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.
Velocity Prediction of Wing-Sailed Hydrofoiling Catamarans
The paper presents a Velocity Prediction Program for hydrofoiling catamarans with solid wing sails. Starting from a description of the mechanical model, suitable models are identified for the forces that act on the boat components. The study is deliberately limited to means for restricted methods where computational resources and budgets are limited. Enhanced lifting line approaches are described for the wingsail and appendages. Windage is calculated from force coefficients and dynamic pressure while hull resistance is determined by means of a potential flow solver. The description of the implementation is followed by the presentation of the results including a comparison to measured data. Additionally significant findings in terms of overall force composition and distribution as well as loading on specific components of the catamaran are presented and discussed. Finally, some of the challenges encountered during the study are discussed. It was found that the VPP predictions compared favourably with measured data from the 34th America’s Cup in San Francisco in 2013.
A relatively new phenomenon within the sailing world is the use of hydrofoils to boost sailing performance. This technique is applied to a wide range of boats, from dinghies to ocean racers. An interesting question is whether one of the slowest racing boats in the world, the Optimist dinghy, can foil, and if so, at what minimum wind speed. The present paper presents a comprehensive design campaign to answer the two questions. The campaign includes a newly developed Velocity Prediction Program (VPP) for foiling/non-foiling conditions, a wind tunnel test of sail aerodynamics, a towing tank test of hull hydrodynamics and a large number of numerical predictions of foil characteristics. An optimum foil configuration is developed and towing tank tested with satisfactory results. The final proof of the concept is a successful on the water test with stable foiling at a speed of 12 knots.
Fluid Structure Interaction Design Development of Passive Adaptive Composite International Moth Foil
The International Moth is a single-handed ultra-lightweight foiling development class boat, and it fol- lows open class rules. Therefore, the designer and builder have full liberty to develop and produce the fastest boat . It is possible to adapt the internal structure of the fixed foil to achieve a tailored twist angle for a given load. Exploring the possibility of using Passive Adaptive Composite (PAC) on the moth hydrofoil to control its pitch angle enables the boat to achieve a stable flight in a wide range of weather conditions whilst reducing the induced drag, passively decreasing the angle of attack in increased boat speed. Using PAC in a multi-element foil, such as the International Moth one, will allow the structure to achieve a constant lift force with speeds higher than the design take-off speed with less need to con- stantly modifying the rear foil section. Toward the development of a PAC moth fixed foil, experimental and numerical results for a single element aerofoil, able to achieve a linear decrease in lift coefficient with increase in wind speed, are presented and discussed. The results present the aero-elastic response of the foil explaining the complexity involved in fluid-structure interaction problems.
Towards Unsteady Approach for Future Flutter Calculations