The problem of a two-dimensional pressure field moving over a free surface is analysed by dynamic modelling techniques. Using a simple second order linear differential equation, it is possible to obtain all the classical theory rersults for a uniform field in deep water. Squire’s results for the non-uniform pressure field of a planing wedge are also duplicated. Further results, not hitherto obtained with classical theory, may explain some anomalies associated with the classical theory. The method has the advantage that results for a large number of “pressure field distributions” have already been tabulated by workers studying the response of simple lumped parameter mechanical dynamic systems.

A conclusion of some practical importance in applied hydrodynamics is that the wave drag of a pressure field varies with its distribution. The more non-uniform a pressure field the greater its wave drag. The theory also gives insight into the occurrence of “humps and hollows” in model resistance curves, and gives some insight as to why a minor change in form may cause a major change in wave resistance.