The OP says they 'found' a fin keel - did they actually see it or just surmise what they hit was a keel? - I have seen some old keels on the ocean floor on occasion but but they have always been laying flat on their side and usually close to the reef or rock that sank the vessel - there are still some scattered very broken up hulls sunken during Klaus,Hugo and Marilyn in the VI. But I would think that in CGB outside the mooring field on the Myetts side the OP likely hit the reef.