We have broken rudder castings on the N20, F18,F20c and I would say it was from stress from the surf launchings. We did sail the rest of the GT300 with the castings off our F18 with no problems.
As far as the comment about the F20c not making it in the Tybee I would disagree. The only problems we had in the GT300 were the boards breaking
which was do to a first generation of board with only one stringer(now the boards have 2 stringers) and the spin pole breaking going out through the surf. The pole is just to light of gage and is not supported out far enough to handle the large waves. We tied a line from the forestay bridle intersection to the spin pole in front of the snuffer ring to help give support to the pole which worked for the rest of the GT300. Mike now has a distance racing spin pole that is a heaver gage. The boat seems to be plenty strong and really well made it just needs to work some bugs out which is the case for all new designs. The first year we did the Worrell 1000 on the I20 we broke rudder castings and gudgeons,rudders,boards and most of the boats were getting holes in the bottoms from beach landings. All those items were addressed to make the N20 what it is today.