Comparative study on manoeuvring performance of model and full-scale waterjet propelled planing boats

Abstract

Waterjet propelled planing boats generally have excellent propulsion efficiencies and steering performance at high speeds. They should have good manoeuvrabilities for the safe high-speed operation. It is necessary to estimate the full-scale manoeuvring performance by model test techniques at the design stage of planing boats. In this study, speed and manoeuvring performances of a designed 3-ton class planing boat are predicted by scaled model tests, and the model test results are compared with full-scale trials. At first, a 1/6.5 scaled bare hull model boat is straightly towed in a tank in order to investigate the running attitudes and resistance according to its forward speeds. The model boat is equipped witha model waterjet for free running tests. The waterjet thrusts of the model boat with forward speeds are predicted by towing and free-running test results. Turning and zig-zag model tests are carried out at the speeds of around 20 knots in full-scale. Next, full-scale manoeuvring trials are performed with the same approach speeds. The resistances and waterjet thrusts are estimated by model test results and waterjet thrust curves. The full-scale boat may have smaller frictional resistance coefficients than the scaled model boat at the same Froude number, so the full-scale boat requires relatively smaller waterjet thrusts than the scaled model boat. Because of the smaller steering force, the turning radius of the