Abstract：The maximum pipeline efficiency is applied to design water-jet propulsion in traditional design methods. However, the parameters under operation condition often deviate from the rated point and the efficiency of water-jet propulsion is always less than the expected one. In this paper, the inlet flow passage of SDPM-450 water-jet propulsion was examined to overcome this discrepancy. Based on the analysis results of the efficiency in water-jet propulsion under the optimal operating point, the parameter selection methods was optimized to meet with the object of the maximum whole propulsion efficiency. The optimal operating point is the working point with the maximum propulsion efficiency. According to the extreme value theory, the mathematical equation was deduced to determine the optimal operating point. The mathematical equation is listed as K=2εα. The numerical simulation of UDS back tracing method was used to verify the derived mathematical equation. The mathematical equation was applied to determine the designed parameters of water-jet propulsion after the correction. The higher efficiency designed method, which the variables of nozzle diameter and wake fraction are selected in the designed equation, is obtained. These all provide the theory foundation for the higher efficiency design of water-jet propulsion.
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