Always a lively debate. I will agree there is a potential performance increase in the use of NACA foils, but im also on the side of simplicity. Flat metal plates work as leeway prevention,but not as efficient as a NACA foil. As Ed has pointed out, rig and sails can make more of a difference to windward performance than plate alone,as can all the other aspects of hull shape,crew ability etc etc ad nausism. I have just made a set of foils,rudder and daggerboard for a dayboat,theres about 30% flat sides and the rest is tapered,thicker at the nose and shallow angle all the way to the back square edge. Took about 2 hours to do both with an electric plane and a disc sander. Im guessing it wont stall as soon as a flat plate, but it also wont have as much lift as a true NACA foil, but as its going in my own dayboat with a balanced lug rig i was not prepared to spend the extra hours creating a true foil. That does not mean i dont respect the years of work gone into foil research,but as an owner/builder,its up to me to decide on what i think is performance worthy in terms of time invested.
Another project will have a 0012 drop keel and a 0009 rudder section,but that project will be built as a performance boat. Cheers