Kids Corner - Lab Experiment

Ballast and Stability
Semi-submersible Drilling Unit
Have you ever been in a boat at sea in large waves? The boat moves up and down as the waves pass under the boat.

In the Gulf of Alaska and other areas of the world, waves can be greater than 50 feet high. Imagine trying to drill an offshore well from a vessel that is moving up and down 50 feet each time a wave passes by.

Semisubmersible drilling units utilize water ballast to minimize the up and down motion of waves. They are the most stable floating offshore drilling unit available. How do they work? Conduct this lab experiment to find the answer. Here is what you will need:

  • An empty plastic soda bottle with cap,
  • Bath tub or large kitchen sink,
  • Cutting board.
Fill a large sink or a bath tub with six to eight inches of water. Screw the cap on the empty bottle and place it in the water. The empty bottle will serve as a model of a ship.

Now take the cutting board and place it near the end of the tub so that it touches the bottom of the sink or tub. Gently move the cutting board back and forth to create small waves.

Observe the motion of the bottle. How much does it bob (move up and down)?

Now fill the bottle 3/4 full of water. The partially full bottle will serve as a model of a semi-submersible. Make sure there is enough water in the sink or tub so that the bottle will float.

Create some more waves with the cutting board and observe the motion of the bottle. How much does it bob (move up and down)? Which one would make a more stable drilling platform?

 Ship Test


Semi Test
Semi-submersibles use water in the same fashion as the partially full bottle to stabilize them for offshore drilling. The water is stored in the pontoons and columns located under the water. The open area between the upper deck and the water provides an air space so that waves can pass freely through the structure.

Some ships also use ballast to provide stability, but none are as stable as a semi-submersible drilling unit.

A quick reminder: This lab experiment requires the use of precious resources- water and oil. The plastic bottle is made from petroleum and you can help conserve energy by recycling it. Water is also an important resource that shouldn't be wasted. If you conduct this lab test before you do the dishes, give yourself an "A" for helping to conserve water.

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Last Updated 5/21/96