It is actually a "chain tensioner" used to hold the
anchor tight in its chocks. If I could ever figure out how to attach a
photo on this forum, I would gladly do so. Looks like I am not the only one who has not figured it out, as I have not seen any photos so far.
Good luck on your future crossings of Bass Straits. We opted to fly from
Sydney to Hobart after friends went up on the rocks at Eden.