Looks like a wind vane attachment for a tiller pilot or other sort of autohelm. It would allow the auto pilot to steer to a wind angle rather than a compass bearing.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"