Section 5 Hull envelope framing – Longitudinally framed ships

5.1.1 This Section covers the arrangements and requirements for longitudinal hull framing of the midship region of flush deck and trunk deck tankers.

5.1.2 The scantlings given in Table 6.5.1 Hull framing - Longitudinally framed ships - Secondary structure (see also Pt 4, Ch 6, 5.4 Primary structure 5.4.1) are based on end connections in accordance with Pt 3, Ch 10, 3 Secondary member end connections. Where brackets having arm lengths differing from the standard are fitted, the modulus of stiffening members is to be corrected in accordance with Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections.

Table 6.5.1 Hull framing - Longitudinally framed ships - Secondary structure

Item	Parameter	Requirement (See Notes 1 and 2)
Bottom longitudinals single skin	Modulus	Z = K [0,34 + 0,46h b + L 1 (0,112 – 0,009h b)] hbksle2 cm3
Bottom longitudinals double skin	Modulus
Inner bottom longitudinals double skin	Modulus	Z = 6ksle2hg cm3
Side longitudinals single skin	Modulus	Z = (4 + 0,04L1) ksle 2hg cm3
Side longitudinals double skin	Modulus	Z = (4,6 + 0,0342L1) ksle2 hf cm3
Deck trunk side and trunk deck	Modulus	Z = [hg – 3 + (0,18 – 0,02hg) L1] hg ksle2 cm3
longitudinals	Inertia	I = le Z cm4
For Symbols, see Table 6.4.1 Hull framing - Transversely framed ships
Note 1. In case the scantlings of longitudinal members result in an appreciable excess in the hull midship section modulus as required byPt 3, Ch 4 Longitudinal Strength for the ship type concerned, a reduction in the relevant members may be applied, provided the permissible combined bending stress and the permissible local bending stress are not exceeded. For permissible stresses, see Pt 4, Ch 6, 12 Direct calculation procedures. Note 2. The minimum compartment thickness of the tank structure is not to be less than as required by Pt 4, Ch 6, 1.10 Compartment minimum thickness.

5.1.3 Outside the midship region the structure is to be scarfed into the fore end and aft end structure as provided for inPt 3, Ch 5 Fore End and Aft End Structure and Pt 3, Ch 6 Machinery Spaces so far as applicable.

5.1.4 It is recommended that the bottom of ships regularly resting aground be additionally strengthened to withstand the stresses to which it may be subjected. In such ships scallops or openings (unless reinforced) are not to be made in the lower region of the bottom framing.

5.2.1 For dry-docking purposes, single hull ships without a centreline bulkhead are to be fitted with a centreline girder having the same height and thickness as the bottom transverses and provided with suitable anti-tripping arrangements.

5.2.2 For dry-docking purposes, double hull ships are to be fitted with a centreline girder. Centreline girders in double bottom structures are to be suitably stiffened. For further details and scantlings, see Pt 4, Ch 6, 5.6 Double bottom arrangements.

5.3.1 Bottom, inner bottom, side shell, deck, trunk side and trunk deck longitudinals are to comply with the requirements of Table 6.5.1 Hull framing - Longitudinally framed ships - Secondary structure.

5.3.2 On Type C Tankers, where the width of the double skin is less than 1,0 m, the side shell longitudinals are to comply with Pt 4, Ch 4, 3.6 Special requirements for Type C tankers.

5.3.3 Longitudinals are, generally, to be carried through transverse bulkheads. If they stop at transverse bulkheads, brackets are to be fitted inter-connecting the longitudinals. These are to be arranged such that the cross-sectional area of the longitudinals is maintained, see Pt 3, Ch 10, 3.3 Basis for calculation of bracket connections 3.3.1.(c).

5.3.4 Scallops in longitudinals may not be fitted in way of end connections, crossings with transverses or tripping brackets. Where openings for drainage in longitudinals need to be fitted in way of end connections, etc. reinforcements are required.

5.3.5 Longitudinals which are cut in way of deck openings are to be connected to efficient carlings.

5.4.1 Longitudinal stiffening members are to be supported by transverses arranged to form ring systems. The spacing of the transverses is not to exceed 3,5 m and their scantlings are to be in accordance with Table 6.5.2 Hull framing - Longitudinally framed ships - Primary structure. They are to have bracketed end connections, see Pt 4, Ch 6, 5.1 General 5.1.2 and Pt 4, Ch 6, 5.4 Primary structure 5.4.8.

5.4.2 On certain Type C Tankers, the maximum webspacing may be further limited, see Pt 4, Ch 6, 5.5 Double skin arrangements 5.5.4.

5.4.3 For the maximum spacing of floors in double bottoms, see Pt 4, Ch 6, 5.6 Double bottom arrangements 5.6.3.

5.4.4 The depth of transverses is, generally, to be not less than twice the depth of the slots for the longitudinals.

5.4.5 Transverses fitted on the inboard face of longitudinals are to comply with the requirements of Pt 3, Ch 3, 3 Structural idealisation and associated Figure 3.3.4 Rolled or built sections fitted on top of supported stiffening members.

5.4.6 When the span of transverses exceeds 3 m, tripping brackets connected to the longitudinals are to be fitted about mid-length of the span.

5.4.7 If pillars are fitted to support deck transverses, they are to comply withPt 4, Ch 6, 4.6 Deck support – Flush deck tankers 4.6.4 and their scantlings are to be in accordance with Table 6.4.1 Hull framing - Transversely framed ships.

5.4.8 As an alternative to bracketed end connections, side shell transverses may be fitted without brackets, provided their section modulus at the intersection with the bottom transverse is at least equal to the modulus of the bottom transverse, and in way of the deck transverse, at least equal to the modulus of the deck transverse. In this case, the respective face bars of the bottom and deck transverse are to be continued beyond their point of intersection and are to be connected to the nearest sideshell and bottom longitudinal in way. In case the facebars do not line up with any longitudinals they are to be sniped in way of the sideshell or bottomplating. The web plate of the bottom and deck transverse is to be stiffened in line with the face of the side transverse, see also Pt 4, Ch 6, 7.1 General 7.1.2.

5.5.1 The scantlings of the secondary structure in the double skin are to be in accordance with Table 6.5.1 Hull framing - Longitudinally framed ships - Secondary structure.

5.5.2 The scantlings of the primary structure in the double skin are to be in accordance with Table 6.5.2 Hull framing - Longitudinally framed ships - Primary structure.

5.5.3 Where the inner skin forms the boundary of cargo tanks, the scantlings of stiffening members are to comply with the requirements of Pt 4, Ch 6, 7 Longitudinal and transverse bulkheads of integral cargo tanks. Otherwise, the scantlings of stiffening members of the inner skin are to comply with the requirements for deep tanks or watertight bulkheads, as applicable, see Pt 3, Ch 7 Bulkheads.

5.5.4 For details regarding the accessibility and the standard required width of the double skin on Type C tankers, reference is made to Pt 4, Ch 4, 3.6 Special requirements for Type C tankers. Requirements are also given for strengthening the double skin in cases where the width is reduced to the minimum value as allowed by the ADN. In that case the requirements for reinforcing sideshell structure by means of strengthened sideshell longitudinals in association with a maximum web frame spacing of 1.80 m is also to be complied with.

5.5.5 For details regarding the accessibility and the standard required width of the double skin on Type N tankers, reference is made to Pt 4, Ch 4, 3.7 Special requirements for Type N tankers.

5.6.1 The scantlings of the structure in the double bottom are to be in accordance with Table 6.5.3 Double bottom (longitudinal framing).

Table 6.5.3 Double bottom (longitudinal framing)

	Item	Parameter	Requirements
(1)	Double bottom of centreline	Minimum depth	d f = 650 mm
(2)	Centre girder and side girder	Thickness	t = (0,01d f + 1) mm
(3)	Floors, watertight floors and floors in line with web frames	Thickness	t = (0,009d f + 2) mm
For Symbols, see Table 6.4.1 Hull framing - Transversely framed ships.

5.6.2 All parts of double bottom tanks are to be accessible for cleaning and inspection. The tanks are to be well ventilated. Reference is made to Pt 4, Ch 4, 3.6 Special requirements for Type C tankers with regard to general requirements concerning the minimum double bottom height, accessibility, the minimum size of openings and minimum free distances between structural members for passage and inspection.

5.6.3 A centreline girder is to be fitted as required by Pt 4, Ch 6, 5.2 Bottom centreline girder. Floors are to be fitted at a spacing not exceeding 2,5 m. Vertical stiffeners having a depth not less than 50 mm are to be fitted to the floors at every fourth longitudinal. Additional stiffening is to be fitted in way of manholes. Where the spacing of the floors exceeds 2,0 m brackets are to be fitted midway between the floors on either side of the centreline girder and at the margins of the double bottom, extending in each case to the nearest bottom and inner bottom longitudinals. The free edges of the brackets are to be suitably stiffened.