Ballast is heavy material—traditionally solid (stones, sand) but now typically water—placed in a ship's lower holds or tanks to increase stability, manage trim, and improve safety by lowering the center of gravity. It ensures the vessel stays upright and maintains proper draught (depth) when not carrying cargo, sometimes using thousands of tons of seawater.

Key Aspects of Nautical Ballast:

Purpose: Prevents capsizing, improves handling, increases submersion for better propulsion efficiency, and manages structural stress on the hull.

Ballast Water: Modern ships use dedicated ballast tanks, taking on water in one port and discharging it in another to compensate for changing cargo loads.

Solid Ballast: Historically, sand or rocks were used. In modern sailing, heavy materials like lead or iron are often placed in the keel.

Environmental Impact: Ballast water can carry invasive marine species, making it a major environmental concern managed by the International Maritime Organization (IMO).