This next toy is an example of the simplest steam engine you will ever see. It has no valves, no moving parts (in the traditional sense of the phrase), and yet it can propel it's little boat easily across the largest swimming pool or quiet duck pond.
The boat is a plastic bottle, cut in half lengthwise. I used a soft plastic bottle that contact lens saline solution comes in. It is made of white High Density Polyethylene (HDPE), and is very easy to cut using an Xacto knife or other sharp utility knife.
Near the bow of the boat is a small candle, such as those used to keep food warm on the table. I chose a candle that comes with a small aluminum can, and is less than an inch high, so it would sit low in the boat and not drip wax all over. The aluminum cup keeps the melted wax in place, so the boat can go for hours. I used a small amount of sticky tape to keep it in place.
The engine is made of 1/8 inch soft copper tubing. This can be found at the better hardware stores, and is normally used in refrigerators. You can use the easier to find 1/4 inch soft copper tubing, but the 1/8 works best with the candle's small heat source, and weighs less, so it is less likely to tip the boat.
The best way to cut the tubing is with a tubing cutter (get it at the hardware store when you get the tubing). You can use a hacksaw, but you will have to clean the debris out of the cut with a knife or sandpaper.
