有any other means of propulsion other than a propeller?

We put this question to Tristan Smith from UCL...

There are some other types of propulsor than propellers and ducted propulsors are one of them, which I think the second question is referring to. But if we just start with a few of the other propulsors first, we've got water jets which are used on very fast ships and they're a bit like a pump that pumps water in from the sea, and then it expels at a high speed out of the back of a ship. You often see them on the back of catamarans that you might take across the channel to go to France. Those are good if you're travelling very fast. Another one that's worth mentioning is some flapping paddles. So people have actually experimented over the years and to try and recreate the motion of a whale's tail in order to propel a ship along the sea. In fact, this might be any more efficient than the propeller that you typically have on the back of a ship. At the moment, noone's come up with something which is as robust or as efficient as the propeller or reliably efficient as the existing propeller.