Righting arm (GZ)

The righting arm $GZ$ is the horizontal distance between the lines of action of weight through G and buoyancy through B at a given heel, so the restoring moment is $\Delta \cdot GZ$. At small angles $GZ \approx GM \cdot \sin\phi$; beyond that the full $GZ$ curve is read from cross-curves of stability (KN curves) via $GZ = KN - KG \sin\phi$. The IS Code 2008 sets minimum areas under the curve to 30 and 40 degrees and a peak $GZ$ at or beyond 25 degrees.