In the last decades, the use of foils on sailing yacht has highly increased. Whether they are mono or multihull, yachts are using foils to reduce their drag forces and then, to increase their speeds in a large range of wind and sea conditions. Several CFD-based studies have already been carried out in order to optimize the foil’s shape and location on the hull, but feedbacks on the yacht’s behaviour is mainly given by the crew when sailing at sea. The aim of the presented paper is to propose a complementary and faster approach that could help to predict and quantify the yacht behaviour in calm water and in waves while sailing under foil’s action. This approach is well known as a system-based modeling and is a mathematical method that leads to understand the complexity of a system from the study of its interactions in their entirety. The paper will present the ability of the system-based approach to predict the attitude of a catamaran while performing maneuvers such as turning circles with 35 degrees of rudder deflection and zigzag tests 10-10 and 20-20 shapes.

Hydrofoil sailing has been able to unlock performance characteristics previously confined to speed records, making them available to multiple racing fora. The America’s Cup is now regularly sailed at 40 knots, Moth sailing dinghies and A-Class catamarans achieve up to 30 knots on standard race courses. The systems employed to achieve these speeds have been refined to such an extent that high speeds are regularly attained. However, there are still large gaps in our understanding of the fundamental hydrodynamic phenomena to enable safe control of these machines and continued increases in performance. For example, arbitrary ventilation pathways have been noticed and yet are not fully explained. This paper provides the means to unlock the methods of quantitatively establishing a pathway for arbitrary ventilation and for measuring the flow regime complexity around such foils. These two methods have been developed over many years by the collaborators mentioned in this paper. The result is a valuable contribution to capability available to the sailing research community. An additional two methods of experimental analysis have been detailed within the paper.

This paper describes a method to calculate the aerodynamic forces generated by a rigid two-element wing together with a jib. Additionally, investigations of hydrodynamic flow forces generated by water-piercing Lshaped foils are introduced. The aerodynamic and hydrodynamic flow force prediction methods are combined in a velocity prediction program featuring a constraint optimization method in order to predict boat speed and wing and foil trimming parameters for its maximization. A velocity polar calculated by applying this method to a 50-foot catamaran is shown and the result of some studies are presented, varying design parameters of the catamaran.