Now, the boat this will go on, is an S2 7.9, which is a fiberglass boat. However, an awful lot of the parts are wood, so I figure that I can post this, here!
The S2 7.9 has a transom-hung, essentially vertical rudder. There is no skeg. The stock rudder is a kick-up job, but it swivels on a single bolt, which is very substantial. Nonetheless, rudders do snap off, so as documented on this board about 2 years ago, I built a wood core, non-kickup rudder. Here's an S2 7.9 with the stock rudder.
I'm building the Rudder Head Mount and USD windvane as invented by Jan Alkema. You can read Jan's article about the concept here: http://www.windautopilot.de/docs/alkema/RHM-USD.pdf
That article is a good read. The late Walt Murray incorporated a USD vane in to his last set of designs. The Mister Vee vane uses a USD vane, and Mister Vee has archived a lot of Walts truly wonderful hand-colored structural drawings like this one.
So with that in mind, let's get started!