Annie has entrusted me with making the latch mechanism of the vane gear. Being an old-fashioned girl, she wants a simple, easily understood, disc-and-peg kind of mechanism, as in Bill Belcher's fig 46 (a), and the client is always right, so who am I to argue? ;-)
I've based it on a 52 tooth aluminium chainring. This gives 7˚ of course alteration per tooth:
The latch is made from a 60mm diameter nylon bar screwed to a 8mm PVC sheet and sliding on a 3/4" diameter stainless steel tube vaneshaft. There are two holes athwart the vaneshaft for cords that will lead forward to the Brownstick (for those unfamiliar with this kind of antediluvian vane gear, it helps if the latch can be nudged one way or the other to put on a bit of weather helm before dropping the peg into engagement, so the Brownstick, a short piece of wood, is attached to those cords so that one or the other can be pulled a little):
There is a brass bearing in the bottom end of the vaneshaft which will rest on and pass through a piece of 10mm HDPE sheet mounted on the inside face of the lute (the upper end of the vaneshaft passes through another piece of 10mm HDPE sheet screwed to the top of the lute):
A brass peg is tapered so as to engage easily with the chainring. A M8 bolt will engage with the crosslink attached to the tab tillers:
PS This is going right back to the Hasler trim tab gear, circa 1960.