Thanks for your post. W/ respect to Ericsson, I thought he claimed that if the Monitor cannons had used 30 pound charges instead of 15 pounds, the guns would have penetrated the Virginia's hull.
Ah, that one.
Here's the tricky thing about that - firstly, the 11" guns on the Monitor were being given the full authorized charge on that date. 15 lbs was the maximum permitted charge at that time, and later in the war the USN authorized 20 lbs (which required new 20 lb powder bags to be made). Postwar they allowed 30 lbs but "at gunner's own risk".
30 lbs is dangerous overload for a 11" Dahlgren - the "proof" charge, which is a single firing during the acceptance of the gun to test it can deal with maximum strain, is only 25 lbs. The postwar option was actually pushing the gun past what it's proofed to take.
Assuming that it's done, then with
wrought iron shot it might be able to penetrate. This conditional is very important because cast iron shot is much inferior to wrought iron shot at penetrating an ironclad (cast iron shot shatters on impact).
The heaviest known firing of a Dahlgren 11" in action was two wrought iron shot fired at the
Tennessee with 25 lbs of powder, and it didn't penetrate.
The
Monitor had some wrought iron shot on board, but they hadn't been gauged - if they were slightly oversize they'd have burst the cannon straight off (even with regular charges) and killed most of the turret crew. If fired with double charges a hit would probably lead to their penetrating, if the hit is reasonably head-on, but it's a big risk to the
Monitor because you're firing untested balls with an untested powder load.
If you do penetrate, meanwhile, what you've done is put a single ball through the armour scheme. The
Virginia has backed armour so you've not caused spalling, and at best you've taken out a gun.
And when would you say wooden ships were obsolete? By the time of the Maine? The Great White Fleet?
The process of becoming obsolete is a gradual one. In 1866 at the Battle of Lissa the wooden battleship
Kaiser actually fights in the battle line and engages several Italian ironclads at different times; she survives the battle and is ready for action the next day. It's not worth building wooden ships of the line any more but they're still worth using in battle.
The RN stops launching wooden frigates by the middle of the 1860s, but frigate duties are carried out by wooden frigates for the next decade or two (wooden frigates are used in front-line service until the 1870s) and sloops and corvettes and gunboats linger on for a while after that in out of the way places. If you want a ship to cruise the sea for a year or two without coming into a proper dock, the best thing for it to be is a copper-bottomed wooden-hulled cruiser.