The putt-putt boat

Or as some say, the pop-pop boat.

I think my daughter gave me this as a Christmas present ten or so years ago. It hasn’t seen the light of day for some time but it has happy memories for me, particularly when I was a teacher and took it to use in one lesson. It really seemed to inspire and motivate a whole class.

It’s a cheaply made bit of tin plate. It had a bit of the look of a heroin addict’s accoutrements, particularly with its little dropper for filling the boiler. I don’t know where that is now, but you can fill it from a tap with no problem.

Here’s the boat on dry land.


This was taken in artificial light which seems to give silver surfaces a golden hue. The outside of the boat is silver coloured. The metal flag at the sharp end is pure decoration.

Here’s the boiler.


It’s that black disc thing, supported on twin tubes and with the potential to be heated by a bit of candle. Apparently they work with one tube, but it is much easier to fill that little boiler if there’s a route for air to escape as water goes in.

Those twin tubes run along the lower deck and then protrude out of the hull.


I used flash which got the colour rendition rather better!

And you can click here to see the boat in operation in what I promise you was a scrubbed clean kitchen sink.

The science of the thing is strange. Water in the boiler boils and the vapour forces water out of the tubes which pushes the boat. But then, away from the heat of the candle, the vapour condenses and water gets sucked back in through the tubes. It boils and so on. I’d have said that the forward motion caused by the water boiling ought to be matched by an opposite force as the water is sucked back in. But this is clearly not what happens. The little boat continues to go forwards.

If you really want to understand it, having first obtained your degree in physics try this research paper.

Otherwise just enjoy a fun toy.

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