Hi Wouter,

The whole thing would be easier, if you use Stealth type rudders. If you want to have an adjustment for the foils, you could use a flexible trailing edge (aluminium strip) or even a fixed Gurney Flap. The first solution can be seen on many light aircraft, as an aileron trim device. The first big advantage is: no moving parts apart from the sliding rudder itself. The second (maybe even bigger) advantage: No edges, gaps, slots, etc. between rudder and horizontal foil, which easily could create drag and cavitation (I have had servere problems with cavitation on my Dart rudders, when I rebuilt the rudder nose).
If you seriously consider the solution with fixed foil and adjustable trailing foil edge, you can contact me directly for more information about this trailing edge devices.

Cheers,

Smiths Cat

By the way: If you balance the pitch trim of your boat with such a device, you do nothing else than putting additional weight on the stern of it, which causes drag... and I am wondering that foils are legal in F16. Maybe the F16 scene will be dominated by hydro foil cats in a few years.