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The Plimsoll 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. This depth varies with a ship’s dimensions, type of cargo, time of year, and the water densities encountered in port and at sea. Once these factors have been accounted for, a ship’s captain can determine the appropriate Plimsoll line needed for the voyage.
TF = Tropical Fresh Water • T = Tropical • F = Fresh Water • S = Summer • W = Winter • WNA = Winter North Atlantic • AB = Letters indicating the registration authority (American Bureau of Shipping in the image shown; the circle with the line through it indicates whether or not the cargo is loaded evenly)
Samuel Plimsoll (1824–1898) was a member of the British Parliament who was concerned with the loss of ships and crews due to vessel overloading. In 1876, he persuaded Parliament to pass the Unseaworthy Ships Bill, which mandated marking a ship’s sides with a line that would disappear below the waterline if the ship was overloaded. The line, also known as the Plimsoll mark, is found midship on both the port and starboard hulls of cargo vessels and is still used worldwide by the shipping industry.
The advent of insurance in the 19th century, created an incentive for ship owners to purposely sink their own ships and collect the insurance money. This grim practice became so widespread, and killed so many merchant seamen, that the over-insured, overloaded vessels became known as “coffin ships.” Samuel Plimsoll (“the sailors friend”) fought for sweeping merchant shipping regulation that led to the adoption of the load marking that bears his name. http://www.youtube.com/watch?v=YpCyP1sM_cA
Interesting side note: When rubber sole shoes with canvas tops were introduced in the 1920’s they became known as “Plimsolls” because the line that divided the sole and upper canvas resembled the Plimsoll line. If water gets above the line, your foot gets wet. “Plimsoll line”
