margin line

noun

, Nautical.

1. an imaginary line used in making calculations regarding the flooding of hulls, running fore-and-aft 3 inches (8 centimeters) below the upper surface of the bulkhead deck at the side.
2. the line along which the planking on a transom-sterned vessel terminates aft.

Word History and Origins

Origin of margin line¹

First recorded in 1840–50