dinghy design questions

One weird thing about developing lift off hulls, though, is that windsurfers (particularly longboard windsurfers) go better upwind when the board is heeled to leeward. People talk as if the rail digging in is improving lift.

Good points Chris and Rupert.  

Originally posted by Chris 249 One weird thing about developing lift off hulls, though, is that windsurfers (particularly longboard windsurfers) go better upwind when the board is heeled to leeward. People talk as if the rail digging in is improving lift. I have strong reservations about that, because as noted earlier a hull is a very low aspect lifting surface and therefore even to the extent that it does provide lift, it would do so at a very different angle of attack than the centreboard and fin. I can't see how any reduction in wsa or waterline beam would apply. It's baffling to me, because you DO go faster with the board heeled.

I always attributed it to the foiling effect of the plate as it came away from the vertical, I do it in light winds on the dinghy, deliberately railing it, it works on them as well in light winds, well on the EPS that is.

I had it very dramatically demonstrated once when I fitted a gybing plate to a Div2 board, it went like a knife through butter in light conditions got three bullets on an inland shifty lake (Rutland) not normally expected, but then became virtually unmanageable because of the extreme lift in puffier wind (I didn't finish the race had to take it out), somebody heavier might have used it to better effect but back then I wasn't about to pass on those sort of findings to competitors.

Has anyone seen a modern Marblehead. If speed is calculated in boatlengths per second they are faster than the last AC 'boats'.

A 20 foot Marblehead with the keel replaced by a rugby team out on the wire... hold on - don't they already have boats like that on the Swiss lakes.

Originally posted by JimC Originally posted by iGRF I always attributed it to the foiling effect of the plate as it came away from the vertical, That seems to make sense to me. Assuming one has enough foil to prevent excessive leeway, then converting the rest to lift ought to work, especially if wetted area reduces as well. And of course with the board the sail is decoupled from the hull, so the rig stays giving as much power as possible, not dumping air over the top as it would with a dinghy.

Well the whole technique got sprung on us with the advent of the round board which tended to roll naturally, prior to that, the fast technique for the original windsurfer was to over sheet put a lot of pressure on the rear of the hull so the nose came into the wind and the plate acted as if it had been gybed so you were exerting as much pressure on the lee side of the foil as possible, that techniques is probably gone now long forgotten and the foils that come with boards like techno's and RSX wouldn't work anyway, much to flex.

The railing/foiling techniques carried over into race boards and with it remember you also have the uplift and unweighting of the helm by the rig being canted over, the early you did this the free-er and faster you could move into what I call fast glide rather than planing, it's not planing but nor is it displacement because the board becomes lighter when you get the groove dialled.
It's interesting to note it's carried over into foils as they can't to weather, I imagine the main down foil that attaches to the T acts like the windsurfing centreboard to counter anything lost from the lower T foil, either way it works you can see them hauled over to weather.

Edited by iGRF - 10 Oct 14 at 2:16pm