bad vibes

[Brion Toss]

Hi again,
Lovely puzzle. If you have eliminated the lift pendant and any other running rigging (I once had a problem with very tight lazyjacks), then that probably means it is vortex shedding.This is not usually affected by rig tune (more on that later), and the oscillations from a fine buzz might not be visible as you look up the mast. If the fender trick didn't work, please try either a line attached to a main luff slide. This slide lives, unattached to the main, on top of the sail. It should go up and down with the main. Attach the main halyard to it, and a separate line that is something over half the length of the mast. Hoist the slide with the halyard to about halfway up. Take the second line aft to the cockpit and tighten it. Experiment with different heights. Report back.
As for tune, if it is going to affect this problem, it will be by imposing bend. See what happens if you take up on the forestay (inner stay), ease off on the aft lowers, and take up on the forward lowers. Go for 12% forward and 10% aft. Should get at least a couple of inches of bend. This will be a better tune, regardless.
Fair leads,
Brion Toss