When I clicked on this I thought, why not just have a cable-guided ferry instead? (Which already is a common thing) I assumed they'd have to make maneuvers not possible with a cable. But it already is?!

Then why not just tug the cable instead, much better efficiency then propellers.

Edit: ok, it is. Though what I've seen is that the motors are pulled from shore rather than on the boat. Which seems simpler, but this is maybe easier to retrofit.