Ballast

Ballast is weight carried low to control draft, trim, and stability when cargo is light or absent, almost always seawater pumped into dedicated ballast tanks. A ship sails in ballast on the return leg of a one-way cargo trade. Ballast water carries non-native organisms between regions, which the IMO Ballast Water Management Convention (in force 8 September 2017) controls by treatment to the D-2 discharge standard. Permanent solid ballast (kentledge) is fixed iron used to correct a built-in trim or stability deficiency.