Vertical Centre of Gravity
Abbreviation: KG
Vertical distance from the keel to the ship's centre of gravity. Lower KG = more stable.
In practice
Recalculated at every loading change in the loading instrument. Heavy lifts on hatch covers raise KG; the master signs off on the new condition before sailing. Bunkering raises KG slightly because fuel sits in low tanks.
Regulatory detail & full definition
KG is the vertical distance from the keel to the ship's centre of gravity; the lower the KG, the more stable the ship. It is calculated by summing the moments of every weight on board (lightship plus cargo, fuel, ballast and stores) about the keel and dividing by the total weight, and it is combined with KM to give the metacentric height, GM = KM - KG. Slack tanks reduce stability through the free-surface effect, which raises the effective KG, so an apparently stable ship with large partly-filled tanks can still be vulnerable.
Authoritative source: 2008 IS Code ↗
Related
Source: IS Code 2008; standard naval-architecture text
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