I agree with barnakiel - I think you need to think about the top swivel, simply attaching the head
of the sail, and the halyard, to a collar that rotates around the foil is not sufficient - the two (head of sail and halyard) need to rotate _independently_. The idea is for your gizmo to allow the halyard to _hoist_ the sail but allow the halyard to stay put while the sail is furling
Some clever assembly of plastic bushings might accomplish this. I'd try a flanged inner bushing that fits over your "foil", then a second outer bushing that fits over the flanged one. Assembly would have the flange on the bottom, halyard would attach to the top of the flanged (inner) bushing, head
of the sail would attach to the outer bushing. I just drew a picture because this paragraph is probably useless. (see attached "homemade_halyard_swivel.jpg".
Good luck - neat project
, but I'm not sure the foil will be strong enough to handle the torsion of furling
without going all candycane on you and breaking. If you could double up and use a router to make your luff guide rather than going all the way through the foil material that might help.
Also, not being able to douse a sail is in my opinion a pretty serious safety