Deballasting

Deballasting is the operation of pumping ballast water out of a ship’s tanks, usually as cargo is loaded so the vessel returns to its design draft and trim. Under the BWM Convention the discharged water must meet the D-1 exchange standard (95% volumetric exchange, normally at least 200 nautical miles from land in water at least 200 meters deep) or the D-2 treatment standard limiting viable organisms in the discharge. Every deballasting operation is logged in the Ballast Water Record Book with position, tank, and volume. Improper deballasting spreads invasive species and is the harm the Convention was written to stop.