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The Pop Pop Boat
Otherwise known as flash-steamers, hot-air-boats, toc-tocs or more accurately a Pulsating Water Engine (P.W.E.), the pop-pop boat originated in an 1891 British patent for the coil type water pulse engines by an inventor named Thomas Piot.The popularity of the boats spread quickly, however, and they were soon being manufactured in many countries.
In early publications, mention is made of a series of boats made in the early 20th century by the German toy makers Ernst Planck. In 1916 a US patent was granted to Charles McHugh for the diaphragm type engine. The German name for the boat, toc-toc, originated as a product brand name for a diaphragm-boilered boat in the late 1920's, while they have also been called put-put, phut-phut, and pouet-pouet boats elsewhere
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The name comes from the noise the boats make. Other names are putt-putt boat, crazy boat, flash-steamer, hot-air-boat, pulsating water engine boat. Around the world they may be called Can-Can-boot, Knatterboot, toc-toc, Puf-Puf boat, Phut-Phut, or Pouet-Pouet. The heat engine of a pop pop boat is a steam boiler. Water in it flashes into steam, which pushes the slugs of water in the exhaust pipes propelling the boat by a pulse of water. The steam bubble then condenses slowly and this sucks water in. The key principle is that the water being propelled out the back of the boat is directional, but the water being sucked back in on the second half of the cycle is not a directional jet, but instead is sucked in roughly hemispherically, that is, from all directions equally. This asymmetry is what propels the boat forward.
The same principle can be demonstrated by blowing out a candle. It is easy to extinguish a candle by blowing on it, since all of the air being expelled is moving in one direction, being concentrated. However, it is difficult to put out the flame by sucking in air, since the air being sucked in comes from all directions, and not just the direction of the candle. There are two types of pop-pop engines. One is a copper tube coiled in the middle with both ends protruding from the rear of the boat. The other has two tubes connected to a boiler with a diaphragm that improves thrust and produces a popping sound.
The coil type boats are powered by a basic boiler comprising a thin coiled copper tube. The coils in the middle of the tube are positioned over a flame, which heats the water in the coils. The end of the tubes protrude from the back of the boat into the water. When the water boils, the expansion of the steam pushes the water out the tube at the back of the boat as a jet of steam, and the boat moves forward. After expansion, the steam cools to create a partial vacuum, sucking water back into the tubes to allow the cycle to begin again. It's that simple.
The diaphragm type engine is a slightly more sophisticated version which substitutes the coil with a shallow chamber with a flexible diaphragm for the coil. The flexing of the diaphragm gives a little more impulse to the escaping steam, as well as making a louder pop.
The diaphragm boiler is a variant of the coil boiler. This type of boiler is more efficient than the coil. However the flip side of it is the fact that it is much harder to make. This type of boiler was patented by Charles McHugh. Below is a snippet by Vance Bass. It illustrates the function and the make up of the Diaphragm boiler. "A more efficient boiler is the diaphragm type. This variant replaces the coils with a small metal pan whose top is a slightly concave piece of very thin, springy metal such as brass shim. The diaphragm has two apparent effects when the steam flashes under it: first, it makes a click sound to augment the quiet pup-pup-pup of the coil boiler; second, as it pops up and then back into its original shape, it may impart some more concentrated energy to the exhaust jet. The result is a boat which runs well and makes a vaguely motor-like noise. " An internal combustion version would be a valveless pulse jet which works on the same principle, only the working fluid is air, even though it is not a liquid. |
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