Plimsoll’s Line (aka the International Load Line) – Saves Lives

by John M. MacFarlane 2013

Plimsoll Detail

Plimsoll Mark / Line on the side of a ship (Photo courtesy of the Murray Polson collection)

The first modern loading standards were introduced by Lloyd’s Register of British and Foreign Shipping in 1835. In early days, overloaded ships were known as ‘coffin ships’ referring to the increased risk of sinking due to the loss of freeboard from being heavy laden. Overloaded ships were often over–insured, yielding a large profit for greedy owners on the loss of the ship and crew. In the 1860s, after increased loss of ships due to overloading government regulations were proposed by Samuel Plimsoll, a British Member of Parliament.

Samuel Plimsoll was known as ‘The Sailor’s Friend’ and was elected as the Member of Parliament for Derby in 1868. He had been a brewery manager and London coal dealer. His early attempts at reform were unsuccessful, and a bill he introduced to mitigate improve the danger of over loading was defeated. He published "Our seamen" detailing the hard and dangerous conditions that British seamen had to endure in their work. Plimsoll was re–elected to Parliament in 1880 but resigned to become the President of the Sailor’s and Fireman’s Union.

The Plimsoll Mark or Plimsoll Line was adopted in 1876. Since that time every vessel was required to have a line painted amidships on both sides of the hull to act as a visual indicator of the limit to which ships could be loaded. It is a circle with a horizontal line drawn through it. This has, over time, become adopted worldwide.

Displacement tonnages are calculated in relation to draught and the statutory free board that must be shown on the ship’s side. The more cargo weight that is loaded the more water a ship displaces and the lower in the water she will lay. At some point the vessel will ride so low in the water as to be dangerous to its stability (and possibly sink).

Plimsoll Mark

The original Plimsoll Mark was a circle with a horizontal line through it to indicate the maximum draft of a particular ship. Here is a typical Load Limit/Plimsoll Mark on a hull.

Plimsoll Mark

Some Plimsoll Marks are difficult to read from any distance. (Murray Polson photo)

The marks (also known as Plimsoll Lines) are required to be placed amidships. Various lines indicating the level of the ship in various conditions (based on the specific gravity of the water) are indicated. (A ship will sink deeper in the water in warm areas of the tropics than in winter conditions in the North Atlantic.) Warm water provides less buoyancy as it is less dense than cold water and fresh water is less dense than salt water so it provides less buoyancy. Load limits are calculated for each type of operating environment.

  • LR – the name of the authority setting the load limit (in this case the LR stands for Lloyd’s Register)
  • TF – tropical freshwater
  • F – fresh water
  • T – tropical salt water
  • S – summer salt water
  • W – winter salt water
  • WNA – winter North Atlantic

The load limit is required to be painted amidships but on a surface that is still visible if the paint is worn off. This prevents unscrupulous owners from overloading vessels when the paint is gone. It provides inspectors an easy reference point to ensure that loads meet certificated limits. Because of its placement anyone (casual observer to crew member) can check the status at any time.

Classification Societies (such as Lloyds of London) issue the certificates. Their initials bracket the plimsoll mark (as above). The commonly seen initial letters include:

  • BV - Bureau Veritas
  • GL - Germanischer Lloyd
  • LR - Lloyd’s Register
  • NV - Det Norske
  • RI - Registro Italiano Navale

American ships use the ABS mark of the American Bureau of Shipping - four lines amidships that show maximum loading conditions in freshwater, and saltwater in summer and winter.

Propeller Warning

There are sometimes other marks visible on the hulls of some vessels. This one warns nearby vessels of the presence of a bow thruster (usually a propeller) which could potentially be a hazard to tugs or other vessels closely approaching the hull (Photo from MacFarlane collection.

Draught Line

The draught lines are slightly different from Plimsoll Lines and indicate the loading of the vessel and its position relative to the sea surface. This gives an indication to ship’ officers of the amount of water being drawn by their vessel (usually on a non–freight carrying vessel). (Photo from MacFarlane collection.)


In 2018 marine photographer Loch McJannett had a tattoo placed on the calf of his leg in honour of Samuel Plimsoll. This must surely be unique in the world.

To quote from this article please cite:

MacFarlane, John M. (2013) Plimsoll’s Mark. 2013.

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