In this paper we propose a rational viscous Computational Fluid Dynamics (CFD) methodology applied to sailing yacht rig aerodynamic design and analysis. After an outlook of present challenges in high speed sailing we emphasized the necessity of innovation and Computational Fluid Dynamics to think, validate and optimize new aero-hydrodynamic concepts. Then we present our CFD methodology through CAD, mesh generation, numerical and physical modelling choices and their validation on typical rig configurations through wind-tunnel tests comparisons. The methodology defined, we illustrate the relevance and wide potential of advanced numerical tools to investigate sailing yacht rig design questions like the relation between sail camber, propulsive force and aerodynamic finesse, and like the mast-mainsail non linear interaction. Through these examples, it is shown how sailing yacht rig improvements may be drawn by using viscous CFD (RANS). Then the extensive use of viscous CFD based on Reynolds Averaged Navier-Stokes equations rather than wind-tunnel tests on scaled models for the evaluation or ranking of improved design open the door to time saving. The last part illustrates on a preliminary study of the Y. Parlier Hydraplaneur double rig how the proposed CFD methodology may be applied to this complex largely unknown rig. We show how it is possible to increase our understanding of his flow physics with strong sails interactions and we hope this will open new roads toward optimized design. Along the paper, the necessary mutual comparison presented between CFD and wind-tunnel test will be also the occasion to focus on limitations and drawbacks of viscous CFD tools to discuss them and address their future improvements.