I wonder if these electric ferries have diesel backup systems? A little 100 horsepower backup engine wouldn't use much space/weight/cost, but would still be

I wonder if these electric ferries have diesel backup systems? A little 100 horsepower backup engine wouldn't use much space/weight/cost, but would still be enough to get the ship slowly home in case of other failures. The energy required to move a ship isn't proportional to speed - so just a little slower saves a lot of energy.