These ram air kites by Skysails power flying in a figure eight circuit can develop power and also work as ship propulsion. Ideas like this have probably been toyed by many, it’s nice to see some execution. The biggest current product is 320 square meters and produces something equivalent to 2 MW of propulsion.
A flexible structure might be easy to store and the absolute lift is probably much more important than lift to drag at these low vessel speeds. I still wonder what high speed high aspect ratio glider style vehicles (tailed or tailles) could do in these applications. Control surfaces and all. Since lift is proportional to square of velocity.
And wouldn’t flying a circle or flattened ellipse or oval be more aerodynamically efficient with less tight turns and produce gentler load changes? Maybe there’s symmetry problems if you always go in a particular direction at higher altitude where the wind speed is higher. Or maybe the pull direction varies more.