It is hard to tell from the pic, and even with looking and holding it. I have seen wrecks with several types of spikes, and nails. There are other ways to fairly accurately date it. Sheathing type-lead, copper, and the nails that held it on, ballast type, rocks or iron bars, and the combination of all that, and of course any bottles, coins of course, or any markings you can find. British ships usually had a broad head arrow head marking any metal piece. Anchors too can date a ship and show possibly what country. Do some diving on it and try to decipher anything like that. There were many unfound ships around Key West, it was the largest city in Florida for a while. If you find any bottles I can ID them with era and possibly country of origin, and possibly if you find any artifacts. Do post a pic if you do find anything like that. There were many ships that went down that were moving goods in the 1800s, and they may have had money on them. It would be good to carefully search the areas near the ship, if sunk in less than 100' of water, as it could have rolled in a hurricane. Deeper wrecks once down for a while, usually sit there. But a wooden ship when it rolls and looses its ballast, becomes lighter, and could move in a hurricane. Good luck! Steve.