Flows in sailing

Sailing boats interact with flows of two very different fluids: air and water. Moreover, sailing boats are able to make their way through the water surface only because they work at the interface of these two fluids which are moving relative to one another at different speeds and directions. Before we dive into other aero-hydrodynamic considerations like lift generation, drag, etc., it is essential to describe first the nature and characteristics of these flows that make sailing possible.