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Image: U.S. Navy, YouTube
Right under the Coronado Bridge is California's largest floating drydock. This vessel, christened Pride of California, purposefully floods itself and sinks low enough so a ship can sail inside. The dry dock can then resurface, bringing the ship inside it out of the water for repairs.
How can a vessel sink and float on command? What causes a vessel to float? Why do some objects sink and some float?
Resources:
YouTube: USS Montgomery Enters Drydock