Make your own steam-propelled nautical engine

Setting the scene
Trying out this ‘pop-pop boat’ helps the pupils think about propulsion and can be linked to history lessons on Victorian transport. The technical term for the engine that propels the boat is a pulsating water engine (PWE). They are believed to have been invented by Thomas Piot in 1891.

You will need
Foil tray (or something that floats),
20–25 cm copper tubing (about 3 mm internal diameter),
Dowel (or something else round and about 1–2 cm in diameter),
Modelling clay,
Pipette or dropper,
Small candle (tealight) and match/lighter,
Tub of water to launch your boat on.

Instructions
Firstly you need to prepare the boat. Bend the front of the foil tray to form a prow (the front
bit), then pierce two small holes in the back of the tray (the stern). The holes should be a few
centimetres apart.

Next make your engine. Wrap the copper tubing around the dowel rod about 5 or 6 times to
make a closely-wrapped coil, leaving about 3 cm of straight pipe at either end. These straight
bits at the end will be the engine’s inlet and outlet. Remove the coil from the dowel rod.

Now put the two together. Push the straight ends of the coil through the holes at the back of the boat so about 1/2 cm of the tubing sticks out at the bottom. Seal up any space around the
tubing with modelling clay so the hull doesn’t leak.

Finally, fill up the engine. Turn the boat upside down and using the pipette squirt some water into one end of the copper-coil engine.

Ready to Go! Place the boat on water and rest the lit candle under the coil. Once the water you squirted into the engine has heated up, it should start to move!

Further Information
You need to know Newton’s Third Law of Motion: ‘For every action there is an equal and opposite
reaction’.

This means that if you push something, it’ll push back at you just as much. Think about swimming – you push the water backwards with your arms and you go forwards; if you want to go faster you push faster. It’s ‘equal’ because it’s the same amount of force; it’s ‘opposite’ because it’s in the other direction.

The coil’s acting like a boiler, making steam which gets forced out of the bottom of the boat through the copper tube. The water pushes back at this steam and so propels the boat forwards.
After the steam is ejected, a partial vacuum is created in the tubing thus forcing more water to be sucked into the boiler, starting the whole process over again – a really simple steam engine (or 'water impulse engine’ if you want to sound techie).

This experiment was recommended to us by Dr Allan Paterson of the Magna Science Adventure Centre, near Sheffield. National Curriculum links in KS2 Sc4 2d and 2e. Also can be linked to the history curriculum – 11a (Victorian Britain).

Looking forward – National Curriculum links in KS3. Again, much of the curriculum relevance for this experiment is found in the ‘forces and motion’
section of Sc4. Although this experiment is perhaps not appropriate to the quantitative relationships the KS3 curriculum calls for, it qualitatively underpins ideas of speed, distance and time (Sc4 2a), balanced and unbalanced forces (Sc4 2c) and pressure and forces (Sc4 2g).

Remember BE SAFE: Take precautions with all flames in case anything goes wrong, and
be very careful about handling anything hot!

Click on the link below download a full copy of the Pop-Pop Boats experiment, including details of curriculum links.

Pop-Pop Boats Experiment (220KB)