I am not positive but I think they will work on pretty big boats(50-60'???). I have seen them on 22 footers as well. They are made real strong. I will send you a PM with a couple of links.
Everything is there, you can see in the picture(Vane, mounting tubes, mounts). You may want to make a light wind vane(slightly bigger and lightweight plywood).The site to check out is ariesvane(dot)com. Thanks Hpeer for the heads up about the link!