The bilge /bɪldʒ/ of a ship or boat is the part of the hull that would rest on the ground if the vessel were unsupported by water. The "turn of the bilge" is the transition from the bottom of a hull to the sides of a hull.
https://en.wikipedia.org/wiki/Bilge
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Bilge water can contain anything that is brought to the engine room and not just oil and water. It is a mix of washing chemicals, rust, sewage leaks, boiler water chemicals, lubrication and hydraulic oil, foaming liquids, CIP-fluids, grey water leaks, metals, soot, bacteria, dust etc.
https://www.marinfloc.com/solutions/bilge-water
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https://www.eeaa.gov.eg/portals/0/eeaaReports/soe2006/SOE-PD...

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Note added at 2 days 22 hrs (2022-12-25 17:36:35 GMT) Post-grading
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