It's basically a kite. A water-kite, but the principle remains.,(reply>), @Bonsai Herman I'm serious in a vaccume like outer space you can use light to a degree to push something granted it might have to be a laser but still. look up solar sails.,(reply>), @Sheila olfieWay <br>I think I really like you😊<br>My exact sense of humour…<br>It’s like looking at a mirror. With a flashlight. And a bottle of bourbon 😂,(reply>), Row row row your boat gently down the stream,(reply>), @Kim2506you I didn't mean to imply any use of wind. My point is that analogically to a rising kite, it uses the part of the force exerted by the flowing medium (be it water or air) that's not cancelled by the anchoring line to move across the stream.,(reply>), This is powered by water flow only no wind effect required. And above all it’s been invented long before any sort of water kite.