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maritime DC & PPE Information Center


Main Drainage System


The main drainage system runs throughout the machinery compartments. In some ships, however, it may extend forward and aft of the machinery compartments. In smaller ships, the drainage main consists of a single pipe running fore and aft, usually along the centerline. In larger ships, it is a loop system extending along both sides of the engineering compartments and joined at the ends. Main drainage systems may be used in many newer ships to drain floodable voids used in counterflooding, after such voids have been flooded, and to empty fuel tanks which have been ballasted with seawater. Main drain piping is galvanized pipe or copper-nickel tubing. The branch suction lines leading to valves or manifolds from various bilge wells, tanks or other compartments are of smaller size than the main line. Two and one-half-inch hose fittings are installed in the main so that standard two and one-half-inch suction hoses can be connected.


For more information, see the Index.