Kiteforum.com

i am not a scientist, so i don't know squat about aero or hydro dynamics, but one element that i haven't heard anybody mention is the sail rockets curved 'foil', which is one of the only two parts of the boat in the water at speed (the other being a small skeg or rudder beneath the front right float. ) my instincts tell me that one of the keys for faster speed on a kiteboard will be to incorporate some version of that foil, eliminating all drag from the flat surface of the kiteboard. whether this would work or not, i don't know, but a sub surface foil, working in opposition to the kite, might eliminate drag, and recoup some of the speed wasted by leaning against the kite. is idea retarded? i know that the 'righting moment' on the sail rocket is neglible, or non existant, puttting the forces in balance so that wind, and, more importantly, apparent wind, can be converted to forward motion. why not put those forces in balance on a kiteboard w/foil extending to windward?

pluvious2002 wrote:i am not a scientist, so i don't know squat about aero or hydro dynamics, but one element that i haven't heard anybody mention is the sail rockets curved 'foil', which is one of the only two parts of the boat in the water at speed (the other being a small skeg or rudder beneath the front right float. ) my instincts tell me that one of the keys for faster speed on a kiteboard will be to incorporate some version of that foil, eliminating all drag from the flat surface of the kiteboard. whether this would work or not, i don't know, but a sub surface foil, working in opposition to the kite, might eliminate drag, and recoup some of the speed wasted by leaning against the kite. is idea retarded? i know that the 'righting moment' on the sail rocket is neglible, or non existant, puttting the forces in balance so that wind, and, more importantly, apparent wind, can be converted to forward motion. why not put those forces in balance on a kiteboard w/foil extending to windward?

3.73kn differential seems negligible, what % of this difference can be attributed to wind speed differences? What was the wind speed difference between Rob's last performance vs Sail Rocket? It would seem that 6% difference could be due to wind differences? Certainly finetuning the kite rig/setup is in order..

polarstorm wrote:

pluvious2002 wrote:i am not a scientist, so i don't know squat about aero or hydro dynamics, but one element that i haven't heard anybody mention is the sail rockets curved 'foil', which is one of the only two parts of the boat in the water at speed (the other being a small skeg or rudder beneath the front right float. ) my instincts tell me that one of the keys for faster speed on a kiteboard will be to incorporate some version of that foil, eliminating all drag from the flat surface of the kiteboard. whether this would work or not, i don't know, but a sub surface foil, working in opposition to the kite, might eliminate drag, and recoup some of the speed wasted by leaning against the kite. is idea retarded? i know that the 'righting moment' on the sail rocket is neglible, or non existant, puttting the forces in balance so that wind, and, more importantly, apparent wind, can be converted to forward motion. why not put those forces in balance on a kiteboard w/foil extending to windward?

3.73kn differential seems negligible, what % of this difference can be attributed to wind speed differences? What was the wind speed difference between Rob's last performance vs Sail Rocket? It would seem that 6% difference could be due to wind differences? Certainly finetuning the kite rig/setup is in order..

Sailrocket's best is 65.45 knots for the 500m set in about 30 knots of wind.

Rob's record is 55.65 knots set in about (I think) 50 knots of wind. The kiters seem to be more efficient this year according to the figures they are claiming.
http://www.luderitz-speed.com/

@ JS:
@ pluvious2002: Good instinct!
@ Tilmann, @ ChristoffM: More to stability than LE diameter vs AR.

Why Sailrocket is faster - Ian K from seabreeze.com - forum explains it very well (see page 1 and 2 !):
http://www.seabreeze.com.au/forums/Wind ... 0m/?page=1

After reading lots of technical excuses about problems for increased speed - it seems to me that youve all missed what the real issue - a hint would be to stop thinking like a kiteboarder or your forever restricted by 'conditioning' !!!
There was an early experimental kitesurf board that came close to the right equation but he did not understand what he had designed...

at the end of the day the rider wind drag is a bit of a show-stopper for the kiters. But once you start talking about aerodynamic rider fairings and pods etc, you might as well go the whole hog and build a purpose built vessel.

I think regarding sailrocket, that there is an alternative configuration that would involve "pushing" down on the water with a pair of ventilated meat cleaver like fins rather than pulling up on the water like sail rocket's curved fin.

For 100kt, i expect you will also need some sort of ballast scoop system to load up with water as you go faster, other wise I would expect that you will have trouble holding down the same lightweight setup you need to get through the first 20-30knts. The whole project would become a huge materiels science endeavour along the way. It is doable, but really, who cares anymore? there isn't really a forseeable recreational or commercial application for as long as we have fossil fuel technology available.

If you want to go 150knts, with energy derived from the wind, just go gliding in a sailplane and take the nasty water part out of the equation completely.
Furthermore, any sailing speed record involving a vessel speed less than the actual windspeed needs to be voided anyway, as otherwise it is just a hurricane waiting game at your local ditch/trench or whatever.

IMHO all sailing record should be done in ONshore conditions in water depth of at least some decent minimum(a fathom?) with no land shadow or artificial water smoothing barrier. Otherwise why not just take things to their conclusion and go ice yachting in a bathtub with a parachute and a hurricane.....

You could cut Sailrocket down to the bare minimum.

It would be something like a Carafino hydrofoil board with the hydrofoil wings turned upside down and the kiter lying on his side on the board flying the kite. The foil has to stay in the water and the rider is attached to the top of the board with the kite powerline attached to the board so the pull is all in a straight line. The board is probably only necessary to get the thing going, then it is up in the air.

I've no idea how it would be controlled and the survival rate could be low.

having the pilot lay down may be the solution to the upright rider wind resistance issue. much simpler than elaborate speed suits, carbon leg cowlings, etc, etc. (rob douglas as transformer man)

sounds weird, but my hunch says the solutions will not be what we expect. doesn't the sail rocket look daft? sure does, at least to me. but no more daft than a kiteboarder laying prone inside a cone shaped board, that only touches the water at sub 30 knot speeds, after which time its magic curved inverted super foil takes over.....

i like the lay down stance, and also think a semi-submerged FOIL of some sort will be providing most of the resistance and lift.

following on from my post above, while we are talking about 70knts current performance capability of sailrocket, I do wonder if 100knt is even in the same ballpark at all- the forces and ride quality will be twice as much and I imagine their semi-cavitating fin(from what I can gather in my research of their project) isn't up to that realm of speed.

Bearing in mind what driving over tiny bridge partition gaps in the highway at 120mph is like, (and we are talking about bumps a few millimetres high), I imagine getting shaken to bits on the chop is the big hurdle to overcome sailing on water at 80knt+. A way of getting through this might be to build something truly massive and heavy, but then you won't have the required energy budget to get planing at lower speeds without some motor assistance.

FWIW probably the best way to go 100knt+ over water, using wind energy alone is probably this: (0:35-0:55s to see what i mean )




i.e don't touch it at all !