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 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.
History
Credit for the first pop pop boat is usually given to a Frenchman named Thomas Piot. In 1891, Piot filed a patent application in the UK for a simple pop pop boat using a small boiler and two exhaust tubes. 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. 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. In 1920, William Purcell filed a patent for the coiled tube type of engine. This type of engine has been common over the years in homemade pop pop boats, due to its simplicity of construction. The Cub Scout book (published by the Boy Scouts of America) contained a project called a "Jet Boat" for many years. This project used a coil type of engine based on Purcell's design which was placed in a wooden hull. Many commercial pop pop boats have also used this type of engine, due to its low cost. McHugh filed for another patent in 1926. This was again a diaphragm engine design, refined so that it could be more easily fabricated commercially. In 1934, Paul Jones filed a patent for another diaphragm design which could be produced industrially from simple stamped parts. Many pop pop boats produced in the 1920s had a single exhaust pipe. Designs using two exhaust pipes are easier to fill, and have been much more common over the years. Pop pop boats were popular for many years, especially in the 1940s and 1950s. Pop pop boats declined in popularity along with other tin toys in the latter half of the 20th century as plastic toys took over much of the market. While they are no longer produced in such large numbers, pop pop boats continue to be produced. These toys have come in many varieties over the years. Some have been simple and inexpensive, while others have been much more ornate and artistic. As with many toys, pop pop boats are often sought by collectors, and the prices paid vary depending on rarity and design.
Design and construction
A pop pop boat is powered by a simple heat engine. This engine, sometimes referred to as a pulsating water engine, consists of a boiler and one or more exhaust tubes. A heating element of some sort is placed under the boiler. Candles or small oil burners are commonly used. 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. The boiler and exhaust tubes are usually made out of metal, with tin or copper being common. 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. 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 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.
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