This pop-pop boat was made specifically for the WWPPBB (World Wide Pop Pop Boat Build) 2011. It won the "BEST IN CLASSIC BOATS" category, much to my surprise.
It's a fairly traditional design with a single coil heated by a candle stub. Initial tests implied that it would need two candles but formal sea trials (in the bath) showed that it worked better with one. The initial tests also showed the necessity of a rudder; not to make it go round in circles but to keep it in a straight line! Without it, the poor thing was spinning randomly depending on which end of the tube "fired".
The hull started life as a tin of ham (contents were disposed of down my gullet first), the coil was formed from a length of 4mm copper pipe, the rudder, deck and chimney from sheet aluminium. The sandpaper under the coil is to stop the candle stub moving about. The whole thing is stuck together with epoxy. If you're wondering about the lump of Blu-Tack; the superstructure caused the hull to be slightly bow heavy so I stuck some ballast in the stern using the Blu-Tack. It turned out that the Blu-Tack was sufficient on it's own.
I've taken two videos; a short one just to prove it works (and more suitable for those with slow connections) and a long one with introduction and commentary on the trials.