Bath-tub steam boat really works!

Craft & Design
Bath-tub steam boat really works!

Steve writes in with these build instructions for a classic bathtub playtoy, the tugboat. At first glance it seemed like a regular old wooden play boat, but there is something cooler here- it has a working steam engine!

I hadn’t heard of pop-pop boats before, but apparently they used to be common toys. The pop-pop motor is a phase-change heat engine (fancy name for a device that converts heat into kinetic energy), and the popping sound is caused when the water turns into steam and causes the metal cavity to expand. Here is a video of someone else’s build:

This looks like a pretty fun experiment- anyone make one of these before? Bonus points if it can be remote controlled.

10 thoughts on “Bath-tub steam boat really works!

  1. StefanJ says:

    I read about these in an old Boy Scout handbook. My father mentioned that they were around when he was a kid (1940s). I was intrigued but never built one.

    A putt-putt boat figures in the animated film “Ponyo.” I guess Miyazaki had one as a child.

    The leading boy’s toy is magically enlarged and provides transportation around a flooded landscape. It used a candle as a heat source and had to be primed by blowing water into the chamber.

    I seem to recall that American Science & Surplus offered one of these for sale a few years back.

  2. Simon says:

    My father also mentioned these when I was a kid but he couldn’t remember exactly how they worked and I never knew how to make one until I came across one some where a few years ago. He called it a putt-putt boat.

    I made one from some soldered tin and a piece of copper tube. I made the simpler version where you just wrap the tube around a piece of dowel to make a loop in the tube about 15mm across.

    This works quite well and is very simple. You still need to prime the tube by filling it with water first. It’s still sitting on my bookcase at home.

    I used thin copper capillary tube I got from an old thermostat that is only a couple of mm diameter.

  3. Durgaba says:

    We made them in metalshop. Old fashioned school I guess.

  4. acidrain69 says:

    I was going to say the anime Ponyo had one, but someone beat me to it! Go check out Miyazaki’s films, they are great. Opensky built a mehve glider from Nausicaa, you can see it at

  5. jbalas says:

    I made one when i was.. 10 year old maybe, around 1985.
    The “easy” way to do one is to use a narrow copper pipe and make a spring like shape by wrapping it around a bigger tube.
    You should end with an Alembic-condenser thing.

    You put in on a non-flammable boat, light some cotton+alcoohol in the middle and you are all set.

    The ship move slowly with a pop-pop sound. I don’t remember the name we use for this kind of ship a the time. Probably “steam boat”…

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