1 General assumptions

  1.1 For the purpose of calculating the adverse heeling moment due to a shift of cargo surface in ships carrying bulk grain it shall be assumed that:

• .1 In filled compartments which have been trimmed in accordance with A 10.2, a void exists under all boundary surfaces having an inclination to the horizontal less than 30° and that the void is parallel to the boundary surface having an average depth calculated according to the formula:

  
  Where:

  Vd	=	average void depth in millimetres
  Vd 1	=	standard void depth from table B 1-1 below
  d	=	actual girder depth in millimetres.

• In no case shall Vd be assumed to be less than 100 mm.

• .2 Within filled hatchways and in addition to any open void within the hatch cover there is a void of average depth 150 mm measured down to the grain surface from the lowest part of the hatch cover or the top of the hatch side coaming, whichever is the lower.

• .3 In a filled compartment, untrimmed, which is exempted from trimming outside the periphery of the hatchway by the provisions of A 10.3.1, it shall be assumed that the surface of the grain after loading will slope into the void space underdeck, in all directions, at an angle of 30° to the horizontal from the edge of the opening which establishes the void.

• .4 In a filled compartment, untrimmed, which is exempted from trimming in the ends of the compartment under the provisions of A 10.3.2, it shall be assumed that the surface of the grain after loading will slope in all directions away from the filling area at an angle of 30° from the lower edge of the hatch end beam. However, if feeding holes are provided in the hatch end beams in accordance with table B 1-2, then the surface of the grain after loading shall be assumed to slope in all directions, at an angle of 30° from a line on the hatch end beam which is the mean of the peaks and valleys of the actual grain surface as shown in figure B 1.

  1.2 The description of the pattern of grain surface behaviour to be assumed in partly filled compartments is contained in B 5.

  1.3 For the purpose of demonstrating compliance with the stability criteria in A 7, the ship's stability calculations shall normally be based upon the assumption that the centre of gravity of cargo in a filled compartment, trimmed, is at the volumetric centre of the whole cargo space. In those cases where the Administration authorizes account to be taken of the effect of assumed underdeck voids on the vertical position of the centre of gravity of the cargo in filled compartments, trimmed, it will be necessary to compensate for the adverse effect of the vertical shift of grain surfaces by increasing the assumed heeling moment due to the transverse shift of grain as follows:

In all cases the weight of cargo in a filled compartment, trimmed, shall be the volume of the whole cargo space divided by the stowage factor.

  1.4 The centre of gravity of cargo in a filled compartment, untrimmed, shall be taken to be the volumetric centre of the whole cargo compartment with no account being allowed for voids. In all cases the weight of cargo shall be the volume of the cargo (resulting from the assumptions stated in B 1.1.3 or B 1.1.4) divided by the stowage factor.

  1.5 In partly filled compartments the adverse effect of the vertical shift of grain surfaces shall be taken into account as follows:

  1.6 Any other equally effective method may be adopted to make the compensation required in B 1.3 and B 1.5.

Figure B 1