RE-ANALYSIS OF WILLIAM FROUDE’S STUDIES OF PLANING CRAFT

Abstract

One of William Froude’s lesser-known contributions to the field of Naval Architecture was in conducting some of the earliest studies on planing craft. Froude’s research was prompted by the idea of an inventor, Reverend C.M. Ramus who in 1872 proposed a high-speed ship concept using a flat-bottomed, stepped planing hull. Ramus later suggested the use of this hullform for rocket-propelled rams. Froude conducted towing tests on a model of the Ramus hull, as well as on a model three-point hydroplane concept of his own design. He also derived a solution for the optimum trim angle and minimum resistance of planing craft, using his recently developed formulae for estimating frictional resistance on flat plates and lift forces on submerged plates. Froude’s study demonstrated that Ramus’s ideas were not feasible at the time and the study received very little attention. It was not until the advent of lightweight internal combustion engines, thirty years later, that planing hulls became a reality. In the current paper, the Ramus tests are re-analysed and the data are put into a modern format. Comparisons are provided between the Ramus hull, Series 62 and a planing flat plate. The Ramus concept is shown to have had significantly more drag than would be expected from a planing hull. New model tests explore the effects of the rounded stern of the Ramus hull, and show that this feature significantly increases the resistance. Froude’s derivation of the minimum resistance of planing craft is discussed and contrasted with modern methods for prismatic planing hull resistance prediction.