Section 7 Forward deep tank structure

7.1.1 The requirements given in this Section apply to the arrangement of primary structure supporting the side framing, the arrangement and scantlings of wash bulkheads and perforated flats, and the scantlings of boundary bulkheads in way of deep tanks situated forward of 0,2L from the F.P.

7.1.2 For deep tanks situated aft of this position, see Pt 4, Ch 1, 9 Bulkheads.

7.2.1 The bottom structure is to comply with the requirements given in Pt 3, Ch 5, 5.2 Single bottoms − Transverse framing 5.2.2, Pt 3, Ch 5, 5.3 Single bottoms − Longitudinal framing 5.3.1 and Pt 3, Ch 5, 5.4 Double bottoms, as applicable.

7.3.1 Above the floors, transverse framing is to be supported by one of the following arrangements:

1. Side stringers spaced not more than 5 m apart and supported by web frames. The upper ends of the web frames are to be supported under the tank top by suitable deep beams or buttresses which should generally form a ring system.

2. Side stringers spaced not more than 5 m apart and spanning from bulkhead to bulkhead. The ends of these stringers are to be connected to horizontal stringers on the transverse bulkheads to form a ring system.

3. In the case of narrow tanks, perforated flats spaced not more than 5 m apart. The area of perforations is to be not less than 10 per cent of the area of the flat, and the plating is to be suitably stiffened in way of openings.

7.3.2 Where the side framing is supported as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.1 and the depth of the tank exceeds 16 m, the web frames are to be supported by one of the following:

1. One or more side stringers spanning from bulkhead to bulkhead.

2. One or more perforated flats having deep beams or transverses in way of the web frames.

3. One or more cross ties.

7.3.3 Where the side framing is supported as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.1.(c) and the length of the tank exceeds 14 m, additional transverse strengthening in the form of transverse wash bulkheads or web frames is to be provided.

7.3.4 The scantlings of stringers and web frames as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.1 are to be determined from Pt 3, Ch 5, 4.5 Primary structure at sides.

7.3.5 The scantlings of side stringers supporting framing as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.1.(b) are to be determined from Item (5) in Table 5.4.4 Primary structure forward.

7.3.6 The scantlings of side stringers supporting web frames as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.2 are to be determined from Item (6) in Table 5.4.4 Primary structure forward.

7.3.7 The scantlings of perforated flats as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.1.(c) or Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.2.(b) are to be determined from Table 5.6.1 Fore peak structure.

7.3.8 The scantlings of cross ties are to be determined as for cross ties in the cargo tanks of oil tankers, see Pt 4, Ch 9, 9 Primary members supporting longitudinal framing . Where the span between the side shell and longitudinal bulkhead exceeds 0,3B, additional fore and aft or vertical support for the struts may be required.

7.4.1 The spacing and scantlings of side transverses supporting longitudinal framing are to be as required by Pt 3, Ch 5, 4.5 Primary structure at sides.

7.4.2 Where the depth of the tank exceeds 16 m, the side transverses are to be supported as required by Pt 3, Ch 5, 7.3 Side structure − Transverse framing 7.3.2.

7.5.1 Where the breadth of the tank at its widest point exceeds 0,5B, a centreline wash bulkhead is generally to be fitted. If the maximum breadth of tank exceeds 0,7B, it is recommended that the centreline bulkhead be made intact. In the case of an oil tanker or similar ship having longitudinal bulkheads port and starboard, these may be extended to the fore end of the deep tank in lieu of a centreline bulkhead.

7.5.2 Wash bulkheads are to have an area of perforations not less than 5 per cent nor more than 10 per cent of the area of the bulkhead. The plating is to be suitably stiffened in way of openings.

7.5.3 The scantlings of wash bulkheads are generally to be as required by Table 5.6.1 Fore peak structure, but see also Pt 3, Ch 5, 7.5 Wash bulkheads 7.5.4 to Pt 3, Ch 5, 7.5 Wash bulkheads 7.5.6. Stiffeners are to be bracketed at top and bottom.

7.5.4 The thickness of longitudinal bulkheads may be required to be increased to ensure compliance with the shear strength requirements of Pt 3, Ch 4, 6 Hull shear strength. In the case of a centreline or perforated wing bulkhead, the proportion of the total shear force absorbed by the bulkhead will be specially considered.

7.5.5 The thickness of plating of wash bulkheads may also be required to be increased to take account of shear buckling.

7.5.6 Where longitudinal wash bulkheads support bottom transverses, the lower section of the bulkhead is to be kept free of non-essential openings for a depth equal to 1,75 times the depth of the transverses, and the plating thickness may be required to be increased to meet local buckling requirements.

7.6.1 The transverse bulkheads forming the forward and after boundaries of the tank are generally to comply with the requirements of Pt 4, Ch 1, 9 Bulkheads, except that when the after bulkhead forms the boundary of a cargo tank or cofferdam in an oil tanker or ore carrier, the minimum thickness requirements of Pt 4, Ch 9, 10 Construction details and minimum thickness are also to be complied with.