Introduction Oil/water separators are necessary aboard vessels to prevent the discharge of oil overboard when pumping out bilges, deballasting or when cleaning oil tanks. The requirement to fit such devices is the result of international legislation The need for such legislation is that free oil and oily emulsions discharged in a waterway can interfere with natural processes such as photosynthesis and re-aeration, resulting in destruction of the algae and plankton so essential to fish lifeIntroduction • Oil/water separators are necessary aboard vessels to prevent the discharge of oil overboard when pumping out bilges, deballasting or when cleaning oil tanks. The requirement to fit such devices is the result of international legislation. The need for such legislation is that free oil and oily emulsions discharged in a waterway can interfere with natural processes such as photosynthesis and re-aeration, resulting in destruction of the algae and plankton so essential to fish life