Section 7 Double bottom structure
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Inland Waterways Ships, July 2022 - Part 4 Ship Structures (Ship Types) - Chapter 9 Passenger Ships - Section 7 Double bottom structure

Section 7 Double bottom structure

Parent topic: Chapter 9 Passenger Ships

7.1 General

7.1.1 Requirements are given in this Section for a transversely framed or a longitudinally framed double bottom.

7.1.2 The scantlings of structural members of the double bottom, transversely or longitudinally framed, are to comply with the requirements of Table 9.7.1 Transversely and longitudinally framed double bottom.

Table 9.7.1 Transversely and longitudinally framed double bottom

Item Parameter Requirements
Longitudinal and transverse framing systems
Double bottom height at centreline Minimum depth The greater of:
    d f= 40B mm
   
Centreline and side girders Web thickness t = (0,01d f + 2) mm
Inner bottom plating Thickness for dry spaces t = 10s mm
Thickness for tanks The greater of:
t = 12s mm
t = 5,5 mm
Transverse framing system
Plate floors and brackets of bracket floors Web thickness The greater of:
    t = (0,008df + 1,5) mm
    t = 5,5 mm
Bracket floors:    
bottom frames Modulus Z = 6,6ks-D1le 22 cm3
reverse frames Modulus Z = 5,6ksD1le2
Longitudinal framing system
Plate floors Web thickness t = (0,009d f + 1,5) mm
Double bottom longitudinals Modulus Z = 6ks D1-le 2 cm3
For Symbols see Table 9.6.1 Transversely and longitudinally framed single bottom

7.1.3 The depth of the double bottom is to comply with the requirements of Table 9.7.1 Transversely and longitudinally framed double bottom, but it is recommended that the double bottom be accessible for inspection and surveys.

7.1.4 Provision is to be made for free passage of air and water from all parts of the double bottom compartments to the air pipes and suctions, account being taken of the pumping rates required. Where access openings are cut in the floors and girders, the height of openings should not, in general, exceed 50 per cent of the double bottom depth. Openings in way of ends of floors and girders are to be avoided.

7.1.5 Where the double bottom is not continuous over the full breadth of the ship (for example at the centreline to form a pipe recess), the transverse strength of the bottom structure is to be maintained and is to comply with the minimum requirements of this Section.

7.1.6 Where a margin plate is proposed to form a bilge, the thickness of the margin plate is to be 1 mm more than required for the inner bottom plating.

7.1.7 Passenger ships of a length, L, longer than 110 m are to:

  1. have a double bottom with a height of at least 600 mm and subdivision to ensure that, in the event of flooding of any two adjacent watertight compartments, the vessel does not immerse lower than the margin line and a residual safety clearance of 100 mm remains, or have a double bottom with a height of at least 600 mm and a double hull with a distance of at least 800 mm between the side wall of the vessel and the longitudinal bulkhead;

  2. be fitted with a multi-propeller propulsion system with at least two independent engines of equal power and a bow thruster system which can be operated from the wheelhouse and which operates longitudinally as well as transversely.

7.1.8 A double bottom is required according to Pt 4, Ch 9, 7.1 General 7.1.7. The double bottom is to be fitted extending from the collision bulkhead to the after peak bulkhead, as far as this is practicable and compatible with the design and proper working of the ship.

7.2 Girders

7.2.1 A centreline girder is required in ships with a breadth, B, of more than 6 m. A side girder is generally to be fitted on each side of the centreline in ships with a transversely framed bottom and a breadth, B, of more than 12 m. Proposals to omit the centreline girder and/or side girders will be specially considered, but adequate support must be provided on the centreline for docking purposes.

7.3 Floors

7.3.1 In transversely framed double bottoms, plate floors are to be fitted at every frame. Alternatively, bracket floors may be fitted (see Pt 3, Ch 5, 3.5 Double bottoms), provided plate floors are fitted, spaced not more than 2,5 m apart.

7.3.2 In longitudinally framed double bottoms, floors are to be fitted at a spacing not exceeding 3,5 m. Vertical stiffeners having a depth not less than 50 mm are to be fitted to the floors at every fourth longitudinal. In between the floors, brackets are to be fitted in the double bottom in line with the transverse side frames, connected to the tank top and shell plating and extending to the nearest bottom and inner bottom longitudinal. Midway between floors, brackets are to be fitted on either side of the centreline extending to the nearest bottom and inner bottom longitudinals. Free edges of the brackets are to be suitably stiffened.

7.3.3 Plate floors are also to be arranged under bulkheads and in line with web frames fitted in the side structure.

7.4 Inner bottom plating

7.4.1 The thickness of the inner bottom plating is to comply with the requirements of Table 9.7.1 Transversely and longitudinally framed double bottom.

7.5 Bottom and inner bottom longitudinals

7.5.1 The scantlings of bottom and inner bottom longitudinals are to comply with the requirements of Table 9.6.1 Transversely and longitudinally framed single bottom and Table 9.7.1 Transversely and longitudinally framed double bottom and are based on end connections in accordance with Pt 3, Ch 10, 3 Secondary member end connections.

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