There are few ways, though, as gentle and serene as the warmth of a candle.
Step 1: What You Need.
My Clubbers used foil pie-tins as the hulls of the boats, kitchen foil as the sails and tea-lights to provide the heat.
We have, in the past, had success with normal-sized candles trimmed to only half an inch in height, or small clusters of birthday candles.
Step 2: Construction
A certain amount of intuition is also desirable.
Tear a piece of the foil to a suitable size, and fix it to the side of the pie-tin by scrunching the edge of the foil along the lip of the tray.
Curve the sail over the top of the boat. If it droops too far, add a crease or curve along the middle of the sail to ~~stop it drooping~~ add structural integrity.
Stand the candle in the boat, and you're ready to go.
The photos in this step are of the fire boats made by my Science-clubbers, before they took to the water. Some required tweaking, but they all worked to some degree.
Step 3: The Circular Fire Boat.
This effect can be used on purpose as well - setting up two candles and sails facing in opposite directions on a circular metal lid created a boat that spun on the spot.
The clubbers had the idea that the idea could be used to make decorations which floated and spun in garden ponds or pools during a barbecue or garden party - the shiny foil sails would cast changing reflections around as the boats spun.
Step 4: Float Your Boat.
We poured shallow pools of water into plastic trays and left them to settle. We also closed all the windows and doors to prevent draughts, and walked slowly so that the breeze of our passing wouldn't disturb the boats.
Place the boat at one end of the tray and light the candle.
As the candle burns, it heats the air around it. As you are probably aware, warm air rises. This is a convection current.
When the rising air hits the sail, it is deflected from its vertical path, which exerts a small, but real, force on the sail. Since the sail is fixed to the boat, the boat moves.
This video shows a couple of the boats my clubbers made: