Two guesses, both prefaced by the fact that the boat is a 71 and could have some odd devices from the early days of boat electronics, back when things were a bit less sophisticated. The limited swing range of the vane is interesting.
First guess is some sort of aid to detect lifts or headers. Mount it to the bow pulpit and it would give feedback regarding wind angle. Maybe a training device for windward racing?
Second guess is a sensor to detect dramatic wind change when at anchor. Attach the post to a stantion when the anchor is set, then, if a big enough wind shift hits, the vane pings against one of the stops and sets off a signal before the boat moves.
Last edited by BigZ; 08-23-2010 at 09:02 PM.