[usrusr]

You have it reverse wind turbines need mooring, stay upright and so on. That's highly impractical. No, you build a fast-going sail vessel (using big traction kites, because it's not the 19th century anymore) and power the generator from much smaller turbine blades in the water. Hydrogenerator is the term established in recreational boating.

I sure would not expect any returns in days, more like months or years. But if we (humanity) could just solve the purely man-made problem of piracy (or would it technically be salvage?), I believe that a robotic fleet of cruising hydrogenerators could be a huge contribution to our energy needs.

[Earw0rm]

The main issue is that prevailing winds have a direction, and there's not a continuous open ocean path other than the Southern Ocean which is harsh even by the standards of oceans. Sure you can steer along trade winds in the Atlantic or Pacific but there's quite some efficiency loss.

(Give climate change another decade or so and the Arctic Ocean maybe becomes an option, although by then we'll have bigger fish to fry, or perhaps poach).

[usrusr]

Sailing technology has gone beyond "we can go downwind, yay!" for quite a while now...

[Earw0rm]

Certainly of course, but not while delivering maximum continuous energy from a kite to a turbine.

[usrusr]

Boats go considerably faster, as in overcoming more water drag, going crosswind than going downwind. I suppose that adding extra drag with a hydrogenerator will change the maths of that relationship, but certainly not so much that it would be prohibitively wasteful to not specialize a hydrogenerator carrier to downwind-only. (if the downwind-only setup can be competitive at all, not sure I'd take that as a given)