Physics Form 4: Chapter 3 - Application of Archimedes Principle (Plimsoll Line)

Plimsoll line is a mark on a vessel’s side indicating the maximum depth to which it may be safely immersed when loaded with cargo.

The maximum safe loading depth varies with ocean regions and seasons. In the tropics the water is warmer and therefore less dense than in temperate regions, so with the same load ships will float higher in cold regions than in the tropics. Summer and winter cause similar changes.

• The density of water is determined by the salinity of water at different locations
• A ship will submerge deeper in freshwater than that in sea water because the density of freshwater is smaller. 
• The ship can be loaded with heavier load in sea water than in freshwater.