Deballast

Deballast is the process of removing ballast water or ballast mass from a vessel to reduce weight, alter trim, or decrease draft. It is the counterpart to ballasting, which adds weight to meet stability or loading requirements. On ships, ballast water is typically taken on to compensate for cargo loading, weather, or sea conditions, and deballasting returns water to the sea or other designated outlets when no longer needed.

Deballasting uses ballast pumps, valves and piping to discharge water from ballast tanks. It may occur at sea, in port, or at offshore facilities, often coordinated with the ship’s ballast water management plan. Care must be taken to avoid adverse free-surface effects, maintain stable trim within safety limits, and comply with local discharge rules. In many cases, ballast water is discharged through dedicated overboard outlets or to shore reception facilities.

Regulatory and environmental aspects: Since the Ballast Water Management Convention of the International Maritime Organization, ships are required to manage ballast water to minimize biological transfer; many ships are fitted with ballast water treatment systems to reduce organisms in discharged water. Ships must carry a Ballast Water Management Plan and maintain a Ballast Water Record Book. Deballasting operations may be restricted by coastal regulations and environmental protections.

Related topics include ballast water, ballast, vessel stability, and ballast water management plans.