Turning characteristics of waterjet propelled planing boat at semi-planing speeds

It is necessary to investigate the turning characteristics of a waterjet propelled planing boat at the design stage for its safe operations. In this research, two kinds of model tests were carried out for the analyses of turning abilities of a designed planing boat. Towing tank tests were performed for a 1/6.5-scaled bare hull model to confirm the resistance performance according to its forward speeds. Flow patterns around the hull were investigated at semi-planing speeds. And turning tests were carried out for a 1/2.3-scaled free-running model at semi-planing speeds. When the heels during steady turns are less than about 5 degrees, running trims of the free-running model boat are similar to those of the bare hull model boat straight-towed at the same speeds. Speed reduction ratios and advances over tactical diameters of waterjet propelled planing boats show similar tendencies in comparison to those of displacement ships. When the waterjet propelled planing boat turns rapidly with high impeller rpm, 'side-slip' can be occurred. In that case, tactical diameter becomes so small and steady turn speed is relatively high. Waterjet propelled planing boat shows large inward roll angles at the beginning of turn, and inward heels increase with increasing steady turn speeds.