"no satisfactorily designed turret ship has yet been built, or even laid down.....the middle of the upper deck of a full-rigged ship is not a very eligible place for fighting large guns"
While true that it was said, nevertheless
Monarch was a ship capable of firing on the broadside and was probably more capable than was believed at the time (as axial fire was considered desirable, which is now thought to be largely an error - this is the basis of Reed's complaint). Your wording was
fatally flawed, and
Monarch's primary failing was that she could not do axial fire (which no broadside ironclad could do by definition anyway). This is not "fatally flawed", it's "less than it could be" and is a less severe complaint against a warship than, say, being unable to see to aim the guns (USS
Manhattan) or being unable to steer (
New Ironsides) or having four feet of freeboard over the gun ports and armour thinner than that of ships from eight years prior (
Dunderberg)
Your definition of the ideal turret ship seems to be that it should have the ability to engage at all angles (thus no raised forecastle or aftercastle), but to have a high freeboard, but to have shallow draft, but to also be able to sail long distances; that is, that it should be an
Admiral class. Fine when it can be built, but the
Admirals relied on plenty of development work in the prior decades.
In any case the breastwork monitors answer this issue, before
Devastation.
as to a double standard. Yep, I have one. The monitors are not supposed to patrol in deep water in one of the roughest bodies of water in the world (North Atlantic off the coast Maine to New York). They were supposed to and able to patrol in shallow coastal waters. The British ironclads can't do that because of their draft, so a deep draft and shallow freeboard is a problem for the British ironclads. They can't run for the shallows in severe weather. The Monitors could and did.
I'm glad you admit a double standard, though your justification for it is somewhat lacking. The
Miantonomoh class you cite as being seaworthy were of 13 feet of draft (not insignificant) and were able to transit seas only with considerable difficulty; that you cite their ability to dash for the shallows in bad weather as positive suggests you do not care about an inability to
fight in bad weather and thus the armament being low down doesn't matter.
The
Colossus class had a high enough freeboard to ride out waves comfortably without needing to dash for the shallows at all (30%
over the rule of thumb) and while the guns would be somewhat wet in very heavy seas the same seas would have long since sunk any Monitor. To call
Miantonomoh seaworthy while criticising the freeboard of
Colossus is not merely a double standard, it's a double meaning of what
seaworthy means in the first place - especially when claiming the ability to make oceanic transit as you do for the
Miantonomoh class. If
Colossus runs into a storm anywhere, including halfway across the Atlantic, she battens down the hatches and uses her high forecastle to push through the waves; if
Miantonomoh runs into a storm (or indeed a heavy sea state) halfway across the Atlantic she cannot run to port, gets heavily battered due to slamming, and may if she loses her pumps (or just comes side on to waves) promptly sink.
The important fact is that only the broadside and central battery type ironclads were what we would consider 'seaworthy' in terms of routine oceanic operations. However as the USN didn't need any for the historic war it fought, it didn't build many as they couldn't operate inshore where the mission was. I suspect they would build some now in your timeline. Possibly something derived both from the New Ironsides and Dunderberg.
Inshore operations isn't an issue for a broadside ironclad so long as it's built right - the TTL
Zodiacs and OTL Crimean Ironclads were both
more seaworthy and
shallower draft than the Monitor and her ilk. (
Monitor draft 10 feet 6 in;
Miantonomoh and
Passaic class 12-13 feet;
Aetna class draft 9 feet or less, and the
Terror of similar draft was considered sufficiently seaworthy to cruise under her own sail up and down the US coast before
Monitor was even launched). The New Ironsides was also a terrible ship for sailing, but that's by the by - her battery was used for bombardment of e.g. Fort Fisher and considered very useful (not surprising, she could fire far more guns and much faster than a Monitor and was probably worth anything from four to seven of them on bombardment work).
Dunderberg is a little better, but I've actually rather helped the US by having them take their inspiration from
Defence (very much a second class ironclad compared to
Warrior, but eminently seaworthy and still a powerful fighting warship) instead of
Dunderberg which was... problematic (3.5" armour is not enough to protect a serious fighting ship during the time she was built, by the time she was launched the British had guns in service that could penetrate her with Palliser shell at a range of nearly a mile - a similar British ship's armour was on the order of 5-6 inches)... or
New Ironsides which needed to be towed into position on occasion due to terrible water flow around the control surfaces.
As for the mission being inshore, this isn't really the case for blockading the South either - blockade ships of force can lie quite a long way offshore to minimize the danger from pounces by enemy ships, relying on smaller vessels to do the actual work of chasing down potential blockade breakers. A properly built (and fairly well armoured) ironclad of the
Terror class could get closer inshore than a Monitor type, and a very heavy ironclad of deep draft like
Royal Oak or
Monarch could just follow the shipping channel and blow the forts to bits at long range with her heavy guns.
In short, for the design requirements you cite for the Monitor type ships the British already had perfectly capable vessels (Crimea-type ironclads) which were also capable of crossing long distances at sea in a pinch. For the design requirement of a seagoing ironclad the British built vessels (broadside ironclad frigates) which served the role much better than the Monitor type ships.
For the turreted ironclad concept the British built
Monarch (advantage over contemporary broadside ships is that the full very heavy armament can bear on both broadsides; disadvantage is small number of guns) and
Captain (stability problems largely unrelated to use of turret) as well as the breastwork monitors (all seven of which are superior to US-type monitors in most ways the Monitors are lacking) before
Devastation.
