The points, levers and criteria
| Symbol | Meaning |
|---|---|
| G / B / M | Centre of gravity / centre of buoyancy / metacentre |
| GM | Metacentric height; the measure of initial (small-angle) stability |
| GZ | Righting lever at a given angle of heel |
| KG / KB / KM | Heights of G, B and M above the keel |
| Angle of vanishing stability | The heel beyond which the ship will capsize |
| The core stability terms. |
A positive GM means the ship returns upright; the GZ curve shows how the righting lever grows and then falls with heel, and its shape — the maximum GZ, the range of positive stability and the angle of vanishing stability — describes the ship's safety at large angles. The Master works from the ship's approved stability book and loading computer, checking each condition against the stability criteria (the required minimum GM, GZ and area under the curve) for the intended voyage, and never proceeds in a condition that fails them.
NOTE — Work from the approved information At command level stability is managed from the ship's approved stability book and loading computer, verified against the criteria. Command means keeping the ship in a condition a naval architect has approved for the voyage.
WARNING — Never sail failing the criteria A loading condition that does not meet the stability criteria is not a fine judgement to be overruled by commercial pressure — it is a condition the ship must not sail in. Correct it before proceeding.