How do load lines limit how deeply a ship can be loaded?

In maritime law, load lines—commonly known as the Plimsoll line—serve as critical safety markers that indicate the maximum depth to which a ship may be legally loaded. By marking the hull, these lines establish a mandatory limit on the vessel's draft, ensuring that a sufficient amount of freeboard—the vertical distance between the waterline and the main deck—remains above the water.123

This system was established to prevent the operation of overloaded, unseaworthy vessels, historically referred to as "coffin ships," which posed severe risks to the lives of seamen. The regulations, which originated from the Merchant Shipping Act of 1875, have since been standardized through international agreements like the International Convention on Load Lines. By enforcing these limits, maritime authorities ensure that ships maintain the necessary buoyancy and stability required for safe operation at sea.2134