The idea has came out at the end of a recent post
How can a foilboard join an international kite race event ?
By being compliant with the "box rule".

So, for the techies out there, here is food for thoughts.

Scope of work
- the board must be compliant with the box rule - max depth under the board is 50cm
- the board must ride as flat as possible as opposed to current kitefoils that can ride with a 45 degree tilt angle when going upwind
- the height control must be automatic and preferably mechanical,
- the change of direction at buoys must not be a problem
... tbd
- I will add any suitable point

Points to look after:
- keep costs down
- security aspects
- rescue aspects
.... . .

+++++++++++++++++++++++++++++++++++++++++++++++

So this is one of the possibilities I have in mind. A board with a front T-foil and a rear T-foil.



- Two 50cm high T-foil for the box rule - However height control not based on flap angle variation as on a plane or Moths but got by varying the incidence of the T-foil mast thus the wing angle of attack, thus the wing lift.
Explanation:



A possible Implementation of the mechanism as seen on Don Montague's latest boat at 2'52 and 3'06
http://edition.cnn.com/video/#/video/sports/2012/06/14/mainsail-a-new-sport-kiteboarding.cnn

Vertical aspects: the 2 masts
One advantage of using 2 T foils is that the rider's weight is shared between 2 masts.
If a single 11 mm mast thickness is enough for one kitefoil with suitable materials and know how, as seen at the recent kite race worlds in France last May, two 7 or 8 mm blades could do the job nicely wiith little impact on the drag

Horizontal aspects : wing surfaces:
For a solution with front wing + stabilizer, if 600 square mm (450 front + 150 rear) are enough to lift a racer and bring him/het to 30 knots, we can imagine a tandem set up with less surface that is 280sq mm at the front and 270mm at the rear.

One issue I see with this solution is the change of direction.

This is a link to Don Montague's hydrofoil kite catamaran with trimming foils. The video you need to see is called 'Fastest man on the water.' so look for it if this link doesn't take you to the correct video.

http://edition.cnn.com/video/#/video/sp ... -power.cnn

Another way to alter the lift may be to channel air down through the hydrofoil to release it over the foil to reduce lift.

I already mentioned a wing-in-ground-effect (WIG) hull, because if the hull is supposed to be up in the air, maybe it should be wing shaped instead of boat shaped.

For the box rule, because the board will be canted slightly, the wings of the foil will need to be a shallow V shape as it may be argued that the fin is longer than 50 cm when measured from its base.

My personal preference would be that they have the rules set up so that most kite course racing is with planing hulls.
It seems to me that while hydrofoils are very interesting and may be ultimately very high performance, I worry about them for light winds because of the problems with self-rescue. If they have a large volume planing hull and 50 cm fin and can be paddled in, then I dont mind if the fin is a foil - especially if you can get away with that one fin instead of three.