Rolf,

Excellent question. Not much information out there. I would like to know what the area on an existing F16, F18 and N20 board is, as well as the basic chord length.

I need to pull up my numbers, but if I recall correctly a few things came to light in my analysis:

1) The NACA 6 series laminar foils offered very very little performance over the NACA 0012 or 0009. All is lost if the foils gets gummed up in any way.
2) Need to check the Eppler foils again, they were better in higher lift conditions than the NACA series but the NACA foils have lower drag in low to modest lift coefficient regime (sub Cl=0.5).

Here is a white paper from Tom Speers on his H105 foil, but I don't think the .dat file is available: http://www.foils.org/hysecdes.pdf

More info from Tom: http://www.boatdesign.net/forums/sailboats/best-foil-shape-rn-250-000-750-000-a-1577.html

I would use a NACA0009 on the daggerboards and NACA0012 on the rudders if I were to build tomorrow.