4.5 Free surface effects
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC/Circular.456 – Guidelines for the Preparation of Intact Stability Information – (Adopted on 13 October 1986) - Annex - Guidelines for the Preparation of Intact Stability Information - 4 Category 1A - 4.5 Free surface effects

4.5 Free surface effects

 Tables and/or curves for every tank as a function of volume showing the effect on the stability of the ship of liquids in partially filled tanks.

 These tables/curves should give the free surface moments necessary to correct the initial metacentric height and those to correct the righting lever values when the ship is inclined.

  4.5.1 In the case of tanks containing liquids which may be consumed, discharged or transferred to and from other compartments whilst the ship is at sea, including anti-rolling tanks and/or heeling tanks, the maximum free surface moments which may be developed should be given.

 For the purpose of correcting the initial metacentric height, the data provided for such tanks should be a function of the maximum attainable second moment of liquid surface area about the principal axis of rotation parallel to the centreline of the ship when not inclined.

 Corresponding data for correcting the righting lever values may be computed using the method described in section 3 of appendix I to resolution A.167 (ES.IV). This method provides a means for calculating the maximum free surface moments of tanks which are approximately trapizoidal in cross-section. In the case of irregularly shaped tanks such free surface moments should be obtained independently by direct calculation.

  4.5.2 When holds or deep tanks containing liquids are maintained partially filled whilst the ship is at sea, the free surface moments used may be based upon the actual quantity of fluid contained.

 If due to the service of the ship different amounts of liquids are carried, the free surface moments for such a space may be calibrated against volume and depth of filling.

 Alternatively, the method described in 4.5.1 may be used.

  4.5.3 Where it can be shown that by using methods which do not correctly obtain the free surface moments for a particular space but which nevertheless show the ship's critical stability parameters to be more onerous than they are in practice, such methods may be used subject to agreement by the Administration.

Parent topic: 4 Category 1A
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