We have 3 electrical ferries in Oregon crossing the Willamette but they use 3 overhead wires to deliver 3phase AC. Works great for short hops.
For example, the Canby ferry
> "This most recent ferry differs from its predecessors in that it has a capacity of nine cars, rather than the six Daniel Matheny IV carried, and it has its own self-contained diesel-electric generator. As its source of electricity is now an onboard generator, the current ferry is no longer reliant on electricity from overhead wires. The overhead cable serves the sole purpose of bracing the ferry against the current."