So your GM is good, your GZ areas exceed the required minimums, you’re all set for a safe passage, right?
Not necessarily. Your calculations may become invalid once you cast-off because stability is a moving target.
There are dynamics at work on your vessel, a mechanism that depletes stability reserves in a dynamic process whereby energy is gained from the wind and waves.
A ship underway at sea has energy on all six axes of motion and there are energy exchanges between these axes. The 6 axes are pitch, roll, heave, sway, surge, yaw.
For example energy on the yaw axis can build until directional control is lost, rudders and thrusters become ineffective.