How to Make a Self-Propelled Toy Boat

Lay the balsa wood on a cutting surface and draw the shape of a boat hull on one end. On the other end draw a square, 3 inches wide and 3 inches deep. Leave one inch on either side of the square, with the end of the balsa wood comprising one of the four sides of the square.

Cut along the pencil lines with the knife, so that one end is a pointy boat shape and the other end has a square cut out of it.

Cut the piece of balsa wood that came out of the square-cut piece on the boat, so that it is a 1x2-inch rectangle. This will be the paddle

String the rubber band over the end of the boat, so that it passes over the center of the square cut out portion, and around the sides of the boat.

Thread the paddle through the center of the rubber band, and twist it around repeatedly so that the rubber band is wound tightly between the boat frame and the paddle.

Hold the tension of the rubber band and place the boat in a small body of water--a swimming pool or bathtub will do fine. Release the hold on the rubber band and the boat will self-propel as the rubber band unwinds and moves the paddle around in the process.