The best study on proa foils I have read was made by Tom Speer. You can find the material here:http://www.basiliscus.com/ProaSections/ProaIndex.html . Tom is (was?) working for Boeing and later involved in the design of the wingmast of the BMW Oracle for America's Cup this year. His level of knowledge on foils is so high that it is sometimes difficult to follow with the quite basic knowledge level I have... But read the paper and see attachments and you will know a lot more.