There are many different kinds of ship-markings, among them is the Plimsoll line. This important marking shows the deepest possible safe draft (or draught) of the vessel for a given season and type or location of a body of water. Developed and proposed in 1875 by English Member of Parliament (MP) Samuel Plimsoll, of Derby, England, this marking first became required in 1876 as part of an amendment to the British Merchant Shipping Act.
Samuel Plimsoll first proposed the markings around 1869 after the rise of coffin ships led to high casualty rates as ships were overloaded in order to maximize profitability of each voyage for a vessel. He published the book Our Seamen in 1873, which presented evidence that as many as 1000 people each year were drowning around the British coast as a result of unseaworthy ships. To codify regulations to reduce these drownings, MP Plimsoll introduced the Unseaworthy Ships Bill in 1875 to require a line be marked on a ship, which if submerged would indicate the overloading of that same ship.
Plimsoll faced significant opposition to the bill in 1875 due to pressure from ship-owners. It was widely believed that the wealthiest ship-owners already exceeded the requirement of seaworthiness as they were already surveyed and class-approved, with the costly arrest of ships being overwhelmingly applied only to the ships of the poorest ship-owners. As such, it was improper for further regulations in the form of a load line be implemented. Despite this, with the support of Benjamin Disraeli the bill passed during its second reading in 1876. Mr. Disraeli purported that “[t]he Vox populi has not coerced us, but has aided us, and it is with the greatest satisfaction that I now see the possibility of passing a measure which I trust will be both salutary and sufficient.”[1]
The following year in 1877, the British Merchant Shipping Act was again amended to include specific weight limits for cargo carriage on ships. This was a clear refinement of the Plimsoll line, which was based on the total tonnage of the ship, not the cargo tonnage.
The marking is a freeboard marking indicated by a line drawn on the side of the hull at midship. The original marking is a circle with a line drawn through it.
The original Plimsoll line has been constantly modified since its introduction. It has been codified into international law in 1930 and again modified in 1966 as part of Safety of Life at Sea (SOLAS) regulations. Presently the line is continually improved and monitored by the International Maritime Organization (IMO). In another article modern day load lines will be introduced, along with their calculations and impact on cargo carriage and voyage planning.
[1] https://hansard.parliament.uk/Commons/1875-07-30/debates/a76d65a2-66cc-4b71-a34f-9cb57e69641e/UnseaworthyShipsBill%E2%80%94Bill274