We teamed up with the folks behind BBC World Service’s CrowdScience to answer your questions on one topic — this week it’s all about living underwater.

[Tom Clancy]’s The Hunt For Red October is a riveting tale of a high-level Soviet defector, a cunning young intelligence analyst, a chase across the North Atlantic, and a new submarine powered by a secret stealth ‘caterpillar’ drive. Of course there weren’t a whole lot of technical details in the book, but the basic idea of this propulsion system was a magnetohydrodynamic drive. Put salt water in a tube, wrap a coil of wire around the tube, run some current through the wire, and the water spits out the back. Yes, this is a real propulsion system, and there was a prototype ferry in Japan that used the technology, but really the whole idea of a caterpillar drive is just a weird footnote in the history of propulsion.

This project for the Hackaday Prize is probably the closest we’re going to see to a caterpillar drive, and it can do it on a small remote-controlled boat. Instead of forcing water out of the back of a tube with the help of magic pixies, it’s doing it with a piston. It’s a drive for a solar boat race, and if you look at the cutaway view, it does, indeed, look like a caterpillar.

Instead of pushing water through a tube by pushing water through a magnetic field, this drive system is something like a linear motor, moving a piston back and forth. The piston contains a valve, and when the piston moves one way, it sucks water in. When the piston moves in the opposite direction, it pushes water out.

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