Rudder design data for small craft

The purpose of this paper is to review available design data and provide a design procedure for the rudders of high performance small craft. While adequate background is presented to satisfy the user with a theoretical bias the needs of the practical designer are borne in mind and all the required data are presented in graphical form which does not require a full appreciation of the theoretical aspects for its use. A design approach is outlined which basically employs free-stream data together with the relevant corrections for effective aspect ratio, inflow angle of attack and velocity. Free-stream data applicable to the design of small craft all-movable and skeg rudders are presented and reviewed. Applicable design criteria regarding speed, angle of attack and influences of proximity of hull to top of rudder are discussed; data relevant to surface effects as applied to transom rudders, or other types operating near the surface, are considered and the influence of free surface assessed. The data are presented in non-dimensional form whereby comparisons between the various rudder types, or variation in parameters for a particular rudder type, can be made; some worked examples are included in appendices to illustrate the use of the data. General conclusions are drawn from the available data and design recommendations made.