Regulation 13

The following minimum stability criteria shall be met unless the Certifying Authority is satisfied that operating experience justifies departure therefrom: ( a ) the area under the righting lever curve (GZ curve) shall not be less than 0.055 metre-radians up to 30 degrees angle of heel and not less than 0.090 metre-radians up to 40 degrees or the angle of flooding θ f if this angle is less than 40 degrees. Additionally, the area under the righting lever curve (GZ curve) between the angles of heel of 30 degrees and 40 degrees or between 30 degrees and θ f , if this angle is less than 40 degrees shall not be less than 0.030 metre-radians. θ f is the angle of heel at which openings in the hull, superstructure or deckhouses which cannot rapidly be closed water-tight commence to immerse. In applying this criterion, small openings through which progressive flooding cannot take place need not be considered as open; ( b ) the righting lever GZ shall be at least 200 millimetres at an angle of heel equal to or greater than 30 degrees; ( c ) the maximum righting lever GZ max shall occur at an angle of heel preferably exceeding 30 degrees but not less than 25 degrees; and [S 60/96 wef 02/02/1996] ( d ) the initial transverse metacentric height GM shall not be less than 150 millimetres.