What does "load line" refer to on a ship?

The term "load line" specifically refers to a marking on the ship's hull that indicates the maximum safe loading level for different water types. This marking is crucial for ensuring the vessel's stability and safety at sea. Load lines, also known as Plimsoll lines, inform crew and operators how heavily the ship can be loaded with cargo without compromising its seaworthiness. The markings vary based on the type of water the vessel intends to navigate, taking into account factors such as salinity and density, which can affect buoyancy.

In contrast, the other options do not accurately represent what a load line signifies. The center of gravity is related to stability but does not pertain directly to loading limits. A measurement of the ship's length is an entirely different aspect of vessel dimensions, and emergency evacuation routes are vital safety measures but are unrelated to cargo loading specifications.