The load line mark
The familiar circle-and-line mark on a ship's side, often called the Plimsoll mark, shows the maximum permitted loading. Additional lines account for different water densities and seasons, because a safe draught in tropical salt water differs from one in winter North Atlantic conditions.
Zones, seasons and certificates
The Convention divides the world's oceans into zones and seasonal areas, each with its own permitted load line. Compliance is evidenced by the International Load Line Certificate, supported by surveys that confirm the hull, closing appliances and freeboard arrangements remain sound.