The present work discusses an upwind case study about full scale measurements gathered during navigation on the Politecnico di Milano Sailing Yacht Laboratory (SYL). SYL is a 10m sailing boat, consisting in standard instrumentation, integrated dynamometer, a 3D flying shape detection system and distributed pressure sensors on sails. Particular attention was devoted to pressure measurements: full scale results are analysed and compared with wind tunnel test. The comparison of full scale/wind tunnel pressure distributions holds consistently, with the highest differences observed in the regions close to the leading edge. Critical aspects related to performing full scale measurements are also discussed.

The paper presents an overview of a joint project developed among Politecnico di Milano, CSEM and North Sails, aiming at developing a new sail pressure measurement system based on MEMS sensors (an excellent compromise between size, performance, costs and operational conditions) and pressure strips and pads technology. These devices were designed and produced to give differential measurement between the leeward and windward side of the sails. The project has been developed within the Lecco Innovation Hub Sailing Yacht Lab, a 10 m length sailing dynamometer which intend to be the reference contemporary full scale measurement device in the sailing yacht engineering research field, to enhance the insight of sail steady and unsteady aerodynamics [1]. The pressure system is described in details as well as the data acquisition process and system metrological validation is provided; furthermore, some results obtained during a wind tunnel campaign carried out at Politecnico di Milano Wind Tunnel, as a benchmark of the whole measuring system for future full scale application, are reported and discussed in details. Moreover, the system configuration for full scale testing, which is still under development, is also described.

Following the 33rd America's Cup which featured a trimaran versus a catamaran, and the recent 34th America's Cup in 2013 featuring AC72 catamarans with multi-element wing sail yachts sailing at unprecedented speeds, interest in wing sail technology has increased substantially. Unfortunately there is currently very little open peer-reviewed literature available with a focus on multi-element wing design for yachts. The limited available literature focuses primarily on the structures of wings and their control, rather than on the aerodynamic design. While there is substantial available literature on the aerodynamic properties of aircraft wings, the differences in the flow domains between aeroplanes and yachts is significant. A yacht sail will operate in aReynolds number range of 0.2 to 8 million while aircraft operate regularly in excess of 10 million. Furthermore, yachts operate in the turbulent atmospheric boundary layer and require high maximum lift coefficients at many apparent wind angles, and minimising drag is not so critical. This paper reviews the literature on wing sail design for high performance yachts and discusses the results of wind tunnel testing at the Yacht Research Unit at the University of Auckland. Two wings with different symmetrical profiles have been tested at low Reynolds numbers with surface pressure measurements to measure the effect of gap geometry, angle of attack and camber on a wing sail’s performance characteristic. It has been found that for the two element wing studied, the gap size and pivot point of the rear element have only a weak influence on the lift and drag coefficients. Reynolds number has a strong effect on separation for highly cambered foils.