Building a cardboard boat is a fun project for kids and adults! Whether you just want to have fun in the summer such as you want to win your local cardboard boat regatta, you can build your own cardboard boat at home without spending a lot of money. All you need are basic materials, some creativity, and a few hours.
Part 1 of 3: Design the ship
Step 1. Follow the rules if you are going to build the boat for a contest
If you're making a cardboard boat for a regatta, there are probably some pretty strict rules. Read them carefully to make sure they don't disqualify you. Avoid using any materials that are prohibited, which may include pre-treated or waxed cardboard, wood, metal, plastic, fiberglass, Styrofoam, screws, epoxy, and certain caulking compounds, glues, adhesives, or paints.
There may also be size regulations or other rules that you must follow. Many regattas insist that the crew area must be open for safety reasons in case the boat begins to sink
Step 2. Build a flat-bottomed boat to prevent it from capsizing
Although there are many different types of boats, a flat bottom boat is the best type of cardboard construction, as it is more stable than other designs. Similarly, a wider boat displaces more water and will do better than a long, narrow boat.
A simple rectangular design works well! If you want a little more style, try making a V-shaped helmet
If you want to make a simple boat, start with a sturdy cardboard box in any size you like (from a small shoe box to a giant refrigerator box). Cover the seams with reinforced paper tape and paint the entire box with exterior latex paint to seal it. Once it's dry, you're ready to put it in the water!
Step 3. Reinforce the sides of the boat to prevent it from collapsing
Plan to install a strong, horizontal piece of cardboard across the width of the boat to make it sturdier. You can position this piece of reinforcement so that it separates the hull from the crew compartment or put it in the center of the boat to create 2 separate compartments for the crew, just make sure to balance the weight on each one.
Step 4. Determine the dimensions of the boat based on the size of the crew
You plan to keep the width of the boat between 24 and 32 inches (61 to 81 cm) wide, depending on how many people sit on the boat to row. Make the sides of the boat 10 to 18 inches (25 to 46 cm) high so that you can easily reach the water with the oars.
Base the length on the number of people in the crew. For a small group, you can use a length of 3-6 ft (1.8 m), but for a crew of 6 or more, make the boat 3-3.7 m (10 and 12 feet) long
Step 5. Calculate how much water the boat will displace to make sure it can hold the crew
Do the math carefully to make sure the boat can support the weight of the people in it without sinking. Find the volume of the ship, and therefore how much water it will displace, multiplying the length by the width by the height. To find out how much weight the boat can support, multiply the volume of the boat in cubic feet by 62.4 lb / ft.3, which is the weight of the water.
- For example, if the ship is 10 feet (3 m) long, 3 feet (1 m) wide, and 1 foot (0.3 m) high, the volume is 30 cubic feet. Multiply 30 feet3 for 62.4 pound / feet3, which is equal to 0.8 kg (1.872 pounds).
- Don't forget to take into account the weight of the boat itself!
Step 6. Sketch and build a small scale model, and then put it to the test
Once you've finished your design, sketch on a piece of graph paper. Use solid lines to indicate folds and dashed lines to indicate cuts. Then build a small version of the boat out of cardboard. Test it in a sink or basin filled with water and note if there are any problem parts in the design.
- An easy way to reduce the dimensions of the boat is to use the same number of units, but smaller. For example, if the finished boat will be 10 ft (3 m) by 3 ft (1 m) by 1 ft (0.3 m), change the units to centimeters or inches to make the boat smaller but keep the model. Provided: Make the model 25 cm (10 inches) by 8 cm (3 inches) by 2.5 cm (1 inch).
- Fill the model ship with coins or rocks that are proportional to the weight of the crew to ensure it will float.
- If the ship doesn't float, modify the plans, build another small version, and put it to the test again. Repeat until you have a solid design that you are sure will float when you scale it up.
Part 2 of 3: Build the Boat
Step 1. Use large flat sheets of corrugated cardboard
Corrugated cardboard is much stronger than normal cardboard. While you can certainly flatten boxes and use them to build the boat if that's all you have on hand, using giant flat sheets of corrugated cardboard will make the process a lot easier. It's best to fold the cardboard to create the sides, front, and back rather than putting multiple pieces together. The fewer seams you have, the more waterproof the boat will be.
- You can find large sheets of corrugated cardboard at your home office and at hardware stores.
- Make sure the corrugation or grain of the cardboard runs vertically along the length of the boat.
Step 2. Cut or fold the pieces to shape the boat
Use the sketch and model you made earlier to guide your work. Use a measuring stick to make straight lines, trace them with a marker or pen, and use a box cutter to cut the cardboard. Work carefully and measure twice before cutting to avoid mistakes. Use a tool like a screen roller to crease the cardboard before folding it for the cleanest results.
Step 3. Glue the pieces together with wood glue and then hold them together until they are dry
If you have multiple pieces of cardboard that you need to join together, use wood glue to ensure that they adhere completely. Completely coat one of the boards or pieces of cardboard with an even layer of wood glue, and then glue it to the next piece. Secure the pieces with cable ties to ensure the cardboard doesn't move or separate. Let the glue dry for an hour or more, then remove the clamps.
If you don't have cable ties handy, a paper clip will work
Use at least 2 layers of cardboard for the hull and 3 layers of cardboard for the bottom of the boat.
Step 4. Cover the seams with reinforced paper tape
Reinforced paper tape will adhere and hold better compared to other types of tape. Cover both the inside and outside of each seam with several pieces of tape to make sure they are airtight and no cracks or gouges are exposed.
Duct tape can work if you're in a hurry, but it can shrink when painted. Similarly, clear tape melts when you paint it. Avoid using duct tape, as it is not waterproof
Part 3 of 3: Decorating and Using the Boat
Step 1. Seal the cardboard with latex paint
Use exterior house paint to decorate and seal the boat. Avoid using oil paint, as most regattas prohibit it as it can leave oil in the water, or water-based paint, which will dissolve in the water. Use rollers or large brushes to coat the entire cardboard with a light, even layer of paint. If you want to add a second coat of paint, wait at least 4 hours between coats.
To cut costs, ask your local paint store if they have any returned paint as they will sell it to you for less than a new can
paint both the inside and outside of the boat. When you put the boat in the water, there will be a high chance that some of it will splash inside, so it is important to seal all the cardboard.
Step 2. Decorate the boat to match the theme
If you are competing in a cardboard boat regatta, you and your crew have likely chosen a theme for the boat. Now you can have fun decorating the ship to match the theme. Just make sure the add-ons don't damage the structural integrity of the boat or break the rules. Don't forget to paint the ship's name on the side too!
For example, if you want the ship to look like a pirate ship, add a mast and sail, a Jolly Roger flag, cannons, anchors, and a crow's nest
Step 3. Put the boat in the water a few minutes before the race
Although you may be tempted, avoid experimenting with the boat before the race as the cardboard could start to deteriorate. Just before the race, carefully place the boat in the water and make sure it can float. Have one crew member go up at a time. It is better to sit deep in the center of the boat than to try to kneel or stand. Don't forget your paddles and life jackets!