...oh for goodness sakes. You can't claim the successes of the CSA as a triumph for USA ironclad design. That is not how it works - the ships were ironclad to different specifications and following different design philosophies.
The US, if they ironclad-convert their scant few frigates rather than leaving them as they are, will be making them into
Roanokes because that's what they did OTL and fits their design philosophy. This means:
Her conversion was not very successful as she rolled excessively and the weight of her armor and turrets strained her hull. Her deep
draft meant that she could not operate off shallow Confederate ports and she was relegated to harbor defense at
Hampton Roads, Virginia for the duration of the war.
Assuming that they survive (Roanoke's conversion took over a year and the New York coastal defences are seriously undergunned compared to design, a design which is based on technologies a generation behind those the Royal Navy can bring to the battle), then they will be coming out of the shipyards sometime in mid-1863, in a state where firing the guns means dismounting them completely.
Frankly it would be a significant
disimprovement to the US Navy to put their only large warships out of action for a year to convert them into unstable turret ironclads like that.
So, let's put it this way. Hampton Roads is the USN sending out a new kind of warship against something converted from a sunken vessel by a navy with limited resources. The said navy with limited resources fights their brand new kind of warship to a standstill, and this is promptly framed as a ringing endorsement for the new kind of warship and they build almost nothing armoured but that new kind of warship for the next thirty years.
This tends to suggest that the US Navy considered the Monitor type highly superior to the Virginia type, in spite of the inconclusive results - either because it was or seemed easier to build in numbers, or for some other reason.
Now.
What would it look ike if the USN was basically Monitor obsessed in defiance of a rational consideration of what the best qualities of a ship were?
I think the answer is that it would build dozens of them, of varying quality, without proper scrutiny and without properly considering the design.
Now look again at that list of Monitors I compiled. Most of them have some kind of design problem, twenty of them didn't even
float and nothing in service before 1864 has both a 15" gun and the ability to
aim it accurately for more than one shot.
This is not what it looks like when a nation is able to rush build a large fleet of ironclads.
As such, we can effectively assume that for the first year of the war the USN's ironclad fleet will be largely unable to fight much beyond harbour defence - and that for the first few months it will not possess much in the way of ships capable of
that either, which might mean it's unable to actually build those required harbour defence ships...
...I'm not seeing how they're going to be able to prevent the Royal Navy imposing a blockade. If they follow the Smith idea of converting their frigates into ironclads, they've basically given up on them for the year, so their entire battle force consists of some sloops plus converted merchant ships and sail ships.
The idea that some sloops can force open a blockade supported by 90+ gun steam battleships is, frankly, comical.
(And, honestly, looking at some ACW incidents it's not all that sure that slow early coastal ironclads will be able to break the blockade either.)
EDIT: I like this post, so:
....what I decided to do was to do some random sampling of the Union Navy's official records: ten pages at random, every ship on those ten pages (forty ships total). The purpose of this exercise is to demonstrate to the viewers at home exactly what kind of ships the Union navy might be taking on the British with.
Firstly, I discounted six ships that were bought to be sunk (USS George P Upshur, USS Mechanic, USS W L Bartlett, USS Patriot, USS Advocate, USS A Holly). Most of these were with the Charleston stone fleet.
Next we have ten ships which would not have been suitable for sea service. These included ships that were never finished (USS Virginia), ships that were finished after the war (USS Minnetonka), tugs (USS Mayflower, USS Juniper), tenders (USS Julia), coal hulks (USS A J View), mortar vessels (USS George Mangham), steam launches (USS Paul Jones Jr), and riverine vessels (USS Vindicator, USS Juliet). Your calculation required five Royal Navy vessels to be hypothecated for service against each of these ships.
Next we have the pre-war purchases: two 40-gun screw steam frigates (USS Minnesota, USS Wabash) and two 20-gun wooden sailing sloops (USS Germantown, USS Jamestown). These are dependable ships for their size, though some considered the Dahlgren too heavy to work in a seaway. While the sailing sloops would have accomplished little against either a steam blockading force or a steam convoy escort, the screw frigates had the potential to cause difficulty for the Royal Navy. However, there are only a limited number of them: they can either be raiding commerce, or they can be trying to sortie from blockaded ports, but they can't do both.
Next we have the iron steamers: USS Memphis, USS Virginia, and USS Monocacy. The former two were blockade runners, captured and pressed into service. Unfortunately, the Royal Navy discovered that unarmoured iron ships are unsuitable for combat because the spall from projectile impact slaughters the crew. If these ships are fired at, they're going to die quickly.
After them are the sail ships, four in total (USS James L Davis, USS James S Chambers, USS A. Houghton, USS George W. Rodgers). The same objections apply to these as the sail sloops above, with the additional proviso that all are poorly armed: none with more than 4 guns. As converted merchant ships, these would struggle to fight a single adequately-armed British merchant ships, let alone either a convoy of them or a British warship. The fact that three of the four were purchased in September and October 1861 shows the extent to which the Union navy was dependent on merchant sail ships in the early years of the war.
Next come the eight paddle steamers (USS James Adger, USS Vixen, USS Paul Jones, USS Agawam, USS Mingoe, USS Geranium, USS Mendota, USS Volunteer). There are a few Royal Navy paddle steamers still in operation, but paddle wheels are archaic technology for warships. Their propulsion systems are easily damaged, they slow the ships down while under sail, and they prevent them firing a full broadside. As such, these ships would make extremely poor commerce raiders.
Next, we have the wooden screw warships: two purchased merchant vessels (USS Patroon, USS Violet), and two screw sloops built for the Navy (USS Juniata, USS Monongahela). The screw sloops could probably stand in a fight with a similar British vessel: the converted merchant ships, particularly the Violet with its armament of two 12pdr guns, could not.
Lastly, we have the single armoured vessel: USS Montauk. At 7 kts max speed, it's going to have to take the Royal Navy by surprise; with two slow-firing smoothbore guns, it's going to have to hope they don't start moving until very, very late on; with barely any freeboard, it's going to have to hope it doesn't get rammed. Just like the Confederate coastal ironclads, it seems wildly optimistic to pin your hopes on this doing enough damage to the Royal Navy to open one port even for a day. Almost as optimistic as giving raw recruits muskets and expecting them to out-range trained skirmishers with rifles, really.