AKA Plimsoll mark or draft mark
- Markings on the side of an ocean-going vessel that indicate the draft and legal load limits which the vessel may have under various conditions and in waters of different densities due to temperature and salinity.
19th century. From Samuel Plimsoll, a British MP who was responsible for passing legislation involving safety at sea in 1876.
There’s a lot to discuss when it comes to draft marks (it deserves a dedicated post), but the markings in the above image have the following meanings:
- TF = Tropical freshwater
- F = freshwater
- T = Tropical seawater
- S = Summer temperate seawater
- W = Winter temperate seawater
- WNA = Winter North Atlantic seawater
- BV = Bureau Veritas (the registration authority)
Simply put, the Plimsoll line is there to ensure that the vessel isn’t overloaded and has sufficient freeboard, and thus reserve buoyancy, to transit certain waters.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport.