Improvement of Turning Performance by Cyclic Control of Motor-driven Waterjet Propulsion System

This study was aimed at improving the turning performance of an electric ship with a waterjet propulsion system under low load operation by applying cyclic control of motor output. The required patterns of the cyclic control, including duty ratio and waterjet frequency, for improvement of turning performance were estimated by predicting thrust power of the waterjet during cyclic control. The effectiveness of the cyclic control was also evaluated through turning performance tests using an electric boat “Raicho-S”. By analyzing the average thrust power of the waterjet based on predicted motor revolution during cyclic control, it was confirmed that the contribution of cyclic control was more enhanced at waterjet frequencies ranging from 0.8 to 2.0 s-1 and at duty ratios ranging from 0.33 to 0.6. These estimated patterns of cyclic control were included in the turning performance test conditions of “Raicho-S”. Improvement of turning performance, including increase in turning speed and decrease in turning radius, was confirmed. The increasing and decreasing tendencies of turning speed in relation to the jet frequency and the duty ratio were in qualitative agreement with those of thrust power predicted in the preliminary analysis. The turning performance during cyclic control was confirmed to be optimized at the condition in which the jet frequency and the duty ratio were respectively 1 s-1 and 0.33 in the present test conditions.