There are many ways to power a boat - propellers, aquajets, sails, powerful fans, turbo-jets, rockets, and pulse-jets.
There are few ways, though, as gentle and serene as the warmth of a candle.
Step 1: What you Need.
Fire-boats need two important properties - to be light, and non-flammable.
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.