I'm not sure how it would work on a G cat but I used to mix up some of that epoxy stick stuff. and jam it in the bottom of the casting. Wrap the corrisponding part of the rudder with saran wrap and lock the rudder down, let it dry overnight. You can always knock the chunk back out if you want to make an adjustment, an re-do it. It worked really well on my Hobie 20, I haven't tried it on the N-20 but I probably should.