Try a main downhaul
Joe, You didn't mention if your main sail has sail slugs or just a bolt rope, but either way a downhaul should help. Before I changed over to sail slugs and half way through the firstseason with them I had the same problem. The came from the fact that even though I pulled the halyard taught, the sail would work loose from the sail ties and create slack in the halyard. If you add a main downhaul you can cleat it tight and this will keep the halyard taught, not to mention it makes it easier pull the sail down if you use slugs. The downhaul is inexpensive and easy to install and rig. You need 30 to 35 feet of 1/4" polyester line, a small clam cleat, and a small block (if you want to run it back to the cockpit). On one end of the line tie a bowline through the halyard shackle where it attaches to the headboard or if using slugs tie it around the first slug below the headboard. Than run the line down the right side of the mast to the bottom where you can mount a cleat to the mast or mount a block on or near the mast and than a cleat on the cabin top. This has worked out very well for me for about five years especially on windy days. PS, Its a big help when reefing the main.Barry BroylesNorth East Md.LTBROYT6D@cs.com