Hi Alan,
Air and water at low speeds behave very similarily. The same equations and laws can be used. As far as we are concerned the air flowing across our sails is incompressible.
I doubt that sailboard skegs cavitate. It takes horsepower to make a propellor in water cavitate. I think they probably ventilate, pump air down the leading edge, because of a swept back leading edge and the foil becomes ineffective when this happens. The aerodynamics that are most closely applied to sailboats are those from other slow moving ships of similiar size like gliders. The highest performance gliders in the world are all carbon with slightly swept forward wings, foils, and they are built in Germany.
Bill