The Metacentre (M)
“M” is a point, generally on the centreline, at which the initial upward forces acting through B cut the upward forces acting through B¹ after the vessel has been inclined by an external force. For a vessel to be stable G must be below M. This creates a positive righting lever returning the vessel to her initial condition. Applicable for small angles of heel (up to about12 degrees) where M is assumed to remain fixed.
The metacentric height (GM) is GM = KM-KG