Float that boat!
Build a small floating boat from recycled materials, test in water how many coins it can carry, and learn about buoyancy.
Step-by-step guide to Float that boat!
Step 1
Gather all the materials listed and clear a spot on a table to work.
Step 2
Pick one recycled container to turn into your boat.
Step 3
Use scissors to cut the container into a shallow open hull shape so it can hold coins.
Step 4
Wrap waterproof tape around any cut edges and seams to make the hull smooth and watertight.
Step 5
Press a piece of aluminium foil inside the hull if you want to plug tiny holes and make a flatter bottom.
Step 6
Decorate your boat with a marker or stickers so it looks awesome.
Step 7
Fill your bowl sink or bathtub with water to a safe depth where the boat can float.
Step 8
Gently place your finished boat in the water and make sure it floats stably.
Step 9
Add a single coin to the center of the boat.
Step 10
Repeat adding one coin at a time until the boat starts to tip or sink.
Step 11
Count and write down how many coins the boat held before it sank or tipped.
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.
Step 13
Take a photo and share your finished floating boat and what you learned about buoyancy on DIY.org.
Final steps
You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!
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.
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Facts about buoyancy and floating
♻️ Upcycling fun: empty plastic bottles, foam, corks, and bottle caps are common recycled bits kids use to build tiny boats.
🧪 Archimedes' principle: an object submerged in a fluid is buoyed up by a force equal to the weight of the fluid it displaces.
🌊 Big ships float because their overall density (including trapped air) is lower than the water around them, not because the metal itself is light.
💰 Coin test: adding coins one by one is a simple way to find the exact tipping point when a boat can no longer stay afloat — great for counting and measuring.
🛶 Shape matters: a hollow, wide hull can float more weight than a solid block of the same material because it displaces more water.
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