Wind tunnel tests on the influence of propeller loading and the effect of a ship hull on skeg-rudder performance

The results of wind tunnel tests on a rudder operating downstream of a propeller and hull combination are presented. The tests used the 3.5m x 2.5m low speed wind tunnel at the University of Southampton. This report presents the results for two rudders, one all-movable the other a semi-balanced skeg-rudder. The rudders both have a mean chord of 667mm and NACA 0020 sections, but with varying taper ratio. A four bladed, 800mm diameter, adjustable pitch propeller was used. This propeller is a modified version of the Wageningen B4.40 series. Open-water results for the modified design were validated against published data. The rudder propeller combinations were tested both in a freestream and in way of a representative Mariner stern hull form. The test consisted of a series of parametric studies into the effect of the longitudinal and lateral distance between the propeller and rudder, propeller thrust loading, presence of a hull, and presence of a hull at a yaw angle. A five-component strain-gauge dynamometer was used to measure lift, drag and three moments on the rudder. A rotating strain gauge dynamometer measured the developed thrust and torque of the propeller. In addition, both spanwise and chordwise pressure distributions were measured on the rudder and hull surface to provide a detailed knowledge of the distribution of forces over the hull and the rudder. A tunnel wind speed of 10m/s was used and propeller revolutions were varied between 0 and 2100 rpm. Results are presented in the form of non-dimensional coefficients of lift (C subscript L), drag (C subscript D), spanwise (CP subscript S) and chordwise (CP subscript C) position of the centre of pressure variation with incidence for the rudder. The influence of rudder on propeller performance is given in terms of non-dimensional thrust (K subscript T) coefficient variation with advance ratio (J). The surface pressure measurements on the rudder are presented as both a spanwise distribution of the local lift coefficient and as a surface pressure distribution. The surface pressure measurements on the hull are presented as spanwise and chordwise distributions together with integrated normal force coefficient over the range of rudder angles. The results provide data data for detailed rudder design, for numerical modelling of the rudder/propeller and hull interaction problem and for use in manoeuvring simulations.