Ship Stability normally refers to the ability of a floating vessel to resist the overturning forces encountered in the course of its operations. These forces may arise from weather (wind and waves), from tow lines, from abrupt changes of course, from shifting of cargo or passengers, or from flooding due to damage.
Stability calculations quantify these forces and apply them in a practical way to a mathematical model of the ship so that the response of the vessel can be examined for various magnitudes of overturning moments.
When approached as an hydrostatic problem, the dynamic wave-induced forces of acceleration and inertia with their attendant resonance phenomena are not accounted for directly. Rather, a measure of static or quasi-static stability is sought which is deemed to be sufficient to prevent capsize in the presence of the actual dynamic environment.
Measures of stability include the range of heel angles between upright stable equilibrium and the angle where the righting moment vanishes; the maximum value of the righting arm in this range; the area under the righting arm curve between certain angles, etc. These measures are usually compared with standards which are recommended by national and international regulatory authorities for the type of vessel and the service involved.
GHS applies to all phases of these calculations, from the construction of detailed vessel models, including tanks and compartments, to the comparison with stability criteria.