Hi Guys. Shape, rocker, concaves, vee, mastfoot position, sailors weight location are all factors included in the balance of board design for speed. But one thing at a time - fast finishes first.

I did some research in my younger years for board design on this topic. I got some hydrodynamic books from the library, and the topic of golf balls was discussed.

The dimples on the golf ball dont create a slippery surface. They enable the flow of air to break away, ie: flow separation, from the widest point of the ball, thus preventing the air being sucked back around the rear of the ball which makes the ball slow. Much the same way a sharp trailing edge on your rails allows the water to separate away from your board for quick planning.

So the dimple principle doesn't apply to a long wetted under surface of a board.

With all the research I did, I still didnt get the answer on surface finishes. But I have an idea!

I would be happy to make up a couple pieces of flat MDF, glassed up, around 130cm x 60cm. One with a sanded finish, the other with a super polished finish.

Them drag them both behind a boat with tension scales on the rope. Throw some weight on the boards and vary the boatspeed and see what happens. I just need a boat and some flat water in Sydney.

How do you type an apostrophe in these threads? The Quick Find box keeps popping up instead?

Why don't boards have a tread on the bottom of the hull? eg like a F1 wet weather tyre.
Wouldn't this help release water when planning in marginal conditions and at higher speeds...anyone got a router

Getting back to wetted area - The wetted area is variable and is a function of all up weight, speed and aoa. Just cutting area off the bottom has no effect on the "required" wetted area. All you can do to reduce wetted area is to make the bottom shape as simple as possible - ie flat with no v or channels or concaves.

Another thought - although v is good for control it may well cause fluid perturbation because the board does not go across the water in the direction the hull is pointing in.

Given that control always comes at a cost, it would seem to be reasonable to attack the problem of hull design by starting with the simplest conceivable design and systematically modifying it to achieve specific control objectives, so the thing doesn't end up over controlled.

Sounds like a good way to ventilate your fin and spin out at speed.... keep it for hydroplanes and float planes

quote:

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Originally posted by yoyo

Sounds like a good way to ventilate your fin and spin out at speed.... keep it for hydroplanes and float planes

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Got no idea how it would work, but they wouldn't need to be upstream from the fin. especially on wider boards.

OK here's another slight diversion.
Thinking wave boards now, when dropping down the face of a wave, the water surface is curved, does that effectively turn flat rocker into -ve rocker and rocker that matches the curve of the wave into flat????

Wondered about this for a while now (about 40 years), my gut feeling is that there is this sort of effect. Wondering if there's any solid theory/evidence concerning it?