The ships anchor

This old anchor was dredged up off the coast about 6 miles out to sea. Its apparently a sailing ships anchor, origin unknown at Patiti Point.
It is now a intrigue, to wonder at. All cast iron although looking like wood, the corrosion of the salt water has etched the iron till it resembles the texture wood. The ship it was made for must have been massive as the anchor ring where the mooring rope would have attached really heavy even today. I wonder how the ship came to lose its anchor, so many miles out to sea?