Just looking at a couple problems:

> Probably you want the catenary at 20m depth then. How does a small get their pantograph (or whatever you'd call it) down to that depth,

Does the connection from the 'pantograph' to the boat need to be rigid? Use a cable? Maybe it's not for the smaller boats which can't handle a 20m (probably more like 40m for the angle and slack) cable, but also need less power and thus pollute less.

> and then move forwards without the pantograph sticking 20m down creating a huge amount of drag

Presumably, the catenary's route would be cleared of obstructions - maybe even on a frame elevated over the floor, maybe at relatively constant depth - or do I misunderstand? Would a 40m cable cause that much drag? Obviously the pantograph would have to be low friction and highly reliable.