Section 6 Trunked construction

6.1.1 The requirements of this Section are additional to those of Pt 4, Ch 10, 1 General to Pt 4, Ch 10, 5 Primary members supporting non-oiltight bulkheads.

6.1.2 Where a trunk is fitted it is to extend over the full length of the cargo tanks and is to be effectively scarfed into the main hull structure.

6.1.3 The minimum thickness and constructional detail requirements of Pt 4, Ch 10, 7 Construction details and minimum thickness are also to be complied with.

6.2.1 The symbols used in this Section are defined as follows:

(see Figure 10.6.1 Equivalent depth).

6.2.2 Other symbols are defined in Pt 4, Ch 9, 1.6 Information required for CSR Double Hull Oil Tankers.

6.3.1 The trunk deck and sides are to be longitudinally framed, and the transverse primary members are to be aligned with the deck transverses.

6.3.2 Particular attention is to be given to the arrangements in way of the connection of the trunk side to the deck at side. The construction is to be such as to ensure adequate rigidity and continuity of strength.

6.3.3 Typical arrangements of primary structure are shown diagrammatically in Figure 10.6.2 Primary structure, which also indicates the effective spans to be used in the determination of scantlings.

6.3.4 Where the trunk primary stiffening is fitted externally, individual consideration will be given to the arrangement and scantlings.

6.3.5 Where longitudinal stiffening is fitted externally to the trunk, tripping brackets are to be fitted to maintain lateral stability in way of transverse bulkheads and elsewhere as necessary.

6.3.6 Extension brackets and web stiffeners or equivalent arrangements are to be provided at the forward and after ends of the trunk to ensure full continuity of strength from the trunk into hull and superstructures.

6.3.7 Where the carriage of heated cargoes is contemplated and, in particular, bituminous cargoes, special attention is to be given to the alignment of the scarfing arrangements and softening of the extension bracket toes at the trunk ends to alleviate the effects of thermal stressing.

6.4.1 The thickness of the trunk top and side plating is to be not less than as required by Pt 4, Ch 9, 4 Hull envelope plating for hull envelope plating, the item numbers for these being as given in Figure 10.6.3 Hull envelope plating - Itemisation of parts.

6.4.2 The section modulus of trunk longitudinals is to be not less than as required by Pt 4, Ch 9, 5 Hull framing for deck longitudinals.

6.4.3 The section modulus and moment of inertia of the transverses is to be not less than as required by Pt 4, Ch 10, 2.8 Deck transverses for deck transverses.

6.5.1 The thickness of the deck plating outboard of the trunk side is to be that necessary to obtain the required hull section modulus, but is to be not less than that required by Pt 4, Ch 9, 4 Hull envelope plating multiplied by the factor

6.5.2 The scantlings of the shell plating, framing, primary structure and bulkheads are to be determined on the basis of the equivalent ship depth D ₁, i.e. where the depth, D, enters into the calculation or structural arrangement it is to be replaced by D ₁.

6.5.3 The head to the deck at side is to be increased by (D ₁ − D).

6.5.4 The head to the highest point of the tank is to be replaced by the actual distance to the highest point of the tank, reduced by the amount (D + h _t − D ₁).