when the detail of the armament is settled. An important point in connection with this is the number of rounds taken per gun. 3. Machinery. When the I.H.P. is provisionally settled,1 an estimate is prepared by the Engineers of the necessary weight. This will depend on several things, e.g. the type or types of boiler to be used; the revolutions and stroke of the engines and the speed of the pistons; the degree to which the boilers are to be forced. For the largest set of engines fitted up to date (15,000 I.H.P.), 120 revolutions is the maximum; as engines of lower power are reached higher revolutions are possible; thus the engine for 6250 I.H.P. has 180 revolutions, and for 4900 I.H.P. has 250 revolutions. Destroyer engines are faster still. The adoption of watertube boilers has had a great influence on design in recent years, enabling a larger power to be developed on a given weight than formerly. The employment of turbine machinery will doubtless greatly influence the conditions of design in the near future. 4. Engineer's stores.-The allowance of these stores depends on the intended service of the ship as well as on the power. 5. Coals. It is the practice in the designed displacement of H.M. ships to include a certain weight of coal. This is called the legend weight. Thus the Royal Sovereign has 900 tons, as also Majestic, Formidable, and Duncan classes. The total capacity available for coal is considerably more than this, being over 2000 tons in the latest battle-ships. All the official steam trials to test the speed are carried out at the draught corresponding to the legend condition. Sometimes, however, trials are carried out before the completion of the ship to determine the acceptance of machinery from the contractors. These trials are simply for I.H.P., and not for speed, and then the ship is not necessarily ballasted to her normal load line, so long as proper immersion is given to the propellers. 6. Armour and deck protection.-The weight devoted to protection may be divided into (a) Vertical armour for the protection of the buoyancy and stability; (b) Vertical armour for the protection of the armament; and (c) Deck protection. The percentage of each of these of the total weight of protection in a recent battle-ship was as follows: (a) 38 per cent.; (b) 34 per 1 See Chapter XXII. cent.; (c) 28 per cent. This shows clearly how large a proportion is devoted to the effective protection of the armament. This includes barbettes and casemates, but not gun shields, which are taken in the armament. The barbettes especially are well protected. Thus in the Duncan the side armour is 7 in., but the barbette armour is 11 in. The reason is that each barbette represents such a large proportion of the fighting power of the ship. A single shot piercing the belt might not be a serious matter, but one shot through the barbette armour would probably cripple nearly one-half of the ship's fighting capacity. A feature of modern battle-ship designs has been the larger area covered with armour than formerly, with a corresponding reduction of thickness. This has been fully dealt with in Chapter XIII. The improvements made in the quality of armour has also had a great influence on cruiser designs. Up to the Diadem the protection was considered to be best obtained by a thick protective deck at the waterline, as Figs. 21 and 22. Owing, however, to the introduction of Krupp armour, this system of protection was modified by the adoption of a broad patch of 6-in. armour in the Cressy, over about half the length, in association with thick decks and bow protection (see Figs. 136 and 137). Armour protection has been adopted up to the present time for first class cruisers. 7. Hull. The weight devoted to the hull comprises— (a) Weight of the structure; and (b) Weight of fittings, etc., not contributing to the structural strength. The total weight of hull in large ships varies from 35 to 40 per cent. of the total displacement, and it is only by a most careful arrangement of the material, combined with high-class workmanship, that the weight can be brought as low as this. The corresponding weight in large merchant steamers is considerably in excess of the above figure; this is very notable when we consider that about one-half of the weight of hull in a war-ship is concerned with fittings, etc., which do not contribute primarily to the structural strength. Economies of weight during building are important to keep weights down, and a great deal can be done in this direction with no loss of strength. Lightening holes are largely employed. Thus in Fig. 16, showing a longitudinal, we notice that the plate must be weakened by holes connecting it to the transverse frame, so that we can well afford to cut away the plate by a hole between the frames without causing any reduction in strength. The lightened liner, shown in Fig. 47, is also an instance of reduction of weight with no reduction of strength. Such small savings of weight do not appear to be in themselves of much value, but in the aggregate they amount to a considerable saving of weight. Considerable reductions of weight have been effected in recent ships by lessening the duplication, etc., formerly fitted. One instance of this is seen in the abolition of relieving tackles to the steering gear. The stockless anchors now adopted have enabled the large weight formerly devoted to catheads, bill-boards, etc., to be saved. A large amount of weight has been saved in recent ships by the omission of teak linings and light boxes to magazines, omission of wood decks, simplification of pumping arrangements, etc. 8. Board margin.—This is a weight provided for at the time of the design to cover alterations or additions made during the progress of the building of the ship. Any weight thus required, not provided for in the original legend of weights, has to be taken out of the Board margin, and specially submitted for approval to the Board of Admiralty. Influence of Weight saved or added on a Design.1—It is worth noting that a weight saved in any way has an influence on a design far greater than is given by the number of tons thus saved. Thus, suppose in any part of a design, say the equipment, 50 tons can be saved. The influence of this 50 tons less is felt in all parts of the design. The ship thus lightened requires less I.H.P. for the same speed; the engines, etc., thus weigh less and require a smaller complement. A smaller-sized ship will then be sufficient, which will weigh less than before and require less I.H.P. These things thus act and react upon one another, and, as a final result, we should find that by saving 50 tons on the equipment a saving on the whole design, amounting to 100 tons or more, would be possible. As an extreme case, it is calculated that the adoption of two 56-ft. steam pinnaces (each 18 tons), now used instead of the two 37-ft. steam pinnaces (each 9 tons) formerly supplied, has caused a weight of about 150 tons to be added to the total weight of the design of large ships. The actual additional weight of the boats carried is only 18 tons. But the heavier boats require strong 1 See a paper on "The effect of modern accessories on the size and cost of warships," by Mr. Whiting, Assistant-Director of Naval Construction (I.N.A., 1903). masts, derricks, and steam or hydraulic hoists for lifting, and special stowage; so that the result is an additional weight of 70 tons to be carried about. The influence of this is to necessitate a design to be about 150 tons heavier than would have been necessary had the lighter boats been carried. Stability of a Design.-Besides fixing on the legend of weights, we need concurrently to make a calculation for the C.G., both in a vertical and horizonal direction. The first is required to obtain sufficient stability, and the second to see that the vessel when complete shall float at the desired trim. The type of calculation, as prepared for a small cruiser, is shown in the following table: Thus the estimated metacentric height in the legend condition is 2 ft., and the form of the ship must be made to displace 2650 tons, with the centre of buoyancy 11.8 ft. abaft mid-length, in order that the vessel may float at the required draught and trim. Also, the transverse metacentre must be 2.9 ft. above L.W.L. to get a metacentric height of 2 ft. This determines the initial stability. Calculations must, however, be made to determine the "curve of stability," to see that the ship has sufficient stability at large angles of inclination. The detailed calculation of the weight and position of the C.G. of hull is a long and complicated operation, and although this is usually done as the design proceeds, yet in the early stages it is necessary to make an approximation. For this the information obtainable from the inclining experiments of previous ships is invaluable. It is the practice now to incline the ships of the Navy, not only to ascertain the stability of the ships themselves, but also to afford data for future designs. The D. 284 form filled up by the dockyard, and the D. 211 form filled up by the ship's officers, are also of extreme value in affording information as to weights to the designing staff at the Admiralty. The tendency of modern designs is to lead to increased weight above, by the adoption of an armoured battery and heavier guns. on the upper deck, protected by heavy shields. This tendency necessitates the stability being carefully considered, because of the higher position of the C.G. thus caused. The influence of this is seen, for example, in the breadth given to the Duke of Edinburgh as compared with the Drake of greater displacement. Drake, 500 ft. x 71 ft. x 26 ft. x 14,100 tons; 2 9.2-in. guns with shields; 16 6-in. guns in casemates. Duke of Edinburgh, 480 ft. x 73 ft. x 27 ft. x 13,550 tons; 6 92-in. guns with shields; 10 6-in. guns in battery. It will be remembered that in Chapter XVII. we saw that the breadth of ship has a great influence on the position of the transverse metacentre. In a ship where the conditions of the design lead to a high C.G., the transverse metacentre must also be high to get sufficient metacentric height. Horse-power and Speed.-The methods adopted to obtain an estimate of the horse-power necessary for any desired speed have been dealt with in Chapter XXII. The length of a ship in relation to the speed to be attained has a most important influence on economical propulsion. To say that a ship has a speed of |