IMO Requirements for Intact and Damage Stability of the Ship

Intact stability
  For a cargo vessel, the intact stability requirements are follows-
·         Initial GM or metacentric height should not be less then 0.15 m.
·         Righting lever GZ should be at least 0.2 m and angle of heel Ѳ ≥ 30̊.
·         Maximum righting lever should occur at heel >30̊ preferably but not less than 25̊.
·         The Area of the GZ curve should be at least:
a)      0.055 m radian up to Ѳ = 30̊
b)      0.090 m radian up to Ѳ = 40̊
c)     0.03 m radian between 30̊ and 40̊ or between 30̊ and angle of down flooding.
The angle of down flooding is an angle at which deck immersion takes place with subsequent water ingress.

Fig: GZ Curve implying IMO Criteria
Damage Stability
A damage stability criterion varies from ship to ship and the requirement for the same is given in SOLAS chapter II-1. It may be single compartment flooding, multi compartment flooding, engine room flooding etc.
Under all the criteria as applicable, vessel margin line should not be submerged after the damage. Margin line is an imaginary line drawn 75mm below the free board deck.
Intact and damage stability are very important factors that govern the overall stability of the ship

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