Development of Resistance Test Using Small Model of High Speed Planing Craft

—Scale Effects on Drag Force—

Abstract

In order to develop a resistance test method for high speed planing craft using a very small model, the scale effects on wetted surface area, frictional resistance and pressure forces acting on a small model are experimentally investigated using geometric similar prismatic planing surface models. Froude number and Reynolds number covered in the experiments are Fn=1.0∼4.0 and Rn=5×10⁵∼3×10⁶, respectively. Through the analysis of resistance components, it is found that a resistance component created by disappear of hydrostatic pressure on the transom due to high-speed, called transom pressure resistance in the paper, plays an important role in the resistance of a planing craft. The wetted surface area is confirmed to slightly decrease for a very small model at large trim angle, and to cause the reduction of the pressure force acting on the hull. The frictional resistance acting on a very small model can be predicted on the basis of the equivalent flat plate concept if appropriate prediction formulas, in which laminar and transient flow effects are taken into account, are used.