Streamlines around a downwind sail Streamlines around an up sail

Conventional Sails

Computational Fluid Dynamics allows the calculation of the lift, drag and centres of effort of a sailing rig and will inherently account for the complex interaction between sails. Even modern velocity prediction programs rely on simple empirical formulae for lift and drag coefficients along with complex geometric calculations for centre of effort and sail area. Inaccuracies, or approximations, within this long series of calculations lead to rig optimisation that does not reflect the reality of the physical situation.

Interactions between sails is a complex and important part of rig design. A full sailing rig simulation will inherently include these interactions as it calculated the lift and drag coefficients of each sail, or all sails together.

CFD simulations of sails is equally suited to high quality promotional material, or serious scientific study. The following is a quick study into the lift and drag coefficients of a downwind sailing configurations. Notice how the optimum sheeting angle of the spinnaker and main sail are determined through a series of tests. Automatic trimming of sails is also possible with additional feedback of aerodynamic forces. This quick demonstration is carried out with a 1 million cell calculation for each angle of attack. Higher resolutions and sail area calculation based on accepted formula will increase accuracy.

Sail Force Coefficients for downwind sailing

See the Rigid Wing Sails section for addition information.