Using computational fluid dynamics to model sail interaction—the ‘slot effect’ revisited

This paper investigates the effects of interaction between the foresail and the mainsail on a sailing vessel, using Reynolds Averaged Navier Stokes based Computational Fluid Dynamics to provide flow visualisation and quantitative analysis. The effect of the foresail sheeting angle upon a sailing rigʹs performance is compared and discussed. The phenomena of ‘Upwash’ and mainsail separation are investigated in an attempt to demonstrate both visually and quantitatively the importance of the foresail and its correct orientation in maximising lift. The paper hopes to finally lay to rest the misconceptions surrounding the ‘slot effect’ between sails, showing how the foresail increases upwash and reduces the velocity of the flow in the slot. It aims to clarify the theory behind sail interaction.