How to build a toy sailboat

Build a boat powered by a candle

Rattle boats, also known as putt-putt or puff-paff-boats, have been around since at least the late 19th century. After the Second World War, they were forgotten in Europe, in India they are still a popular toy to this day. With the following instructions we can build our own crackling boat.

Traditionally, rattle boats were made of sheet metal - but nobody should feel restricted in their imagination. Styrofoam, milk cartons or even Dutch wooden shoes are just as suitable. Rattle boats use a water impulse drive to move; the "motor" consists of a pipe and a heat source (in our case: a tea light) and does not require any electronics. Unfortunately, the degree of efficiency is rather weak: in engine construction, the principle was therefore quickly discarded. However, it is ideal for self-built toy boats.

Manufacture of the spiral evaporator

In a first step, the spiral is formed: To do this, the pipe is wrapped tightly around the broomstick in the middle: one and a half turns are sufficient. The result should be a flat circle with 2 protruding tube ends. Incidentally, steel pipe can be deformed relatively easily; To avoid kinks in the pipe, it is sufficient to fill the pipe with quartz sand. Because once you have kinks in the pipe, the drive no longer works. A handle fixed in a vice will of course simplify the work, but it is not essential. If you work in a group, it is also sufficient if another co-builder holds the handle.

Now each side of the pipe must be bent slightly twice: once in the first third behind the spiral and once in the second third behind the spiral (see photo). The length of the side pipes from the spiral to the end of the pipe should be between 12 and 15cm. It is advisable to mark the bending points on both tubes before bending so that they are safely bent in the same way. In the next step you bring the pipes to the same length with a hacksaw and deburr the ends with sandpaper. Now only the cladding remains: the spiral is tightly wrapped with some aluminum foil.

Manufacture of the boat hull

The styrofoam body is first cut to size with a sharp knife or cutter. With the jet nozzles in front, the evaporator is now speared diagonally through the styrofoam. You have to pay attention to several things: The spiral itself has to be high enough above the fuselage that you can still mount a burning tea light underneath. The jet nozzles must always remain below the surface of the water, ideally they are also bent a little upwards: This allows water to penetrate the pipe more easily - essential for the “motor” to work. The last step is to mount a rudder on the rattle boat. Simply score the styrofoam on the bow and clamp a small piece of Tetrapak - done.

If you make the hull of thinner materials, you may need a bracket for the spiral; You can easily make this yourself from a rectangular piece of Tetrapak. Use a pointed object to drill two holes approximately 3mm wide in the bracket. Their distance is determined by the spiral evaporator to be carried out; the holes should be small enough that it is firmly seated in the bracket. The spiral evaporator is passed through the bracket and the boat hull and the bracket is glued to the hull in such a way that the evaporator remains firmly in the desired position.


Before starting, you fill the steel pipe completely with water and put the boat in the bathtub, a large bowl, a pond ... Now you light the tealight mounted under the spiral. After about 30 seconds the boat should start with a jerky movement and after another 30 seconds a regular propulsion begins: The rattle boat can now theoretically travel for up to several hours - until the tea light goes out ...


Rattle boats use a water impulse drive for propulsion. Before the start, the entire steel pipe is filled with water: If the boat is now placed on a surface of water, the liquid cannot escape. If you light a tealight under the spiral, however, the water there is heated to the boiling point. The resulting mixture of water vapor and air has a larger volume and presses water out of the pipe ends: the boat pulls away in a jerk.

While the candle continues to heat the spiral, the water level in the pipes slowly rises again. In addition, parts of the water vapor condense in the unheated part of the pipe and become liquid water again. A negative pressure slowly builds up in the spiral part - new water is now actively drawn into the pipes from the outside. When the water approaches the heated part of the brass pipe, it evaporates again: a slight overpressure is created, which presses the water out of the pipes. The principle is the same as with the first jolt, but less powerful because the system is now balanced. In a weak but regular oscillation, water is sucked into the pipes and then pressed out again.

But why does the boat move from the spot, are the same amounts being sucked in as well as being pressed out? Quite simply: when it is sucked in, water enters the pipes from all directions; it is pulse-neutral. When pressed out, however, it forms a jet; here the force goes in one direction and thus propulses the boat.


Sometimes the rattle boat doesn't work the way you imagine it ...

- The jet nozzles do not work evenly, the boat has a twist to one side: Here it is often sufficient to wrap the jet nozzles with aluminum foil. It acts as a cooling plate and ensures an even temperature in both nozzles.

- The rattle boat has been on the road for a long time and then simply stops: Provided the candle is still burning, the reason for this behavior is often a layer of soot on the aluminum. Scrape this off and start again.

- The rattling boat has been sailing for a long time, goes under a strong propulsion and stops: The engine is dry, the candle has warmed up the evaporator too much. In this case, refill the tubes and position the candle at a slightly greater distance from the spiral. It also helps if the jet nozzles are pointed slightly upwards, as this makes it easier for new water to enter.

- The rattle boat does not go at all: The candle does not heat the spiral evaporator enough, the reason is either too great a distance to the evaporator or a wick that is too short.


Rattle boats can be made from all possible underground materials; it just has to be able to swim. Styrofoam is very well suited for boat building, but unfortunately cushions the rattling noise that is otherwise typical for boats. If you want to build a typical loud rattle boat, a metal hull is best.


Author: Joseph Rodesch (FNR), Liza Glesener