Float that boat!
Build a small floating boat from recycled materials, test in water how many coins it can carry, and learn about buoyancy.
About this activity
Build a small floating boat from recycled materials, test in water how many coins it can carry, and learn about buoyancy.
What you need
Step by step
- 1
Step 1
Gather all the materials listed and clear a spot on a table to work.
- 2
Step 2
Pick one recycled container to turn into your boat.
- 3
Step 3
Use scissors to cut the container into a shallow open hull shape so it can hold coins.
- 4
Step 4
Wrap waterproof tape around any cut edges and seams to make the hull smooth and watertight.
- 5
Step 5
Press a piece of aluminium foil inside the hull if you want to plug tiny holes and make a flatter bottom.
- 6
Step 6
Decorate your boat with a marker or stickers so it looks awesome.
- 7
Step 7
Fill your bowl sink or bathtub with water to a safe depth where the boat can float.
- 8
Step 8
Gently place your finished boat in the water and make sure it floats stably.
- 9
Step 9
Add a single coin to the center of the boat.
- 10
Step 10
Repeat adding one coin at a time until the boat starts to tip or sink.
- 11
Step 11
Count and write down how many coins the boat held before it sank or tipped.
- 12
Step 12
Try one change like moving the coins to a different spot or adding more foil and test again to see if the number changes.
- 13
Step 13
Take a photo and share your finished floating boat and what you learned about buoyancy on DIY.org.
Fun facts
How do you do the "Float That Boat!" activity step by step?
Start by choosing recycled materials (bottle, foam, cardboard) and sketch a simple hull. Assemble pieces with tape or non-toxic glue, sealing edges to keep water out. Add a flat deck or small cargo area for coins. Test in a shallow tub, pond, or sink and place coins one at a time, noting when it sinks. Adjust shape or buoyancy (add corks, redistribute weight) and repeat to learn how design affects floatation.
What materials do I need to build a small floating boat from recycled items?
Collect a recycled plastic bottle, sturdy cardboard, foam scraps, corks, straws, or small yogurt tubs for hulls. You’ll also need tape, non-toxic glue, scissors, and a marker. Use small coins or washers as cargo and a shallow tub, sink, or basin for testing. Optional: waterproof sealant, craft sticks for a deck, and a towel for drying. Avoid sharp metal and supervise cutting tools.
What ages is the "Float That Boat!" activity suitable for?
This activity works well for preschoolers through elementary ages. Ages 3–5 enjoy simple building and watching float/sink with adult help for cutting and coins. Ages 6–10 can design, test, and record results independently with supervision. Older kids can try more advanced hull shapes and measurements. Always supervise water play and small objects for younger children to prevent choking and ensure safe tool use.
What are the benefits and safety tips for the "Float That Boat!" activity?
Building boats teaches basic buoyancy, problem-solving, fine motor skills, and scientific observation. It encourages creativity and recycling awareness. For safety, use shallow water, supervise children closely, and keep coins and small parts away from very young kids to avoid choking. Cut materials for little ones, avoid hot glue with kids, and dry work areas to prevent slips. Try variations like races, timed tests, or changing cargo to extend learning.
Watch & Learn
Need help?
What can I use if I don't have aluminium foil or waterproof tape?
If you don't have aluminium foil, press a small piece of food-safe plastic wrap or a thin sheet of scrap plastic into the hull to plug tiny holes and flatten the bottom, and if you lack waterproof tape, wrap clear packing tape or duct tape around the cut edges and seams of your recycled container to make it watertight.
My boat keeps leaking or tipping—what should I check and fix?
Check for rough or open cut edges and reseal them with extra waterproof tape, press aluminium foil inside the hull to plug tiny holes and make a flatter bottom, and be sure to place coins one at a time in the center as you test stability so the boat doesn't tip from uneven weight.
How can I adapt this activity for different ages?
For younger children have an adult pre-cut the recycled container and use large washers or plastic tokens and a shallow bowl with close supervision while older kids can cut their own hulls, decorate with markers or stickers, count and write down how many coins the boat held, and try the suggested change tests like moving coins or adding more foil.
How can we extend or personalize the boat experiment?
Personalize your boat with marker or stickers, add a paper sail or a clay ballast to test different stability designs, mark a waterline to compare how adding more aluminium foil changes buoyancy, and take a photo to share your final build and results on DIY.org as described.