Section 6 After peak structure
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 3 Ship Structures (General) - Chapter 6 Aft End Structure - Section 6 After peak structure

Section 6 After peak structure

Parent topic: Chapter 6 Aft End Structure

6.1 Bottom structure

6.1.1 Floors are to be arranged at every frame space and are to be carried to a suitable height, and at least to above the sterntube, where fitted. They are to have a thickness as determined from Table 6.6.1 After peak structure and are to be adequately stiffened. In way of a propeller post, rudder post or rudder horn, the floors are generally to be carried to the top of the space and are to be increased in thickness. The extent and amount of the increase will be specially considered, account being taken of the arrangements proposed.

6.2 Side structure − Transverse framing

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

  1. Side stringers spaced not more than 2,5 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 to form a ring structure.

  2. Perforated flats spaced not more than 2,5 m apart. The area of perforations in each flat is to be not less than 10 per cent of the total area of the flat.

  3. A combination of the above arrangements.

6.2.2 The scantlings of side stringers supported by web frames, and also of the web frames are to be determined from Pt 3, Ch 6, 4.5 Primary structure at sides.

6.2.3 The scantlings of perforated flats are to be determined from Table 6.6.1 After peak structure. Stiffeners are to be fitted at every frame.

6.3 Side structure − Longitudinal framing

6.3.1 The spacing and scantlings of side transverses supporting longitudinal framing are to be as required by Pt 3, Ch 6, 4.5 Primary structure at sides.

6.3.2 Suitable transverses or deep beams are to be arranged at the top of the tank to provide end rigidity to the side transverses.

Table 6.6.1 After peak structure

Item Parameter Requirement
(1) Floors Thickness t = (7,5 + 0,025L 2) mm
(2) Perforated flats and wash bulkheads Thickness see Note t = (7,5 + 0,015L) mm
Stiffener modulus z = cm3
Symbols
b = 1,4 for rolled or built sections
= 1,6 for flat bars
h 6 = vertical distance from middle of effective length of stiffener to top of tank, in metres
s 2 = spacing of stiffeners, in mm, but is to be taken not less than 800 mm
L 2 = L but need not be taken greater than 215 m

Note The thickness for perforated flats and wash bulkheads may be reduced by 1 mm for ships of 40 m and under with no reduction for ships of 90 m and above. Reduction for intermediate lengths to be by linear interpolation.

6.4 Wash bulkheads

6.4.1 A centreline wash bulkhead is to be arranged in the upper part of the after peak space and counter or cruiser stern. Where the overhang is very large, or the breadth of the space at the widest point exceeds 20 m, additional wash bulkheads may be required port and starboard.

6.4.2 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, and the arrangement of openings is to be such as to maintain adequate shear rigidity.

6.4.3 The scantlings of wash bulkheads are to be determined from Table 6.6.1 After peak structure, and stiffeners are to be fitted at every frame and bracketed top and bottom. The plating thickness may be required to be increased locally in way of the upper part of the sternframe or the rudder horn.

6.5 After peak bulkhead

6.5.1 The position and height of the after peak bulkhead are to be in accordance with the requirements of Pt 3, Ch 3, 4 Bulkhead requirements.

6.5.2 The scantlings of the after peak bulkhead and of the flat forming the top of the peak space are to be determined from Pt 4, Ch 1, 9 Bulkheads, but the plating thickness is to be increased locally in way of the sterntube gland.

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