Well, we didn't see any coral heads because it was DARK
On our route
, it was the kind of shallow that you associate with that nice sandy bottom - all very gradual depth
changes, nothing seemed to be poking out at us. There are some little "plus signs" on the chart, that I think signify rocks - most "always underwater/submerged"....
On the dawn picture I attached in a previous post, you can see some little cays - one of these is at 23*34.53'N, 77*20.34'W, if you want a reference point. No coral heads there, anyway!