Section 4 Constructional arrangement

4.1.1  Figure 1.4.1 Structural components of a trimaran shows the general terminology for the principal structural components of a trimaran.

Figure 1.4.1 Structural components of a trimaran

4.1.2  Cross-deck. The cross-deck is defined as a structure which connects the side hulls to the main hull, in general comprising an enclosed plated box structure bounded by the wet-deck, weather deck and forward and aft transitions.

4.1.3  Wet-deck. The wet-deck is defined as the lowest plating of the cross-deck structure potentially exposed to sea loads.

4.1.4  Tunnel. The tunnel is defined as the area beneath the wet-deck, bounded between the side and main hull.

4.1.5  Shell envelope. The shell envelope is defined as the bottom and side shell areas of the main and side hulls, excluding the wet-deck.

4.2.1 Sufficient transverse strength is required in the cross-deck to support the side hulls.

4.2.2 Cross-deck length structural arrangements are to be sufficient to provide effective integration of the side hulls to the main hull.

4.2.3 The connection of the forward and aft ends of the cross-deck to the main hull are potential areas of high stress. Suitable arrangements should be provided to ensure effective integration at the point of intersection. The use of castings in these areas to eliminate welding is recommended.

4.2.4 The connections between the wet-deck and hulls are potential areas of high stress, see Figure 1.4.2 Region of potential high stress concentration. The use of castings in these areas to eliminate welding is recommended.

Figure 1.4.2 Region of potential high stress concentration

4.2.5 Increased plating thicknesses in the region depicted in Figure 1.4.2 Region of potential high stress concentration may be required and are to be evaluated in accordance with the Direct Calculation Procedure as described in Vol 4 Direct Calculation Procedure.

4.2.6 Continuity of transverse structural strength is to be maintained. All primary transverse members are to be continuous through the side hull and integrated into transverse bulkheads or other primary structure within the main hull.

4.2.7 Insufficient wet-deck clearance can result in severe slamming of the wet-deck. Impact loads due to slamming and the probability of occurrence of slams decrease with an increase in wet-deck clearance. The optimal clearance is a function of several parameters such as the length of the cross-deck, water level elevation, sea state and ship motions. Whilst the Rules give formulae for slamming loads, the determination of optimal clearance is outside the scope of these Rules.