Ref: http://www.dreesecode.com/other/aflprimer.pdf

Read this first. Then consider that there is no free lunch <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> It is all compromises and what you want to optimize your boat for. Aspect ratio is the most important property in my opinion, but it can be a double edged sword, especially so in rough weather.

When that has been said, there is a good chanche the world have moved on since your H-18 was built. I would not have modified the existing foils, but got some new ones (or buildt some) and modified the daggerboard wells to accept new boards.