2 Special Requirements

2.1 Minimum thickness of keel plating

2.1.1 The net thickness of the keel plating is not to be taken less than the offered net thickness of the adjacent 2 m width bottom plating, measured from the edge of the keel strake.

The width of the keel is defined in Ch 3, Sec 6, [7.2.1].

2.2 Bilge plating

2.2.1 Definition of bilge area

The definition of bilge area is given in Ch 1, Sec 4, [3.8.1].

2.2.2 Bilge plate thickness

a) The net thickness of bilge plating is not to be taken less than the offered net thickness for the adjacent bottom shell or adjacent side shell plating, whichever is greater.
b) The net thickness of rounded bilge plating, t, in mm, is not to be taken less than:
t = 6.45 × 10^–4 (P_ex s_b)^0.4 R^0.6

where:

P_ex : Design sea pressure for the design load set SEA-1 as defined in Ch 6, Sec 2, [2.1.3] calculated at the lower turn of the bilge, in kN/m².
R : Effective bilge radius in mm.
- R = R₀ + 0.5 (Δs₁ + Δs₂)
R₀ : Radius of curvature, in mm. See Figure 1.
Δs₁ : Distance between the lower turn of bilge and the outermost bottom longitudinal, in mm, see Figure 1.
- Where the outermost bottom longitudinal is within the curvature, this distance is to be taken as zero.
Δs₂ : Distance between the upper turn of bilge and the lowest side longitudinal, in mm, see Figure 1.
- Where the lowest side longitudinal is within the curvature, this distance is to be taken as zero.
s_b : Distance between transverse stiffeners, webs or bilge brackets, in mm.
c) Longitudinally stiffened bilge plating is to be assessed as regular stiffened plating. The bilge thickness is not to be less than the lesser of the value obtained by [1.1.1] and [2.2.2] b). A bilge keel is not considered as an effective ‘longitudinal stiffening’ member.

2.2.3 Transverse extension of bilge minimum plate thickness

Where a plate seam is located in the straight plate just below the lowest stiffener on the side shell, any increased thickness required for the bilge plating does not have to be extended to the adjacent plate above the bilge provided the plate seam is not more than s₂/4 below the lowest side longitudinal. Similarly, for the flat part of adjacent bottom plating, any increased thickness for the bilge plating does not have to be extended to the adjacent plate provided that the plate seam is not more than s₁/4 beyond the outboard bottom longitudinal. For definition of s₁ and s₂, see Figure 1.

Figure 1 : Transverse stiffened bilge plating

2.2.4 Hull envelope framing in bilge area

For transversely stiffened bilge plating, a longitudinal is to be fitted at the bottom and at the side close to the position where the curvature of the bilge plate starts. The scantling of those longitudinals are to be not less than the one of the closer adjacent stiffener. The distance between the lower turn of bilge and the outermost bottom longitudinal, Δs₁, is generally not to be greater than one-third of the spacing between the two outermost bottom longitudinals, s₁. Similarly, the distance between the upper turn of the bilge and the lowest side longitudinal, Δs₂, is generally not to be greater than one-third of the spacing between the two lowest side longitudinals, s₂. See Figure 1.

2.3 Side shell plating

2.3.1 Fender contact zone

The net thickness, t in mm, of the side shell plating within the fender contact zone as specified in [2.3.2] is not to be taken less than:

2.3.2 Application of fender contact zone requirement

The application extends within the cargo hold region as defined in Ch 1, Sec 1, [2.4.3], from the ballast draught T_BAL to 0.25 T_SC (minimum 2.2 m) above T_SC.

2.4 Sheer strake

2.4.1 General

The minimum width of the sheer strake is defined in Ch 3, Sec 6, [8.2.4].

2.4.2 Welded sheer strake

The net thickness of a welded sheer strake is not to be less than the offered net thickness of the adjacent 2 m width side plating, provided this plating is located entirely within the top wing tank or double side tank as the case may be.

2.4.3 Rounded sheer strake

The net thickness of a rounded sheer strake is not to be less than:

The offered net thickness of the adjacent 2 m width deck plating, or
The offered net thickness of the adjacent 2 m width side plating,

whichever is greater.

2.5 Deck stringer plating

2.5.1 The minimum width of deck stringer plating is defined in Ch 3, Sec 6, [9.1.2].

2.5.2 Within 0.6 L of amidships, the net thickness of the deck stringer plate is not to be less than the offered net thickness of the adjacent deck plating.

2.6 Supporting structure in way of corrugated bulkheads

2.6.1 General

Requirements for the arrangement of bulkhead as given in Ch 3, Sec 6, [10.4] are to be considered together with [2.6.2] to [2.6.4].

2.6.2 Lower stool

a) The net thickness of the stool top plate is not to be less than that required for the attached corrugated bulkhead and is to be of at least the same material yield strength as the attached corrugation. The extension of the top plate beyond the corrugation is not to be less than the as-built flange thickness of the corrugation.
b) The net thickness of the stool side plate, within the region of the corrugation depth from the stool top plate, is not to be less than the corrugated bulkhead flange net required thickness at the lower end and is to be of at least the same material yield strength. The net thickness may be reduced to 90% of corrugation flange thickness if continuity is provided between the corrugation web and supporting brackets inside the stool as defined in (c).
c) For oil tankers, continuity between corrugation web and lower stool supporting brackets is to be maintained inside the stool. Alternatively, lower stool supporting brackets inside the stool are to be aligned with every knuckle point of corrugation web.
d) The net thickness of supporting bracket is not to be less than 80% of the required net thickness of the corrugation webs and is to be of at least the same material yield strength.
e) The net thickness of supporting floors is not to be less than the net required thickness of the stool side plating (excluding the application of GRAB requirements as defined in Pt 2, Ch 1, Sec 6) connected to the inner bottom and is to be of at least the same material yield strength. If material of different yield strength is used, the required thickness is to be adjusted by the ratio of the two material factors k, as defined in Ch 3, Sec 1, [2.2.1].
f) Where a lower stool is fitted, particular attention is to be given to the through-thickness properties, and arrangements for continuity of strength, at the connection of the bulkhead stool to the inner bottom. For requirements for plates with specified through-thickness properties, see Ch 3, Sec 1, [2.5].

2.6.3 Upper stool

a) The net thickness of the stool bottom plate is not to be less than that required for the attached corrugated bulkhead and is to be of at least the same material yield strength as the attached corrugation. The extension of the top plate beyond the corrugation is not to be less than the as-built flange thickness of the corrugation.
b) The net thickness of the lower portion of stool side plating is not to be less than the greater of the following,

The net thickness obtained from [1.1],
80% of the net thickness of the upper part of the bulkhead plating as required by
- [1.2],
- Pt 2, Ch 1, Sec 3, [3.1], or Pt 2, Ch 2, Sec 3, [2.2.1] as applicable,
where the same material is used.
If materials of different yield strength are used, the required thickness is to be adjusted by the ratio of the two material factors k as defined in Ch 3, Sec 1, [2.2.1].

2.6.4 Local supporting structure in way of corrugated bulkheads without a lower stool

a) The net thickness of the supporting floors and pipe tunnel beams in way of a corrugated bulkhead are not to be less than the required net thickness of the corrugation flanges and are to be of at least the same material yield strength. The inner bottom and hopper tank in way of the corrugation is to be of at least the same material yield strength as the attached corrugation, and Z grade steel as defined in Ch 3, Sec 1, [2.5] is to be used unless through thickness properties are documented for approval.
b) Brackets/carlings arranged in line with the corrugation web are to have a depth of not less than 0.5 times the corrugation depth and a net thickness not less than 80% of the net thickness of the corrugation webs and are to be of at least the same material yield strength. Where support is provided by gussets with shedder plates instead of brackets/carlings, the height of the gusset plate, see h_G in Pt 2, Ch 1, Sec 3, Figure 5, is to be at least equal to the corrugation depth. The gusset plates are to be fitted in line with and between the corrugation flanges. The net thickness of the gusset and shedder plates is not to be less than 100% and 80%, respectively, of the net thickness of the corrugation flange and is to be of at least the same material yield strength.

2.7 Aft peak bulkhead

2.7.1 The net thickness of the aft peak bulkhead plating in way of the stern tube penetration is to be at least 1.6 times the required thickness for the bulkhead plating.