Williwaw hydrofoil

Designs (and general discussion) about catamarans, proas, trimarans, and other craft that do not need ballast to stay upright
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Chris Clarke
Posts: 3
Joined: Sun Jan 21, 2018 2:06 pm

Williwaw hydrofoil

Post by Chris Clarke »

The subject of Wiliwaw, the pioneering hydrofoil trimaran, came up during comments on the (very good) zoom meeting on the Americas Cup. One interesting connection is that Tom Speer, an aerodynamicist who has worked on at least one Cup campaign, has done a very comprehensive design study about what a modern-day (well he did the study 20 years ago) Williwaw might look and perform like. All the details can be found at:


It is a fascinating read.


It is also worth pointing out that 'Hydrofoil Voyager: WILLIWAW, From Dream To Reality and Toward the Sailing Yacht of the future' by David Keiper was reprinted a few years ago and is currently available on Amazon UK for less than £10.

John Perry
AYRS Chairman
Posts: 94
Joined: Tue Nov 08, 2016 6:39 pm

Re: Williwaw hydrofoil

Post by John Perry »

Yes, David Keiper was truely a pioneer with Williwaw. David's book about it all is still available, the title is
'Hydrofoil Voyager: WILLIWAW, From Dream To Reality and Toward the Sailing Yacht of the Future' I think you should be able to get a copy for about £10 from internet book sellers.

Tom Speer's design inspired by Williwaw is also interesting, I don't know if Tom is still persuing this idea, if he reads this maybe he can update us.

One point I would make is that the development of sailing hydrofoils has moved generally in the direction from complex to simple. Williwaw had a lot of bits and pieces in the water. When I played with sailing hydrofoils my aim was for a simpler design and I built and sailed what was probably the first sailing hydrofoil to 'fly' on two centreline hydrofoils, relying on moveable crew weight and sail adjustment for lateral stabilty and heel to windward to get leeway resistance from the main lifting foil. A bit later the Moth class added the wand system, and many small sailing hydrofoils have followed on from that. Then more recently came hydrofoil windsurfers with just a single centreline strut connected to a main foil and stabiliser and a sophisicated control system built into the sailor's brain. So only that one strut piercing the water surface. Then the same configuration with kites, and indeed with no rig at all, just relying on wave currents to keep up. And I now believe that some people are doing this without the stabiliser behind the main foil - you cant get much simpler than that - just a small float to stand on when stationary and a single inverted 'Tee foil' - nothing else, not even a rig.

The really simple configurations are probably not appropriate for craft too large for crew weight movement to provide the main roll stability, so the America's Cup boats and the F50s have three foil units, but only two of them normally in the water at the same time and the big French ocean racing trimarans have three, or more recently four, foil units but just simple L or Tee shapes, not complex ladder foils.

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