Section 6 Cross-deck structure for multi-hull craft

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

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

6.1.3 In the determination of the clearance, the following factors are to be considered:

1. Relative motion in waves.

2. The wave generated between the hulls when running.

3. The bow sinkage.

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

6.1.5 Where it is not possible to provide sufficient clearance to avoid slamming of the cross-deck structure, the equation given in Pt 5, Ch 2, 6.2 Impact pressure is to be used for the assessment of the impact pressures.

6.2.1 The impact pressure, P _pc, acting on the underside of the cross deck (`wet deck') is to be taken as:

V _R is the relative vertical speed of the craft at impact, in knots. If this value is unknown, then the following equation is to be used:

6.2.2 The impact pressure, P_pc, should not be taken less than zero.