11.3 Motor Vessels Complying with Section 11.1.1.2

  11.3.1 The lightship weight, vertical centre of gravity (KG) and longitudinal centre of gravity (LCG) of a monohull vessel should be determined from the results of an inclining experiment.

  11.3.2 The LCG of a multihull vessel should be obtained by a displacement check or by weighing. The KG should be determined either by calculation or by experimental means, noting however that a conventional inclining experiment may not produce satisfactory results.

  11.3.3 The lightship weight may include a margin for growth, up to 5% of the lightship weight at the discretion of the Certifying Authority, positioned at the LCG and vertical centre of the weather deck amidships or KG, whichever is the higher. (The lightweight margin should not be used in practice to increase maximum cargo-deadweight.)

  11.3.4 Curves of statical stability (GZ curves) should be produced for:-

• .1 Loaded departure, 100% consumables;

• .2 Loaded arrival, 10% consumables;

• .3 Anticipated service conditions; and

• .4 Conditions involving lifting appliances (when appropriate).

In addition, simplified stability information in the form of a Maximum KG Curve should be provided, including a worked example to illustrate its use.

Maximum free surface moments should be included within the Loaded Departure condition, and as a minimum, factored according to tank percentage fill for all other conditions.

  11.3.5 Generally, buoyant structures intended to increase the range of positive stability should not be provided by fixtures to superstructures, deckhouse, masts or rigging.

  11.3.6 The curves of statical stability for the loaded conditions should meet the following criteria:-

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

• .4 the maximum GZ should occur at an angle of heel of not less than 25 degrees; and

• .5 after correction for free surface effects, the initial metacentric height (GM) should not be less than 0.35 metres.

  11.3.7 If a vessel of catamaran or multihull type does not meet the stability criteria given in Section 11.3.6, the vessel should meet the following criteria:-

• .1 the area under the righting lever curve (GZ Curve) should not be less than 0.085 metre-radians up to θ_GZmax when θ_GZmax = 15° and 0.055 metre-radians up to θ_GZmax when θ_GZmax = 30°.

  When the maximum righting lever, GZmax, occurs between θ = 15° and θ= 30° the required area under the GZ Curve up to θ_GZmax should not be less than:

  
  where:

  θGZmax

  =

  is the angle of heel in degrees at which the righting lever curve reaches its maximum.

• .2 the area under the righting lever curve between θ = 30° and θ = 40° or between θ = 30° and the angle of downflooding θ_f, if this angle is less than 40°, should not be less than 0.03 metre-radians;

• .3 the righting lever GZ should not be less than 0.2 metre at an angle of heel of 30 degrees;

• .4 the maximum righting lever should occur at an a angle not less than 15 degrees; and

• .5 the initial metacentric height GM_o should not be less than 0.35 metre.

  11.3.8 Vessels complying with ISO 12217 Part 1 'Small craft - Stability and buoyancy assessment and categorisation - Non-sailing boats of hull length greater than or equal to 6 metres', assessed using Options 1 or 2 of Section 5.3 - 'Test and calculations to be applied', may as an alternative, after verification of the stability assessment by the Certifying Authority, be assigned an area of operation in accordance with Section 11.3.9.

  11.3.9 Permitted areas of operation.