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Clasification Society Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, January 2016 - Part 10 SHIP UNITS - Chapter 3 Scantling Requirements - Section 5 Aft end

Section 5 Aft end

Parent topic: Chapter 3 Scantling Requirements

5.1 Symbols

5.1.1 The symbols used in this Chapter are defined as follows:
L = Rule length, in metres
L2 = Rule length, L, but need not be taken greater than 300 m
s = stiffener spacing, in mm.

5.2 General

5.2.1  Application.
  1. The requirements of this Section apply to structure located between the aft peak bulkhead and the aft end of the ship unit.
  2. The requirements of this Section do not apply to the following:
    1. rudder horns;
    2. structures which are not integral with the hull, such as rudders, steering nozzles and propellers;
    3. other appendages permanently attached to the hull. Where such items are fitted, the relevant requirements of the Rules for Ships are to be complied with.
  3. The deck plating thickness and supporting structure are to be suitably reinforced for the steering gear, mooring windlasses, and other deck machinery.
5.2.2  Structural continuity.
  1. Scantlings of the shell envelope, upper deck and inner bottom are to be tapered towards the aft end. See also Pt 10, Ch 3, 1.6 Tapering and structural continuity of longitudinal hull girder elements.
  2. Longitudinal framing of the strength deck is to be carried aft to the stern.
  3. All shell frames and tank boundary stiffeners are, in general, to be continuous or bracketed at their ends.
5.2.3  Minimum thickness.
  1. In addition to the scantling requirements as given in Pt 10, Ch 3, 5.3 Bottom structure to Pt 10, Ch 3, 5.8 Miscellaneous structures, the plating and stiffeners are to comply with the minimum thickness requirements for the cargo region, except as given in Pt 10, Ch 3, 5.2 General 5.2.3.

    Table 3.5.1 Minimum net thickness of structure aft of the aft peak bulkhead

    Scantling location Net thickness (mm)
    Pillar bulkhead plating 7,5
    Bottom girders and aft peak floors 5,5 + 0,02L2
    Web plating of primary support members 6,5 + 0,015L2

5.3 Bottom structure

5.3.1  General.
  1. Floors are to be fitted at each frame space in the aft peak and carried to a height at least above the stern tube, where fitted. Where floors do not extend to flats or decks, they are to be stiffened by flanges at their upper end.
  2. The centreline bottom girder is to extend as far aft as is practicable and be suitably scarphed into the stern frame or transom.
  3. For self-propelled units with conventional propulsion and steering arrangements, the relevant Sections of the Rules for Ships are to be complied with.

5.4 Shell structure

5.4.1  Shell plating.
  1. The net thickness of the side shell and transom plating, tnet , is to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2.
  2. The net plating thickness of shell, t net, attached to the stern frame is to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 and is not to be less than:

    tnet = 0,094 (L2 – 43) + 0,009s mm.

  3. In way of the boss and heel plate, the shell net plating thickness, tnet , is not to be less than:

    tnet = 0,105 (L2 – 47) + 0,011s mm.

  4. Within the extents specified in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4, the thickness of the side shell plating is to comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4.
5.4.2  Shell local support members.
  1. The section modulus and thickness of the hull envelope framing are to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 and Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2.
5.4.3  Shell primary support members.
  1. The requirements of Pt 10, Ch 3, 5.4 Shell structure 5.4.3 apply to single side skin construction supported by a system of vertical webs and/or horizontal stringers or flats.
  2. Where a longitudinal framing system is adopted, longitudinals are to be supported by vertical primary support members extending from the floors to the upper deck. Deck transverses are to be fitted in line with the web frames.
  3. Where a transverse framing system is adopted, frames are to be supported by horizontal primary support members spanning between the vertical primary support members.
  4. The scantlings of web frames supporting longitudinal framing, stringers and transverse framing are to be determined from Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3.
  5. The web depth of primary support members is not to be less than 14 per cent of the bending span and is to be at least 2,5 times as deep as the slots for stiffeners if the slots are not closed.

5.5 Deck structure

5.5.1  Deck plating.
  1. The thickness of the deck plating is to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2.
5.5.2  Deck stiffeners.
  1. The section modulus and thickness of deck stiffeners are to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 and Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2.
5.5.3  Deck primary support members.
  1. The section modulus and shear area of primary support members are to comply with the requirements in Pt 10, Ch 3, 3.11 Scantling requirements 3.11.3.
  2. The web depth of primary support members is not to be less than 10 per cent and 7 per cent of the unsupported span in bending in tanks and in dry spaces, respectively, and is not to be less than 2,5 times the depth of the slots if the slots are not closed. In the case of a grillage structure, the unsupported span is the distance between connections to other primary support members.
  3. In way of concentrated loads from heavy equipment, the scantlings of the deck structure are to be determined based on the actual loading.
5.5.4  Pillars.
  1. Pillars are to comply with the requirements of Pt 10, Ch 3, 3.5 Deck structure 3.5.4.

5.6 Tank bulkheads

5.6.1  General.
  1. Tanks are to comply with the requirements of Pt 10, Ch 3, 3.6 Tank bulkheads.

5.7 Watertight boundaries

5.7.1  General.
  1. Watertight boundaries are to comply with the requirements of Pt 10, Ch 3, 3.7 Watertight boundaries.
5.7.2  Aft peak bulkhead.
  1. The scantlings of structural components of the aft peak bulkhead are to comply with the requirements in Pt 10, Ch 3, 3.6 Tank bulkheads and Pt 10, Ch 3, 3.7 Watertight boundaries 3.7.2, as applicable.

5.8 Miscellaneous structures

5.8.1  Pillar bulkheads.
  1. Bulkheads that support girders, or pillars and longitudinal bulkheads which are fitted in lieu of girders, are to be stiffened to provide supports no less effective than those required for stanchions or pillars. The acting load and the required net cross-sectional area of the pillar section are to be determined using the requirements of Pt 10, Ch 3, 5.5 Deck structure 5.5.4. The net moment of inertia of the stiffener is to be calculated with a width of 40tnet of the plating, where tnet is net plating thickness, in mm.
  2. Pillar bulkheads are to meet the following requirements:
    1. the distance between bulkhead stiffeners is not to exceed 1500 mm;
    2. where corrugated, the depth of the corrugation is not to be less than 100 mm.
5.8.2  Rudder trunk.
  1. Where a rudder trunk is fitted, the scantlings are to be in accordance with the shell plating and framing in Pt 10, Ch 3, 5.4 Shell structure 5.4.1 and Pt 10, Ch 3, 5.4 Shell structure 5.4.2. Where the rudder trunk is open to the sea, a seal or stuffing box is to be fitted above the deepest load waterline to prevent water from entering the steering gear compartment.
5.8.3  Stern thruster tunnels.
  1. The net thickness of the tunnel plating, ttun-net , is not to be less than required for shell plating in the vicinity of the thruster. In addition ttun-net is not to be taken less than:

    ttun-net = 0,008dtun + 1,8 m

    where

    dtun = inside diameter of tunnel, in mm, but not to be taken less than 970 mm.
  2. Where the outboard ends of the tunnel are provided with bars or grids, the bars or grids are to be effectively secured.
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