The ship’s METACENTRIC HEIGHT (GM) is not
only a measure of the ship’s RIGHTING ARM (GZ)
but is also an indication of whether the ship is stable or
unstable. If M is above G, the metacentric height is
positive, the moments which develop when the ship is
inclined are RIGHTING MOMENTS, and the ship is
stable, as shown in view A of figure 12-23. But if M is
below G, the metacentric height is negative, the
moments that develop are UPSETTING MOMENTS,
and the ship is unstable, as shown in view B of
figure 12-23.