Predicting the Effects of Interaction between Yachts Sailing Upwind

Abstract: The ever-growing yachting industry has come to play an important role in the maritime sector, resulting in an increasing demand for highly technologically advanced cruising and racing sailing yachts. In the aim of producing faster yachts and faster sails designers and sailors has come a long way understanding the science of sailing. While the theories and reality of airflow around one or more sails is widely explored the influence of introducing another yacht in close proximity is however not. The principal value of investigating the influence of interaction between yachts would apply to methods of using this knowledge to create an advantage in a racing situation. In extension practical applications would be on-board decision support software rather than progression of yacht and sail design. The aim of this thesis project is to create a greater understanding for the phenomena of interaction and how to better predict the effects of interaction by conducting a series of experiments in The University of Auckland Twisted Flow Wind Tunnel. A general approach to the problem was used including investigation of obvious factors such as the yachts relative position, sail trim and wind angle but also more specific factors such as heel angle and sail design were considered. After establishing the distribution and range of significant interaction influence, a 3-dimensional flow field mapping was performed following an investigation attempting to quantify the influence of 2-dimensional versus 3-dimensional effects. Evaluation of different techniques for measuring interaction and the accuracy of the measurements has been fundamentally important throughout the project. The results, presented as a summary of performed wind tunnel tests, show the effects of interaction that may be experienced for a specific sailing scenario (Stage 1) and how the theory of interaction may be approached in three dimensions (Stage2) The implication of these results reveals the difficulty of fully explaining all aspects of the interaction phenomena or even more so creating a theoretical model valid for all conditions and scenarios. With consideration made to the limitations and possibilities of an creating an empirical model addressed in this report extensive full-scale testing may however serve as sufficient input to future decision support software.