bilge

Bilge is the lowest interior compartment of a ship's hull, where water, oil, and other liquids tend to collect. It accumulates from seepage, condensation, rainwater, and drainage. The bilge space is built to be watertight but remains a lower point in the hull that must be routinely drained to prevent flooding.

Bilge water is removed by bilge pumps and sometimes by gravity drain when conditions allow. In modern vessels, the bilge contents are directed to treatment systems, including oily-water separators, before any discharge. Regular cleaning of the bilge reduces corrosion, odors, and the growth of bacteria.

Discharge of bilge water is regulated under international conventions such as MARPOL. Most ships are equipped with an oily-water separator and an oil content monitor; discharge of bilge water containing oil is only allowed if the treated effluent meets limits (commonly 15 parts per million) and the vessel is at an approved distance from land.

Bilge also appears in nautical terms such as bilge pump, bilge keel, and bilge rat; in figurative language, "bilge" means nonsense or rubbish, drawing on the idea of the ship’s bottom as a place for detritus.