4 points
You took the worst possible path to calculate all of this. Just compare energy to energy, that’s the whole point of Watts.
1 point
True but efficiency is not the same and not as simple to compare since we don’t know how much of the ship’s battery is converted into motion. Similarly we don’t directly know it’s mass. ICE cars can use ~20% of the energy in fuel while EVs 90%+ of the energy in a battery. But now much can that ship effectively use? I have no idea how efficient boats are or aren’t, hence the roundabout method above.