an imaginary line used in making calculations regarding the flooding of hulls, running fore-and-aft 3 inches (8 cm) below the upper surface of the bulkhead deck at the side.
the line along which the planking on a transom-sterned vessel terminates aft.
Origin of margin line
First recorded in 1840–50
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019