The officers who would've been ordered to carry out a blockade thought it would be a tough job, because they didn't have enough of the right kinds of ships, but what did they know? They actually thought the Americans were ahead in some critical technological areas, but what did they know?
You should read
what the other side had to say:
'About the middle of November we heard of the "Trent Affair"... In our then excited condition there was general exultation over Captain Wilkes' violent capture of the rebel emissaries. We had no idea of international law, and we viewed this violation of it as a proper exercise of our right to suppress the rebellion. Almost without exception the public expression was jubilant and laudatory. But soon came the menacing echoes from England, the outcry against the violation of neutral rights, the rapid military and naval preparations and the prospect of a foreign war superadded to our domestic troubles. There was some foolish ebullition of defiance, but to the thoughtful the prospect was very threatening and almost fatal. In case of war with Great Britain the brunt would have to be borne by New York. Its long sea coast, its great vulnerable metropolis, its long boundary at the north, coterminous with Canada, and its important ports on the great lakes, were all points of probable attack or invasion. So soon as the intelligence of hostile preparations in England reached this country, we who were engaged at the Governor's headquarters recognized the gravity of the situation, and that under existing conditions our State would have to provide largely for its own defence. Indeed there were many official and semi-official intimations from Washington that the threatened safety of that city would require the retention there of all the troops then near it, and that few could be spared from other quarters should there occur a declaration of war by England, as then seemed imminent — in other words, that we would have to take care of ourselves. This was a very serious consideration. Our organized militia, very feeble at the best except in New York city, had everywhere been weakened by the volunteering of a large part of its best element, since a considerable share of the officers in the new regiments had been drawn from the militia. There were several regiments within the State not yet completed, but they were comparatively few and at the best were raw and undrilled, and would count for little in a sudden contest with the disciplined soldiers of the regular British army. So far as the approach from Canada was concerned there was some relief in the imminence of winter, which would lock up the St. Lawrence in ice and make an invasion by land very difficult. We were more particularly concerned about New York city, which, as the largest and most important of our commercial cities, would be the principal objective point of a hostile navy, and England was then the best equipped naval power in the world...
'the engineers had decided that at least 300 pieces at the Narrows should be so mounted as to concentrate their fire upon a vessel passing between them, but not half that number were then available. At Governors, Bedloes and Ellis Islands only three-quarters of the armament had been supplied, though it is now evident that a fleet that had passed the Narrows might disregard these inferior works and readily destroy the city... In fact, the conditions of defence of the city were very faulty, and though the United States engineers had plans for completing the works and armaments so as to bring them fully up to the times, these would require years, and the dangers we were confronting were imminent...
'Some attention was also given to the defences on the lakes and northern frontier, though nothing practical was attempted...the construction of canals around the several rapids of the St. Lawrence river and of the Welland canal, connecting Lakes Ontario and Erie, would enable the British Government to place upon the great lakes a fleet of war vessels at the very outbreak of hostilities... Our Erie canal locks would not admit boats with more than 98 feet of length, 17 3/4 feet width and 6 feet draught, or of less than 100 tons. We would therefore have to depend upon fitting out the mercantile lake craft for naval purposes, and though I do not doubt that had the pressing occasion required such a recourse, we would have rapidly improvised an excellent navy on the lakes, we would still have been at a great disadvantage with our antagonist, who could have brought upon those waters its sea-going naval vessels of small tonnage...
'The terrible emergency never came, and the threatening war cloud that had so suddenly gathered from over the sea as suddenly passed away, but none of those who participated in the anxieties and discussions and bore a part of the responsibilities in those portentous days can forget them. Had the conflict ensued we should have been in a terribly unprepared condition, our harbor and frontier forts in bad condition, with very inadequate armament for them or for our improvised navies, and with only a raw, hastily gathered militia to encounter the British regulars seasoned in the Crimea and India. With little aid from the forces of the General Government, the menaced States would have had to depend upon such resources as each could gather within its borders... There was in the matter a plain reminder of the weakness of our coast and frontier defences...'
Colonel Silas W. Burt (former Assistant Inspector General of the New York National Guard),
Memoirs of the Military History of the State of New York during the War for the Union, 1861-65.
Now, the thing is - as
@EnglishCanuck has explained - those officers who would've been ordered to carry out a blockade
are labouring under a misapprehension. They think that this whole thing is a dastardly ploy on the part of the Union: that they're going to abandon the war against the South and turn their full attention to the British, in the hope of salvaging some martial glory against an unprepared enemy after what has been a very humiliating few months. People like Colonel Burt, frantically scrabbling to prepare for a second war they are completely unable to fight?
They have no such misapprehensions.
Taking their capital units out of the mix leaves near parity in naval strength in American Home waters, making it hard to maintain a blockade on a long coastline.
Why not take all the Royal Navy ships out of the mix, and make it even harder to maintain a blockade? After all, it's not as if the battleship was intended to play a sophisticated role in the enforcement of a blockade - acting as a depot for smaller gunboats, and a ship of force in the event that the US tries to launch a sortie with something that might be a more even match for the frigates, corvettes and sloops assigned to the force.
Incidentally, I do hope when you talk about 'near parity in naval strength' you're comparing like with like - not, say, elderly paddle steamers, sailing frigates, and commandeered merchant ships to purpose-built steam screw warships. Because it's a terribly easy trap to fall into...
In the event of war the Union planned to build a class of 17kt raiders, to prey on British Merchant ships.
These were the raiders that
weren't completed until after the war, nearly universally failed to make their design speeds, and all suffered horrendous engine problems? They sound super.
Almost all guns of the period suffered failures. Breech Loading Krupp guns in the 1870 war had a very bad safety record, and had to be replaced after the war, but they were good enough to defeat the French in a short war.
Pretty effective argument in favour of the Armstrong gun - particularly as the Armstrong gun is only part of the British arsenal, and the Krupp gun was the whole of the German arsenal.
It's not the Middle Ages, wars are massively expensive in lives, and money. Britain is a mercantilist power, with global commitments, and assets to protect. The Government answers to the tax paying, monied classes, who don't like trade disrupted, or their taxes raised. One would hope their capable of rational calculation. Gain, and lose was their primary motivation in the Mid Victorian Era, not national duels of honor.
This isn't how historians characterise the period.
'A community, and early nineteenth-century Britain was no exception, recognizes honour by praising valour and honesty; it fosters shame by admonishing cowardice and deception. Honour was closely associated with virtue: society expected a gentleman to sacrifice his personal well-being for the good of the community and, by doing so, earn moral superiority and power... In foreign affairs, honour had the same meaning. It required officials, acting honestly and consistently, to honour their obligations by carrying a policy into effect even in the face of defeat... Honour was a practical, not an ideal, conception. Failure to act honourably provoked public outrage in the form of petitions to parliament and the possible loss of a majority in the house of commons... Honour governed what we today call 'linkage' or credibility because loss of honour would affect what Palmerston referred to as Britain's 'moral power' to influence the actions of other states by undermining confidence in its ability to follow through on its decisions. These states must not forget, when facing a British frigate, however small, for example, that the 'Flag of England must be respected'. In an era when policy was guided by the principle that Britain should not interfere in the internal affairs of other states, the ability to influence their behaviour was more important than in a period in which the use of force was the norm. However difficult for the late twentieth century to comprehend, honour as a motive for violence was taken for granted before the First World War. To dismiss it as a "veneer" tells us, sadly, rather more about the moral values of contemporary historians than it does about the motives of those with whom they deal.' (Glenn
Melancon, 'Honour in Opium? The British Declaration of War on China, 1839-40,' International History Review vol. 21 no. 4 (December 1999), pp.857-8)
It isn't how the participants talked either.
'There is no doubt that all nations are aggressive; it is the nature of man. There start up from time to time between countries antagonistic passions and questions of conflicting interest, which, if not properly dealt with, would terminate in the explosion of war. Now, if one country is led to think that another country, with which such questions might arise, is from fear disposed on every occasion tamely to submit to any amount of indignity, that is an encouragement to hostile conduct and to extreme proceedings which lead to conflict. It may be depended on that there is no better security for peace between nations than the conviction that each must respect the other, that each is capable of defending itself, and that no insult or injury committed by the one against the other would pass unresented. Between nations, as between individuals, mutual respect is the best security for mutual goodwill and mutual courtesy; and there fore, in my opinion, the course pursued by Her Majesty's Government is one much more likely than that suggested by my hon. Friend the Member for Birmingham to secure the continuance of peace.' (Lord Palmerston,
explaining in the House of Commons why he almost went to war over the Trent)