Hi Jerry, I also have a Mk IV and other than the downhaul adjustment I have not changed anything on the diamond wire setup. On windy days the mast will start to slap from side to side after hoisting the sail easing the downhaul until launch keeps that to a minimum. Have you asked the guys over at www.ahpc.com.au yet? It might be a local call for you and Im sure they will know the answer. Keep intouch I'm learning more about cats on this site than anywhere else. Great group here!