Pop-pop boat

pop-pop boat is a small toy boat propelled by a rudimentary steam engine , typically heated by a candle. This toy was invented in the 1890s by the French engineer Désiré Thomas Piot and it was later perfected. Very fashionable in Europe and the United States at the beginning of xx th century, this toy inexpensive and easy to build is still common in our time in some countries (Asia, South America).

The name “pop-pop” is an onomatopoeia evoking the repetitive noise of certain models. This boat has different names depending on the language: pop-pop , put-put, puff-paff, toc-toc(German), phut-phut, pouet-pouet 1 , can-can …


The hull of the boat is usually built with a thin sheet of metal (tinplate, copper), to avoid any flammable material near the fireplace flame. Some boats have a movable rudder to turn the boat.

The pop-pop engine is rudimentary and has no moving mechanical parts:

  • a source of heat: typically a small, flat candle, but sometimes an oil or alcohol burner. On some models, a removable support with a handle (spoon) makes it easier to light the candle or adjust the intensity of heating.
  • a small boiler filled with water at the beginning, and typically two fine tubes starting from this boiler, with the other end under the water level and directed towards the back. A single tube would suffice for operation, however the initial filling of the boiler would be difficult.

A boat cabin (possibly removable) can often hide the fireplace and boiler and protect the flame from the wind.


The inventor is Desire Piot Thomas (born 1835), who, while he was in London, filed two patents o 20081 (1891) 2 and o 26823 (1897). This French engineer, a specialist in electric generators , has distinguished himself in the Lépine contest , and his first known action in “pop-pop technology” is a patent application on an improvement of steam boilers. However, it seems so convinced by his invention he mentions that his engine could be used to propel toy 3 .

Its motor consists of a coil, containing water, heated by a heat source. Both ends of the coil end at the stern (the stern) of the boat below the waterline . The coil must be filled with water before starting the engine. If the motor is correctly made, it stops only when the fire is extinguished.

As a result of this invention, several toy manufacturers in the United States and Europe market pop-pop boats according to the Piot engine until 1924 3 .

On October 10, 1916, CJ Mc Hugh was granted US Patent No. 1,200,960 ( US Patent ) 4 . It consists in improving the invention of the engineer Piot , by creating an evaporation chamber equipped with a flexible membrane at its upper part. The noise generated by this flexible capsule is at the origin of the name of pop-pop, the engine Piot being almost silent.

In 1967, the boat Hell’s popin carrying two people who would have worked with two pop-pop engines, participated in the race in Cowes Torquay before sinking 5 .

More recently, patents have been filed for the perfect pop pop boat McHugh and extend its applications 6 .

In France, the name “pop-pop motorboat” was filed with the INPI in 1995 7 but no longer seems protected in 2017 8 .

Mechanism of the pop-pop engine

The pop-pop engine is generally described as a ” steam pulser ” 9 . The physical principles of the pop-pop propulsion are complex and they have long been poorly understood, research misconduct and scientific publications sufficient by the end of 2000 10 .

A steam engine

The pop-up engine is a thermal machine , subjecting the water cyclic transformations and transforming thermal energy (candle) into mechanical energy (water displacement). The flame heats the tank and then there appears an oscillation of gas bubble (water vapor) with a phase of expulsion of water followed by a suction phase. A simplified pop-pop engine, consisting of a single tube (without tank) works perfectly 10 . In a two-pipe (or more) pop-pop engine, the water does not enter a tube to flow through the other tube. The water is ejected simultaneously by the two tubes during the first phase of the cycle,

This cyclic mechanism is not completely understood and it generally simplified as follows: The heat vaporizes a little water; the created gas bubble pushes the water column towards the end of the tube. By inertia , the ejection movement continues in the cold part of the tube. In contact with the cold wall of the tube, the water vapor contracts and condenses. As the gas volume decreases, the water is sucked back to the hot zone and the cycle begins again.

It is observed that more heat, the greater the amplitude of the oscillation increases (the amount of water ejected / drawn), but the frequency (cycle time) does not vary 10 . The frequency of the oscillation is related to the dimensions of the tube.

A pulse jet

The physical mechanisms resulting from the pop-pop aspiration are comparable to those of Feynman’s turnstile , a mobile device immersed in a liquid: will it turn if the liquid is sucked? An issue debated since 1883 11 .

The pop-pop engine is a pulse jet engine , that is to say a cyclic reaction engine . During the ejection phase of the water, the boat is propelled by the “reaction” to the projection of the jet of water ( hydrojet ) out of a nozzle 9 .

The operation of the pop-pop boat may seem surprising: one might expect that, if the water comes out and enters through the exhaust tube, the boat would be pushed alternately forwards and backwards, and so be immobilized. But the pop-pop boat is moving forward. This phenomenon is observed by the physicist Ernst Mach in 1876: an apparatus that sucks and rejects alternately the surrounding liquid moves as if it was only rejecting liquid (like the squid ).

Some authors have taken up the old hypothesis of Mach (1883) of Feynman’s turnstile : during the pop-pop aspiration, it would be the flow of water in front of the pipe, observed as coming from all directions, which would provoke the lack of recoil of the boat 12 , 11 . Nevertheless this solution is wrong according to the physicist Jenkins (2011), who refers to the theory of the conservation of the momentum . When passing the end of the exhaust pipe, ejected water and sucked water have the same amount of movement(in opposite directions) in relation to the boat: the water movements outside the pipe do not explain why the boat does not go back 11 . The suction flow only reveals the large energy loss of suction by dissipation and viscousturbulence , in the case of a non-perfect fluid such as water 11 .

According to Jenkins, during the suction phase, the water quickly collides with the walls of the tank and thus transfers its momentum to the boat. The initial reaction force of the boat (theoretically provoking its recoil) is quickly canceled by the thrust of the water against the tank 11 .


According to theory and experiments, the performance of the pop-pop engine is extremely low; the use of this engine is therefore restricted to the field of toys and is not interesting for industrial applications 10 , 11 . Only 10% of the mechanical energy of the water displacements in the pipes is converted into propulsion energy 11 (to compare with the 75% efficiency of a propeller ). But above all the thermodynamic efficiency of the steam engine is very low, because the vaporization and recondensation are carried out in a single chamber at a temperature close to 11 . The pop-pop engine generates a great deal of heat loss and very little thrust 11. For example, for a small pop-pop boat of homemade construction heated by burner, the overall efficiency of the engine measured was of the order of 0.003% (ratio between heating power and mechanical power delivered); compare to the performance of a conventional propulsion (35%) 13 .

The speed of a commercial toy is of the order of 10 cm / s ( 0.36 km / h ), the world record would be around 0.7 km / h 12 .

Manufacturing and distribution

The main manufacturers of commercial toys are located in India and Southeast Asia 14 . The raw material used for the hull is the tinplate, sometimes the brass for the tank of the boiler and the piping. They are available for sale, on the Internet and at some toy and souvenir shops.

The pop-pop boat can also be a homebuilt 15 . The construction or the study of pop-pop boat is sometimes playful and educational way to introduce children and adults to the construction, the physical (steam engine, strength, fluid …) and the scientific method 16 these toys can be dangerous because they burn and should not be left in any hands 17 .


Since 1996, a gathering of boats in pop-pop engines, dubbed “World Championship Loguivy-de-la-Mer pop pop boat vessels” is held each year to Loguivy-de-la-Mer in Brittany 18 .

Cultural references

In the animated film of Hayao Miyazaki , released in 2008, Ponyo on the cliff , little Sôsuke goes in search of his mother aboard a pop-pop boat, a toy magically enlarged by Ponyo. The start-up scene details the filling of the boiler and the ignition 19 .


  • Horn, Arques, Vasseur, “Modeling and simulation of a steam pulser”, 2001 read online  [ archive ]
  • “The pop-up boat” in Étienne Reyssat, “Drops, films and jets: when flows shape the interfaces”, thesis of physics of liquids, 2007, University Paris-7, p.163-176 (appendix). online  [ archive ]
  • Laura Fourgeaud, “Analysis of the dynamics of the liquid film in an oscillating heat pipe”, (dynamics of the fluids), Grenoble 2016, p. 11. read online  [ archive ]

References and notes

  1. ↑ ( in ) The pop-pop pages  [ archive ]
  2. ↑ Patent 1891  [ archive ]
  3. ↑ a and b http://waterocket.explorer.free.fr/piot.htm  [ archive ]
  4. ↑ ( in ) the US Patent of October 10, 1916 No. 1,200,960 McHugh  [ archive ]
  5. ↑ Pop Magazine Winter 1993/1994  [ archive ] p.2
  6. ↑ Among these, a patent of Peter R. Payne of 1975 ( in ) A patent of Peter R. Payne 05/580096 of May 22, 1975  [ archive ]
  7. ↑ the 26/10/1995 under o 95,595,116 by the Marine Chemist
  8. ↑ Based on an automatic search on the INPI database  [ archive ]
  9. ↑ a and b Horn, Arques, Vasseur, 2001
  10. ↑ a , b , c and d Reyssat 2007
  11. ↑ a , b , c , d , e , f , g , h and i Alejandro Jenkins (2011). “Sprinkler head revisited: momentum, forces, and flows in Machian propulsion”. European Journal of Physics. 32 (5): 1213-1226. arXiv: 0908.3190 Freely accessible. Bibcode: 2011EJPh … 32.1213J. doi: 10.1088 / 0143-0807 / 32/5/ 009 .
  12. ↑ a and b Fourgeaud 2016
  13. ↑ http://www.odpf.org/images/archives_docs/17eme/memoires/gr-14/memoire.pdf  [ archive ] p. 36
  14. ↑ ( in ) [1]  [ archive ] site of a traditional pop-pop maker: Enterprise Rattandeep
  15. ↑ See for example http://blognature.fr/brico-detente-fabriquer-un-bateau-pop-pop/  [ archive ]
  16. ↑ competition in kindergarten  [ archive ] , Memory for the Physics Olympiad [ archive ] …
  17. ↑ ( en ) tutorial allow to build a simple pop-pop boat from basic materials [ archive ]
  18. ↑ http://www.lapressedarmor.fr/2016/03/31/affichepop-pop-21-championnats-du-monde-samedi-2-avril/  [ archive ]
  19. ↑ Extract from Ponyo on the cliff  [ archive ] (5 min.) Detailing the start-up and operation of the pop-pop boat

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