Free Surface Correction

Reduction in effective metacentric height (GM) caused by liquid moving in a slack tank. The correction is computed as the moment of inertia of the free surface divided by the displacement, and is subtracted from the solid GM to give the fluid GM used in stability assessment. The correction grows with tank breadth squared so wide tanks are problematic; pressed-up tanks have no free surface and no correction. Loading instruments compute FSC continuously as tank levels change. The classic loss case is multiple slack tanks producing combined FSC sufficient to give negative effective GM.