ABSTRACT An analytic method is presented whereby the differential pressure distribution on a submerged horizontal flat plate, 'induced by the passage of gravity waves, can be calculated. Plates having cord lengths of the same order of magnitude as the wave length are considered, making the analysis applicable to large offshore structures. The results of an experimental program, designed to test the validity of the theory, are presented and show good agreement. In the analysis, the plate is imagined to be rigidly suspended at an arbitrary fixed depth and then replaced by a vortex sheet whose strength varies both temporarily and specially. The velocity potential of this sheet is adjusted such that, when combined with the potential of the oncoming waves, boundary conditions on the plate, the free surface, and the bottom are approximately satisfied. The final vortex strength distribution can be determined allowing the velocity field and hence the pressure distribution on each side of the plate to be calculated. The experimental program was conducted using 4 × 4 × 40 ft. flume with a generator capable of producing waves having a broad frequency and amplitude spectrum in varying water depths. A flat plate of sandwich type construction was instrumented with small pressure transducers whose outputs were processed and recorded on an oscillographic recorder. Results are presented as instantaneous differential pressure distributions for associated wave positions, sequentially as the wave progresses. Analytic and experimental results are compared and show good agreement. An advantage of the analytic approach is that pressure distributions as well as total forces may be readily obtained. This is important in designing a structure against maximum local differential pressure. The method can be extended to more complex shapes and finite length plates. INTRODUCTION The prediction of forces, or more precisely, the pressure distributions, experienced by submerged structures due to the passage of gravity waves has become important with the advent of large offshore structures. If the size of a structure is small compared to the wave length then the forces can be evaluated by the assignment of suitable drag and inertia coefficients using an approach similar to that of Morison (5) in which case it is necessary to determine the coefficients experimentally for any given geometry (2). If the size of the structure is a significant fraction of the wave length the above method is invalid and a more complicated analysis such as the diffraction theory of Garrison and Rao (1) is needed. Unfortunately, the application of diffraction theory for a given geometry is exceedingly difficult unless one assumes the structure size is small compared to the wave length, which may not be realistic.