How Big A Keel Verses Sail Area?

Looking to change the fixed keel on my boat to a retractable one, more of a daggerboard with a ballast bulb. Looking at the newer race boats I get the sense they have a lot less lateral plane area than older designs. My boat appears to have two to three times the lateral area that it needs. The boat is a custom 40' ultralight design from the 1980s. Ideas on just how much area one needs relative to sail area or overall length? Preferred NACA foil? Thanks

 

There is a good discussion of that in http://www.boatdesign.net/forums/hy...vs-keel-area-stability-calculation-43280.html

 

Ah... found some articles by Sponberg and Vacanti that answer all my questions- thanks!