§ The speed and other trials of the ships recently built, together with the working of their engines and hydraulic mountings, have on the whole been satisfactory. In most instances the anticipations of the Constructors have been realized, although difficulties have occurred in some of the earlier trials in obtaining from certain of the engines the speed of the contract. In one important particular there is a discrepancy between the estimate of the original design and its result, which, in the case of the "Impérieuse," and her sister-vessel, the "Warspite," attracted some attention, and which is likely to recur in the case of the bolted cruisers, seven in number, the "Warspite," and the armoured vessels of the "Admiral" class.
§ The following statement, though referring to the belted cruisers alone, is typical of all the vessels whose draught is deeper than was designed; and it will also record the Regulations as to design and trial which the present Board have made. (See Appendix I.)
§ The designs for the belted cruisers wore prepared in 1884, and the sketch design received the final approval of the Board of Admiralty during that year.
§ It was intended that, with all their legend weights on board, they should have a mean draught of 21 feet, and that 18 inches of the armour belt, which is 5 ft. 6 in. in width, should be above water.
§ After the designs were approved, tenders for the construction of five vessels were invited. Some of these tenders provided for the substitution of triple expansion engines of 8,500 horse-power in place of the compound engines of 7,500 horse-power originally contemplated, and the advantages of the offer were so manifest that it was decided to adopt this type of engine for all five ships.
§ To compensate for the increased weight entailed by these engines, and in view of the economy in fuel that would result from their adoption, it was decided to reduce the legend weight of coals to be carried by GO tons; this placed the legend weight of coals at 440 tons, in place of the 500 tons originally approved.
§ The extra weight of the engines, of increased complements, and of armament, amounting in all to 186 tons, increased the draught of the ships by 7 inches, placing the top of the belt 11 inches out of the water.
§ It appears to have been decided, although the bunkers of these ships were constructed to hold 900 tons of coal, that 500 tons (afterwards decreased to 440 tons) should be taken as the amount they were to carry under ordinary conditions—in other words, as their normal supply of fuel.
§ It was calculated that this amount of coals would carry the ships about 4,500 knots at 10 knots an hour, and with this the Board of Admiralty at that time appear to have been satisfied.561
§ The present Board, however, are of opinion that it is far preferable that ships should carry to sea with them the largest amount of coal they are able to carry.
§ If the whole of the 900 tons, with the additional weights alluded to, be placed on board, instead of 440 tons, the top of the belt will be, on the ships first going to sea, 6 inches below the water.
§ Thus, although the position of the belt may have been correctly calculated for the weight of coals it was at the time decided to carry, and which was adopted as their deliberate policy by the then Board of Admiralty, the same is undesirably low if coals to the full stowage (which is the policy of the present Board) are put on board.
§ Though the policy which placed the position of the bolt so low does not commend itself to the present Board, it is right to say that some claim for it certain compensating advantages, their contention being—
- (1.) That there would be above the armour belt, running along 140 foot of its length, when the full fuel supply is on board, a coal protection of 6½ feet in height and of 11 to 17 feet in depth.
- (2.) That the coal protection would not be disturbed until, by the consumption of coal in the lower bunkers, the ship had lightened, and the armour belt had risen above water.
- (3.) That a shot, which during a roll might have struck below the belt, would, in its present lower position, be deflected.
§ From the only trial under steam which has yet taken place with one of these vessels, there is every reason to believe that the speed for which they were intended will be attained, with the ships fully equipped and the bunkers full.