A pop-pop boat (also known as a flash-steamer, hot-air-boat, or toc-toc after a German version from the 1920s[1]) is a toy with a 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.
Initially patented in 1891, the concept has undergone a number of changes and subsequent patents.
The engine consists of a boiler and one or more exhaust tubes, in which an oscillation of the water is established in the tubes to eject water out the exhaust tubes in pulses to propel the boat.