How to Build a Sturdy Cardboard Boat

Learn how to engineer a floating vessel using recycled cardboard and basic crafting supplies. HowTo: Family Edition: family how-tos that actually help.

1. Measure and cut your base. Measure a rectangle on your largest piece of cardboard that is long enough for you to sit in. Ask a grown-up to help you cut it out, then fold up the sides about 10 inches to create your hull walls.
2. Reinforce the corners. Fold the corners of your walls and secure them tightly with plenty of duct tape. Add extra cardboard triangles to the inside corners to make the structure rigid and strong.
3. Waterproof your hull. Wrap the entire bottom and the outside walls of the boat in a plastic drop cloth or trash bags. Use duct tape to seal every seam so that no water can touch the cardboard.
4. Test for leaks. Place your boat in a shallow pool or bathtub with a few inches of water. Check for any spots where water might be seeping through the tape and add more layers if needed.