Regarding the tip vortex: Is there anything in the A cat rules that would prohibit a winglet to address that tip vortex? The A rules are open enough to allow hard sails, and winglets are a proven win on airfoils...

The winglet could be hard (like a wing sail) or soft (like a kite) or pressure-inflated (like a baloon) or wind inflated (like a parasail). If wind-inflated, it might be possible to design one that blows full on the windward side and flattens itself to leeward.

If the winglets were hard (e.g.: Carbon) and pivotted around a batten, and settled to a '^' position at rest by gravity, then the wind underway would lift the windward winglet into position and press the leeward against the sail. It would even work in light air if the rotational axis was near the center of gravity of the part that rotates. If fitted to a hard sail, the leeward foil might fit in a rebate on the leeward side for cleaner airflow.

*That* would be radical. Not sure it's legal or worth the weight aloft, though.

Another possibility is a simple end plate atop the mast or as the top part of the sail. End plates are another proven win for constrained airfoils. If you extend the '^' flopper concept to an end plate, the plate could have camber on each side to match the target sail camber, so that when it flopped from side to side the leeward plate would be flush with the sail cloth, and the windward side would have useful camber to help it do its job. Care would be required to pick the right angle of attack and profile for such a cambered end plate, but it could be used to form a featherweight simple auto-tacking winglet.

</brainstorm>,
--Glenn