Hey Robert,
What was the water temp like? Anyways, first question, what is the mast made of? Metal or wood? How tall is it? If it's large enough, someone probably already ran it over, wrapped the rope in their prop, cussed like crazy and they now have a new pole for a street light, LOL!!! Where they able to mark coordinates of the capsized boat or did they just go back to a presumed spot? It is way to easy to say, well I think it was here and be off alot.
Furthermore, I wouldn't go off looking for something that you know is an entanglement hazard(rigging) without backup either in the boat or a buddy even in 10 feet of water. Even when we make a dive with Public Safety Dive, we have a primary diver, a back up diver and a 90 percent diver. That's two back ups for just one diver, LOL!!! Also, if it's near the X on the pic you posted, there a few live bait boats that trawl through there. They could have very easily drug it off by now. I'd run a slow grid with a depth finder on the boat first and see what you can find. If it's still in one piece, you should see something on there if it's got any size.
Shrek