page_title: Waterline
section_title: Subdivision load line marks
hierarchical_section_title: Waterline / Subdivision load line marks
caption_attribution_description: Drawing of a Subdivision Load Line mark with two subdivision load marks
context_page_description: The waterline is the line where the hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line, that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of waves that may arise. Varying water temperatures will affect a ship's draft, because warm water is less dense than cold water, providing less buoyancy. In the same way, fresh water is less dense than salinated or seawater with the same lessening effect upon buoyancy.
  For vessels with displacement hulls, the hull speed is determined by, among other things, the waterline length. In a sailing boat, the waterline length can change significantly as the boat heels, and can dynamically affect the speed of the boat.
  The waterline can also refer to any line on a ship's hull that is parallel to the water's surface when the ship is afloat in a normal position. Hence, all waterlines are one class of "ships lines" used to denote the shape of a hull in naval architecture plans.
context_section_description: Passenger ships having spaces which are adapted for the accommodation of passengers and the carriage of cargo alternatively may have one or more additional load line marks corresponding to the subdivision drafts approved for the alternative conditions. These marks show P1 for the principal passenger condition, and P2, P3, etc., for the alternative conditions; however, in no case is any subdivision load line mark placed above the deepest load line in saltwater.
caption: Passenger vessel with two allowed subdivision load lines
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