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Board outline difference

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Larse
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Board outline difference

Postby Larse » Mon Feb 21, 2011 1:48 pm

Hi

Which outline gives the least drag? Many big light wind boards have and s-shape, so that they become narrower right at the middle of the board. I can see that there is less surface in the water, which equals less pressure on the board. And therefor less drag?? Or what?

And the big light winds boards are often ridden more flat and not edged. Is that why the s-shaped outline works for light wind boards?

I guess my question is, would a s-shaped board in smaller sizes (135x40) get any advantages? Low end maybe? And what would the compromise be?

This is what I mean by s-shaped. The board to the right gets more narrow in the middle.
Image

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perroloco
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Re: Board outline difference

Postby perroloco » Mon Feb 21, 2011 2:59 pm

The board on the right is a flat water board. Killer upwind machine. Not good for chop or waves. Zero rocker and zero concave.

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Larse
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Postby Larse » Mon Feb 21, 2011 4:02 pm

Take out rocker and concave from the board. Nevermind those. Will the s shaped outline give better upwind and worse chop qualities?

tomatkins
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Re: Board outline difference

Postby tomatkins » Mon Feb 21, 2011 4:57 pm

I think the term used to describe the concave shape of the edge of a board is "side-cut". I think I have heard other terms like 'parabolic', but never "S" shape.

Other sports like skiing and snowboarding design this shape into equipment...but I think the big difference between the use of "side-cut" in those board sports and the use of "side-cut" in kiteboarding is that skis and snowboards use the "side-cut" to facilitate the ability of the equipment to smoothly carve a turn, and hold a firmer edge in the turn...whereas the use of "side-cut" in kiteboards serves a different function.

I would like to hear some other opinions on what the "side-cut" design actually does to a kiteboard...both the 'pros' and 'cons'.

My opinion is that the "side-cut" functions mainly to allow the area near the tips of the board to act a as a "surrogate fin" when the board is edged, and that this characteristic allows the board to go upwind more efficiently. I would also think that the "side-cut" characteristic makes the board turn less smoothly than a board with a straight edge or a convex edge.

I have kited using a fin-less Spleene "Door" and an old fin-less Wipika "Park" model, both of which have 'side-cut", the Door having about 2 cm of rocker (very flat) and the Park model having about 8 cm of rocker (very rockered), and both boards have similar characteristics...efficiently going upwind, slippery feel without fins, throwing off spray from the leading tip, poor ability to "load and pop", a slappy ride in waves (the Park model, less so, due to the rocker), and good tracking ability (up to the point where the board starts to slide).

Here is a picture of the Park model:
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wipika%20board.JPG
wipika%20board.JPG (120.21 KiB) Viewed 1534 times

tomatkins
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Re: Board outline difference

Postby tomatkins » Mon Feb 21, 2011 5:14 pm

You also asked about the use of "side-cut" in a smaller version of a board, than the larger "door" types.

I once experimented with different lengths of this style board, by making them out of plywood. I was surprized by a characteristic that appeared in the shorter boards (and thinner). I can only describe this characteristic as "Tomahawking"...a kind of rhythmic 'chopping' by the board, which would probably be called (by an engineer), a "forced harmonic resonant" of some sort, and this characteristic was very annoying, at certain speeds. I never did figure out why this "Tomahawking" ocurred, but I suspected it had something to do with the 'torque' or lateral flexing of the wood and the flat rocker, along with the shorter board length. Anyway, this characteristic resulted in poor performance of the board.

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Re: Board outline difference

Postby yakapelli » Mon Feb 21, 2011 9:55 pm

I don't mean or intend to hijack the thread.. but along similar lines:

Does the tip out line affect the drag of the board?


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