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28th June 2011 03:46 PM
board size and sail size?

What is the board size and sail size? I've heard that smart fins are great.
21st June 2011 08:42 PM
Ken I think we all agree.
21st June 2011 02:48 PM
Floyd Energy involved breaking surface tension is hardly ever mentioned but it must have a good deal of effect especially on flat water.Not sure wether it would be beneficial or otherwise ???? Who knows.

There is no trully scientific way of explaining all effects of boardshape or if there is I cant find it ?? Think its why its a mixture of science and art ?? (a black one ?)

Pretty sure a lot of "developments" are just marketing gimmicks but some work ?? Air tubes from F2 was a good one ?? Remember lots of years ago some builder putting round dints all over base of board ?? (Golf ball ???) Think SB have done their fair share too ??? Original Hypersonic ???

Perhaps failed engineer knows ???????????
21st June 2011 01:52 PM
Farlo Yes we all agree that there is water displacement at high speed and the lift comes primarily from that. There might be phases where the hull doesn't touch water and air speed may help, but it won't last. Now depending on surface tension and sharpness of the rails, water may not have time to wet the edges but will rather be sprayed around. And depending on its outline, the tail of the board may have no grip at all due to the way water is released. IMO this is more likely to happen when going downwind over chops.
21st June 2011 05:20 AM
Floyd But Ken the only reason it bounces is because of water its moved !!! Newtons third law;action and reaction !!! Failed engineer explains it well !!!

PS Dont think he`s talking about bouyant displacement;he`s talking about water displacement through motion !!
21st June 2011 01:37 AM
Ken Ah, but a board in chop with enough speed does "skip" over the surface with no displacement for a short time. However, I agree with your point. If you watch speed sailing runs that Antoine Albeau and others have made on very flat water, the boards don't seem to skip as you say, and it looks like displacement is consistent.

When they do "blow up" or leave the water, the crash usually begins with a spin out. Small fin with too much force. However, I do believe that at some point, it's possible for the apparent wind to get under the board and lift it off the surface of the water. This isn't too likely given the narrow, short boards plus the heavy sailors with weight jackets all designed to keep the board on the water to prevent "take off" (and to allow the use of larger sails).
21st June 2011 12:42 AM
Failed engineer

But yes I think you are correct that faster the board the more the relative contribution the fin makes.After all the board is planing higher but never so high to just "skip" over surface. (As it appears to do)
21st June 2011 12:37 AM
Failed Engineer

What ever speed you are doing there is always some displacement into the water and therefore the rail must be in contact to some extent.IMO it appears rail is exposed but probably water has been shed away but even if it has it would be playing it part. (if it sprays off at high speed trhe momnentum exchanged would be massive)

Putting it simply board never just touches surface ; even at really high speeds (way higher than board is capable of) there would still be a channel of some description.Without it no momentum exchange can take place.
21st June 2011 12:13 AM
Farlo Ha ha, nice argument. Do you agree that over a certain speed the hull may be wet but not the rail, and the grip would come predominantly from the fin? Just for fun...
20th June 2011 10:43 PM
Failed engine here 2 , piston broke

Fins on sailing craft

The use of angled foils for powered craft is relatively easy.They provide reducing SA with speed and hence greatv efficiency and high top speeds. This is far from the case with sailing craft. Generallyt for recreationaL purposes (eg Moth foiling;windsurfers) a T foil is utillised which gives better efficiency (lift/drag) to a planinbg hull but does not reduce its SA with speed (as angled foils would) Hence no better top speed than a "normal" windsurfer.

If angled foils are tried as used let say on a hydro foil (ie foils angled outwards) the down wind foil will ,rather than give lift , pull the hull under with negative lift.(because of leeway/slip angle) If foils are angled inwards (not ideal;as craft rises its doing so an a reducing width base ) the windward foil will now give negative lift !! This can (and is) utilised in foiling cats/trimarans; where the windward foil rather than lifting craft is used to counteract leaning forces. (As in Hydroptere.Windward foil holds hull down; leeward foil gives lift and a T foil on thge rudder gives added lift to balance craft fore/aft)
I beliueve when inward angled foils are utilised with the windward one opposing heeling forces and the downwind giving lift they are known as Bruce foils.

It can be seen from this that when a foil (our skeg) on a windsurfer is angled downwind it will under its own forces try and return to vertica(Negative lift)l. As it angles upwind (railing) it will satrt producing true lift against gravity.
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