Just another woman's perspectives:

Would your wife like to continue racing if it were on another kind of boat?

Or does she just not want to race on sailboats any more at all, and her knees are just her excuse to opt out?

If she still wants to race, you guys should talk about what kind of boat to get that you can still race on together. If she really does NOT wnat to race any more on any kind of boat, then you are free to do your own thing.

But it is always possible that she will not tell you that she really wants to continue to sail but on a different kind of boat, since she knows how much you love your beach cats.