Plimsoll Lines


Search the hull of a merchant ship and you will find a curious ladder of lines punched or welded to the hull and picked out in paint. It will consist of a vertical line with horizontal steps to left and right labelled with letters, such as TF and F to one side and W, S, T and sometimes WNA on the other. Close to this is a circle with a horizontal line through it, like the planet Saturn with its rings, and some more letters. These will be the initials of one of twelve international bodies responsible for ship safety, such as LR for Lloyds Register or AB for the American Bureau of Shipping. The line that bisects the circle is called a Plimsoll line, and is named after a nineteenth century campaigner for sailor’s welfare.


Shipowners have an obvious incentive to maximise the load carried by a ship, since this will increase the profit generated from a voyage. However, after a certain point the size of cargo can become dangerous for the vessel. All ships need sufficient freeboard (the height from the water line to the main deck) to prevent being swamped by heavy seas and to provide a reserve of buoyancy in the event of a leak. But an unscrupulous shipowner with no regard for the fate of his crew might be willing to take such a risk, particularly if the ship is old and not particularly valuable, or well insured.


Overloading is a very old problem, and several maritime states have attempted to combat it. During the medieval period the Venetian and Genoese Republics in the Mediterranean and the members of the Hanseatic League in northern Europe introduced lines painted on the sides of their ships to try and stop the abuse. Later the Lloyd’s Register of shipping attempted to introduce a mandatory minimum freeboard of three inches per foot of hold depth in 1835, but still the problem of dangerous ships persisted. But in the 1860s Samuel Plimsoll decided to try and do something about the problem.


He was born in Bristol, a busy sea port, although his family soon moved to Yorkshire. He left school at an early age to become a clerk in a local brewery, rising in time to be its manager. When he was 29 he left Yorkshire and moved to London to start his own business as a coal merchant. This failed, leaving Plimsoll almost destitute, which proved a turning point in his life. For several years he lived in lodging houses among the capital’s poor, which bought him into contact with impoverished sailors. It was here that he learned of some of the shocking working conditions seaman had to endure. Many of his concerns centred on what were called coffin ships.


These were old, rotten sailing ships at the end of their lives that were patched up, repainted, renamed and then passed off as new vessels when insured. Once insured for an inflated value, they were worth more to their owners sunk than afloat. Overloaded with cargo, if they made their destination they would return a good profit for their owner, while when they eventually sank, they would produce a handsome insurance pay out. This problem was not unique to Britain, with similar scams existing in the US, Germany and the Netherlands.

Plimsoll’s business interests eventually recovered, and by 1867 he was able to get elected as a member of the British Parliament. But he never forgot the sailors he had met, and he used his new position to investigate their issues. He campaigned for them in Parliament, and wrote a book called Our Seamen which aroused considerable interest among the public. In 1873 he succeeded in getting a Royal Commission to investigate the shipping industry. What they found was shocking. Seamen on sailing ships had a death rate that was over four times that of coal miners, previously thought to be the country’s most dangerous job. Worse still, the law was making matters worse, with over two thousand cases found of sailorswho had signed on as crew for a ship being tried in court for refusing to board upon seeing its condition. Plimsoll would later tell Parliament that, "The Secretary of Lloyd's tells a friend of mine that he does not know a single ship which has been broken up voluntarily by the owners in the course of 30 years on account of its being worn out". Of course not – there was a much more lucrative way of disposing of an old ship.


In 1875 the government finally introduced legislation to reform these practices, but withdrew the bill after pressure from ship owners. Plimsoll was incandescent with rage, and was suspended from the House of Commons for calling government ministers “villains” and shaking his fist under the Speaker’s nose. However, his ceaseless campaigning had brought the country to a point where the pressure for change was now too great. The following year a new bill, the Merchant Shipping Act was passed, reforming the industry by giving the Board of Trade the power to regulate it. One of the new rules was a compulsory maximum loading line to be marked on the hulls of all British merchant ships, which was soon being referred to as a Plimsoll line. The drop in the accident rate for sailors was dramatic.


Further regulation followed on an international basis to vary the original loading line to take account of different climatic conditions. Salt water is denser than fresh and cold water is denser than warm. And since water density affects ship buoyancy, different conditions call for different load lines, which brings us back to all those letters on the ship’s side. F is fresh water, while TF is tropical fresh. The other letters refer to seawater. W is winter temperate seawater; S is summer and T is for tropical seawater. Thanks to Samuel Plimsoll, they ensure that, whatever the conditions, no sailor’s life should be threatened by an over-loaded ship.

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