BTW, 'bout your mod: I myself didn't really try it out yet since - what do you know - I had some trouble to shoot first.
Going to be some more mod testing for me the next few days to find out what works best for me. Remember, I come fresh from SHIII stock install.
After seeing the manual nav tutorial vids though on youtube, I can imagine that the helmsman's incompetence in sticking to a course would bother me greatly though and I guess that problem is hardcoded. :/