What the Dock?
Did Julius Caesar expand the port in Antwerp? Is a tug as strong as 10,000 trained dockworkers? And does a container ship sail with a limited crew on board? We distinguish fact from fiction in the new "What the Dock" section!
2025-06-23
Fact or fiction: A container ship floats because it is lighter than water
Container ships are enormous vessels, built from steel and often loaded with heavy cargo. So how do these giants manage to stay afloat on the ocean?
Archimedes' principle
The reason container ships float lies in Archimedes’ principle. Over 2,000 years ago, the Greek physicist Archimedes discovered that any object submerged fully or partially in a fluid displaces that fluid and, in doing so, experiences an upward force. This buoyant force equals the weight of the fluid displaced by the object.
Big, heavy and yet floating
It's not just about weight, the density of an object also matters. That is the ratio between how much something weighs (its mass) to how much space it occupies (its volume). Container ships have a large volume, but their special design keeps their average density lower than that of water.
In other words, a container ship floats not because it is lighter than water. It floats because it weighs less than the amount of water it displaces.
