For those not up to building a full-sized bottle catamaran, a nifty toy catamaran might fill a need.

The Fun Mechanics Kit Bottle Catamaran includes everything needed (except for the bottles themselves, and a screwdriver) to make a working toy catamaran. Once assembled, a propeller is connected to the included battery-operated motor and the Bottle Catamaran is ready to launch. 

This simple science project will keep a couple of plastic bottles out of the landfill and deliver fun in both the building and boating process.