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Load Line Usage and History

By Andy Jones

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Load Lines are markings on ships' hulls that indicate how low they can sit in the water when fully loaded. Load Lines are also sometimes referred to as plimsoll lines after a 19th century politician named Samuel Plimsoll. Maritime laws governing the loading of ships date back thousands of years and play an important part in safety at sea. A set of port guides or specialist maritime maps can provide detailed information on international load line zones.

Early mariners soon learnt that you overload a ship at your own peril. Evidence of early maritime legislation governing the loading of ships dates back to 2500BC, originating in Crete. This type of legislation was also seen in the Roman Empire and throughout the middle ages. During the industrial revolution trade and shipping grew at a rapid pace as well as the construction and powering of ships and many vessels were lost during this period due to new designs and lack of standards. In the 19th century Lloyd's developed the 'Lloyd's rule' which only governed shipping underwritten by the company. Even then it wasn't totally understood that overloading a ship was a dangerous practice. It wasn't until the 1860's that steps were taken to limit the increasing loss of shipping and understand why it was occurring. Samuel Plimsoll a Liberal MP in England took up the cause raised by James Hall, a ship owner of the time. Plimsoll faced strong opposition from a small number of ship owners who saw this as a limitation on their cargo potential; however the UK merchant shipping act of 1876 was passed as a result of Plimsoll's efforts and made load lines compulsory for English shipping. Other international standards followed but global standardisation didn't occur until the 1930 Load Line Convention.

Over time technology changed ship design and size once again and new regulations were needed. This paved the way for the 1966 load Lines Convention formulated at the newly created International Maritime Organisation in London. The 1966 Convention set out rules governing the calculation of freeboard which is the distance from the top of the hull down to the waterline which changes with load. This convention was last amended in 2003 and is still in force today. The load line marks the minimum freeboard needed for safety of the vessel.

Load lines vary globally due to the effects of temperature, weather and salinity of sea water. Cold water provides more buoyancy than warm water because of its greater density; salinity also increases density and buoyancy. Due to these factors a number of lines (in hand with global geographical zones) will make up the load or plimsoll line, these are; a tropical fresh water line, a fresh water line, a tropical seawater line, a summer temperate seawater line, a winter temperate seawater line and a winter north Atlantic line. Various publications will provide information on international load line zones such as a ships atlas, a set of port guides and specialist maritime load line maps; these can be obtained from port information specialists.

Andy writes for Shipping Guides who provide port data including a port directory. For more visit: http://www.portinfo.co.uk

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