Do you think it's part of the Hull? If it is it's probably a small ship. Or it could be part of a cabin wall.
Just from the looks of the spike I'd say 1800's at least.
Dano
That type of fastener is mid to late 1800's.
If you can find a copy, Get Mendel Petersons book "History under the sea." He goes into great detail on dating objects.
It might be available through the Smithsonian bookstore if it is still in print.