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

Yes counter intuitive and it has been posted a few times over the years. But there's bound tobe people that haven't seen it. No apologies necessary.
I've had it on my mind to make one for ages, but there's just so many other things to do.

I wonder if we get as many responses from people that don't believe it this time?

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

Yes at any instant the prop blades are just broad reaching downwind. On water? How about an AC 75 doing tight downwind gybes. If it towed a water skier who could do a relative slalom behind such that he traced a straight downwind course would that count?

Why they went to the trouble of building a full scale manned version to prove what is obvious after a bit of thought is strange. Though when it first came up on this forum many years ago I was in the "it's a hoax" camp until I'd clocked up several hours of deep thought.

You've got to hand it to the fellow who first thought of it.

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 it's been done for real
www.cousteau.org/legacy/technology/turbosail/

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

"""Alcyone is blessed with the most modern technology; computers optimize the functioning of Turbosails and engines. To maintain a constant speed, the engines take over automatically when the wind dies down, then they stop completely when the wind is strong and from the right direction. A crew of five is all it takes to maintain the ship but, theoretically, with all her control systems, she could sail without a crew.""

Select to expand quote

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.

30 years ago!
Imagine if someone actually pumped some money and modern technology into the idea.
I can just picture a modern miracle riding on foils balanced by gyroscope, or even something like a swath yacht would eclipse old boys efforts by miles.