A Momentum Theory Approach to the Seakeeping of Planing Crafts

Leisure boats market has constantly grown during the latest years entailing an increasing need of design tools, dealing with technical problems like seakeeping of planing boats, whose complexity still present a high challenge for designers. The present paper describes a methodology for the calculation in time domain of the vertical motions of a planing boat in head waves, capable of predicting the non-linear vertical motions of the boat in both regular / irregular head waves. The formulation makes recourse to a ‘strip-theory’ approach to get the 3D hydrodynamic forces as a linear superposition of the sectional forces. The determination of the 2D planing forces is based on ‘momentum theory’ using Wagner’s wedge-theory to model the sectional characteristics, while non-linear Froude-Krylov forces are directly evaluated accounting the relative motions at each cross-section. Moreover, from the time-series of the vertical motions an overall passenger comfort index and slamming pressures are evaluated. A validation of the code is presented against the model-test results available in literature.