1) Polished fins spin-out quicker than sanded fins.
2) Most of the fin lift comes from the vacuum side (side you're standing)
3) Spin-out is often because air is sucked in @ vacuumside

1)I agree, but what size sand paper to use?
2)Disagree, the pressure side provides the lift.Because when you 're going faster ,you get more pressure, the more pressure the more dificult to push the board to the other side and in the end the board goes up. It can't go to the pressureside or the vacuumside which you are pushing ;-)
3 I don't know for sure but wasn't it a cavition problem?

1) Polishing is sand it with 150/300/600/1000 than you can choose to even use some polish stuff and do the last in the end. There are a few riders in the speedworldcup that polish their fins for perfect conditions.

That said it is logic not to use polished fins in heavy conditions, just to hard to handle @ lower speeds. Once you are sailing highspeeds the chance of spinout decreases

2)Check this picture, it is kind of extreme, but makes the point: http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/Abraham_Tsigonis/hydrodiagram.png

3) Cavitation (vacuumbulb) is the speedlimiter, when cavitation happens your foil has reach the end of efficiency. Going faster is not possible for human windsurfer. Cavitation for most normal foils/profiles happen @ 40-42kn

I think this guy has been experimenting a lot with these anti spinout principles, see: http://www.cameraid.com/Lessacher/chameleon.html

That is a good one Mark, I think you're right!

Never thought that way about Lessacher his fins! But it does explain why Lessacher his fins are spin-out proof!

2) Yes the picture is clear (airplanewing)but it is up-side down imho. Like wolfgang says the nose will point a bit upwards so the other side of the fin (from which you stand) will become the underside of the wing in the picture.

Simply said: you push with your feet, the fin pushes back (not pull). This combination of forces will end up lifting the board (sometimes let it fly ;-))

Chris

ps nice background very 'leesbaar'

Chris

Yes you're right a surfer does stand on the upper side of the 'wing'. I am very pleased the background is now 'leesbaar'

ps Chris heb je ook zo'n zin om weer eens het Amstelmeer onveilig te maken??

Did you ever thought of using the new swimming gear fabrics (sharkskin) to mount under the board (last 60 cm) or even the Fin. It looks to me that it have to be tested.

Yes, the Amstelmeer is very quiet without us. This is my first winterstop for 3 years, but i can loose my frustations on the MTB trail of Schoorl.

Windsurfers are not the only ones trying to solve ventilation/cavitation. It happens on hydrofoiling dinghys such as the hydrofoiling International Moths. Take a look at http://www.youtube.com/watch?v=s58KsP9GvHE you can clearly see the bubble forming.

It looks to me that the Bladerider model of these boats angle the dagger board and rudder forward a bit which another paper I read proposes (it says to use 4 degrees). Looks like Hydroptere angles the edges of their boards at the water/air border too.

I saw a documentary recently on US Navy Submarines which said that they supposedly were able to eliminate or drastically reduce cavitation of nuclear submarine props. I'm pretty sure this would have to be done without fences. Of course these are completely underwater so the solution would have to come from the perspective of pressure rather than leading air down from the surface.

very nice video!!!