Science project

Boat Depth

The purpose of this experiment is to see whether the depth of a boat in the water changes how fast it moves and how straight it sails.

  • Why do boats take on water?
  • How is the maximum load on a boat determined?
  • How fast do boats usually travel?
  • How were ancient sailboat designed?
  • How has the evolution of the boat changed over the past few centuries?
  • How has the design of the boat changed since boats were first invented?
  • What did early boats look like?

Most boats are designed to float with only part of the boat above the surface. The part of the hull that remains underwater helps the boat remain stable. Boats that are weighed down with cargo can sink even further down into the water, which can slow them down as they sail or motor across the ocean. Knowing how depth affects speed and stability is useful for sailors and engineers. This information can help them design boats that sink the proper amount in order to maximize the speed and the stability as the boat travels. Many boats are even designed to take on water when they are not fully loaded in order to increase their stability.

  • An egg-shaped piece of Styrofoam about 9 inches long on the longer side
  • A serrated knife
  • Pebbles
  • A playing card
  • A set of chopsticks
  • A small piece of cloth
  • A battery powered fan
  • Glue
  • A swimming pool
  • A timer
  • A ruler
  • A scale

You can get an egg-shaped piece of Styrofoam from a craft-supply store.

  1. Using a serrated knife, cut the Styrofoam egg in half.
  2. Discard one of the halves or use it for another project.
  3. Hollow out the other half of the boat, leaving about an inch thickness all the way around.
  4. Turn the boat upside-down so that the rounded part is facing up. This will be the bottom of the boat.
  5. Draw a line through the middle from the thick part of the egg to the thin part. This line will help you reference where the middle of the boat is from front to back.
  6. Place the short end of the playing card against the line about 1/3 of the way from the thick end. The side of the boat with the card on it is the back.
  7. Press the card into the Styrofoam about ½ inch deep.
  8. Glue the card into the bottom of the boat.
  9. Wait for the glue to dry completely.
  10. Carefully turn the boat back over.
  11. Place the chopsticks on the edges of the boat on opposite sides of the line from each other, a little closer to the front than to the back.
  12. Press them down about ½ inch into the sides of the Styrofoam so that they lean into each other on the top, above the midline of the boat.
  13. Glue the chopsticks onto the hull and to each other where they touch at the top.
  14. Allow the glue to dry completely.
  15. Cut the fabric so that it will fit between the chopsticks with at least ½ left over around the sides.
  16. Attach the fabric to the chopsticks by wrapping it around them and gluing the edges down.
  17. Allow the glue to dry completely.
  18. Take the boat, the small rocks, the ruler, the timer, the scale and a battery powered fan to the pool. Be very careful not to get the fan wet at all during this experiment.
  19. Take the mass of the boat and record this information on a chart such as the one below.
  20. Determine how far you will attempt to sail the boat. A distance between 3 and 6 feet should suffice.
  21. Place the fan on the side of the pool, pointing towards the boat, far enough away that there is no danger of it falling in. Make sure the fan is not in any standing water and will not be splashed during your experiment.
  22. Place the boat in the water.
  23. Turn on the fan and start the timer.
  24. Record the amount of time it takes for the boat to reach the end of the experimental area on a chart such as the one below. If it does not make it to the end, record this information.
  25. Describe the motion of the boat on the chart. Did it sail straight? Did it wobble? Did it spin? Did it move towards one direction or the other?
  26. Take the mass of one of the rocks.
  27. Record this information on your chart.
  28. Place the rock in the hollow section of the boat.
  29. Turn on the fan and start the timer.
  30. Record the amount of time it takes for the boat to reach the end of the experimental area on a chart such as the one below.
  31. Describe the motion of the boat on the chart.
  32. Repeat steps 26-31 until the boat can no longer sail at all due to the weight of its cargo.





Boat alone




Rock 1




Rock 2




Rock 3




Rock 4





Terms/Concepts: Displacement;  Stability; Speed; Momentum


Author: Crystal Beran
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