Surface Effect Ships (SES) have great potential to increase the speed and cargo capacity of modern surface vessels. The resistance characteristics of an SES vary widely as a function of speed, with notable presence of one or more drag humps. The magnitude of these drag humps has been shown to be greatly affected by changes in water depth (Mantle, 1973; Van Dyck, 1972; Doctors, 2006). Additional variations in resistance due to sea state must also be accounted for and consequently, the selection and sizing of an appropriate propulsion system is not trivial. For highly loaded applications, SESs typically employ the use of waterjet propulsion. The propulsion system must satisfy many criteria, including cavitation avoidance, powering limitations, and maximizing fuel efficiency. These three goals are difficult to meet simultaneously, particularly when the performance of the system over the full operational range needs to be considered. Hence, an appropriate methodology is necessary to choose the optimal solution. The objective of this work is to develop a systematic methodology for the first-order design of a waterjet by optimizing the overall efficiency and satisfying all performance requirements over the entire operating regime, as opposed to selecting a discrete number of design points. In this work, a preliminary design of a waterjet propulsion system for a full-scale SES with a top speed of 40 knots is performed with consideration for cavitation inception and variations in resistance due to changes in water depth and sea state. The resistance characteristics are determined from model tests as reported by Van Dyck (1972). The waterjet performance is then predicted for various nozzle sizes using one-dimensional momentum theory. The optimal waterjet size is then selected based on the joint probability distribution of the operational space as functions of the vessel speed and resistance. Finally, the thrust characteristics of the optimal waterjet are presented and compared against ones designed for the endurance speed and top speed.

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