Part 5

The Scotts had worked steadily at the solution of the problem from their trials with the _Thetis_ in 1858 (see page 34 _ante_). In 1860 the late John Scott, C.B., laid before the Admiralty a system of water-tube boilers and compound engines, but objection was raised to the system. The French Naval authorities, with whom the Scotts then had close business connection, took up the scheme, largely because of the favour with which it was viewed by M. Dupuy de Lôme, the head of the Department. The first ship fitted was a corvette of 650 tons displacement; the boilers worked at a pressure of 140 lb., while the initial pressure at the compound three-cylinder engines was 120 lb. These were the first engines of the compound type in the French Navy.

The Scotts were at the time building engines for four corvettes under construction at the Woolwich and Deptford yards for the British Navy; and the Admiralty agreed to have fitted in one of them water-tube boilers and engines similar to those built for the French boats. The boilers may be said to have belonged to the same general type as the Thornycroft and Normand water-tube steam generators. It was subsequently found impossible, however, to ensure that the top of the boilers should be at least 1 ft. under the load-line--a condition then enforced in steam vessels for the Navy--and the adoption of the water-tube boiler was deferred, the ordinary machinery of the period being fitted to work at 25-lb. pressure instead of 120-lb.[60]

This was unfortunate, as it removed the incentive to continued research needed to make the water-tube boiler a really satisfactory steam generator. The Scotts, however, continued to work for the successful application of high pressures, and it was this that brought them into contact with the late Mr. Samson Fox, with whom they were closely identified for many years in connection with the development of the corrugated flue and the cylindrical steam boiler.

Opinion being adverse to the water-tube boiler, notwithstanding its acceptance by many foreign Navies, there was a strong agitation fostered by engineers to induce the societies for the registry of shipping, and also the Board of Trade, to increase the ratio of the working to the test, pressure in boilers. The British Admiralty allowed the boiler to be worked up to within 90 lb. of the test pressure, whereas in the Merchant Service the working pressure was limited to one-half of the test pressure. In 1888 the Scotts, being convinced that the Admiralty system afforded quite a satisfactory factor of safety, undertook the experiment of submitting a warship boiler, then being built by them to Admiralty specification, to the highest possible pressure, even up to bursting-point. The boiler ultimately leaked to such an extent, after the pressure had been maintained for a long period at 620 lb. per square inch, that it was not considered necessary to proceed further. The stresses at this stage worked out to 48,130 lb. per square inch; and the result proved that there was some justification for a reduction in the minimum scantlings of the shells of marine boilers to, at least, the scale adopted by the Admiralty.[61]

These suggestive experiments were carried out in connection with the boilers constructed in 1888-9 for two war vessels built by the Scotts. These vessels were the _Sparrow_ and the _Thrush_. At the same time, the Scotts engined two other vessels of the same type, constructed at the Royal Dockyards. A view is given on Plate XVII. of the _Thrush_, which was commanded by H.R.H. the Prince of Wales on the North American and West Indian stations in 1891. She was a vessel of composite build, of 805 tons displacement, with machinery of 1200 horse-power, to give a speed of 13 knots; but, as is shown by the illustration, she was fitted as a three-masted schooner, and utilised her sails when the wind was favourable. In this respect, she marks the transition stage between the days of the sailing craft and the modern ship, depending entirely on steam for propulsion. Indication is afforded of the progress towards this transformation by Table III. on the opposite page, which shows the improvement in economy in the machinery of warships at various stages in their development.

The figures in the Table are average results rather than highest attainments during the periods. For 1890-95 we have taken the _Barfleur_, the engines of which were constructed by the Scotts in 1894; whilst the particulars for 1895-1900 refer to the _Canopus_, engined by them in 1900. In 1902 they also supplied the machinery for the battleship _Prince of Wales_, and commenced the construction of the armoured cruiser _Argyll_. But before referring in detail to these latter ships, we may briefly review the advances in applied mechanics, metallurgy and chemistry, which have contributed largely to the perfection of these modern fighting ships in respect of offensive and defensive qualities.

TABLE III.

PROGRESSIVE TYPES OF WARSHIP MACHINERY, AND THEIR ECONOMY, 1840 TO 1905.

+-------------+-------------+-------------- |1840 to 1855.|1855 to 1875.|1875 to 1890. | | | ------------------------+-------------+-------------+-------------- Type of boiler | Rectangular | Rectangular | Single-ended | box | box | cylindrical | | | Steam pressure per | 3 lb. | 25 lb. | 90 lb. square inch | to 4 lb | | | | | Coal consumption per | 7 lb. | 4 lb. | 2-1/2 lb. indicated horse-power | | to 5 lb. | per hour | | | | | | Type of engine | Geared | Simple | Three- | screw | horizontal | cylinder | | surface | compound | | condensing | | | | Piston speed in feet | 220 | 500 to 600 | 750 per minute | | | | | | Weight of machinery per | 10 cwt. | 3 cwt. | 3 cwt. indicated horse-power | | to 5 cwt. | per minute | | | | | | Speed of ship | 8 to 9 | 14 | 16 | knots | knots | knots ------------------------+-------------+-------------+-------------- ------------------------+-------------+-------------+-------------- |1890 to 1895. |1895 to 1900.|1900 to 1905. | [A] | [B] | [C] ------------------------+--------------+-------------+------------- Type of boiler | Single-ended | Belleville | Water-tube | cylindrical | water-tube | | | | Steam pressure per | 155 lb. | 300 lb. | 300 lb. square inch | | | | | | Coal consumption per | 2 lb. | 1.8 lb. | 1.8 lb. indicated horse-power | | | per hour | | | | | | Type of engine | Three- | Three- | Four- | cylinder | cylinder | cylinder | triple- | triple- | triple- | expansion | expansion | expansion | | | Piston speed in feet | 840 | 918 | 1000 per minute | | | | | | Weight of machinery per | 2-3/4 cwt. | 2 cwt. | 1.6 cwt. indicated horse-power | | | per minute | | | | | | Speed of ship | 18 | 18.25 | 23 | knots | knots | knots ------------------------+--------------+-------------+------------- [A] Battleship, _Barfleur_.

[B] Battleship, _Canopus_.

[C] Armoured Cruiser.

The gun most in favour at the close of the eighteenth, and at the opening of the nineteenth, centuries was the cast-iron, smooth-bored, muzzle-loader: first the 32-pounder and later the 68-pounder. Carronades were used for "smashing" rather than for penetrating the skin or structure of ships. Although the 68-pounders were improved by a lining of wrought iron being inserted in the bore, whereby the energy at 1000-yards range was increased from 290 to 600 foot-tons, little progress was made until after the Crimean War, when chemists undertook the investigation of the action of explosives and metallurgists sought to produce stronger metals.

The general idea as regards the powder used as a propellant was that the ignition was instantaneous, and that the more violent the explosion the greater would be the velocity of the projectile. Under such conditions short weapons naturally found favour; and indeed, with a light, spherical, ill-fitting projectile, there was very little advantage to be gained by lengthening the bore. But with the introduction of rifled cannon, much heavier and better-fitting shot became possible, and a rapid-burning powder gave rise to dangerous pressures in the gun. It was then realised that it was not an explosion that was wanted, but a continuous pressure acting on the base of a shot for a relatively considerable period. This needed a slow-burning explosive, and led to the manufacture of powder as pebbles or prisms; the enlargement in the late 'seventies of the chamber of the gun, and the provision of air spaces for the expansion of the powder, greatly added to the velocity with which the shot left the gun, and therefore augmented its carrying power.[62]

Gun-makers had meanwhile improved the strength of the weapon by a recognition of the fact that wrought iron was twice as strong in the direction of the fibre as across it; and thus in the 'sixties they began to coil the central tube, surrounding it by hoops, welded or shrunk on. The full advantages of fibre were thus secured for resisting circumferential strain. The bore was rifled to give the shot that rotatory motion which prevents irregularity in flight and conduces to accuracy of fire at long range. The smooth-bore gun was effective up to only 1000 yards range, as compared with the 6000 yards and 7000 yards for the modern weapon. Breechloading was first introduced into the Navy in the 'sixties, but discarded because the details for closing the breech end proved unsatisfactory. Finally, it was reintroduced in 1878, a satisfactory mechanism having been devised.

These various improvements gradually increased the power of the gun. The length and weight had enormously grown, as is shown by the particulars of successive large Naval guns, shown in Table IV. on the next page; but the increase in energy up till the 'eighties was not commensurate with the augmentation of the weights of the projectile and charge.

The advance from the 38-ton gun of 1870 to the 110-1/2-ton gun in 1887 involved the multiplying by five of the charge of powder, which quadrupled the energy of the gun, but the carrying power of the shot was still deficient. The velocity had increased in twenty years from 1600 to 2000 ft. per second, slower-burning powder having been introduced.

TABLE IV.

PARTICULARS OF THE SUCCESSIVE LARGE NAVAL GUNS, 1800 TO 1905.

+--------+---------+-------+--------+-----+-----+--------+------- | | | | |Weight of |Penetra- | | | | |Projectile. |tion of | | | | | |Weight of |Wrought- | | | | | |Charge. |Iron at | | | | | | |Muzzle |1000 Year.| Type. | Weight. |Length.|Calibre.| | |Energy. |Yards -----+--------+---------+-------+--------+-----+-----+--------+------- | |tons cwt.| in. | in. | lb. | lb. |ft.-tns.| in. 1800 |Cast- | 2 12 | 114 | 6.4 | 32 | 10 | 400 | -- |iron | | | | | | | |smooth- | | | | | | | |bore | | | | | | | | | | | | | | | 1842 |Ditto | 4 15 | ... | 8.12 | 68 | 16 | 700 | -- | | | | | | | | 1865 |Woolwich| 4 10 | ... | 7 | 115 | 22 | 1400 | 7 |wrought-| | | | | | | |iron | | | | | | | | | | | | | | | 1870 |Built-up| 38 0 | 200 | 12.50 | 810 | 200 | 13,900 | 17 |muzzle- | | | | | | | |loader | | | | | | | | | | | | | | | 1880 | Ditto | 80 0 | 321 | 16 |1700 | 450 | 27,960 | 22-1/2 | | | | | | | | 1887 |Built-up| 110 10 | 524 | 16.25 |1800 | 960 | 54,390 | 32 |breech- | | | | | | | |loader | | | | | | | | | | | | | | | 1895 |Wire- | 46 0 | 445.5 | 12 | 850 | ... | 33,940 | 34.6 |wound | | | | | | | |breech- | | | | | | | |loader | | | | | | | | | | | | | | | 1900 |Ditto | 51 0 | 496.5 | 12 | 850 | 210 | 36,290 | 35.4 | | | | | | | | 1905 |Ditto | 58 0 | 540 | 12 | 850 | ... | 49,560 | 42 -----+--------+---------+-------+--------+-----+-----+--------+-------

Attention was further directed to the improvement of explosives; and ultimately, instead of gunpowder having a potential energy of 480 foot-tons per pound, modified gun-cotton was introduced, with an energy of 716 foot-tons per pound, and still later there were evolved explosive compounds of which the potential energy per unit of weight was fourfold greater than in the case of gunpowder, namely, 1139 foot-tons per pound. Finally, the explosive has taken the form of cordite, which ensures slow burning, great expansion, and, consequently, augmented propelling power behind the projectile, without material addition to the maximum strain upon the weapon. But in any case the constructional strength of the modern gun is enormously superior to the earlier built-up weapons, as around the inner tubes there is coiled something like 120 miles of wire, which itself has a breaking-strain of between 90 and 110 tons per square inch, and is put on under a tension of from 54 tons per square inch on the inner wires to 32 tons per square inch on the outer wires,[63] so that the ultimate resistance to strain consequent upon the firing of the gun is enormously increased. Velocities of 2600 ft. per second are thus realised, and even more is quite feasible, so that penetration of wrought iron at 1000 yards range has now been increased to 42 in.

If we compare the 12-in. gun to-day with the weapon of the same calibre of twenty years ago, when there was no widened chamber for the explosive, when prismatic powder of low expansive power was used, it is found, as shown in the Table opposite, that the penetration at 1000 yards has been doubled, and the possible effective range multiplied fivefold. There has also been an enormous gain in quicker fire by improved breech mechanism and efficient hydraulic and electric mountings, whereby the gun and all its loading, elevating, and training machinery is rotated.

The metallurgist has also been successfully occupied, and it is probable that the armour plate of to-day is still invulnerable. The earlier wrought-iron plates were increased from 4-1/2 in. in thickness on the _Warrior_ of 1861, to the 24 in. on the _Inflexible_ of 1881; the area protected being almost proportionately reduced. The artillerist with improved projectiles ultimately defeated this heavy cleading on the ships; but compound armour, first made in 1879, enabled the maximum thickness on the broadside to be reduced to 18 in., permitting a greater area to be covered for the same weight. At first the 80-ton gun failed in its attack, but heavier weapons, with improved projectiles, prevailed. The next step was the introduction of all-steel armour in 1890. Two years later there was introduced the super-carburising and subsequent chilling of the face of plates made of an alloy of nickel steel. In 1897 the process of hardening was still further developed, and now the 9-in. plate on the modern battleship is equal in resistance to a 26-in. wrought-iron plate of the 'sixties, or a 20-in. compound-plate of the 'eighties, or a 13-in. plate of the early-hardened type. For the present, therefore, the armour seems to have secured the victory, as at 5000 yards range 9-in. armour can scarcely be defeated by even the 12-in. gun.

With the increased resistance of armour and the consequent reduction in its thickness, the naval designer can spread his protecting plates over a much wider area, so that the whole broadside of ships like the _Prince of Wales_, or the cruisers _Argyll_ and _Defence_, is clad with armour of satisfactory resisting power. At the same time the gun-power and speed of ships have been greatly increased without making the displacement inordinately high. On the opposite page a Table gives the main features of representative ships at different epochs, which will show this at a glance.

The growth in the size of battleships has been steady, with the exception of the class represented by the _Barfleur_ and _Canopus_, both of which were engined by the Scotts. These vessels are embodiments of a desire to check the advance in the size and cost of the battleship. The deficiency in the number and calibre of their guns was partly compensated by the introduction, for the first time in battleships, of quick-firing weapons of large calibre. The _Barfleur_ had four 12 in. breechloaders and ten 4.7 in. quick-firers; while the _Canopus_ had four 10 in. breechloaders and ten 6 in. quick-firers. But opinion has again strongly grown in favour of having in each British ship the best that can be achieved; and thus the _Prince of Wales_ has a displacement greater than any previous ship, while in the _King Edward_ and the _Lord Nelson_ classes there has been a further growth in every element of power. The probabilities, too, are that we have not yet by any means seen the end of this advance.

TABLE V.

SIZE AND FIGHTING QUALITIES OF BRITISH BATTLESHIPS OF DIFFERENT PERIODS.

+--------------------------------------------------------- | Date of Completion. | +---------------------------------------------------- | | Displacement. | | +----------------+------+---------+----------- | | | | | Total | Collective | | | | | Weight | Energy at | | | | | of Shot | Muzzle of Name. | | | Side Armour. |Speed.| in One | One Round. | | | | | Round. | ------------+----+------+----------------+------+---------+----------- | | tons | in. | knots| lb. | foot-tons | | | | | | _Warrior_ |1861| 9,210| 4-1/2-in. |14-1/2| 3800 | 61,476 | | | wrought iron | | | | | | | | | _Hercules_ |1868| 8,680| 9-in. to 6-in. |14 | 5400 | 70,200 | | | wrought iron | | | | | | | | | _Alexandra_ |1877| 9,490| 12-in. to |15 | 5426 | 71,400 | | | 6-in. wrought | | | | | | | | | | | | | | | _Inflexible_|1881|11,880| 24-in. to |13 | 6936 | 123,120 | | | 16-in. wrought | | | | | | iron | | | | | | | | | _Benbow_ |1888|10,600| 18-in. |16.75 | 4600 | 135,560 | | | compound | | | | | | | | | _Royal |1892|14,150| 18-in. and |17.5 | 5800 | 159,610 Sovereign_ | | | 5-in. compound | | | | | | | | | _Barfleur_ |1894|10,500| 12-in. |18.5 | 2450 | 67,670 | | | compound | | | | | | | | | _Canopus_ |1900|12,950| 6-in. hardened |18.25 | 4600 | 178,720 | | | steel | | | | | | | | | _Prince of |1902|15,000| 9-in. |18.25 | 4600 | 194,400 Wales_ | | | super-hardened | | | | | | steel | | | | | | | | | _King |1904|16,350| 9-in. |18.50 | 5920 | 270,040 Edward VII._| | | super-hardened | | | | | | steel | | | | | | | | | _Lord |1905|16,500| 10-in. |18.50 | 7960 | 413,900 Nelson_ | | | super-hardened | | | | | | steel | | | ------------+----+------+----------------+------+---------+-----------

As to the machinery made by the Scotts for these battleships, the _Barfleur_ had three-cylinder, triple-expansion twin-screw engines, to run at 108 revolutions, and to develop 13,000 indicated horse-power. On her trials the power was 13,163 indicated horse-power. There are eight single-ended, return-tube, cylindrical boilers, working at 155 lb. pressure. Other details are given in the Table on page 53.