Is it possible that this could have been part of a capstan or similar anchor winch? The circular worn cuts in the fins are not even. Has everyone been able to use the PDF file? I think it is the most useful tool in viewing this object.
I'm not sure of the chain size and anchor that would have been required for a ship of this type. The vessel was approximately 225 ft long at main deck level and 214 ft 3 inches, at the water line. This is all due to the overhanging main deck supported by horizontal sponsons.