Flat or round bottom for a foiler "board"

Discussion in 'Sailboats' started by mm7, Jan 21, 2014.

  1. Andrew Mason
    Joined: Mar 2003
    Posts: 397
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    Location: Perth, Western Australia

    Andrew Mason Senior Member

    You make a good point about rounder hulls getting up to speed easier in the pre-foiling stage, but the reality is that this is a very minor consideration which is over-ruled by other factors for wind-foiling. For example, my current foilboard is a 6'8" long Slingshot Wizard, 34" wide, flat bottom i.e. very short and wide. In 10-12 knots of wind I can get it up and foiling pretty easily with a 7.0 sq.m. sail, and if I wanted to foil in lighter winds I could go to a bigger sail or bigger foil. The board is short for good reason, reducing the swing weight makes it more manoeuvrable, but to compensate it needs to be wide and relatively thick to get the volume and stability necessary for up-hauling the sail. A round bottom board would need to have reasonable length to be effective, and stability at rest would be a real issue, so it would be difficult to find a compromise that was superior overall to the conventional board.

    That set of compromises applies to wind foiling where there is a requirement to have sufficient stability to stand on the board and power from the rig is readily available. However the area of wing foiling and downwind SUP foiling, the compromises are different, and in this area the boards are getting quite boat shaped. In stead of wide flat bottoms they are getting quite thick to gain volume, then reducing planing area and wetted surface by having large bevels adjoining the bottom of the board. For example, this is the latest downwind SUP/ wing foiling board from One, an Australian manufacturer:

    Screen Shot 2020-06-01 at 9.05.51 am.png

    Similarly, the Sunova Aviator is going in the same direction, short and thick but with bevels and a V up forward:

    Screen Shot 2020-06-01 at 9.19.37 am.png .

    I think that part of the explanation for this is that you have less available power with a wing than you do with a windsurfer rig, but also that you don't have the same stability requirement for a wing, as you can start in a kneeling position and stand up as you sheet on the wing, which also stabilises your body. So boards for winging can be smaller and narrower, but potentially need more help to unstick them and get up on the foil. So a rounder bottom may be advantageous for them.
    Jethrow likes this.

  2. Paul Scott
    Joined: Sep 2004
    Posts: 413
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    Location: San Juan Island, Washington

    Paul Scott Senior Member

    B7A71CEE-F0EE-4E5E-B59F-852A0EF0A472.jpeg I know this is an old thread, but it didn’t address crashing off foils, and what hull shape would help in real time & not throw the sailor into a bad situation, whether strapped in, or not. (I tried a foiling windsurfer in the 80’s, and crashing off of foils was made worse by board shape- stuffing the nose-but there was no consensus on which board type was better.). Has this come any further since 2020? I can’t find anything. Nederpelt’s hydrofoils resisted nose tripping as well as keeping the board lower in the air than the current airplane foils, but did not catch on- falling on those all those foils wasn’t pleasant) There was a guy on Maui (IIRR) that tried an airplane hydrofoil under a speed needle that was better, in that the nose was out farther, but it tore the board up when the nose lifted up the board during a crash- the hydrofoil kept going down while the nose of the board was turning up as the bow touched the water. Seems to me longer would be better, but weight argues against that? The Moth crashes I’ve seen aren’t saved by hull shape- has anything been tried? I get the feeling getting stuffed and tangling with the foils is just part of Windsurfing, Kitefoiling & Wingfoiling, although at least some Wingfoilers don’t have straps, so you have chance of floating free as the nose stuffs.

    Nederpelt’s foils up on top^
    Last edited: Feb 16, 2023
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