This paper takes a first principles approach to the prediction of dynamic forces on ships in waves. A time domain strip theory applicable at high Froude numbers, previously extensively validated for motions, is used. From the calculated dynamic force distribution and the hull mass distribution, rigid body dynamic hull bending moments, shear forces, and pitch connecting moments are obtained. The frequencies of interest are those of significant wave energy, coinciding with wavelengths (due to spatial matching with the hull) or frequencies (due to dynamic effects) that produce significant hull girder forces. For typical ships these are substantially lower than the flexural natural frequencies of the hulls, and, for regular motions, significant dynamic effects are therefore confined to those originating from the rigid body modes. In random seas, in the absence of severe transient events such as slamming, the neglect of flexural dynamic forces is therefore justified. This paper applies the theory to an Incat wave-piercer catamaran, forming the basis of validation in progress against full scale strains measured both in service and during delivery voyages on two similar catamarans.
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