Bilge
The Bilge is the lowest inner part of a ship's hull, where water inevitably collects — from condensation, leaks, deck drainage and machinery. This accumulated bilge water is typically contaminated with oil from the engine room, so it cannot simply be pumped overboard.
Under MARPOL Annex I, oily bilge water must be passed through an oily-water separator (OWS) and monitored by a 15 ppm oil-content meter before any discharge, or retained and landed ashore, with every operation logged in the Oil Record Book. Managing the bilge — keeping it pumped, the OWS working, and records accurate — is a core engine-room duty and, like sludge handling, a heavily policed pollution-prevention obligation checked by port state control and vetting inspectors.
The bilge is where a ship's dirty water ends up — and discharging it untreated is a serious pollution offence. Proper bilge management (a working oily-water separator, honest Oil Record Book entries) keeps the operator clear of the same heavy penalties that surround sludge. It is unglamorous but high-stakes engine-room compliance.
Why can't bilge water be pumped overboard?
It is contaminated with oil; under MARPOL it must be treated through an oily-water separator to below 15 ppm or landed ashore, with every discharge logged.
What is an oily-water separator?
Equipment that separates oil from bilge water so the water can be discharged within the 15 ppm limit, while the oil is retained as waste.