This is a boat that I made out of a plastic box, some motors from a remote controlled airplane, and some alligator clips. It can speed along a pool or a lake at a relatively fast speed, due to 6AA batteries. The motors are held onto the box by a metal rod, found in a hanging folder, and they are held to the rod by the magnets in the motor. The rod is held to the boat by duct tape. It was made easily within 15 minutes, and was made with no additional cost to myself as I had the parts for it lying around.
My family occasionally has everybody make a boat, and then we race them to see whose boat was the fastest overall. This is a simple project that can turn out to be a lot of family fun.
The following video shows how the boat works, by turning it on, and then off. This was done on land to give a better video of what was happening.