Bill & Pete’s Science Experiments

Self-propelled jet boat

This toy, first sold in 1948, makes a great vehicle for demonstrating Newton’s Third Law of Physics— that for every action there is an equal and opposite reaction. It is quite simple in construction, with a hole in the smokestack, a few internal baffles, and a small hole in the rear of the boat.

Simply plug the rear hole with your finger, pour water into the smokestack, set it down in the water, and release your hand. The boat will start accelerating due to water being ejected from the boat. Adding a few drops of foodcoloring to the boat, thereby showing the stream of water leaving the boat, and what happens as it gets dispersed in the currents.

This is also a good demonstration of a fundamental behavior of water—that it seeks its own level. The water will provide thrust for the boat only as long as the level of water inside the boat is higher than that outside the boat.

I purchased my “Sea Star” boat at Restoration Hardware, though I believe the store has discontinued them now. It shouldn’t be too hard, though, to make a similar model out of materials you have around the house. For example, why not start with a cardboard milk carton—quart-size— and cut the necessary holes in it. You’ll have to find some way to add a keel or ballast to make the “boat” stable, but that’s part of the fun with experiments—figuring out how to build the lab equipment in the first place.

— Peter K. Sheerin

P.S.
If you come up with another source for this boat, or a good, cheap way of building a similar one, please drop me a line.

First published: September 3, 2001

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