Pop pop boat
A pop-pop boat is a toy with a very simple steam engine without moving parts, typically powered by a candle or vegetable oil burner. The name comes from the noise made by some versions of the boats. 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, Poof Poof craft, Phut-Phut, or Pouet-Pouet.
A home-made pop pop boat using a coil type boiler
Commercial pop pop boats have usually been made out of tinplate. The hull of the boat may be made out of any material that floats. Homemade pop pop boats are often made out of wood.
The boat's engine consists of a boiler and one or more exhaust tubes. While a single exhaust tube may be used, two exhaust tubes are much more commonly used. This is because the boiler and the exhaust tubes have to be filled with water, and using two tubes allows water to be injected into one tube while air inside the engine escapes through the other tube. It is more difficult to remove the air and completely fill single exhaust tube types. The boiler and exhaust tubes are usually made out of metal, with tin or copper being common.
Boiler designs vary. Simple metal containers in the shape of a box or cylinder are common. A more efficient boiler can be made by using a metal pan whose top is a slightly concave diaphragm made out of a very thin, springy metal. Many pop pop boats have used a single tube of metal, which is formed into a coil in its center and left straight on both ends to form the exhausts. The coil in this version functions as the boiler.
A heating element of some sort is placed under the boiler. Candles or small oil burners are commonly used.
The guns can be made to fire by filling the .22 shell cases with red or black match heads for extra SPFX!
Beware of over engining!