Section 6 Double bottom construction

6.1.1 The double bottom depth and scantlings are to be as required by Pt 4, Ch 7, 8 Double bottom structure for the double bottom structure of a bulk carrier to which the notation `strengthened for heavy cargoes' is to be assigned. However, where Pt 4, Ch 11, 3.1 General 3.1.2 is not applicable, the requirements of Pt 4, Ch 7, 8.8 Allowable hold loading in the flooded condition need not be applied. The required depth of double bottom and scantlings of double bottom structure are to be verified by direct calculation. The calculation is to be submitted.

6.1.2 Where the proposed depth of double bottom exceeds 1,5 times the Rule minimum depth given in Pt 4, Ch 1, 8 Double bottom structure, the scantlings of the floors and girders may be required to be increased to ensure adequate resistance to buckling.

6.1.3 The thickness of inner bottom plating in the cargo hold is to be not less than required by Pt 4, Ch 7, 8 Double bottom structure for ships having the notation `strengthened for heavy cargoes'.

6.1.4 For all vessels intended to be unloaded by grabs, the thickness of inner bottom plating is to meet the requirements of Pt 3, Ch 9, 8.2 Inner bottom plating 8.2.1 for a maximum design grab weight specified and recorded in the Loading Manual. For vessels of deadweight >200 000 tonnes, the design grab weight is not to be less than 25 tonnes.

6.1.5 Where the requirements of Pt 4, Ch 11, 6.1 General 6.1.4 are met the descriptive note ‘holds suitable for unloading by grabs’ may be employed. Where the design grab weight is 25 tonnes or more the notation ‘strengthened for regular discharge by heavy grabs’ may be assigned.

6.2.1 In way of the cargo hold a centreline girder is to be fitted and side girders spaced not more than 3,8 m apart are generally to be arranged in way of transverse bulkheads. The side girders are to extend at least to the first plate floor adjacent to the bulkhead each side. The outboard side girder is to be continuous, forming the lower part of the longitudinal bulkhead.

6.2.2 Plate floors are to be fitted in line with each transverse in the wing tanks and in way of transverse bulkhead stools. Additional floors are to be so arranged that the spacing of floors does not exceed 2,5 m or 0,01L, whichever is the greater.

6.2.3 Attention is to be given to structural continuity and alignment between double bottom structure and transverses in wing tanks, see also Pt 4, Ch 11, 9.7 Scarfing of double bottom.

6.2.4 Alternative arrangements will be considered on the basis of the results of direct calculations.