash down on your head should it fail. Seems crazy, doesn’t it?
The most effective airfoil in terms of generating lift has an elliptical or semi-elliptical shape. Neither of these is affected by induced drag to anywhere near the extent of the triangle. The heavily roached mainsails that came into vogue on multihulls during the 1990s, and now the trend toward square-topped mainsails on both multis and monos, are steps along the road to more aerodynamically efficient—therefore faster—sails that would also win over the conservative cruising sailor. The wingsail may be at the end of that road.
FIRST, THOUGH, there is a mountain of prejudice to overcome. Show a typical cruising sailor a photo of a wingsail on a production boat and the reaction will range from “That looks weird” to “Dude, that is butt-ugly.” Most sailors raised on bermudian rigs just can’t get their heads around a boat that has no shrouds to hang onto or a sail that isn’t triangular. They certainly view hard wings with suspicion, even after the Cup races.
Of the two types of wingsail, only the soft wing has a chance of catching on with mainstream sailors. If performance is the only goal, then you can’t do better than the hard wing’s aerodynamic efficiency. But you can’t reef it, its variable geometry is complex to control, it is expensive to produce, and its smaller area makes it slow downwind.
The soft wing, on the other hand, can be reefed and stowed, can be made of regular sailcloth, is simple to control and easy to handle, and is robust. Set on a freestanding spar, it puts no compression loads on the hull and in its most basic form is trimmed by just one sheet—though if the spar rotates there must be a means of limiting its travel as well, and a way to control the camber, or depth, of the airfoil. On hard wings like those of the AC boats this is achieved by using multiple hinged vertical elements to adjust the “shape.” Most soft wing variants can also twist in the same manner as a conventional mainsail to account for the differing wind direction aloft, whereas a hard wing needs an array of trailing flaps to achieve this.
Though soft wingsails may be “new” to most sailors, various iterations have existed for decades. Nearly a century ago L. Francis Herreshoff patented a rig that had a two-ply mainsail and jib, each with its leading edge attached to the sides of a rotating spar. This approach would go on to serve as a precursor to the double-skinned variable-camber wing, as developed by Australian company Advanced Wingsail Systems. The AWS mast can be rotated to bend the battens of the double-skinned mainsail, allowing camber to be controlled either manually or electronically. In appearance the AWS sail is much like a conventional bermudian rig.
Another approach to wing design is being taken by former fighter pilot Ilan Gonen with the Omer Wing Sail, which he’s been developing for a decade. The Omer Wing Sail is actually three “sails”—two panels and a fabric leading edge for the wing—all set on a rotating carbon fiber A-frame mast. When setting up the rig, the two mains are hoisted up the A-frame legs, and the leading edge goes up tracks in front of the mast. The angle the boom makes with the leading edge can then be adjusted to control camber in much the same way changing outhaul and halyard tension does on a conventional mainsail.
Once underway the helmsman has just two sail controls to deal with: the mainsheet and the hydraulic ram that controls the boom’s angle to the leading edge. Gonen uses an Elan 37 for a test bed, and boat-for-boat testing has found that despite having 15 percent less sail area, his wingsail outperforms the conventional rig on every point of sail except dead downwind. A gennaker can be set to improve downwind speed.
The wing’s advantages under sail include greater efficiency not just to windward—the wing-equipped boat points 10 degrees higher—but also on a reach, where it performs better in light air than the conventional rig. As wind speed increases and the wing generates lift, the camber can be flattened, and the boat will sail even closer to the wind. Below about 130 degrees, the gap between the two rigs closes until the conventional rig’s greater sail area takes it into the lead going dead downwind.
The reason for this increased performance is that the wing has a lower angle of attack (a line drawn between the leading and trailing edges of the sail and the apparent wind direction) than a conventional sail, and the lower the angle of attack, the less induced drag is generated. For example, the angle of attack on an Omer wing is between 0 and 10 degrees, while on a typical conventional rig it is never less than 15-20 degrees, and can be as much as 90 degrees on a well-eased headsail. This lower angle of attack translates into less heeling moment and more driving force.
Tacking is pretty much a case of putting the helm over and pushing a preset button that changes the camber—on hard-winged boats like the AC45s, this is accomplished by a crewman manually “tacking” the wing. In its present incarnation, the Omer wing has two reefs, which can be managed from the cockpit. Should the boat be overpowered by a gust, all you have to do is let the mainsheet go and the sail will feather; if it’s really blowing hard, dropping the leading edge will depower the sail completely.
Which brings us to gybing, which is much gentler with a wingsail like the Omer because the leading edge projecting ahead of the mast acts as an air brake, slowing the speed at which the sail slams across the boat.
Until very recently, production builders’ responses to the temptations of the wingsail have been the corporate equivalent of clapping hands over ears and saying “la la la la la” loudly. The first big boatbuilding company to seriously investigate the virtues of the wingsail has been Beneteau, which over the last few years seems to have been on a mission to reinvent the cruising sailboat.
Under the auspices of Bruno Belmont, Beneteau’s head of product development, a soft wingsail has been installed on a Sense 43 and sea trials are ongoing. The aim is eventually to offer wingsail-rigged boats as an option to conventional rigs and thereby, says Belmont, attract a whole new breed of sailor.
Belmont’s goal is straightforward: he wants to make sailing easier, and thereby bring new people into the sport. “Sailing suffers from the fact that newcomers see it as too hard to learn,” he says. “We are looking at ways of simplifying boats and sailing.” Bringing new people into the game is of course the holy grail of the sailing industry as a whole—each year, thousands of the baby-boomers who popularized the sport in the ‘70s and ‘80s are aging out, and it is not proving easy to replace them.
Beneteau’s vision extends to rethinking the way other things are done. What if the mainsheet and halyards were led to captive winches, and sails hoisted or trimmed at the push of a button? The absence of shrouds means deck safety needs a fresh look—perhaps there will be solid handrails instead of wire guardrails, maybe incorporated with higher bulwarks. Boats may have to be designed to accept either a conventional or freestanding rig, which means differences in construction too—a hull that doesn’t need to withstand the massive compression loads of a bermudian rig can be made lighter, which means it won’t need as much sail to drive it, which means a smaller rig, which won’t need much in the way of deck gear. Beneteau’s brains trust for this experiment includes such luminaries as famous solo sailor Michel Desjoyeaux, “who thinks we definitely have something,” says Belmont.
The Beneteau soft wing is based on the twin freestanding sails sported by the French schooner Matin Bleu, an experimental Erik LeRouge design which utilizes a variant of the balestron rig that’s commonly seen on model sailboats. Owner/skipper Guy Beaup has sailed tens of thousands of miles under this rig, so it is a proven concept. The only question is whether the wingsail in general will be a viable rig for production boats.
Noted designer Nigel Irens, who has designed both multihulls and monohulls with freestanding rigs, is a fan of the wingsail, but feels that “bizarrely, the main obstacle in getting the rig to market might be one of cost. When you look at a conventional rig on a production boat, you’d be hard pushed to find a cheaper way of spreading out the required amount of sail to drive the boat along.
“Free-standing masts like those supporting the Matin Bleu rig are tapered carbon/epoxy structures and finding ways to build such a spar down to a price is not easy,” says Irens. “Building such a rig into a monohull or even a trimaran is relatively simple because the ‘bury’ between upper and lower bearings is substantial. But a free-standing mast doesn’t seem to be a natural option for a catamaran as the depth between upper and lower bearings is bound to be limited. It has been done successfully in the past, but building such a structure into a production boat at the right price may be challenging.”
None of these obstacles will be impossible to overcome for a determined builder, as long as there is demand for the product. Undoubtedly because of the Cup, which made wingsails a common sight, there is now more understanding of the concept among sailors. The weirdness factor is wearing off. And here’s the thing: the sailors Beneteau has in mind for its wingsail-equipped boats won’t have any prejudices anyway, because they’ll be new to the sport.
Birds of a Feather
There have been many variations on the wingsail concept. Here are some of them.
This 1990s British concept was the spin-off from a failed attempt to build wingsails for cargo ships. Five trimarans were built, all with rotating hard wingsails that were computer-controlled. The public just wasn’t ready for the idea: John Walker was more famous for winning a high-profile lawsuit against British magazine Yachting World than he was for building boats.
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Optimist with Wing
Some enterprising Kiwis adapted the top section of the sail from an A-class catamaran to fit this Optimist dinghy; it proved very fast.
Here is another variant on the wing—as seen on the P-28 foiler, developed in Switzerland.
Advanced Wing Systems
This Australian company has developed soft wing sails for Moths and Mini 6.5 racers, and is working on others.
*F = the combined effect of drag and lift vector forces
|At 30° to the apparent wind, the wing’s 10° angle of attack generates low drag and plenty of lift.|
|With their greater angles of attack (15 and 20° respectively) the genoa and mainsail create more drag and less lift. Heeling force is increased at the expense of driving force.|
|The wing works very well on a beam reach because the lift—and therefore the driving force—is mostly directed forward and there is little drag or heeling force.|
|By comparison, the conventional sailplan suffers because the well-eased genoa does not work as an airfoil, and thereby generates lots of drag and heeling force. The main is still relatively efficient.|
|Downwind, the well-eased wing, still with a 10° angle of attack, retains its airfoil shape and creates lift to windward. Drag is minimal, and most of the heeling force is directed to windward.|
|On the same broad reach, the conventional sails’ angle of attack is 90° so instead of working as airfoils, all their drive is created from drag.|