Wednesday, November 24, 2010



It has been recognized that limit on drafts to which a ship may be loaded make significant contribution to her safety. The first official loading regulations are thought to date back to maritime legislation originating with the kingdom of Crete in 2,500 BC when vessels were required to pass loading and maintenance inspections. Roman sea regulations also contained similar regulations. In the Middle Ages the Venetian Republic, the city of Genoa and the Hanseatic league required ships to load to a load line. In the case of Venice this was a cross marked on the side of the ship and of Genoa three horizontal lines. The first 19th century loading recommendations were introduced by Lloyd's Register of British and Foreign Shipping in 1835, following discussions between shipowners, shippers and underwriters. Lloyds recommended freeboards as a function of the depth of the hold (three inches per foot of depth). These recommendations, used extensively until 1880, became known as "Lloyd's Rule". In the 1860s, after increased loss of ships due to overloading, a British MP, Samuel Plimsoll, took up the load line cause. A Royal commission on unseaworthy ships was established in 1872, and in 1876 the United Kingdom Merchant Shipping Act made the load line mark compulsory, although the positioning of the mark was not fixed by law until 1894. In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line. It was not until 1930 (The 1930 Load Line Convention) that there was international agreement for universal application of load line regulations. In 1966 a Load Lines Convention was held in London which re-examined and amended the 1930 rules. The 1966 Convention has since seen amendments in 1971, 1975, 1979, 1983, 1995 and 2003.
The waterline is an imaginary line marking the level at which a ship or boat floats in the water. To an observer on the ship the water appears to rise or fall against the hull . Temperature also affects the level because warm water provides less buoyancy, being less dense than cold water. Likewise the salinity of the water affects the level, fresh water being less dense than salty seawater. For vessels with displacement hulls, the hull speed is determined by, amongst other things, the waterline length. In a sailing boat, the length of the waterline can change significantly as the boat heels, and can dynamically affect the speed of the boat

The purpose of a 'load line' is to ensure that a ship has sufficient freeboard and thus sufficient reserve buoyancy. The freeboard on commercial vessels is measured between the lowest point of the uppermost continuous deck at side and the waterline and this must not be less than the freeboard marked on the Load Line Certificate issued to that ship. All commercial ships, other than in exceptional circumstances, have a load line symbol painted amidships on each side of the ship. This symbol must also be permanently marked, so that if the paint wears off it remains visible. The load line makes it easy for anyone to determine if a ship has been overloaded. The exact location of the Load Line is calculated and/or verified by a Classification Society and that society issues the relevant certificates. This symbol, also called an international load line or Plimsoll line, indicates the maximum safe draft, and therefore the minimum freeboard for the vessel in various operating conditions

 Example of load lines

The original "Plimsoll Mark" was a circle with a horizontal line through it to show the maximum draft of a ship. Additional marks have been added over the years, allowing for different water densities and expected sea conditions. Letters may also appear to the sides of the mark indicating the classification society that has surveyed the vessel's load line. The initials used include AB for the American Bureau of Shipping, LR for Lloyd's Register, GL for Germanischer Lloyd, BV for Bureau Veritas, IR for the Indian Register of Shipping, RI for the Registro Italiano Navale and NV for Det Norske Veritas. These letters should be approximately 115 millimetres in height and 75 millimetres in width. The Scantling length is usually referred to during and following load line calculations.

The letters on the Load line marks have the following meanings:
  • TF – Tropical Fresh Water
  • F – Fresh Water
  • T – Tropical Seawater
  • S – Summer Temperate Seawater
  • W – Winter Temperate Seawater
  • WNA – Winter North Atlantic

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