One of the key issues at early design stage of a high-speed craft is the selection and the performance prediction of the propulsion system because at this stage only few information about the vessel are available. The objective of this work is precisely to provide the designer, in the case of waterjet propelled craft, with a simple and reliable calculation tool, able to predict the waterjet working points in design and off-design conditions, allowing to investigate several propulsive options during the ship design process. In the paper two original dimensionless numerical procedures, one referred to jet units for naval applications and the other more suitable for planing boats, are presented. The first procedure is based on a generalized performance map for mixed flow pumps, derived from the analysis of several waterjet pumps by applying similitude principles of the hydraulic machines. The second approach, validated by some comparisons with current waterjet installations, is based on a complete physical approach, from which a set of non-dimensional waterjet characteristics has been drawn by the authors. The presented application examples show the validity and the degree of accuracy of the proposed methodologies for the performance evaluation of waterjet propulsion systems. 1. Introduction The last technological advances in marine waterjets have put them ahead of conventional propeller systems for many types of high-speed marine applications, including naval vessels, ferries, workboats, and pleasure craft. Modern waterjet propulsion systems offer, for these applications, several advantages, such as high efficiency, rapid acceleration, and an excellent maneuverability, in addition to minimum possible draft with no protruding underwater appendages. This latter aspect allows operation in shallow waters and in water with floating debris that may foul or damage a typical marine propeller. This means also an increasing safety for persons and animals swimming near the vessel. In the marine jet propulsion, a water mass is drawn into the waterjet unit through an intake screen at the base of the intake, which is mostly mounted flush with the hull bottom. The pumping unit, consisting of impeller and stator, increases the pressure of the flow, which is then discharged at high velocity at the nozzle. The reaction to this high speed jet stream provides the net thrust force, which is fully transmitted to the hull by the thrust bearing. The steering nozzle directs the jet stream as commanded by the helm, providing high turning forces to either port or starboard. An
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