“Ever hankered after the gorgeous sounds of a ‘proper’ historic engine? Well, just listen to the sound a pop-pop boat makes, that original working boat sound could be yours for just a few pounds!!!”
A pop-pop boat is a toy with a very simple steam engine without moving parts, powered by a candle or oil burner. The name comes from the noise some versions of the boats make. Other names are putt-putt boat, crazy boat, flash-steamer, hot-air-boat, pulsating water engine boat – or from around the world the: Can-Can-boot, Knatterboot, toc-toc, Puf-Puf boat, Poof Poof craft, Phut-Phut, or Pouet-Pouet!
Commercial pop pop boats have usually been made out of tinplate, though the hull of the boat may be made out of any material that floats.
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.
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.
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 very common over the years in homemade pop pop boats, due to its simplicity of construction. The Cub Scout book 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.
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 very simple and inexpensive, while others have been much more ornate and artistic.
A pop pop boat is powered by a very simple heat engine. This engine consists of a small boiler, which is connected to an exhaust tube. When heat is applied to the boiler, water in the boiler flashes into steam. The expanding steam pushes some of the water in the exhaust tube, propelling the boat forward. The steam bubble then condenses, creating a vacuum which draws water back in through the exhaust tube. The cooled water that is brought back into the boiler is then heated and flashed into steam, and the cycle repeats. This constant flashing and cooling cycle of the engine creates the distinctive “pop pop” noise for which the boat is named. This noise is more pronounced when a diaphragm-type boiler is used (coil-type boilers are much quieter).
Note that in pop pop boats with two exhaust tubes, the water is expelled from both tubes during the first phase of the cycle, and drawn in from both tubes during the second phase of the cycle. The water does not circulate in through one tube and out through the other. The internal-combustion analog of the pop pop boat engine is the valveless pulse jet.
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ps. if you have a battered old pop-pop knocking about I’d love to get one for our kids to enjoy…
pps. thanks to Graham for suggesting e-bay who have loads of pop-pops for sale…