Thanks Andrew & Jake - but I think I didn't explain. Best way is to look at "Phil's foil" page, http://www.philsfoils.com/designTips.html#gybinghead

It seems to me that if trailing edge of daggerboard is fixed in the trunk, but front edge is a bit sloppy, it produces the efect of a gybing board. No extra mods necessary. What am I missing?