Samuel Plimsoll was born on 10 February 1824. He was very interested in safety at sea and condemned ship owners who risked sailors' lives by dangerously overloading their vessels with cargo.

Samuel discovered that nearly 1,000 sailors a year were being drowned on ships around British shores because ships were being overloaded. He headed a campaign to require that vessels bear a load line marking indicating when they were overloaded, hence ensuring the safety of crew and cargo.

What is a Plimsoll Line?

The plimsoll line (also known as a Load Line or the International Load line) is the marking on a ship's hull that shows how low or high the ship is resting in the water. By examining the plimsoll line you can tell the depth to which a vessel may be safely (and legally) loaded. The marking is now mandatory and international.

Why is the Plimsoll line important?

If a ship is riding too low in the water it will become dangerously unstable and could capsize.

The level of a ship in the water is affected by temperature and salinity as well as load. Temperature affects the level because warm water provides less buoyancy, being less dense than cold water. The salinity of the water affects the level, with fresh water being less dense than salty seawater.

Maximum loading point

In 1876, Parliament was forced to pass the Unseaworthy Ships Bill into law. The Act required a series of 'lines' to be painted on the ship to show the maximum loading point. Unfortunately, the Act allowed the ship owners to paint the line where they saw fit and some chose to paint it on the funnel of the ship! It was not until 1890 that Board of Trade officials applied the regulations that Plimsoll had intended and the line was painted on the side of all ships.

The Plimsoll Line painted on the side of all ships

Different levels are shown with code letters to indicate the type of water.

• TF – Tropical Fresh Water
• F – Fresh Water
• T – Tropical Seawater
• S – Summer Temperate Seawater
• W – Winter Temperate Seawater
• WNA – Winter North Atlantic