How can ferries operate without a motor?

There’s a river, and you need to get across. Bridges are expensive and prone to failure during floods. So you decide on a ferry. What kind of motor should you use? The correct answer could be… none.

For the past 400 years, rivers in Germany have been traversed by ferries that have no motor. They use the power of the river to swing the ferry from one side to the other, much like a giant pendulum. A rope is anchored upstream in the middle of the river and is attached to a box-like ferry. Large rudders swing to either side to divert the flow of the river against the ferry so that it moves in the desired direction. If the river floods or changes speed, it’s no problem, so long as there is enough current and depth to move the ferry. Some of these are large enough to carry 322 people or a dozen vehicles. There are 56 such ferries still in operation throughout Germany.

Next time we’ll learn about pendulums that could kill you.