• 1

    Here are some of the materials you can use

    • container filled with water (bucket, sink, plastic tub)
    • duct tape (8-in. [20-cm] length)
    • paper cup (8-oz. or larger)
    • 25 pennies 
    • plastic wrap (10-in.[25.4-cm] piece)
    • small items to test float/sink (an empty capped water bottle, a Ping Pong ball, a golf ball)
    • 10 straws
    • towels (paper or cotton)
  • 2

    Prepare ahead of time

    • Have paper and a pencil ready to write down ideas and sketches as you design.
    • Place a container away from your building area. Fill it with water.
    • Think about things you know that travel in the water.
    • Think about things that float and sink in the water.
  • 3

    Think about the challenge

    • What causes a boat to float?
    • What causes a boat to sink?
    • Why is it easier to keep a large empty capped water bottle down in the water than a small bottle? 
    • TIP: Buoyancy is the term for describing the force that pushes back up on an object. The more buoyancy something has, the higher it floats in the water. 
    • TIP: A larger object pushes away, or displaces, more water than a smaller one. This creates more force, or pressure, from the displaced water that pushes the large object up and makes it is harder to keep down.
  • 4

    Think about and write down ideas

    • Why might a boat not float well?
    • Will your boat be a platform, like a raft, or an open boat, like a canoe? 
    • How will you waterproof your boat?
    • How big will your boat need to be to hold the pennies?
    • TIP: When engineers solve a problem, they try different ideas, learn from mistakes, and try again. The steps they use to arrive at a solution are part of the design process.
  • 5

    Look at the materials

    • What materials do you have to build the boat?
    • What materials do you have to waterproof the boat?
    • What will you use to balance the pennies so they don’t fall into the water?
    • TIP: A boat can get tippy when one part is heavier than another. 
  • 6

    Design and build the boat

    • Decide how you will construct the boat so it will stay afloat when you add weight to it. 
    • Think about the size and shape you want to make your boat.
    • Choose your boat materials and build the boat.
    • TIP: The width and height of a boat’s sides can affect its buoyance in the water. 
  • 7

    Waterproof the boat

    • Decide what materials will keep the water out of your boat so it will stay afloat.
    • Choose the materials and waterproof the boat.
  • 8

    Test the boat before adding weight

    • Place the boat in the water to test its ability to float. 
    • Leave it in the water for about a minute.
    • TIP: If the boat sinks, the waterproof seal is not tight. Try finding the leak by pushing the boat in the water and watching for bubbles to surface. Or check all openings and seal them tightly.
    • TIP: You can test a design at different steps along the building process. This way you can spot a problem and fix it when it happens instead of at the end of the process. 
  • 9

    Make the weight holder (if you decide to include one)

    • Decide whether or not your boat will have a container to hold the pennies.
    • Decide what materials you will use to hold the pennies.
    • Make the holder and attach it to the boat.
  • 10

    Load up your boat 

    • Place your boat in the water.
    • Put the pennies in your boat. Add them carefully one at a time.
    • TIP: If your boat is tipping over, make sure the weight is well distributed. Spread the weight evenly across the bottom of the boat.
    • TIP: A boat can tip when the load is up high. Place pennies in the lowest part of the boat. 
  • 11

    Time test the boat

    • Set a timer or look at a clock’s second hand. Test whether your boat can stay afloat for 10 seconds or longer.
    • TIP: If the boat can’t support 25 pennies, try increasing its buoyancy by increasing the container’s size and depth. 
    • TIP: If the boat won’t stay afloat, try building a boat with a V-shaped hull. This is generally a more stable design then a flat-bottomed boat.
  • 12

    Did you know?

    • Engineering in Action
      Imagine riding alone on a sailboard all the way across an ocean. That’s just what windsurfer Raphaëla le Gouvello has done—more than once and across more than one ocean!

      In 2006, Raphaëla surfed for 60 days and more then 3500 miles (5600 km) across the Indian Ocean. For this adventure she turned to sailboard designer Guy Saillard. Guy had been experimenting with using durable hi-tech materials to build strong, lightweight sailboats. He designed for Raphaëla a 25-foot-long sailboard with a sleeping compartment, a shower, and a satellite communication system. The cabin was only 8 feet long, 20 inches wide, and 31 inches high (20 x 51 x 79 cm) or slightly bigger than a child’s bed! 
  • 13

    Try this next!

    • Build a boat that will hold a heavier load. Make a boat that holds 50 pennies for at least 10 seconds before sinking.
    • Be environmentally friendly. Build another boat that can hold 25 pennies, but use only half the amount of materials that you used for your first boat.