Many Years Ago,

at school,

we were told of the valuable contribution that Samuel Plimsoll made to the world wide shipping industry, he was born 10 February 1824, died 3 June 1898, and was an English politician and social reformer, now best remembered for having devised the Plimsoll line, the line above on a ship's hull indicating the maximum safe draft, and therefore the minimum freeboard for the vessel in various operating conditions, we were all conversant in its meaning, there was always a question on it in exams, the original “Plimsoll line” was a circle with a horizontal line through it, the symbol spread around the world; additional marks were added over the years, the letters on either side of the circle stand for the ship’s registration authority, the marks and letters to the left of the circle indicate maximum loads under different climatic conditions, salt water is denser than fresh, cold water denser than warm, since water density affects ship buoyancy, different conditions call for different load lines, W marks the maximum load in winter temperate seawater, S in summer temperate seawater, T in tropical seawater, F in fresh water, and TF in tropical fresh water, like that of the Amazon River, the  reason for the lines was that so many ships and crews were lost due to overloading, in 1876 the Board of Trade recorded that 856 British merchant ships were lost within ten miles of the British coast, in conditions that were no worse than a strong breeze, something to prevent overloading had to be done, enter Samuel and his now famous line,

and here it is in it's simplified form, but this is not the only way you can read ships, for a good quick informative read, grab a coffee and have a look at The Secret Language of Ships, a fascinating read.