Thanks for the information everyone. Looks like I need to start with a good cleaning of the swivel and an inspection of the sheave.
Keith - you've got me thinking that I may be tightening the rig too much - does anyone have any base guidlines for right tension by wind speed? This is something I can probably Google, but thought I may ask (I've got a gauge)
I personally wouldn't even bother with a gauge on the 18, and in fact any of the tuning guides I've seen don't reference a gauge. In most conditions I'd have the rig tight enough so it didn't flop on shore unloaded, with it being a little tighter in windy stuff.
When sailing upwind with the main cranked you'll notice that the leeward shroud is loose. No big deal.
Your mast should rotate freely as well - if it doesn't your rig is too tight.
There is a performance tuning guide for the 18, some of it is a bit outdated. I believe it was written Phil Berman, not sure if it is still available. I may have mine still, can't remember if went with the boat or not, I can check.
