Section 2 Rule structural concepts

2.1 Definition of requirements

2.1.1 In Figure 3.2.1 Breakdown of the ship into regions, the breakdown of the ship into regions is shown. Within each region, the applicable Parts and Chapters of the Rules are indicated.

Figure 3.2.1 Breakdown of the ship into regions

2.2 Definition of midship region

2.2.1 The midship region structure is considered to include the structure within the greater of:

the midship 0,5L, length,
the cargo compartment length which on tankers includes the cofferdams and/or pump-rooms under deck.

2.3 Definition of fore end region

2.3.1 The fore end region structure is considered to include all structure forward of the midship region.

2.4 Definition of aft end region

2.4.1 The aft end region structure is considered to include all structure aft of the midship region.

2.5 Principles for taper

2.5.1 The thickness of the shell envelope and deck outside the line of openings between the 0,5L midship and 0,075L from the A.P. and 0,075L from the F.P., may be based on a direct taper from the midship thickness to the end thickness, as shown in Figure 3.2.2 Principles for taper, except where required otherwise in Pt 4 Ship Structures (Ship Types).

Figure 3.2.2 Principles for taper

2.6 Vertical extent of higher tensile steel

2.6.1 Higher tensile steel may be used for both deck and bottom structures or for deck structure only. Where fitted, it is to be used for the whole of the longitudinal continuous material for the following vertical distances:

from the line of deck at side
Z_ht = (1 - K_L)Z_P

from the top of keel

Z_ht = (1 - K_L)Z_B

where

k_L

higher tensile steel factor, see Pt 3, Ch 2, 1.3 Steel 1.3.2

Z_D, Z_B	=	vertical distance, in metres, from the hull transverse neutral axis to the moulded deck line at side and to the top of keel respectively
Z_ht	=	vertical extent of higher tensile steel, in metres

2.7 Grouped stiffeners

2.7.1 Where stiffeners are arranged in groups of the same scantling, the section modulus requirement of each group is to be based on the greater of the following:

the mean value of the section modulus required for individual stiffeners within the group;
90 per cent of the maximum section modulus required for individual stiffeners within the group.

2.8 Principles for rounding off

2.8.1 The thickness of hull structural components calculated by using the formulæ for these components should be rounded off for so far as they deviate from full or half millimetres according to Table 3.2.1 Principles for rounding off.

Table 3.2.1 Principles for rounding off

Thickness in excess of whole number by		Rounded to
Over	Not exceeding	Rounded to
-	0,25 mm	0
0,25 mm	0,75 mm	0,5 mm
0,75 mm	1,0 mm	1,0 mm

2.9 Frame spacing

2.9.1 The frame spacing of transverse or longitudinal frames is generally to be within the range given by the following formula:

Proposals for frame spacings different from this range will be specially considered.