Section 8 Particular requirements for multi-hulls

8.1.1 The requirements indicated in this Section are particular to multi-hull craft and are to be applied in addition to the general requirements of this Chapter.

8.1.2 The craft is to be considered as one complete structure when determining the minimum geometric summer freeboard. The block coefficient is to be calculated using the actual displacement determined from the hydrostatic data and using the total breadth of the structure and not just a single hull.

8.1.3 If, by using normal procedures, the minimum geometric summer freeboard determined is unreasonable for the operation of the craft, special consideration may be given, on a case by case basis, based on the proposed design configuration.

8.2.1 The scantlings and arrangements indicated are for twin hulled craft. Craft with a greater number of hulls will be specially considered on the basis of the Rules.

8.3.1 Structural members which contribute to the overall hull girder strength are to be carefully aligned so as to avoid discontinuities resulting in abrupt variations of stresses and are to be kept clear of any form of openings which may affect their structural performances.

8.3.2 Particular care is to be given to the continuity and alignment in way of the end connections of transverse bridging structures.

8.4.1 For craft with multi-hulls linked by cross-deck structures, sufficient clearance is to be provided between the cross-deck structure and water surface to limit impact loads.

8.4.2 Where part or all of the cross-deck is intended to provide additional buoyancy to limit craft motion, the loading will be specially considered.

8.4.3 In the determination of the clearance, the following factors should be considered:

1. Relative motion in waves.

2. The wave generated between the hulls when running.

3. The bow sinkage.

8.4.4 The submitted clearances must be validated either by calculations according to accepted theories, model test, full scale measurements or by documentary evidence if similar structures have proved to be satisfactory in service.

8.4.5 Where it is not possible to provide sufficient clearance to reduce the likelihood of slamming of the cross-deck structure, direct calculations or other appropriate means are to be used to assess the loads, assuming the most severe conditions for which the craft is to be approved.

8.5.1 The number and arrangement of watertight and non-watertight bulkheads in the bridging structure will be specially considered dependent upon the structural configuration and size of the craft. Attention is drawn to the relevant requirements, e.g. structural fire protection and damaged stability, where these bulkheads are acting to prevent cross-flooding and the spread of smoke or flames.

8.6.1 The forefoot and bow regions of fast craft that may be subjected to frequent impacts from flotsam are to be easily accessible for inspection. Access to the forepeak compartments may be provided through the forepeak bulkhead where access would otherwise be impracticable.

8.6.2 The aft end regions of all craft are to be easily accessible for inspections. Access may be provided through the aft peak bulkhead or by means of deck hatches or manholes.

8.7.1 Where an engine is fitted within a narrow hull, where engineroom temperatures may rise quickly, the ventilation requirements may require to be increased.

8.7.2 Within machinery spaces where space is limited access is to be provided for inspection.

8.8.1 Superstructures and deckhouses which enclose large flat open areas, that are subjected to racking loads and which may be of several tiers, are to be additionally stiffened with large web frames, partial bulkheads and pillars.