As a side note, the original graving dock that the USS Monitor was built in in Brooklyn NY is still in use commercially and every day. It is surrounded by 'bits' which are actually cannon barrels mounted vertically in the cement. Pretty nostalgic.
I was able to tour the impressive old gal while in Boston on business about 15 years ago. One of my favorite objects in my study is a chunk of wood from her 1995 drydock/refit, purchased at the museum store. The cross sectional cut sliced through a copper nail used to attached the copper bottom cladding....I've always wondered if it was one of the original copper nails furnished by Paul Revere's metal shop, as he was said to have furnished the copper for her at one time!