Little Steam Yacht or Pop Pop Boat

The Pop Pop boat contains a simple steam engine without moving parts - the name comes from the noise made by some versions of the boats.

A heat source inside the boat, either a small candle or a solid fuel tablet, causes the water in the boiler to boil. Steam pushes water out of the two tubes at the back of the boat, and the boat moves forwards. Water is then drawn back into the tubes, and the process repeats.