Pop pop boat

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.

[2][3] A 1975 article by Basil Harley mentions a similar boat seen in a French journal from 1880, indicating that this type of toy may have existed for many years prior to Piot's patent.

[citation needed] In 1915, an American named Charles J. McHugh filed a patent application for the diaphragm type of engine, which was an improvement to Piot's design.

This project used a coil type of engine based on Purcell's design which was placed in a wooden hull.

[6] In 1934, Paul Jones filed a patent for another diaphragm design which could be produced industrially from simple stamped parts.

The boiler and exhaust tubes are usually made out of metal, with tin or copper being common.

In the case of a diaphragm type engine, the boiler also bulges inward at this point, also making a popping sound.

Therefore, engines must "burp" out air periodically in order to run for a long time.

The initial reaction force on the boat (which would pull it backwards) is therefore cancelled by the pushing of the water when it hits the inside of the boiler.

[9] Some authors have argued that the reason why the pop pop boat works is that the water being propelled out the back of the boat forms a narrow jet, while the water being drawn back in on the second half of the cycle is drawn in from all directions.

The asymmetry of the shapes of the inflow and the outflow is a consequence of the viscosity of water, whereas the boat would be able to operate in an ideal fluid.

[9] Furthermore, as they pass through the exhausts, the inflowing and the outflowing water carry the same momentum (in opposite directions), relative to the boat.

[13] Toy boats with a diaphragm type engine, like the one shown in the film, were produced and sold as a tie-in when the movie was released.

Video of a pop pop boat in action