The lowest interior space of a vessel where leakage, condensation, and drainage water collects; must be pumped out regularly.
Quick facts
Regulation
MARPOL Annex I
In practice
Bilge water must be processed through an approved oily water separator to bring oil content below 15 parts per million before it may be discharged outside special areas. Every transfer and discharge must be recorded in the Oil Record Book Part I, including quantities, position, and the identity of the 15 ppm monitoring equipment. Port state control officers treat falsified or incomplete Oil Record Books as a serious indicator of illegal discharge and may detain the vessel pending investigation. Regular bilge sounding, pump operation, and pipeline condition checks are scheduled items on planned maintenance systems.
Regulatory detail & full definition
The bilge is the lowest internal compartment of a ship, situated in the double-bottom structure below the engine room and cargo holds, where water from leaking shaft seals, heat exchanger drains, condensation, and deck drainage collects by gravity. Keeping bilges clean and dry is a fundamental housekeeping and safety requirement: accumulation of oily water reduces stability reserve and creates fire and slip hazards, while the presence of untreated oil in bilge water makes overboard pumping unlawful under MARPOL Annex I.
Bilge water must be processed through an approved oily water separator to bring oil content below 15 parts per million before it may be discharged outside special areas. Every transfer and discharge must be recorded in the Oil Record Book Part I, including quantities, position, and the identity of the 15 ppm monitoring equipment. Port state control officers treat falsified or incomplete Oil Record Books as a serious indicator of illegal discharge and may detain the vessel pending investigation. Regular bilge sounding, pump operation, and pipeline condition checks are scheduled items on planned maintenance systems.