Section 1 Double bottom structure

1.1.1 The requirements of this sub-Section are to be applied to single side skin bulk carriers of length, L, 150 m or above, intended for the carriage of cargoes having bulk densities of 1,0 tonne/m³ or above.

1.1.2 The maximum load which may be carried in each cargo hold in combination with flood water is to be determined for the most severe homogeneous, non-homogeneous and packed cargo conditions contained in the Loading Manual. The maximum density of cargo intended to be carried in each condition is to be used.

1.1.3 The ship is to be assumed immersed to the draught, T_F, in metres, in way of the flooded cargo hold under consideration. The flooding head, h_f, see Figure 6.1.1 Loading, is to be taken as the distance, in metres, measured vertically with the ship in the upright position, from the inner bottom to position, d_f, in metres, from the base line given by:

1. In general:

   1. d_f = D for the foremost hold

   2. d_f = 0,9D for other holds

2. For ships less than 50 000 tonnes deadweight with Type B freeboard:

   1. d_f = 0,95D for the foremost hold

   2. d_f = 0,85D for other holds

Figure 6.1.1 Loading

1.1.4 For this application, the double bottom is defined as the structure bounded by the transverse bulkhead lower stools (or bulkhead plating if no lower stools are fitted) and the hopper sides. The floors and girders immediately in way of these structures are excluded.

1.1.5 The determination of shear strength required for the permissible load assessment in Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.9, is to be performed using the net plate thickness, t_net, for the floors and girders:

1.1.6 Shear capacity of the double bottom is defined as the sum of the shear strengths for:

1. all the floors adjacent to both hoppers, less one half the strength of the floors adjacent to each lower stool (or transverse bulkhead if no lower stool is fitted), see Figure 6.1.3 Double bottom breadth, and

2. all the girders adjacent to the lower stools (or transverse bulkheads if no lower stool is fitted).

Where a girder or floor terminates without direct attachment to the boundary stool or hopper side girder, its shear capacity is to include only that for the effectively connected end.

Figure 6.1.2 Double bottom structure

1.1.7 The shear strengths, S_f1, of floors adjacent to hoppers and, S_{f 2}, of floors in way of openings in bays nearest to the hoppers, are as follows:

where

Af	=	net sectional area, in mm2, of floor panel adjacent to hopper
Af,h	=	net sectional area, in mm2, of floor panel in way of opening in the bay closest to hopper
η1	=	1,10
η2	=	1,20 generally
	=	1,10 where appropriate reinforcement is fitted in way of the opening
σ0	=	specified minimum yield stress, in N/mm2 (kgf/mm2)
τp	=	permissible shear stress, to be taken equal to the lesser of:
τ0	=
τc	=
	=

For floors adjacent to the stools (or bulkhead plating if no lower stools are fitted), τ_p may be taken as N/mm² (kgf/mm²).

1.1.8 The shear strengths S_g1, of girders adjacent to transverse bulkhead lower stools (or transverse bulkheads if no lower stools are fitted) and, S_g2, of girders in way of the largest openings in bays nearest to the lower stools (or transverse bulkheads if no lower stools are fitted), are as follows:

1.1.9 The permissible cargo hold loading, W_p, is given by:

where

df, D	=	as defined in Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.3
g	=	gravitational constant, 9,81 m/sec2
h f	=	flooding head, in metres, as defined in Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.3
h 1	=	where Y is in kN/m2
	=
n	=	number of floors between transverse bulkhead lower stools or transverse bulkheads, if no lower stools are fitted
s	=	spacing, in metres, of double bottom longitudinals adjacent to hoppers
ADB,e	=
ADB,h	=
BDB	=	breadth of double bottom, in metres, between hoppers, see Figure 6.1.3 Double bottom breadth
BDB,h	=	distance, in metres, between openings, see Fig. Figure 6.1.3 Double bottom breadth
BDB,i	=	(B DB – s) for floors where shear strength is given by Sf1
	=	BDB,h for floors where shear strength is given by Sf 2
Ce	=	shear capacity of the double bottom, in kN (tonne-f), as defined in Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.6, considering for each floor, the shear strength Sf1, see Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.7, and for each girder, the lesser of the shear strengths Sg1 and Sg2, see Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.8
Ch	=	shear capacity of the double bottom, in kN (tonne-f), as defined in Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.6, considering floor, the lesser of the shear strengths Sf1 and Sf2, see Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.7, and for each girder, the lesser shear strengths Sg1 and Sg2, see Ch 6, 1.1 Allowable hold loading in the flooded condition 1.1.8
Fc	=	1,1 in general
	=	1,05 for steel mill products
Si	=	spacing of ith floor, in metres
TF	=	df – 0,1D
V	=	volume, in m3, occupied by cargo at a level h1
X	=	the lesser of X1 and X2 for bulk cargoes and
X	=	X1 for steel mill products

where

X1	=	where Y is in kN/m2
	=
X 2	=	Y + ρ g (T F – h f μ) where Y is in kN/m2
(X 2	=	Y + ρ (T F – h f μ) where Y is in tonne-f/m2)
Y	=	the lesser of Y 1 and Y 2 given by:
Y1	=
Y2	=
μ	=	permeability of cargo but need not exceed 0,3
	=	0,0 for steel mill products
ρ	=	density of sea water, 1,025 tonne/m3
ρc	=	cargo density, in tonne/m3 (bulk density for bulk cargoes and actual cargo density for steel mill products).

Figure 6.1.3 Double bottom breadth