Compartment (ship)

A compartment is a portion of the space within a ship defined vertically between decks and horizontally between bulkheads. It is analogous to a room within a building, and may provide watertight subdivision of the ship's hull important in retaining buoyancy if the hull is damaged. Subdivision of a ship's hull into watertight compartments is called compartmentation.
Watertight subdivision limits loss of buoyancy and freeboard in the event of damage, and may protect vital machinery from flooding. Most ships have some pumping capacity to remove accumulated water from the bilges, but a steel ship with no watertight subdivision will sink if water accumulates faster than pumps can remove it. Standards of watertight subdivision assume no dewatering capability, although pumps kept in working order may provide an additional measure of safety in the event of minor leaks. The most common watertight subdivision is accomplished with transverse bulkheads dividing the elongated hull into a number of watertight floodable lengths. Early watertight subdivision tested with hoses sometimes failed to withstand the hydrostatic pressure of an adjoining flooded compartment. Effective watertight subdivision requires these transverse bulkheads to be both watertight and structurally sound.
Compartments are identified by the deck forming the floor of that compartment. Different types of ships have different deck naming conventions. Passenger ships often use letters of the alphabet sequentially down from A deck (the highest) above B deck, and B deck above C deck, and so forth. Another popular naming convention is numbering the main deck 1, the deck below it 2 (or the second deck), and the deck below that the third deck, and so forth. Decks above the main deck may be named, like the bridge deck or poop deck, or they may be numbered upwards from the main deck with a zero prefix: 01 above the main deck, 02 deck above 01, and so forth.
The centerline position code is zero for a compartment on the ship's centerline, odd numbers for compartments entirely to starboard of the centerline, and even for compartments entirely to port. For compartments sharing the same deck and forward frame, the first two parts of the code are identical, and the third part of the code is numbered outward from the centerline. For example, four main-deck compartments at frame 90 would be 1-90-1-L inboard and 1-90-3-L outboard on the starboard side of the ship and 1-90-2-L inboard and 1-90-4-L outboard on the port side.