11.2.1 Motor vessels

 The curves of statical stability for seagoing conditions should meet the following criteria:

• .1 the area under the righting lever curve (GZ curve) should not be less than 0.055 metre-radians up to 30° angle of heel and not less than 0.09 metre-radians up to 40° angle of heel, or the angle of downflooding, if this angle is less;

• .2 the area under the GZ curve between the angles of heel of 30° and 40° or between 30° and the angle of downflooding if this is less than 40°, should not be less than 0.03 metre-radians;

• .3 the righting lever (GZ) should be at least 0.20 metres at an angle of heel equal to or greater than 30°;

• .4 the maximum GZ should occur at an angle of heel of preferably exceeding 30° but not less than 25°;

• .5 after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.15 metres; and

• .6 In the event that the vessel's intact stability standard fails to comply with the criteria defined in .1 to .5 the Administration may be consulted for the purpose of specifying alternative but equivalent criteria.

 Where Short Range Yachts are unable to meet the criteria above, the following criteria may be used:

• .1 the area under the righting lever curve (GZ curve) should not be less than 0.07 metre-radians up to 15° angle of heel, when maximum GZ occurs at 15°, and 0.055 metre-radians up to 30° angle of heel, when maximum GZ occurs at 30° or above. Where the maximum GZ occurs at angles of between 15° and 30°, the corresponding area under the GZ curve, A_req should be taken as follows:-

  
  where

  θmax

  =

  is the angle of heel in degrees, where the GZ curve reaches its maximum.

• .2 the area under the GZ curve between the angles of heel of 30° and 40° or between 30° and the angle of downflooding if this is less than 40°, should not be less than 0.03 metre-radians;

• .3 the righting lever (GZ) should be at least 0.20 metres at an angle of heel equal to or greater than 30°;

• .4 the maximum GZ should occur at an angle of heel not less than 15°;

• .5 after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.15 metres.

 The curves of statical stability for seagoing conditions should meet the following criteria:

• .1 the area under the righting lever curve (GZ curve) should not be less than 0.075 metre-radians up to an angle of 20° when the maximum righting lever (GZ) occurs at 20° and, not less than 0.055 metre-radians up to an angle of 30° when the maximum righting lever (GZ) occurs at 30° or above. When the maximum GZ occurs at angles between 20° and 30° the corresponding area under the GZ curve, A_req should be taken as follows:-

  
  where

  θmax

  =

  is the angle of heel in degrees where the GZ curve reaches its maximum.

• .2 the area under the GZ curve between the angles of heel of 30° and 40° or between 30° and the angle of downflooding if this is less than 40°, should not be less than 0.03 metre-radians;

• .3 the righting lever (GZ) should be at least 0.20 metres at an angle of heel where it reaches its maximum;

• .4 the maximum GZ should occur at an angle of heel not less than 20°;

• .5 after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.15 metres; and

• .6 if the maximum righting lever (GZ) occurs at an angle of less than 20° approval of the stability should be considered by the Administration as a special case.

 For the purpose of assessing whether the stability criteria are met, GZ curves should be produced for the loading conditions applicable to the operation of the vessel.

  11.2.1.5.1 The buoyancy of enclosed superstructures complying with regulation 3(10)(b) of the ICLL may be taken into account when producing GZ curves.

  11.2.1.5.2 Superstructures, the doors of which do not comply with the requirements of regulation 12 of ICLL , should not be taken into account.

 In addition to the criteria above, designers and builders should address the following hazards which are known to affect vessels operating in planing modes or those achieving relatively high speeds:

• .1 directional instability, often coupled to roll and pitch instabilities;

• .2 bow diving of planing vessels due to dynamic loss of longitudinal stability in calm seas;

• .3 reduction in transverse stability with increasing speed in monohulls;

• .4 porpoising of planing monohulls being coupled with pitch and heave oscillations;

• .5 generation of capsizing moments due to immersion of chines in planing monohulls (chine tripping).