Section 5 Single and double bottom structure

5.1.1 For dry cargo ships exceeding 120 m in length and for all ships which have the notation `strengthened for heavy cargoes', longitudinal framing is, in general, to be adopted (see also Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers and Pt 4, Ch 10 Single Hull Oil Tankers).

5.1.2 For ships requiring additional strengthening of bottom forward the requirements given in 1.5 are also to be complied with, as applicable.

5.1.3 For ships having the notation `strengthened for heavy cargoes' the requirements of Pt 4, Ch 7, 8 Double bottom structure are also to be complied with, as applicable.

5.1.4 For ships intended to load or unload while aground, see Pt 3, Ch 9, 7 Bottom strengthening for loading and unloading aground.

5.1.5 Provision is to be made for the free passage of water and/or air from all parts of single or double bottoms to bilge or tank suctions, account being taken of the pumping rates required.

5.1.6 For passenger ships, see Pt 4, Ch 2, 6 Double bottom.

5.2.1 In fore peak spaces, for ships of full form the floors are to be supported by a centreline girder or a centreline wash bulkhead. In other cases the centreline girder is to be carried as far forward as practicable. The arrangement and scantlings of the floors and centreline girder are to be sufficient to give adequate stiffness to the structure, but are to be not less than required by Table 5.5.1 Single bottom construction forward. The floor panels and the upper edges of the floors and centreline girder are to be suitably stiffened.

Table 5.5.1 Single bottom construction forward

Item	Parameter	Requirement
Transverse framing system
(1) Centre girder:		The greater of the following:
(a) In fore peak tank, or deep tank, forward of 0,2L from the F.P.	Modulus	Z = 8,5 k S h 5le 2 cm3, or Z = 9,75 ρ k S h 4le 2 cm3
	Inertia	cm4
	Web thickness	t = t w as in Pt 3, Ch 10, 4.4 Geometric properties and proportions
(b) In dry spaces	Web thickness	Forward of 0,075L from the F.P., mm or 6 mm, whichever is the greater. Between 0,075L and 0,3L from the F.P. the thickness may taper from the midship thickness to the end thickness above
	Web depth and face area	As in Pt 4, Ch 1, 7 Single bottom structure
(2) Floors:
(a) In fore peak tank, or deep tank, forward of 0,2L from the F.P.	Maximum spacing	Every frame df = (83D + 150) mm or 1400 mm, whichever is the lesser
	Web depth (at centreline)
	Web thickness	t = mm
	Minimum face plate area in deep tank	Af = 0,85kB cm2
(b) In dry cargo spaces	Maximum spacing	Every frame
	Scantlings	As in Pt 4, Ch 1, 7.2 Girders and floors
(3) Intercostal side girders:
(a) In deep tank, forward of 0,2L from the F.P.	Maximum spacing	0,003s F m
	Web depth	As floors
	Web thickness	t = t w as in Pt 3, Ch 10, 4.4 Geometric properties and proportions
	Minimum face plate area	Suitable stiffener
(b) In dry cargo spaces	Maximum spacing	0,003s F m
	Scantlings	As in Pt 4, Ch 1, 7 Single bottom structure
Longitudinal framing system
(4) Centre girder:
(a) In deep tanks forward of 0,2L from the F.P.	Scantlings	As in Pt 4, Ch 9, 9 Primary members supporting longitudinal framing
(b) In dry spaces	Scantlings	To be specially considered
(5) Bottom transverses:
(a) In deep tanks forward of 0,2L from the F.P., see Note 4	Maximum spacing	3,0 m for L ≤ 100 m 4,2 m for L ≥ 300 m Spacing at intermediate lengths by interpolation
	Scantlings	As in Pt 4, Ch 9, 9 Primary members supporting longitudinal framing
(b) In dry spaces	Scantlings	To be specially considered
(6) Intercostal side girders	Scantlings	To be specially considered
Symbols
L, B, D, S, le, k, ρ as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1
h 4 = tank head, in metres, as defined in Pt 3, Ch 3, 5 Design loading
h 5 = distance, in metres, from mid-point of span to the following positions: forward of 0,15L from the F.P., 3 m above the deck height obtained from Pt 3, Ch 1, 6.1 Principal particulars 6.1.11 at 0.2L from the F.P. the upper deck at side between 0,15L and 0,2L from the F.P., by interpolation between (a) and (b)
s F = transverse frame spacing, in mm
s 2 = spacing of stiffener, in mm, but to be taken not less than 800 mm
L 2 = L but need not be taken greater than 215 m
Note 1. For single bottom construction in way of the cargo tanks of oil tankers, see Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers and Pt 4, Ch 10 Single Hull Oil Tankers Note 2. For minimum thickness of structure within cargo tanks and fore peak tanks in oil tankers, see Pt 4, Ch 9, 10.2 Compartment minimum thickness and Pt 4, Ch 10, 7.2 Compartment minimum thickness. Note 3. For single bottom construction in dredgers, see Pt 4, Ch 12, 6 Bottom structure. Note 4. For ships having one or more longitudinal bulkheads the maximum spacing may be increased but is not to exceed that for the midship region.

5.2.2 In deep tanks forward of 0,2L from the F.P. floors are to be supported by a primary centreline girder or centreline bulkhead together with intercostal side girders. In the case of an oil tanker (see Pt 3, Ch 5, 1.1 Application 1.1.4) 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. The arrangement and scantlings of centreline girder, floors and side girders are to be determined from Table 5.5.1 Single bottom construction forward, but in way of web frames the depth of the floor and size of the face bar are to be not less than those of the web frame. In general, floors are not to be flanged.

5.2.3 In way of dry cargo spaces forward, the arrangement and scantlings of transversely framed single bottoms areto be generally as required in the midship region as given in Pt 4, Ch 1, 7 Single bottom structure, except as required by Table 5.5.1 Single bottom construction forward. The girders forward are to scarf into the normal girder arrangement in the midship region. In ships having considerable rise of floor towards the fore end, the depth of the floors may be required to be increased or the top edge sloped upwards towards the outboard end. In general, floors are not to be flanged.

5.3.1 In deep tanks forward of 0,2L from the F.P., bottom transverses are to be supported by a primary centreline girder or a centreline bulkhead. In addition, an intercostal side girder is generally to be fitted port and starboard. In the case of an oil tanker (see Pt 3, Ch 5, 1.1 Application 1.1.4) 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 primary centreline support and intercostal girders. The spacing of bottom transverses and scantlings of the centreline girder, bottom transverses and side girders are to be as required by Table 5.5.1 Single bottom construction forward.

5.3.2 The requirements for longitudinally framed single bottoms in way of dry cargo spaces will be specially considered.

5.4.1 The minimum depth of centre girder forward is generally to be the same as that required in the midship region by Pt 4 Ship Structures (Ship Types) for the particular type of ship concerned, but in ships with considerable rise of floor, a greater depth may be required at the fore end to provide adequate access throughout the double bottom tank.

5.4.2 Where the height of the double bottom varies, this variation is generally to be made gradual by sloping the inner bottom over an adequate longitudinal extent. Knuckles in the plating are to be arranged close to plate floors. Otherwise, suitable scarfing arrangements are to be made.

5.4.3 The arrangement and scantlings of girders, floors and inner bottom plating and the section modulus of inner bottom stiffening are to be determined from Table 5.5.2 Double bottom construction forward. In other respects the structural arrangements are to be as detailed in Pt 4 Ship Structures (Ship Types) for the particular type of ship concerned.

5.4.4 For double bottom construction in way of the cargo tanks of oil tankers or ore carriers, see also Pt 4, Ch 9 Double Hull Oil Tankers, Pt 4, Ch 10 Single Hull Oil Tankers or Pt 4, Ch 11 Ore Carriers, as appropriate.

Table 5.5.2 Double bottom construction forward

Item and parameter	Requirements
	Transverse framing	Longitudinal framing
(1) Centre girder:
(a) Thickness forward of 0,075L from the F.P.
(b) Thickness between 0,075L and 0,3L from the F.P.	As determined by a taper line from the midship thickness given in Pt 4, Ch 1, 8 Double bottom structure to the end thickness as for (1) (a)
(2) Plate floors:
(a) Maximum spacing forward of 0,2L from the F.P.	0,002s F m	2,5 m
(b) Maximum spacing aft of 0,2L from the F.P.	As for midship region	As for midship region (see Note 5)
(c) Scantlings	As in Pt 4, Ch 1, 8 Double bottom structure	As in Pt 4, Ch 1, 8 Double bottom structure
(3) Watertight floors and bracket floors	As in Pt 4, Ch 1, 8 Double bottom structure	As in Pt 4, Ch 1, 8 Double bottom structure
(4) Side girders, see Note 1:
(a) Maximum spacing forward of 0,2L from the F.P.	0,003s F m	0,004s L or 3,7 m whichever is the lesser
(b) Maximum spacing aft of 0,2L from the F.P.	As for midship region	As for midship region, see Note 5
(c) Scantlings	As in Pt 4, Ch 1, 8 Double bottom structure	As in Pt 4, Ch 1, 8 Double bottom structure
(5) Inner bottom plating, see Note 2:
(a) Thickness at or forward of 0,075L from the F.P.	t = (0,00127(s + 660)) mm or 6,5 mm, whichever is the greater, see Notes 3, 4 and 5
(b) Thickness between 0,075L and 0,3L from the F.P.	As determined by a taper line from the midship thickness given in Pt 4, Ch 1, 8 Double bottom structure to the end thickness as for (5) (a), but not less than 6,5 mm, see Notes 3, 4 and 5
(c) In way of deep tanks or holds used for the carriage of water ballast or where the double bottom tank is common with a wing ballast tank.	t = (0,004 s f + 2,5) mm or 6,5 mm, whichever is the greater
(6) nner bottom longitudinals	As in Pt 4, Ch 1, 8 Double bottom structure, see Notes 2 and 5
Symbols
L, T, S, s, k, ρ = as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1 d DB = minimum depth of centre girder as required by Pt 4, Ch 1, 8 Double bottom structure f = but to be taken not greater than 1,0 h 4 = tank head, in metres, as defined in Pt 3, Ch 3, 5 Design loading s F = transverse frame spacing, in mm s L = spacing of bottom longitudinals, in mm
Note 1. The girders forward of 0,2L are to be suitably scarfed into the midship girder arrangement. Note 2. For double bottom construction in way of the cargo tanks of oil tankers or ore carriers, see also Pt 4, Ch 9 Double Hull Oil Tankers, Pt 4, Ch 10 Single Hull Oil Tankers or Pt 4, Ch 11 Ore Carriers, as appropriate. Note 3. In way of hatches the tank top taper thickness is to be increased by 2 mm if no ceiling is fitted, but is to be taken not less than 7,5 mm. Note 4. Where cargo is to be regularly discharged by grabs the tank top taper thickness is to be increased by 5,0 mm if no ceiling is fitted, or by 3,0 mm where ceiling is fitted. Note 5. For ships having the notation `strengthened for heavy cargoes', the requirements of Pt 4, Ch 7, 8 Double bottom structure are also to be complied with.