Wind tunnel investigation of the influence of propeller loading on a semi-balanced skeg rudder

Performance tests were carried out in the 3.5m x 2.5m working section wind tunnel at the University of Southampton to investigate the behaviour of a semi-balanced skeg rudder behind a ship propeller. The semi-balanced skeg rudder had a mean chord of 667mm, span of 1000mm, taper ratio of 0.8, and with a NACA0020 section. Results were obtained for four different propeller advance ratios of 0.25, 0.36, 0.51 and 0.94 corresponding to propeller rpm of 2850, 2100, 1460, and 800 with a tunnel wind speed of 10m/s. The four-bladed propeller had an 800mm diameter, a mean pitch ratio of 0.95 P/D and was based on a modified Wageningen B4.40. Rudder force characteristics were obtained for rudder incidences between -40° and 35°, for three skeg angles of -5.4°, -0.4° and 4.6°. The corresponding change in propeller performance due to the rudder was also assessed. Pressure measurements were made at 25 positions around the chord at one span and the influence of propeller thrust loading observed. A photographic record was made of a tuft study of the flow over the rudder surface