Selection of Hydrofoil Waterjet Propulsion Systems

Abstract

The selection of water jet propulsion systems for hydrofoil craft requires sophisticated techniques which must take into account the mutual interaction of numerous craft subsystems. These interactions include the effect of parasitic (appendage) drag, cruise and takeoff power levels, subsystem weight fractions, and machinery room arrangements. It is shown that propulsive efficiency, per se, is not a useful parameter as a selection yardstick even when rigorously evaluated to account properly for all internal duct losses. The recommended selection technique consists of the comparative evaluation of over-all craft performance for numerous integrated subsystem combinations by means of a comprehensive digital computer program. It is shown by a specific example, i.e., a 300-ton, 50-knot hydrofoil craft, that through the recommended approach and the use of state-of-the-art pumps with proven design features, power requirements and total water jet-system weight fractions can be maintained at reasonable levels. This objective is achieved without resorting to more sophisticated pump designs which normally require state-of-the-art verification for application to water jet propulsion. Also included is a discussion of the critical elements of water jet subsystems, with particular emphasis on the technique required for the experimental evaluation of suitable inlet configurations.