What is the term used for the line that is perpendicular to the plimsoll mark?

The term used for the line that is perpendicular to the Plimsoll mark is known as the deck line. The deck line is a reference used in maritime contexts, specifically in relation to the load line or Plimsoll line, which indicates the maximum safe loading level for a ship in different water conditions. The deck line serves as a horizontal reference point on the vessel, providing a baseline for assessing how heavily a ship is loaded in relation to the Plimsoll mark.

It is important to note that the Plimsoll mark is designed to ensure vessels have enough buoyancy, and the deck line assists crew members and inspectors in visualizing the relationship between the vessel's loading and its design to remain safe in water. In this context, the deck line is critical for determining whether or not a ship is loaded within safe limits, and understanding its position in relation to the Plimsoll mark is vital for navigation safety.