Section 2 Scantlings of bulkheads

2.1.1 The scantlings of watertight and deep tank bulkheads are to comply with the requirements of Table 7.2.1 Watertight and deep tank bulkhead scantlings. The scantlings of the collision bulkhead are to be in accordance with Pt 3, Ch 5, 6.5 Collision bulkhead. Where bulkhead stiffeners support deck girders, transverses or pillars over, they are also to comply with Table 7.2.3 Bulkhead stiffeners supporting concentrated loads.

2.1.2 Stiffening members of horizontal bulkheads of tanks may be supported by girders or a system of girders and pillars.

Table 7.2.1 Watertight and deep tank bulkhead scantlings

Item and requirement	Watertight bulkheads	Deep tank bulkheads
(1) Plating thickness for plane and symmetrically corrugated bulkheads	The greater of the following: t = 4w + 0,5 mm or t = 4 mm, see Note 3	The greater of the following: t = 4w + a mm or t = 5 mm for oil tanks and fresh water tanks t = 5,5 mm for water ballast tanks, see Note 3
(2) Modulus of rolled and built stiffeners, swedges and symmetrical corrugations	Z = 5 × k × s × le 2 × h 4 cm3	Z = 6 × k × s × le 2 × h 4 × ρ cm3
(3) Stringers or webs supporting vertical or horizontal stiffening
(a) Modulus	Z = 7 × k × h 4 × S × le 2 cm3	Z = 8,5 × k× h 4 × S × le 2 × ρ cm3
(b) Inertia	-	= cm4
(4) Pillars in tanks, cross-sectional area	-	A = 4,5 + 0,9P cm2
Symbols
t = thickness of plating, in mm Z = section modulus of stiffening member, in cm3, see Pt 3, Ch 3, 3.2 Geometric properties of section s = spacing of stiffeners, corrugations, girders or webs, in metres k = higher tensile steel factor, see Pt 3, Ch 2, 1.3 Steel 1.3.3 le = effective length of stiffening member, in metres, see Pt 3, Ch 3, 3.3 Determination of span point I = inertia of stiffening member, in cm4, see Pt 3, Ch 3, 3.2 Geometric properties of section ρ = specific gravity of liquid carried in the tank, but is to be taken as not less than 1 w = plate width, in metres, defined as follows: = (a) for plane bulkheads the spacing of stiffeners, in metres = (b) for corrugated bulkheads the width of flange (b) or web (c), in metres, whichever is the greater, see Figure 3.3.3 Dimensions and symbols for corrugated bulkheads in Ch 3,3 a = 1 mm for oil and fresh water tanks and 1,5 mm for water ballast tanks h 4 = load head, in metres, measured vertically as follows, see also Figure 7.2.1 Heads for watertight and deep tank bulkheads (a) for vertically stiffened watertight bulkhead plating – the distance from a point 0,5 m above the lower edge of the plate to the top of the bulkhead (b) for horizontally stiffened watertight bulkhead plating - the distance from the middle of the first panel above the lower edge of the plate to the top of the bulkhead (c) for vertically stiffened deep tank bulkhead plating - the distance from a point 0,5 m above the lower edge of the plate to a point 1 m above the top of the tank, or to the top of the overflow, whichever is the greater (d) for horizontally stiffened deep tank bulkhead plating - the distance from the middle of the first panel above the lower edge of the plate to a point 1 m above the top of the tank, or to the top of the overflow, whichever is the greater (e) for watertight stiffeners or girders, the distance from the middle of the effective length to the top of the bulkhead (f) for deep tank bulkhead stiffeners or girders, the distance from the middle of the effective length to a point 1 m above the top of the tank, or to the top of the overflow, whichever is the greater P = load supported by the pillars, in tonne f
Note 1. For rolled or built stiffeners with flanges for face plates the web thickness is to be not less than of the web depth, whilst for flat bar stiffeners the web thickness is to be not less than of the web depth. Note 2. Additional requirements for corrugated bulkheads are given in Pt 3, Ch 3, 3.2 Geometric properties of section. Note 3. Bulkhead plating from the bottom to 0,1 m above ceiling in holds is to be at least 6 mm in thickness.

Figure 7.2.1 Heads for watertight and deep tank bulkheads

2.1.3 Pillars in tanks are not to be of hollow construction and are to be bracketed at top and bottom. Scantlings and welding of the brackets are to take account of the maximum tensile force on the pillar.

2.1.4 End connections of stiffeners are to be in accordance with the requirements of Pt 3, Ch 10, 3 Secondary member end connections. Where stiffeners are not fitted with the required end brackets, the modulus of the stiffeners is to be increased in accordance with Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections.

2.1.5 Fuel oil carried in tanks is to have a flash point not less than 55°C. Where tanks are intended for liquid fuels of a special nature, the scantlings and arrangements will be considered in relation to the nature of the fuel, see also Pt 3, Ch 12, 2 Rudders.

2.1.6 If cargo is carried in a compartment adjacent to a fuel oil tank which may be heated, the compartment side of the bulkhead or deck is to be insulated, or equivalent arrangements provided.

2.1.7 Where watertight bulkhead stiffeners are cut in way of watertight doors, the opening is to be suitably framed and reinforced, and the adjacent stiffeners are to be increased in proportion to the greater spacing. Where the stiffener spacing is locally increased on account of watertight doors, the stiffeners at the sides of the doorways are also to be increased. Recesses in bulkheads are generally to be so stiffened as to provide strength and stiffness equivalent to the requirements for the bulkhead.

2.2.1 The scantlings of non-watertight bulkheads acting as hull supporting structure are to comply with the requirements of Table 7.2.2 Non-watertight bulkheads. Where the bulkhead stiffeners support deck girders, transverses or pillars over, they are also to comply with the requirements of Table 7.2.3 Bulkhead stiffeners supporting concentrated loads.

Table 7.2.3 Bulkhead stiffeners supporting concentrated loads

Parameter	Requirements
(1) Cross-sectional area for rolled, built or swedged stiffeners, supporting girders, transverses, pillars or concentrated loads	see Note
(2) Width of effective plating included in the cross-sectional area	The lesser of the following w = 80t mm or w = 700s mm
Symbols
h 4 = load, head, in metres, as specified for watertight bulkheads in Table 7.2.1 Watertight and deep tank bulkhead scantlings
l = overall length of stiffener, in metres, see Pt 3, Ch 3, 3.2 Geometric properties of section
le = effective length of stiffening member, in metres, see Pt 3, Ch 3, 3.3 Determination of span point
r = least radius of gyration of stiffener with effective plating, in mm, and is to be taken as:
s = spacing of stiffeners, in metres, but not to exceed 1,10 m
t = thickness of plating, in mm
w = width of effective plating, in mm
A = cross-sectional area of stiffening member inclusive of effective plating, in cm2
Ip = least moment of inertia of stiffener with effective plating, in cm4
P = load supported by stiffener, in tonne-f
Z = section modulus of stiffening member, in cm3, see Pt 3, Ch 3, 3.2 Geometric properties of section k = higher tensile steel factor, see Pt 3, Ch 2, 1.3 Steel 1.3.3
Note The depth of stiffeners supporting concentrated loads is to be not less than 75 mm.

2.3.1 Bulkheads in cargo holds which are regularly exposed to contact with grabs or falling cargo are to be efficiently protected or the scantlings increased in order to reduce damage.