Ludger,
Thank you for doing some digging. I replaced my halyard, which is now much more free running and doesn't burn the sail, but now it stays cleated even less than before! Really annoying hoisting the chute more than once downwind! As best I can tell, this is the setup on my Nacra F18 Infusion:
http://www.catsailor.com/store/pc/HARKEN-BLOCK-38-MM-PIVOTING-EXIT-150-CAM-MATIC-335p9076.htmAccording to APS,
http://www.apsltd.com/c-308-harkencamcleatsaccessories.aspx, the Harken H150 Cam-Matic is good for 3-12mm line. Maybe we have the Harken 280 Cam-Matic, which is designed for 6mm line on up? I know I'll be checking my setup this weekend and replacing that cleat regardless.
