The free-stream characteristics of a semi-balanced ship skeg-rudder

Abstract

The results of free-stream wind tunnel experiments on a semi-balanced skeg rudder are presented.

The tests on this rudder, which has skeg and overall characteristics which are typical for the rudders fitted to many modern ship types, are the first in a projected series of tests on skeg rudders.

The experiments establish a better understanding of the working and performance of the semi-balanced skeg rudder, and provide design data. Results are presented as lift, drag and normal force coefficients and centre of pressure for the rudder plus skeg combination, for the rudder alone and skeg alone; a complete range of rudder angle of attack was tested for selected positive and negative angles of attack on the skeg.

In order to provide a basis for comparison, the all-movable rudder case was simulated by sealing the gap between rudder and skeg. The results for the all-movable case compare very satisfactorily with existing published data, thus confirming the satisfactory operation of the new dynamometer, instrumentation, test techniques and analysis.

The results for the skeg rudder show that, with increasing angle of attack, discontinuities occur in the growth of lift together with a large movement of centre of pressure. The skeg rudder results are compared with those for the all-movable case, and the flow breakdown accounting for the discontinuities in the skeg rudder characteristics is discussed.

Visual flow studies with supporting photographs are described; these are in general agreement with the flow breakdown indicated by the force measurements.

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