Metacentric Height from Keel
Abbreviation: KM
Vertical distance from keel to the metacentre M; sum of KB (keel to centre of buoyancy) and BM (metacentric radius).
In practice
Read off the hydrostatic curves at the actual mean draft. KM is fixed by hull form and draft; KG is variable. The difference KM-KG = GM, the headline stability metric.
Regulatory detail & full definition
KM is the vertical distance from the keel to the transverse metacentre M, and equals the sum of KB (keel to the centre of buoyancy) and BM (the metacentric radius, BM = I/V). It is read from the ship's hydrostatic curves at the relevant draft and, together with KG, gives the metacentric height GM = KM - KG, the primary measure of initial transverse stability. KM actually changes as the ship heels because the metacentre moves, but for the small angles used in initial-stability calculations it is treated as effectively constant.
Related
Source: Standard naval architecture; IS Code 2008
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