Apologies if this has been posted before, first time I've seen it
It answers the question, can a wind powered vehicle move downwind faster than the wind

I didnt do physics at school. If a sailing craft can be faster than the wind at all points off the wind (beam reach to broad reach) because of the apparent wind effect (twice - on the sail and lift against the fin) then it kinda makes sense it could still be done downwind (now.that it has been explained to me of course) they are using the prop which will still have the apperent wind gain (over a sail which doesnt downwind) and the wheel.diff is a clever way of.coverting the missing lift from the fin. I wonder if it could be done with a super low drag hull on the water with the propellor sail.above and a propellor or hobie moving fin style of arrangement underwater. Probably too many moving bits

Going off on a beam, I wonder if anybody has ever tried mounting a turbine, either type, propellor or eggbeater, on a boat and transferred the rotation to a screw for propulsion. Would that be able to go straight upwind?

EDIT It looks like MUN has had the same idea, more or less, cross their mind

That's not using the wind to drive a screw. It's an advanced motor sailer.

Mr Milk said..
Going off on a beam, I wonder if anybody has ever tried mounting a turbine, either type, propellor or eggbeater, on a boat and transferred the rotation to a screw for propulsion. Would that be able to go straight upwind?

EDIT It looks like MUN has had the same idea, more or less, cross their mind

Yep a few have figured it out. It works.