This extensive video series is all about making your own simple steam engine and boat, which is known variously as the "putt-putt" or "pop-pop" boat. Science Toy Maker gives the full details on making your own homemade steam engine model boat, which is similar to the one seen in the move "Ponyo".
In addition to this build video series, visit the worldwide forum on Yahoo! Groups, focused solely on experimenting and designing pop-pop boats.
See how to build this steam engine boat from scratch, which you can make the body of the boat with a recycled, cut-up milk or juice carton, which is easy to cut, water-proof and paintable. Or you make a simpler boat out of a recycled foam grocery tray. In either case, the engine is the same, made from a cut-up aluminum soft drink can and drinking straws.
Watch the last three parts to see how to make the 3D hull for the boat. This series removes any mystery behind building these pop-pop/putt-putt boats.