Foil Boats (Student Instruction)

How many pennies can your aluminum foil boat hold before it sinks or capsizes? 


Michael Pearse introduces the Foil Boats challenge



  • pennies (or dimes or nickels—all of the same type of coin)
  • aluminum foil
  • scissors
  • ruler
  • shallow bin or a sink
  • water
  • towel


Boats come in different shapes and sizes, depending on their purpose. Some are designed to skim quickly across the water, like powerboats and sailboats. Others, like barges and fishing boats, transport heavy loads.

We challenge you to design a boat made only of aluminum foil that holds as many pennies as possible before it sinks or capsizes (tilts over).

There are 3 constraints for this challenge (an engineering constraint is a limitation on your design):

    • You can only use one piece of aluminum foil.
    • The square of foil must measure 5 inches x 5 inches.
    • The boat must hold at least 15 pennies without sinking or capsizing.

Brainstorm Designs

Get ready to experiment:

  • Use a ruler and scissors to cut a 5-inch square piece of aluminum foil for your boat.
  • Fill a sink or shallow container with a few inches of water.
  • Keep a towel handy to mop up spills.

The hull is the body of a boat. Its shape depends on what the boat is designed to do. Canoes have round-bottomed hulls; powerboats have V-shaped hulls; fishing boats and barges have flat-bottomed hulls.

Try out a few different hull shapes for your boat. As you explore, think about:

  • Which kind of hull will be the most stable as you add pennies?
  • Which hull shape can hold the most pennies before it sinks?


  • Cut out a fresh 5-inch square of aluminum foil.
  • Make the boat into the shape you’ve chosen to test.


  • Set the boat in the water. Make sure it’s seaworthy and has not sprung any leaks.
  • Start adding pennies. Watch carefully: is the boat starting to lean? Help the boat stay upright by adding pennies to a different part of the boat.
  • As you add pennies, notice whether the boat changes shape, tilts strongly to one side, or springs a leak.
  • Keep adding pennies until the boat sinks.

Evaluate and Redesign

  • A boat will stay buoyant (or continue to float) as long as it weighs less than the amount of water it displaces (or moves out of the way when it settles). How many pennies could your boat hold before it sank? Did you meet the challenge of holding 15 pennies?
  • What shape did you make your hull? When you placed your boat in the water, it pushed some water out of the way and took that water’s place. Boats whose bottoms are flat spread their weight out over a larger area, so they can hold more weight before weighing more than the water they displace.
  • Did your boat sink fast? Next time, try distributing the pennies more evenly and see if it stays afloat longer.
  • Did your boat tip over before it sank? How could you change its shape or adjust the placement of pennies to keep it better balanced?

Make Change and Try Again!

  • Improve the design of your boat so that it holds even more pennies.
  • For a different challenge, try using more than one square of aluminum foil. How do you predict more layers will affect the number of pennies your boat can hold? What about still using just one square, but bigger?
  • If you dissolve enough salt into the water to make it noticeably salty, do you think your boat’s buoyancy would change? Would it hold more pennies than in plain water?
  • How does changing the type of coin you use (such as dimes instead of pennies) affect the buoyancy of your boat?

Share Your Results with a Teacher, Parent/Guardian, or DiscoverE!


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