Rhino, are you using the original nacra 5.8 rudders? if you are they're probably too small, especially if you are using a spin.

Not that it would affect your helm. When I sailed the nacra 5.8 worlds a few years back the top guys were swapping out the standard 5.8 rudders with nacra 5.0 rudders which are bigger and the boat was supposedly going better.

And yes, if you don't have much rake on the mast, I would certainly put some in.