Scouting a bit the boatbuilding forums I came across a very clever idea proposed by Ross Langford and appearing on duckworks magazine pages:
another approach to shaping foils
Great idea I thought right away, and I decided to follow its principle. Ross provides the complete solution including an excel sheet to design the router gig he proposes for the purpose.
For the fun of it I decided to apply the method but to redo the calculation, using 2D cartesian equations rather than trigonometry. I therefore wrote a MATLAB script that computes the foils NACA profile, its offset for the router cutter and finally outputs an AutoCAD script for printing purposes.
I am happy to provide the scripts to anyone interested ... they worked out pretty well!
Here's the model for my pathfinder's centerboard NACA profiler:
The process is into two phases and mall portions of the centerboard are left unshaped to allow to turn the board around and shape its other face.
Its great to see the NACA profile appear through the sawdust and the noise of the router.
I have no idea how I could have achieved a precise and constant profile throughout the board otherwise!