Parents, Educators & Engineers


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Materials (per person)

  • container filled with water (e.g., bucket, sink, plastic tub)
  • duct tape
  • paper cups (8-ounce or larger)
  • 10-inch strip of plastic wrap
  • 10 straws
  • towels (paper or cloth)
  • 25 pennies (or 15 standard, flat steel washers, at least 1 inch in diameter)

Your Challenge

Design and build a boat out of straws and plastic wrap that can hold 25 pennies for at least ten seconds before sinking.

Brainstorm & Design

Look at your Materials and think about the questions below. Then sketch your ideas on a piece of paper or in your design notebook.

  1. How will you make a boat that floats well enough to support a heavy load without sinking?
  2. Should your boat be a platform (e.g., a raft or barge) or an open boat (e.g., a rowboat or canoe)?
  3. What's the best way to make your boat waterproof?
  4. How big do you need to make your boat to hold 25 pennies?

Build, Test, Evaluate & Redesign

Use the Materials to build your boat. Then test it by floating it in a container of water and adding pennies, one at a time. When you test, your design may not work as planned. When engineers solve a problem, they try different ideas, learn from mistakes, and try again. The steps they use to arrive at a solution is called the design process. Study the problems and then redesign. For example, if the boat:

  • sinks easily—Increase its ability to float. When you set your boat in water, notice how it sinks down a bit, pushing aside some water. The water pushes right back, pressing on the boat's bottom and sides. The force from these pushes is called buoyancy. To change your boat's buoyancy, experiment with the boat's width and the height of its sides.
  • leaks a lot—See if the straws are filling with water or if the plastic wrap is separating.
  • tips easily—Check how near the weights are to each other. A boat can get tippy when one part is heavier than another.
Watercraft picture