another idea

[Paul No Boat]

So the way I understand it the boat can beat the wind if the surface providing drive (the windmill) is greater than the surface of the driven parts (the hull and related equipment)

a boat going downwind would be pushed whether the windmill is turning or not and the rotory motion produced by the vanes assists in the natural push from the wind while a boat traveling into the wind will lose some but not all speed provided by the wind.

a very interesting technology but I have to wonder if it will ever be usable in anything other than an experimental senerio much like a sterling engine which can make enough power to turn itself but nothing more.

I am not a sailor but I was a private pilot for years until an eye injury diqualified me but could I ask a simple question about windmill powered craft in general? does ground effect have as much bearing on a boat or wheeled vehical as it does on a light airplane? ie: would putting the windmill higher on the contraption cause gain or loss?

[Windmaster]

Think of it this way, as you know, the lift provided by a wing can greatly overcome its drag, and so it is with these "wind-beating" craft. Each blade is a wing which provides more lift than drag, enough surplus to overcome the other drag from the whole craft.
Any system that can gain energy without using any fuel is useful, even if not as a primary source of power but as a "fuel saver".
This is where such a system of this scores over a Sterling engine, which uses fuel and is unsuccessful because it does not use the fuel efficiently. This uses no fuel at all, and therefore is more efficient than anything that uses fuel!
As a pilot you will know about the wind gradient, close to the ground the wind is much slower. Any wind-collecting device, when lifted higher, will intercept faster wind and will therefore produce more power. However, in this case there is a limit because you need to consider the effect on the boat's stability. "Ground effect" is not relevant at all.

[ancient kayaker]

For those who might be interested I started a thread Sailing Directly Upwind to discuss a method of achieving this without using the turbine and prop approach. My last post there was not terribly technical but I have recently started building hardware for testing later this year and will resume posting in that thread as I progress.