The Online Boating and Maritime Exhibition

#2 - Foiling Frenzy

“Boats That Fly Are Closer to Aircraft Than to Watercraft”

Hydroptere CreditPhoto: Paul Bessereau

French sailor Alain Thébault, 54, nicknamed “the flying madman,” is co-creator of the Hydroptère. In 2008, this foiling multihull was the first sailboat to exceed 50 knots. The following year it set the World Sailing Speed Record Council nautical mile record, proving that “a boat that flies is capable of high speeds.” Thébault told us about the obstacles he had to overcome to achieve this.

NauticExpo e-mag: How did the Hydroptère project begin?

Alain Thébault: I left school to windsurf and fly gliders, my two passions. That was 25 years ago. I had designed a boat that flew above the water and went to see some aeronautical engineers to build it. One of them said I’d had the same idea as the French sailor Eric Tabarly, and that I should contact him. That’s what I did.

His initial idea wasn’t a boat that rode above the water, but one with the central hull in the water and support foils on the outriggers to reduce their drag. He took me under his wing. I even did my military service with him, since he was in command of a frigate.

NE e-mag: Tell us about the construction of the boat.

Alain Thébault: To build the Hydroptère, we decided to use balsa models for a real-world reference. We began with small models. The first was at 1:8 scale and was tested on the Grand Canal at Versailles. Little by little, we increased the size.

To build the Hydroptère, we decided to use balsa models for a real-world reference.

Then we moved to 1:3, which I could sail alone. For SeaBubbles, my latest project [see sidebar], we followed the same steps, using models incorporating both theoretical and experimental aspects.

NE e-mag: When did the first “flight” take place?

Alain Thébault: The first “flight” of the Hydroptère was in October 1994. We wound up breaking the boat three times because it was conceived using a hydrodynamic load of 10 tons per square meter. But the hydrodynamic load on a foil at 50 knots is closer to 20 tons per square meter.

As with early airplanes made of wood and canvas, our first design assumptions weren’t always the best. The actual stresses are often greater than the calculated values. Above 50 knots, they become extremely high.

NE e-mag: In the final analysis, is the Hydroptère more like a plane or more like a boat?

Alain Thébault: Boats that fly are more like aircraft than watercraft, both in terms of flight dynamics and stress. You really need aeronautical engineers to maintain stability in flight. It’s fairly simple in flat water, but more difficult in choppy seas. You also need the computing power of companies like Dassault Systèmes to take the stresses into account.

A boat that flies over the water faces a double challenge.

A boat that flies over the water faces a double challenge. It must be very light to “take off” without much wind, and it must be very strong to withstand the considerable stress.

NE e-mag: What was the Hydroptère’s big innovation?

Alain Thébault: When we launched the Hydroptère, foils already existed. But we were the ones who showed that such craft were capable of high speeds. That’s why this sailboat became a legend. Today, the Hydroptère is a bluewater sailboat.

We proved it by sailing the Pacific, from Los Angeles to Hawaii, in June 2015. It’s the first foiling sailboat to cross an ocean, as well as having a top speed above 50 knots. To put this in perspective, an America’s Cup boat can reach 47 knots. In 2009, we reached top speeds exceeding 55 knots and an average speed of 51 knots. It’s not like other boats.

NE e-mag: Will races of the future feature only boats that ride above the water?

Alain Thébault: No. While it’s relatively simple to “fly” a boat in flat water, it’s difficult when there are waves because the angle of attack of the foils in the water changes.

There are solutions. You can put a twist in the foils, which is what we did with the Hydroptère. In other words, in the upper part of the foil the chord is greater, and in the lower part, the twist is close to zero. Because of this, the boat’s height above the water is adjusted automatically.

The other solution is to control the boat mechanically or electronically, using a sensor or to control the attack angle of the horizontal surface.

NE e-mag: What will the next generation of foils be like?

Alain Thébault: The Hydroptère is a trimaran with two foils at 45 degrees. The faster it goes, the higher it climbs onto the tips of the foils. At very high speeds, its six tons are supported by a very small area. At 50 knots, it rides on a surface of two square meters. Since the height above the water is automatically adjusted, it is said to be self-stabilizing.

The next generation will have T-shaped foils entirely below the water controlled by a computer which will continually adjust the height above the water. It’s a bit like what happens in the air. There are stable aircraft, like gliders, and unstable planes, like the Airbus. The latter have a center of gravity close to the aerodynamic center and a computer [called a fly-by-wire control] that continually adjusts the flaps, improving performance, reducing drag, but increasing instability.

Catch a Bubble!

Alain Thébault is collaborating with Swedish windsurfer Anders Bringdal on a new project called SeaBubbles. Driven by twin electric motors, these curious, rounded little vehicles are made of biodegradable materials and are intended for use along the waterways of large metropolitan areas.

seabubbles2Their four foils will enable them to glide just above the water after reaching takeoff speed of 6 to 8 knots. They are silent, do not pollute and create almost no wake. Their batteries can be recharged at charging stations.

Thébault and his team aim to put them in service in mid-2017, initially as hired chauffeured vehicles. They may eventually become accessible to individual operators.

About the Author

Celia Sampol has been a journalist for more than 15 years. She worked in Brussels and Washington for national medias (Agence France Presse, Liberation, Europolitics). She's the editor-in-chief of NauticExpo e-magazine and MedicalExpo e-magazine.

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