It could be a casting quality issue. The early lower castings were flat on the sides and didn't have the rib on them. Nacra saw the problem and mad changes. Possibly they need to beef them up a little more with the 20C. The boat is wider with more sail area and the center of lateral effort moved back, much more so than the N20. A few years ago in the GT300 we were single trapped spin reaching when the leward assembly let loose. It ended up being the upper eyebolt had snapped off. The amount of leverage being put on the castings and rudders is actually pretty impressive. I just think the F20C has out grown the current casting design. Hopefuly Nacra will beef them up again.