Colin, recommending a boatdesign forum thread to anyone desiring a clear and correct explanation of anything is cruel and unusual punishment.

As for Gentry's journal article, it's good as a correct description of lift, but it looks like he screws up the correspondance between upwash and pointing ability. (Fig 35, p15) Anything that increases upwash (jib in the presence of a main) or increases downwash (main in the presence of a jib) decreases pointing ability. I wonder if he meant power to windward, because slats, slots and flaps on a wing will all create more lifting power, but at the expense of an increased downwash angle.