Plimsoll, << PLIHM suhl, >> mark is a load-line marking on the side of a ship’s hull. It shows the draft a ship can be safely loaded to under certain conditions. The draft is the depth to which a ship sinks in the water. The position of the marking depends on the type and size of the vessel. A ship loaded “down to the Plimsoll mark” carries the maximum weight of cargo. Any more cargo would lessen the ship’s chances of a safe voyage.
The name comes from Samuel Plimsoll, a member of the British Parliament who was active in promoting the Merchant Shipping Act of 1876. This act was the first legislation to require a draft mark on the side of a vessel beyond which it could not be loaded.
Load-line regulations for American ships have been established by the United States Coast Guard as provided under the Load Line Act of 1929 and the Load Line Convention of 1966, an international treaty signed by the world’s seagoing nations. These rules apply to deep-sea vessels of 150 gross tons or more.
The distance between the Plimsoll mark and the deck is the ship’s “freeboard.” Special markings were established in 1935 for Great Lakes and Atlantic and Pacific coast voyages. In 1973, Canada and the United States agreed on revised load-line regulations for ships traveling on the Great Lakes.
