Section 6 Single bottom structure

6.1.1 Requirements are given in this Section for transversely framed single bottoms. The scantlings of girders and floors are to be not less than required in Table 1.6.1 Transversely framed singled bottom.

Table 1.6.1 Transversely framed singled bottom

Item	Parameter	Requirements
(1) Centreline girder	Web and face plate	t = (0,008d w + 3) mm,
	thickness	see Note
	Width of face plate	b f = 140s mm
(2) Side keelson bars	Cross-sectional area	A k = 8 + 0,6B cm2
(3) Floors	Web depth at centreline	d w= 40B mm
	Web thickness	t w = (0,008d w + 3) mm, see Note
	Face plate thickness	t≤ tw
	Ratio of unsupported face plate width and face plate thickness	max 15
	Minimum required modulus	Z = 6kT s B 2 cm3
	Inertia	cm4
Symbols
Z, B, T, s, k and t are as defined in Pt 4, Ch 1, 1.5 Symbols and definitions 1.5.1 b f = width of face plate of floor or girder, in mml d w = web depth of floor or girder, in mm t w = thickness of floor web plate, in mm A K = cross-sectional area of keelson bar, in cm2
Note In ships regularly discharged by grabs the thickness of floors and girders is to be not less than 8 mm.

6.1.2 It is recommended that the bottom of ships intended regularly to rest aground be additionally strengthened in order to withstand the increased loads to which they may be subjected. Scallops or openings (unless reinforced) are not permitted.

6.1.3 In general, single bottom structures are only to be used in general dry cargo ships designed for a stowage rate greater than 1,39 m³/tonne, corresponding to a specific weight of cargo less than 0,72 tonne/m³. For stowage rates less than 1,39 m³/tonne, the scantlings will be specially considered.

6.2.1 A centreline girder is to be fitted and is to have the same depth as the floors at centreline. If the breadth of the ship exceeds 7 m, side keelson bars are to be fitted on top of floors spaced not more than 3 m apart. The keelson bars are to be channel bars or other bars with sufficient rigidity.

6.3.1 Plate floors are to be fitted at every frame. The top of floors may be level from side to side, but in ships having considerable rise of floor, the depth of the floor plates is to be suitably increased. The floors may be cut at the centreline, with the centre girder web plate continuous, provided the transverse strength of the floors is maintained. The upper edge of the floors is to be suitably stiffened. Floors which are subjected to concentrated loads will be specially considered.

6.3.2 Floors are to be provided with drain holes, sufficient in number and size, to allow water to flow to the pump suctions.

6.4.1 Close ceiling is to be laid on floors and/or girders of single bottom arrangements, on inner bottom plating of double bottoms and over bilges if fitted, and is to be readily removable. The spaces between the frames at the top of bilge ceiling are to be closed by steel plates or other suitable means such as wooden chocks, cement, etc. Inner bottom manhole covers or fittings, if projecting above the inner bottom plating, are to be properly protected.

6.4.2 The thickness of ceiling is given in Table 1.6.2 Ceilings.

6.4.3 Where the frames are inclined forward and aft in the holds, it is recommended that cargo battens be arranged in these areas.