There is a covered up wreck just off the beach from Avenida 13. I've checked the area a few times and only came up with a couple of bronze spikes that were probably placed there from either broken debris from the wreck that washed up long ago or from the beach re-nourishment program they've been doing. My suggestion would be to go at low tide. You can get tide information online or you can drop by Gulf Breeze Bait & Tackle just over the bridge and pickup a tide chart.
Good Luck!
Pcolaboy