GM and GZ STABILITY CRITERIA
The GM and GZ stability criteria for a ship’s GM (Metacentric Height) and GZ (Righting Arm) are important for assessing a ship’s stability in response to external forces, such as waves and wind.
1) Initial GM to be not less than 0.15 m.
2) Maximum GZ to be not less than 0.20 m
3) Maximum GZ to occur at a heel of not less than 30.
4) For a ship to meet the GM and GZ stability criteria, the area under the GZ curve, in metre radians, shall be not less than:
(a) 0.055 upto 30 degree heel.
(b) 0.090 upto 40 degree heel or the angle of flooding, whichever is less.
(c) 0.030 between 30 and 40 degree or the angle of flooding, whichever is less.
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In summary, the GM and GZ stability criteria are essential for ship design and operation. GM ensures vertical stability, while GZ ensures horizontal stability, and both must be positive to ensure a ship’s safety and stability at sea.
Ref : Ship Stability part III by Capt. H Subramaniam
