This video from instructables shows a really simple way to make an outboard motor from a cordless drill. The drive shaft is a 10 mm wire rod that is attached to a right angle drill-head with a 3-blade propeller. You can extend the run time of this DIY outboard by adding an external battery. It would be really cool to add a solar panel on the dock that charges the battery when not in use.
Makers is a beautiful hardbound book celebrating DIY inspiration and the people behind the projects. Makers introduces you to a brigade of citizen engineers making their own cameras, clocks, airplanes, submarines, musical instruments, weapons, medical equipment, energy- saving devices, robots, and houses. They create their own tools to explore the outer atmosphere, the deep sea, and the behavior of tiny flies in their backyard.