A pop-pop boat (also known as a flash-steamer, hot-air-boat, or toc-toc after a German version from the 1920s) 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

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