Vol.4 : Computational Turbulent Incompressible Flow

Secret of Sailing

The main secret of sailing, known by the Fenicians but not the Vikings, is to advance against the wind. For this purpose the sails act like airfoils creating a lift force with a forward drive component and perpendicular heel component tilting the boat.

The keel also acts like an airfoil generating a lift balancing the heel force.

Vol 4 shows that a sail gives maximal lift at angle of attack of 22 degrees, while the lift/drag ratio quickly drops after 16 degrees, which does not matter since the main drag results from the water flow around the hull.

Vol 4 shows that for the typical 10 degrees of attack of a keel, the main lift force arises at the leading edge (while for larger angles the whole wing section is involved), why explains why modern sailing yachts have a deep narrow keel combining high lift with small skin friction drag (but not narrow sails).

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