| The main spray and whisker spray generated by a planing surface are shown to be the result of the same basic phenomena, which can be explained by analogy to a swept wing, using planes normal to the spray root line. This analogy can be used to estimate the trajectory of the spray as well as the maximum pressures occurring on the planing hull. The spray trajectory is validated by model tests carried out at the Davidson Laboratory. The limitations of slender body theory in the prediction of spray velocity are explored. Empirical formulae are developed to estimate the pressure distribution on the bottom of prismatic planing hulls, by separate consideration of the pressure distribution in the spray root region, the longitudinal pressure distribution of a low aspect ratio planing surface, and the reduction in pressure to atmospheric at both the transom and the chines. Pressure distribution due to buoyancy is evaluated. Both the empirical formulae and the swept wing analogy are used to demonstrate the effect of deadrise and trim on spray volume. The conclusion is made that at a given trim angle; a reduction in deadrise will increase the height of the spray, but decrease its volume flow rate. |
