50kts -500m!

Isn't his board pretty well cranked on its rail for these runs? How else does the dude hold his track if it isn't? If so, that would allow him some cushion against getting the fin in the goop more than needed. It would seem that running in a thicker fluid medium would deter top speed, and not enhance it.

Is there a "ground effect" style of lift bounce working off the bottom against the fin board juncture?

Anyone here with high speed kite experience who can speak to the issues?

 

No it's pretty flat, you can see in the video link.
Compare the video shot of Tilmann going back upwind at the end (L to R) to see the difference. You can see by the angulation of his legs as well as the board an idea of the heel angles.

I have never gone so fast, but at that course angle at 25-30 knots or so I guesstimate my board angle 15-20 degrees from horizontal at most.

The chord of the stainless fin is long and helps with tracking, whether or not it is touching mud. As I recall it or a similar fin he posted online had a chord of 15 or 20cm.

But in 5cm water with a 4cm fin the board could touch bottom at minimal AOA. Unless AOA were rigidly kept under 0.3 degrees, it would have to I think, unless it pushes a significant "hump" of water, which I doubt at the speed.

The vertical lift component from the kite keeps the fin from digging in deep. So does the hydro and aero lift of the board.

The hydrodynamics would be involved, and a little different from normal boating I am sure, including the viscosity accounting for temperature plus extreme shoal plus maybe suspended mud, plan shape of board, etc. And is the board concave bottom, how much does it trap air, etc?

Tilmann is nice to share some things, but has some secrets.

 

Its a good effort - but my interest probably is more in achieving those speeds in adverse sea states. That french Trimaran did nearly that speed in very rough seas, which piques my interest quite a bit more.

 

55/48=1.15. It's a big, big difference. I bet Hydro will hit 50 this spring though.,,,