I have one for my Nacra 6.0 Express. The Express has a large jib, really a genoa, which creates issues with the main when going upwind or close reaching. Mainly the backwinding of the main, and even inverting of the main in higher winds. Randy Smyth of Smyth Sails and I discussed these issues and he developed an amazing square top for my boat. We used Pentex Sailcloth for duarability, we were talking carbon, but this is a fun boat and durabilty played more importance than weight aloft. Fibreform battens, most of them were the original battens from the previous Kevlar sail, except for the top three (not including the vertical head batten). The sail doesn't backwind at all, Depowers gracefully with the downhaul. I recently acquired a Velocitek and were able to get some numbers on my last sail in 3-5 knots of breeze. We were hitting 7.2 knots upwind, sitting in the middle of the tramp, and the windward hull was trying to pop out. Downwind, using an I20 chute rather than the Express Monster, we were going between 9-9.6 with a top speed of 10.3. I am more than happy with the square top that Smyth had built for the boat and highly recommend going that route.