I really like the films of Hayao Miyazaki. Since we just visited Japan, we are re-watching his films (on Netflix).

In the film, after a flood, Sosuke and Ponyo go in a special little steamboat powered by a candle in search of Lisa, Sosuke’s mother. This time, the propulsion of this little boat caught my eye. I googled it, and it turns out to be a puff-puff boat (or pop-pop boot in Dutch).

I didn’t understand how this mechanism worked, but of course, you can always find someone who can explain it clearly. The remarkable dynamic balance that is created by heated in a boiler, pushed out, and sucked back in due to the underpressure that is created.

https://kayakaa.com/how-does-ponyo-boat-work/

PS. I found the first link died. Here is (an even more extensive) description.

http://www.nmia.com/~vrbass/pop-pop/aapt/crane.htm

And for those who like to go down the rabbit hole: