The project described in this thesis was undertaken in order to contribute to the understanding of incompressible fluid flow through a flush entry S-bend intake duct as used for waterjet propulsion. Field tests using a planing hull test boat were carried out to investigate the operating conditions of a typical waterjet installation. Intake velocity ratios (IVR's), pump loading parameters, intake duct static pressure measurements, intake flow directions and the ingested hull boundary layer characteristics are reported here. Wind tunnel tests modelling the intake flow through both the bare intake duct shape and the complete waterjet unit are also reported. The Reynolds number mismatch between these tests and the real waterjet installation is investigated and discussed. Numerical modelling of the intake flow was carried out using a turbulent viscous flow software package. The effects of varying the intake flow conditions, the Reynolds number of the calculation, the ingested boundary layer thickness and the turbulence model employed in the flow prediction are investigated. A thorough understanding of the flow through the intake has been developed. The flow features are discussed and their effects upon and relative importance to the overall performance of the waterjet are reported. A comparison between the field data and results from the wind tunnel tests and numerical modelling procedures is made. The relative merits of each modelling method are investigated and reported.