load line

from The Century Dictionary.

• noun Nautical, a line drawn on the side of a vessel to show the depth to which a suitable or allowable load will cause her to sink in the water. Among English seamen known as Plimsoll's mark. See mark.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun waterlines to show the level the water should reach when the ship is properly loaded