A modified lifting line analysis for semi-balanced ship skeg-rudders. Southampton, UK, University of Southampton, 81pp.
(Ship Science Reports, 20).
A modified lifting line theory is developed which supports the form of skeg-rudder experimental free-stream data obtained previously, and forming the subject of separate reports.
It is demonstrated that satisfactory predictions of the form of the spanwise loadings for different skeg and rudder angles can be made using lifting line theory with the effect of the skeg being incorporated as local incidence reduction and the effects of the mid-span and tip trailing vortices being incorporated as twist corrections to the local incidence. The correct magnitude of the distributions is obtained by applying suitable empirical corrections. Chordwise centre of pressure is derived empirically.
It is concluded that whilst the theoretical approach is relatively simple and requires empirical correction, it gives very realistic predictions of skeg-rudder performance characteristics.
The theory is used to provide a limited extension to the experimental data. Predictions using the modified theory show that, for fixed aspect ratio and taper ratio, changes in the skeg depth have the largest influence on the production of lift whereas changes in the skeg chord and sweep mainly affect the stock position and the required balance area.
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