Thanks Jamie, that has immediately given me more ideas for developing the idea, and it might make it simpler for me to model the fittings.
So far I have a sail head fitting, a ring fitting, and a mast top swivel fitting. the male batten slots into all these as there is a female tube bonded onto each fitting. The fitting is only loaded from batten tension. Therefore the sail head forces will be neutral, compression forces on one side of the ring, and a shear leverage force on the masthead fitting.
I think it looks tempting to go for the sail-head fitting...