Prince Consort-class ironclad

The Prince Consort class of ironclad battleship were four Royal Navy wooden hulled broadside ironclads: HMS Royal Oak, HMS Prince Consort, HMS Ocean, and HMS Caledonia. They were originally laid down as , but were converted to ironclads. Royal Oak was Britain's fifth ironclad battleship completed. Prince Consort, Ocean, and Caledonia were built to a common design and are today known as the Prince Consort class, though contemporaries knew them as the Caledonia class. Royal Oak was their half sister.

The of nine 91 gun two decker steam line of battle ships were laid down between March 1859 and October 1860 (a further three were ordered, but never laid down, and eventually cancelled in 1863). Their dimensions were the same as (101 guns), but had a new timbering plan to suit the smaller armament. The reduction in armament was intended to improve the efficiency of the guns. The remaining seven ships of the Bulwark class were less complete state and were converted into 'ironclad frigates'. Of these Triumph (later renamed Prince Consort), Ocean, and Caledonia were converted to 'broadside ironclads' with 1,000 nhp engines. Royal Oak had a similar conversion but with the original 800 nhp engine. Royal Alfred, Zealous and Repulse were later converted into 'central battery ships'.

"The two decked wooden ship which were turned into armoured frigates had their sides cut down considerably, and the main deck and its battery removed; while the armour, although about equal in weight to the parts removed, is not as high above water. the iron clad is, therefore, less top heavy than the wooden ship was previously to be converted; in other words the conversion has the effect of bringing down the centre of gravity of the ship." As part of the conversion they were lengthened by 21 feet. "The object of lengthening was to provide more space for an armament mounted entirely on one deck except for chase guns. Such extensions are carried out by a process well recognised in naval architecture; which is quote possible at any stage in the building of a ship [or afterwards], not by adding to the extremities, but in cutting her in two at the point of greatest beam and separating the halves sufficiently to insert a new section between them. This is usually done by erecting a launching cradle round the stern half, moving it down the slipways on the cradle as far as required and building up the gap. In such fashion the Prince Consort, Caledonia and Ocean (as well as the Royal Alfred and Royal Oak) were each drawn out 23 feet when already partially on the frame But as the midship portion of a hull is always the part subjected to the greatest sagging and hogging strains in a head or following sea, special care is necessary to ensure the inserted section is sufficiently strongly built in; particularly if it has to bear the burden of the engines as it did in the Prince Consort class. Exceptionally stout timbering was therefore used for the purpose in those ships; even with that their central structure sometimes exhibit signs of stress giving rise to trouble in a minor degree." The bows of the Bulwark class were of the normal knee shape for wooden warships. When they were converted to ironclads, the Prince Consorts and the Royal Oak were completed with stems approaching the upright above water, and this style, which was so much decried at first, had by the late 1860s won aesthetic approval. "The bow has been modified in order to dispense with overhanging weight, to increase its fitness to cleave and surmount waves, and to adapt it for ramming purposes." Though they did not have underwater rams. "The stern has been modified in order to give protection to the rudder head, to deflect raking shot, and to render it more fit to receive easily the blows of following waves."" It should be added that before the introduction of the bracket frame system with the Bellerophon, double bottoms on British iron hulled iron clads were very partial.

"In our earlier iron clads the protection is only partial, extending over a portion of the length of the broadside. No better example of this system can be chosen than the Warrior. Her length is 380 feet, and the armoured portion is only 213 feet in length, the extremities of the ship being left entirely unprotected The rudder head and steering apparatus are left entirely unprotected. This system of partial protection is also adopted in the Black Prince, Defence, and Resistance; but the desire to increase the amount of protection led to the introduction into the Hector and Valiant of a modification of the Warriors disposition of armour. This modification consisted in adding a belt of plating, extending from the upper to the main decks, before and abaft the main portion of the broadside armour, which was arranged similarly to Warriors. The main deck, on which the guns are fought, is thus protected throughout the entire length, but the extremities 'between wind and water' are quite as unprotected as those on the Warrior". "Both these plans of disposing the armour were afterwards considered unsatisfactory, and resort was had in the , and in the converted ships of the Caledonia class, to the system of which had been introduced into the construction of the floating batteries built during the Crimean war, by means of which what is known as 'complete protection' is secured. Throughout the length the armour extends from the upper deck down to about 6 feet below the waterline The principal advantages possessed by this disposition of the armour over that of the Warrior are that the extremities of the ship, especially on the parts near the water line, are iron cased, and that the protected guns can be ranged along the length of the broadside instead of being concentrated in a central battery. There are, however, the accompanying disadvantages of having bow and stern heavily burdened, and of the resulting increase in the total weight of armour. For wood built iron clads this plan has the additional advantage of protecting the upper works throughout the length from the destructive effects of shells. The French ships are, for the most part plated in this manner". "In 1861 many verbal discussions took place between myself [the Controller] and the constructors of the day, as to the cause of the excessive rolling of our ships, when compared with similar French constructions. When I [the Controller] urged upon them the possibility of adding largely to the armour plating of the ships, and of not confining it, as had been done, in the Warrior and other ships, I was met with very great opposition, and my endeavours to get the five wooden ships wholly Armour Plated were met by two reasons against doing so. One was, that extensive armour plating must cause excessive rolling; and the other, that there were doubts of the stability of a ship wholly armour plated. Now it turned out that the stability of these ships wholly armour plated proved excessive, and, if their stability had been lessened, their rolling would have been diminished; but the Constructors of the Navy were not alone in their opinion." "In the wood ships the [4.5 inch thick] armour was bolted on outside the planking of an ordinary line of battle ship, being consequently backed by about 30 inches of timbering and planking." This compared with armour backed by of teak for the , , Achilles and the , and armour backed by of teak for the Minotaur class.

In the 1860s rolling was measured as the sum of the angles to port and to starboard. "Admiral Dacres Report for 1864 [on the Channel Squadron] shows that on the four days when all the ships were together, the means of the extreme rolls recorded were as follow: Hector, 10 degrees; Warrior and Defence, 10.25; Black Prince, 11.05; Prince Consort, 11.75; and Edgar (wooden line of battle ship), 14.25. The Warriors rolling was measured by a different instrument from that used on board the other ships, so that she cannot fairly be compared with them. This record is, however, of great interest, on account of the comparison it renders possible between the behaviour of the iron clads and the wooden two decker, the latter proving the heaviest roller in the squadron. In Admiral Yelverton's Report [on the Channel Squadron] for 1866, there are given examples of the comparative rolling of several of the iron clads, obtained from three days' observations, of which the mean results are: Achilles and Bellerophon, 6.6 degrees; Hector, 11.3; Ocean, 14.3; Lord Clyde, 16.1; Pallas, 17.3. The small size of the Pallas, as compared with the other ships, puts her at a great disadvantage as regards comparative rolling in ordinary waves." "The Achilles has a distance of about 3 feet between the centre of gravity and the metacentre, and is a remarkable steady ship; whereas the Prince Consort, with a distance of 6 feet, rolls much more than the Achilles."