Wind tunnel tests on the effect of a ship hull on rudder-propeller performance at different angles of drift

This report presents the experimental results from a series of wind tunnel tests. The tests investigated the influence of various upstream bodies on the performance of a representative ship rudder-propeller combination for different angle of drift. All the tests were carried in the 3.5m x 2.5m low-speed wind tunnel at the University of Southampton and are an extension to basic rudder-propeller tests which have already been carried out and are reported elsewhere. The model rudders tested were all-movable and the model propeller used was based on a Wageningen B4.40. Rudder forces and moments and propeller thrust, torque and revolutions were measured for all conditions tested. A standard series of flow conditions were used. These were free-stream flow (no propeller present) and tests at propeller open-water advance ratio of J of 0.94, 0.51 and 0.36. For these conditions, forces were measured at rudder angles between -40 degrees and +40 degree. In addition, a select sample of tests were carried out for both larger rudder incidence and for tests in the second quadrant and at a low advance ratio J of 0.17. Three types of test were carried out: 1) the rudder-propeller combination alone was tested at drift angles of -15 degrees, -7.5 degrees, +7.5 degrees, and +15 degrees; 2) at two angles of drift of -15 degrees and +7.5 degrees, three different lengths of centre-board were place upstream of the rudder-propeller combination to simulate the effect of a thin upstream hull on performance; 3) at two angles of drift of -15 degrees and -7.5 degrees a representative ship hull form based on the stern of the Mariner class of vessels was mounted upstream of the rudder-propeller combination to assess the influence of hull thickness. Pressures were measured at 200 locations distributed over the rudder surface for the rudder-propeller combination alone and the results are given as both chordwise pressure distribution for eight spanwise locations and as distributions of spanwise sectional load distributions. The results give an essential insight into the behaviour of flow around the stern of a vessel providing rudder force data for use in more realistic manoeuvring simulations and detailed data for the validation of numerical models of the ship rudder-propeller-hull interaction problem.