Section 4 Primary load criteria for multi-hull craft

4.1.1 For multi-hull craft, the strength of the cross deck structure is to be checked for the loadings specified in this Section, see also Pt 5, Ch 5, 5.3 Primary load combinations applicable to the cross-deck structure of multi-hull craft.

4.1.2 Other values may be used provided they are verified by model experiments, full scale measurements or any other generally accepted theories. Full details are to be submitted for appraisal.

4.1.3  L _R and T are as defined in Pt 3, Ch 1, 6 Definitions.

4.2.1 The twin hull transverse bending moment, M_B, about a longitudinal axis is given by:

4.2.2 The twin hull torsional connecting moment, M_T, is given by:

4.2.3 The vertical shear force, Q_T, at the centreline of the cross-deck structure between the twin hulls is given by:

4.3.1 The design side force acting at mid-draught of the hull is given by:

4.3.2 The lateral pressure acting on the outboard hull may be assumed to be constant and is given by:

where A_FS is the projected area, in m², of the struts with length L_S at waterline at draught T.

4.3.3 The design transverse bending moment, M_B, due to the side force is given as:

where F is the distance, in metres, from the waterline to the top of cross structure.

4.3.4 The twin hull torsional connecting moment, M_T, is given by:

4.3.5 The vertical shear force, Q_T, at the centreline of the cross-deck structure between the twin hulls is given by: