Metacenter (M)

The transverse metacenter M is the point where the vertical line of buoyant action at a small heel angle intersects the line it occupied upright, the apparent pivot about which the ship rolls at small angles. Its height above the center of buoyancy, BM, equals the transverse moment of inertia of the waterplane divided by displaced volume (BM = I_T / V), and its height above keel is KM = KB plus BM. The metacentric height GM = KM minus KG then sets initial stability. M is effectively fixed only for small heel; beyond about 7 to 10 degrees the buoyancy verticals no longer meet at one point and the GZ curve replaces the metacentric model.