Section 6 Single bottom structure

6.1.1 Requirements are given in this Section for a transversely framed or a longitudinally framed single bottom.

6.1.2 The bottom structure of ships of a length, L, less than 25 m is to comply with the requirements of Pt 3, Ch 5 Fore End and Aft End Structure so far as applicable.

6.1.3 The scantlings of structural members of the single bottom of ships having a length of 25 m and over, are to comply with the requirements of Table 9.6.1 Transversely and longitudinally framed single bottom.

Table 9.6.1 Transversely and longitudinally framed single bottom

Item	Parameter	Requirements
Longitudinal and transverse framing system
Centreline girder	Web depth	The lesser of:
		dw = 40B mm
		dw = 50lf mm
Centreline girder and	Web and face plate thickness	t = (0,01dw + 2) mm
side girders	Width of face plate	w = 140s mm
Transverse framing system
Floors	Web depth at centreline	The lesser of
		df = 40B mm
		df = 50lf mm
	Web thickness	t = (0,01dw + 2) mm
	Face plate thickness	t = ≥ tweb mm
	Face plate width	The greater of:
		w = 30lf mm
		w = 60 mm
	Minimum required modulus	Z = 6,6kB2D1 s cm3
Longitudinal framing system
Bottom transverses	Web thickness	t = (0,01dw + 3) mm
	Face plate width	The greater of:
		w = 30lf mm
		w = 60 mm
	Modulus	Z = 6,6kB2D1 S cm3
Bottom longitudinals	Modulus	Z = (3,95 + 0,04L1) D1 ksle2 cm3
	Inertia	I = le Z cm4
Symbols applying to Table 9.6.1 Transversely and longitudinally framed single bottom and Table 9.7.1 Transversely and longitudinally framed double bottom
L, B, D, T, s, S, t, I, k, Z and le are as defined in Pt 4, Ch 9, 1.14 Symbols and definitions 1.14.1 df = depth of floor or bottom transverse at centreline, in mm dw = depth of girder, in mm lb = the width of the double bottom, in metres, and is normally the breadth of the ship. If longitudinal bulkheads or equivalent supports are provided, an equivalent breadth may be used, but this is to be taken not less than 0,8B lf = span of floor or transverses which is normally the breadth of the ship measured on top of the floor under consideration, in metres. If longitudinal bulkheads or equivalent floor supports are provided, an equivalent breadth may be used, but this should be taken as not less than 0,4B t1 = thickness of inner bottom plating or bottom plating whichever is the lesser, in mm w = width of face plate or member, in mm D1 = D, but need not be taken greater than T + 0,4 m or Zone 3, T + 0,7 m for Zone 2, T + 1,0 m for Zone 1 L1 = L but is to be taken as not less than 65 m

6.1.4 The bottom structure of ships of a length, L, longer than 110 m is to have the double bottom structure according to Pt 4, Ch 9, 7.1 General 7.1.7.

6.2.1 A centreline girder is required in ships with a breadth, B, of more than 6 m.

6.2.2 A side girder is to be fitted on each side of the centreline in ships with a transversely framed bottom and a breadth, B, or more than 12 m.

6.2.3 Where no centreline girder is fitted, adequate support on the centreline must be provided for docking purposes.

6.3.1 Plate floors are to be fitted at every frame.

6.3.2 Transverses are generally to be fitted at a spacing of not more than 3,5 m. However special consideration will be given to proposals for a greater spacing.

6.3.3 In ships having considerable rise of floor the tops of the floors and the transverses are to be made approximately parallel to the rise of floor.

6.3.4 Floors may be cut at the centreline, with the centreline girder web plate continuous, provided the transverse strength of the floor is maintained.

6.3.5 Floors are to be provided with drain holes, sufficient in number and size.

6.3.6 The depth of the transverses is generally to be not less than twice the depth of the slot for the longitudinals.

6.3.7 Longitudinals are generally to be carried through watertight floors and transverse bulkheads. If they stop at the watertight floors and transverse bulkheads, brackets are to be fitted inter-connecting the longitudinals, see Pt 3, Ch 10, 3.3 Basis for calculation of bracket connections 3.3.1.(c).

6.3.8 Scallops in longitudinals may not be fitted in way of end connections, crossings with transverses or tripping brackets.