People make cardboard boats for a variety of events, including school projects or races during summer festivals. A cardboard boat may not seems impossible, principles of buoyancy and stability help them stay afloat. As you design your boat, consider how you will use it and the conditions in which it must perform.
A barge is the most basic type of cardboard boat. It has a flat bottom, relatively straight sides and front edges that angle up to allow it to cut through the water. Depending on the weight of the paddlers, you may want to make your boat deeper to account for water displacement; a boat with water coming over the sides will sink quickly. Use duct tape to reinforce the seams and keep water from getting in.
For a boat that moves a bit faster than a square-shaped craft, create a traditional rowboat. The key to this design is the pointed nose, which allows the boat to move through the water easily. To make your craft more comfortable, create ribs on the bottom using folded pieces of cardboard. You can even make seats that will raise you higher, making it easier to paddle.
If you will be manning the oars solo in a cardboard-boat race, consider making a speedy cardboard kayak. Although rounded edges are not advisable for a cardboard boat, you can make a kayak with angled panes. For the bottom, use two pieces of cardboard to make a hull with a slight V shape. The bottom half of the sides should angle out away from the hull, where they meet a centre anchor strip. For the top of the kayak, make a flat deck or repeat the V-shape from the hull. It helps to make a scale model from stiff paper first to work out issues with folding and to refine piece shapes.
If you are confident in your boatbuilding abilities, you can make your cardboard boat into a floating piece of artwork. Once you have a stable base shape, create a concept that will take the boat to the next level. You might design the craft as a pirate ship, complete with cardboard masts and sails, or you might use paint to create a floating tribute to a favourite artist. For a fun twist, make your boat into something that wouldn't normally float, like a car, tank or aeroplane. As long as the base of the boat is steady, you can add on modifications and still float safely.