It's not that they don't exist, it's that current generation tech is not economical without subsidies [that don't exist], and therefore hasn't been scaled up.

It's not that they don't exist, it's that current generation tech is not economical without subsidies [that don't exist], and therefore hasn't been scaled up. And there is no way in hell that a boat filled with batteries is economical compared to one filled with bunker fuel. So if we're not doing economical, it's worth exploring other not-quite-there renewable sources -- especially since a net-zero-CO2 fuel will be more practical: big tanks are cheap, more batteries are not.