To know more about pop-pop boat

To know more about pop-pop boat

A pop-pop boat is a toy with a very simple heat engine without moving parts, powered by a candle or oil burner. It was patented in the UK in 1891, but may have precursors dating to 1880. The name comes from the noise the boats make. Other names are putt-putt boat, crazy boat, flash-steamer, hot-air-boat, pulsating water engine boat. Around the world they may be called Can-Can-boot, Knatterboot, toc-toc, Puf-Puf boat, Phut-Phut, or Pouet-Pouet.

Principle of operation

The heat engine of a pop pop boat is a steam boiler. Water in it flashes into steam, which pushes the slugs of water in the exhaust pipes propelling the boat by a pulse of water. The steam bubble then condenses slowly and this sucks water in. The key principle is that the water being propelled out the back of the boat is directional, but the water being sucked back in on the second half of the cycle is not a directional jet, but instead is sucked in roughly hemispherically, that is, from all directions equally. This asymmetry is what propels the boat forward.

The same principle can be demonstrated by blowing out a candle. It is easy to extinguish a candle by blowing on it, since all of the air being expelled is moving in one direction. However, it is difficult to put out the flame by sucking in air, since the air being sucked in comes from all directions, and not just the direction of the candle.

An internal combustion version would be a valveless pulse jet which works on the same principle, only the working fluid is air.