Do you know what Plimsoll lines on ships are?

Have you ever wondered what Plimsoll lines are? And why are they called Plimsoll? Professionals across the shipping industry may be familiar with the term, but even those not working in the industry, but who are extra observative, may have noticed that ships have some line marks on their hull, just above the waterline. These are Plimsoll lines.

What it is

The Plimsoll line (also known as a Load Line or the International Load line) is a reference mark located on a ship’s hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo.

Why it is useful

It is evident that there is not a standard maximum height into which a ship is allowed to immerse, but the maximum allowed depth varies depending on the conditions, for example:

  • the ship’s dimensions,
  • the type of cargo carried,
  • the time of year, and
  • the water densities encountered in port and at sea.

Considering the above factors, a ship’s captain can determine the appropriate Plimsoll line needed for the voyage. As such, load limits are calculated for each type of operating environment into the following levels:

TF = Tropical Fresh Water

T = Tropical

F = Fresh Water

S = Summer

W = Winter

WNA = Winter North Atlantic

There are also two letters with the name of the authority setting the load limit (for example, AB stands for classification society ABS).

Why ‘Plimsoll’?

The name comes from Samuel Plimsoll (1824–1898), a member of the British Parliament, who expressed concerns in regard to the loss of ships and crews from vessel overloading.

In 1876, he persuaded Parliament to pass the Unseaworthy Ships Bill. This mandated marking a ship’s sides with a line that would disappear below the waterline if the ship was overloaded.

The line is found midship on both the port and starboard hulls of cargo vessels and is still used widely in shipping.

The original Plimsoll Mark was a circle with a horizontal line through it to indicate the maximum draft of a particular ship. Additional marks have been added over the years, taking into consideration different water densities.

It makes no wonder that Samuel Plimsoll has passed through history as the ‘Friend of Sailor’ . . . .

. . . . continue reading the article on the safety4sea website here