(I grew up in a small town that had a two-car ferry pulled by ropes across the river. This story takes place when I’m eight and we’re vacationing in BC.)

Me: *looking at the back of the giant ferry* “Dad, how do they get the ferry to go between the islands? I don’t see the rope.”

Dad: *who’s an engineer* “Well, you see… they have a hook on the bottom of the boat. And each island has a set of ropes and pulleys under water. So the captain has to use the hook to grab the rope and the boat is pulled across that part of the water. He has to grab the rope at just the right time, or the boat will crash into the island. Watch closely, and you might be able to see the hook.”

(Thanks, Dad. You could have just said the boat has an engine and propellers.)