Two Centuries of Shipbuilding by the Scotts at Greenock

Chapter II: Part 2

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The type of machinery in use at this period is illustrated on the opposite page. This particular engine was constructed in 1838. The piston was connected to one end of the side-levers, while the crank was operated from the other. The paddle-wheel of this engine was 25 ft. 0-1/2 in. in diameter, with seventeen floats. For about thirty years this was the standard type of marine engine for paddle steamers.

The Gothic architectural design for the main framing was gradually abandoned for something less ornamental and perhaps more mechanical.

The Royal West India Mail Company's Service, still one of the best known of British lines, was commenced in 1841. Some of the steamers were purchased, but amongst those built originally for the service was the _Dee_ by the Scotts. She was 213 ft. 9 in. long, 30 ft. 4 in. beam, and 30 ft. in depth, the burden tonnage being 1848 tons. On a draught of 17 ft. 6 in. she carried 700 tons of cargo; and, as with most of the oversea liners of the period, the average speed was only about 8 knots. The voyage of 13,650 miles occupied then one hundred and nine days, including stoppages; and the consumption of fuel was 25-1/2 tons per day. The engines, which had cylinders 73 in. in diameter with a stroke of 7 ft., were of 450 horse-power, driving side paddle-wheels 28 ft. 6 in. in diameter.[40]

In the thirty years from the first commercial British steamer, the _Comet_, there had not been much advance in the steam engine, excepting in size, power, and, perhaps, reliability. Wood had continued to be the constructive material for all but the smallest ships. The size of vessels had grown steadily to the 1848 tons of the West Indian mail liner, which started regular steamship service almost contemporaneously with the inauguration of the Atlantic mail line by the Cunard Company in 1840. Speeds on service, even on the shortest routes, were seldom over 13 knots, and on the long routes under 8 knots. But this was in excess of the average attained by all but exceptionally fast clippers. The Table on the opposite page shows the progress made in thirty years.

TABLE I.--EPOCH-MARKING STEAMERS BUILT BY THE SCOTTS, 1819 TO 1841.

-----+------------------+--------+---------+-------+------------------
Year.| Name. |Tonnage.| Horse- |Speed | Remarks.
| | |power.[A]|(Miles |
| | | | per |
| | | | Hour).|
-----+------------------+--------+---------+-------+------------------
1819 | _Waterloo_ | 200 | 60 | 9 |Largest steamer of
| | | | | 1819.
| | | | |
1820 | _Superb_ | 240 | 72 | 9 |Largest steamer of
| | | | | 1820.
| | | | |
1821 | _Majestic_ | 345 | 100 | 10 |Largest steamer of
| | | | | 1821.
| | | | |
1835 |_City of Aberdeen_| ... | 200 | 12 |Strongest steamer
| | | | | of 1835.
| | | | |
1836 | _Jupiter_ | 439 | 210 | 13 |Record speed
| | | | |
1837 | _Tagus_ | 709 | 286 | 10 |Largest constructed
| | | | | on Clyde, 1837,
| | | | | and an early
| | | | | P. and O. liner.
| | | | |
1839 | _India_ | 1206 | 320 | 10 |First steamer to
| | | | | India _viâ_ the
| | | | | Cape and the first
| | | | | Indian liner.
| | | | |
1841 | _Dee_ | 1848 | 450 | 10 |First Royal West
| | | | | India Mail liner.
-----+------------------+--------+---------+-------+------------------

[A] It is difficult to determine in all cases the basis on which horse-power was computed. The figures given represent nominal horse-power, and in Sennett and Oram's "Marine Steam Engine" (page 3), the indicated horse-power is, for this early period, recorded as 1.8 times the nominal horse-power.

We enter now upon the period when iron took the place of timber as a constructional material. It was first used in part in the construction, on the banks of the Monkland Canal as far back as 1818, of a canal barge named the _Vulcan_, a vessel which continued at work for over sixty years.[41] But the first vessel built entirely of iron was a small craft constructed in 1821 in England. It was not, however, until 1832 that the first sea-going vessel was built of this metal. Progress in the adoption of iron was slow, largely because timber had proved so serviceable, and, with lessened restriction upon its importation, had become much cheaper. It was not until the higher strength and greater ductility of steel were demonstrated in the 'eighties that timber was finally superseded. The last wooden ship built by the Scotts was completed in 1859.

The firm built several of the early Atlantic liners, and we reproduce on page 32, as a further step in the development of the steam engine, a drawing showing the double-gear engines constructed early in the 'fifties for an iron screw steamer of 1190 tons, built for the Glasgow and New York service. This engine was pronounced at the time "the most compact specimen of its type then in existence,"[42] for although the power developed was 250 horse-power, and the ship was 260 ft. in length, only 12 ft. 6 in. of the fore-and-aft length was taken up by the machinery. "Every weight was well balanced, the working parts were clear and open, and the combined whole was stable, firm, and well bound together." The cylinders were 52 in. in diameter, were arranged diagonally, and worked at right angles to each other, with a stroke of 3 ft. 9 in. The piston-rods projected through the lower covers, to allow of long return connecting-rods. Each cylinder had two piston-rods, for greater steadiness, their outer ends in each case being keyed into a crosshead, fitted at each end with slide-blocks, working in a pair of inclined open guide-frames, bolted to the bottom cylinder cover, and supported beneath by projecting bracket-pieces, recessed and bolted down upon pedestal pieces on the engine sole-plate. From each end of this crosshead, immediately outside the guide-frame, a plain straight connecting-rod of round section passed up to actuate the main first-motion shaft. The upper ends of the connecting-rods were jointed to side-studs, or crank-pins, fixed in two opposite arms of a pair of large spur-wheels, which gave motion to the screw-shaft by means of a pair of corresponding spur-pinions, fixed on the shaft.

The main spur-wheels were 11 ft. 5-1/2 in. in diameter, and the pinions on the screw-shaft 4 ft. 6 in.; so that the screw propeller made 2-1/2 revolutions to each rotation of the engine. The arrangement ensured that each piston was directly coupled to both of the large wheels, and the increased length of the crossheads, which the plan involved, was counterbalanced by the effect of the double piston-rods, for by this division of the pressure the cross-strain leverage was proportionately diminished.

The use of steam expansively in multiple-cylinder engines was, however, the most important factor in the development of the steamship during the latter half of the nineteenth century.[43] With low steam pressures and simple engines the coal consumption, even for moderate-sized ships, was a serious item in a long sea voyage; and, early in the 'fifties, engineers, recognising the economy which would result from a successful compounding of steam, tackled the problems of steam-generation plant to enable the necessary high initial pressure to be developed with safety. John Elder had fitted several ships, but was, for a long time, content with an initial pressure of from 50 lb. to 60 lb. per square inch.

The late John Scott, C.B., was so convinced of the economy of steam at higher pressures in the compound system that he decided to build, largely at his own expense, a vessel which would enable him to put the system to a thorough test. This steamer, constructed of iron in 1858, was the _Thetis_, which was, undoubtedly, an epoch-marking ship, as her machinery was operated at an initial pressure of 115 lb. to the square inch--exceptionally high for those days.

For the first time, surface condensers were used in association with the compound marine engine. There were, as shown on Plate XI., facing page 36, six cylinders, arranged in two groups, each with one high- and two low-pressure cylinders. The three pistons of each group worked one crosshead, connecting-rod, and crank. Each group had two slide-valves, one for the high-pressure and one for the low-pressure cylinders, and both were attached to one valve spindle and one reversing link.[44] The engines worked up to 51 revolutions per minute--equal to a piston speed of 255 ft. per minute--and the maximum indicated horse-power was 256. The engines were tried by the late Professor Macquorn Rankine, F.R.S., who certified that the coal consumption on trial was 1.018 lb. per indicated horse-power per hour: an extraordinary result, even in the light of modern improvements.[45]

A large part of this efficiency was due to the boilers, which were of the Rowan water-tube type, and are illustrated on the opposite page. They had square vertical water-tubes, and through each of these there passed four hot-gas tubes. They evaporated 11 lb. of water per pound of coal, which was 30 per cent. higher than was attained with the best marine boilers of those days. The coal consumption at sea was about 1.86 lb. per indicated horse-power per hour.

Unfortunately, there soon developed small holes in the boiler-tubes, owing to erosion of the external surface, probably the consequence of the chemical action set up by the steam for cleaning the tubes mixing with the soot and other deposit.[46] Although for this reason this early water-tube boiler did not succeed, there is no doubt that the performances suggested improvements which have since brought complete success to this system of boiler. At the same time, the efficiency of high steam pressures was completely established and resulted in very considerable progress in the size and power of steamships.

Another innovation which suggested future developments was the fitting at the base of the funnel in the _Thetis_ of a series of water-tubes for the purpose of utilising the waste heat from the boilers to evaporate water for subsequent condensation to make up the boiler feed. The time was not ripe for such a utilisation of the waste gases--the heat was insufficient to generate the required steam--but now various schemes are applied for absorbing the waste heat in the uptake to heat air for furnace draught and to superheat steam.

A number of water-tube boilers were made, and a set was fitted into a corvette built for the French Navy. This vessel, completed in the early 'sixties, was the first ship in the French fleet to be driven by compound engines, and will fall to be described with other vessels in our next Chapter, dealing with the work of a century for the Navy.

Perhaps the most significant indication of the success of the Scott compound engine is found in the results of its application to the early Holt steamers. Alfred Holt commenced trading with the West Indies in 1855, while his brother, George Holt, became associated with Lamport in the River Plate trade in 1865. Both lines continue among the most successful in British shipping.

The Holt steam line to China was commenced in 1865, and was the only one _viâ_ the Cape of Good Hope which proved at once successful. Built and engined by the Scotts, the early Holt liners, starting from Liverpool, never stopped till they reached Mauritius, a distance of 8500 miles, being under steam the whole way, a feat until then considered impossible.[47] Thence the vessels proceeded to Penang, Singapore, Hong Kong, and Shanghai. Unaided by any Government grants, they performed this long voyage with great regularity.

The three vessels which inaugurated the very successful Holt line were named _Agamemnon_, _Ajax_, and _Achilles_, and were built of iron by the Scotts in 1865-6. They were each 309 ft. in length between perpendiculars, 38 ft. 6 in. beam, and 29 ft. 8 in. in depth, with a gross tonnage of 2347 tons--dimensions which were then deemed too great for the China trade, but which experience soon proved to be most satisfactory. Sails were fitted to the vessels, as shown in the engraving on the Plate facing page 40.

Alfred Holt was the first to apply the compound engine to long voyages, and his vessels were the earliest of the type built for the merchant service by the Scotts. It is true the Pacific Company had compound engines fitted to one or two ships prior to this, but these were only used in the coasting trade. The engines of these Holt liners are therefore of historical interest, and general drawings are reproduced on the next page and on Plate XII. A feature in these liners was that the propeller was abaft the rudder, which worked in an aperture in the deadwood corresponding to that for the propeller in single-screw modern ships.

A detailed description from the specification of the machinery may be reproduced, as it indicates the practice of the Scotts for a considerable time. Indeed, this type of compound engine, with slight modifications, was the standard engine for Holt liners until the advent of the triple-expansion engine. The details follow:--

The cylinders were: high-pressure, 30 in. in diameter; low-pressure, 62 in. in diameter, with 4 ft. 4 in. stroke, arranged vertically in tandem fashion, with the low-pressure cylinder on the top. There were two connecting-rods, but a common crosshead for the tandem cylinders, and a common crankpin.

The crankshaft was 13-1/2 in. in diameter, with a bearing 30 in. long at the aft end of the bedplate, which took the propeller thrust. The propeller was three-bladed, 17 ft. in diameter, with 26 ft. 6 in. pitch; with 46 revolutions per minute the piston speed was 400 ft. per minute. To ensure smooth working with the single crank, a heavy flywheel was fitted, and the pump levers carried a massive weight to help to balance the weight of pistons and rods.

The condenser had 420 tubes 1-1/2 in. in diameter, giving a cooling surface of 1375 square feet. The tubes were arranged in three nests, the water circulating through the top one first and the bottom one last. The circulating pump, instead of forcing water through the tubes, as was usual in such case, sucked from the condenser and discharged directly overboard. There were: one air pump, 24 in. in diameter; one circulating pump, 24 in. in diameter; two feed pumps, 4-3/4 in. in diameter; and one bilge pump 7 in. in diameter: all the pumps were single-acting, with 17 in. stroke. The diameters of the principal pipes were: main steam, 7-1/2 in.; to low-pressure cylinder, 12 in.; circulating inlet, 10 in.; discharge, 12 in.; air-pump discharge, 10 in.; main feed, 3-3/4 in.; and waste steam, two at 6 in. in diameter.

The two boilers were double-ended, of the locomotive type, with wet-bottomed furnaces. The centre was cylindrical, but the ends were rectangular with semi-cylindrical tops, the total weight, without water, being 78 tons. Each boiler had a long receiver passing through the uptake to dry the steam. On the receiver was a deadweight safety-valve 6-1/4 in. in diameter, to suit a working pressure of 60 lb. per square inch. The grate surface was 112 square feet, and the total heating surface 4506 square feet, there being 328 iron tubes 4 in. in diameter.

The three pioneer ships of the Holt line--the _Agamemnon_, _Ajax_, and _Achilles_--proved most economical. The _Achilles_ came home from China in fifty-seven days eighteen hours, net steaming time, or, including the stoppages at ports, sixty-one days three hours. She travelled during this period a distance of 12,352 miles, on a consumption of coal which did not exceed 20 tons per day for all purposes,[48] equal to 2-1/4 lb. per unit of power per hour, which for those early days, with comparatively low steam pressures, must be regarded as a highly satisfactory result.

The non-stop voyage between Liverpool and Mauritius was made as early as 1866 in thirty-seven days, equal to 10 knots, with a number of passengers and a fair cargo. The higher economy established for the compound engine on long voyages resulted in the ultimate supersession of the sailing ship.[49] Thus the Scotts, while still enjoying the credit of the splendid performance of the _Lord of the Isles_ in the early 'sixties, produced at their foundry the Holt compound engine, which sounded the death-knell of the clipper. The compound system had at once an influence on the size of ships. Up till 1862 no ship of over 4000 tons had been constructed, with the exception of the _Great Eastern_; by 1870 there were fifteen; by 1880, thirty-seven.[50]

The Scotts, aided by Holt, continued their research towards higher economy, and a large fleet of steamers was built, with engines having flywheels which, it was found by experience, considerably improved the economy up to a certain stage, although with increased pressure the proportion of saving was not commensurate with the weight of the wheel, and the three-cylinder three-crank engine was ultimately adopted.

The Scotts throughout the century continued to have a close association with the China trade, constructing a long series of successful steamers for the Holt company and for other lines, with services from Britain to the Far East, and carried out very extensive work in the building up of the coasting trade of Asia and Oceania. For the Holt line alone there have been constructed by the Scotts forty-eight steamers, aggregating 148,353 tons; while the propelling machinery of these represents 19,500 nominal horse-power. For the India and China services there have, in the past fifty years, been completed over one hundred and thirty steamers.

The China Navigation Company, Limited, was formed in 1873 by Messrs. John Swire and Sons, of London, for trading in China, and the first steamers built for them by the Scotts were two vessels of 1200 tons gross, completed in 1876.

Since then the Scotts' yard has practically never been without a vessel for one or other branch of the Eastern trade, and particularly for the China Navigation Company, which runs steamers from China as far south as Australia, as far west as the Straits, and as far north as Vladivostock and the Amur river. They also have ships trading up the Yangtsze Kiang to Ichang, 1000 miles from the sea, where the rapids prevent navigation farther into the interior. For this service the twin-screw steamer was adopted in 1878, much earlier than in many other trades, largely owing to the strong advocacy of the late John Scott, C.B. Up to that time most of the Yangtsze steamers were propelled by paddle-wheels driven by walking-beam engines. The first of the twin-screw steamers was built in 1878--a vessel of 3051 tons gross--and there has been constructed since then a long succession of very serviceable steamers. For this line alone, sixty-four vessels have been constructed by the Scotts, the aggregate tonnage being 115,600 tons, while the nominal horse-power of the propelling machinery fitted to these vessels is 15,000 horse-power.

But having in our brief historical sketch come to times within the recollection of the reader, it may be more satisfactory to depart from the purely chronological review of the company's operations, and to offer rather an analysis of the progress made, deferring a description of typical modern steamers for a separate Chapter.

The direct-acting vertical engine, with inverted cylinders, almost as we know it to-day, and as illustrated in connection with the work of the twentieth century, was introduced in the late 'fifties. The compound engine, introduced in 1854, was developed into the triple-expansion system in 1882, and later into the quadruple-expansion type; but this latter has not been much adopted, only some 3 per cent. of the vessels registered at Lloyds being so fitted. This is in a large measure due to the satisfactory economy attained with triple-expansion engines. As to the progress made, Table II., giving average results at different periods, is instructive.[51]

TABLE II.--PROGRESS IN THE ECONOMY OF THE MARINE ENGINE, 1872 TO 1901.

-------------------------------------------+-----+-----+------+------
|1872.|1881.|1890. | 1901.
-------------------------------------------+-----+-----+------+------
Boiler pressure in pounds per square inch |52.4 |77.4 |158.5 | 197
Coal consumption in pounds per indicated | | | |
horse-power per hour | 2.11| 1.83| 1.52 | 1.48
Consumption on prolonged sea voyages in | | | |
pounds per indicated horse-power per hour |... | 2 | 1.75 | 1.55
Piston speed in feet per minute |376 |467 |529 | 654
-------------------------------------------+-----+-----+------+------

The advance of the century may be popularly expressed by stating that, whereas in the first coasting steamships built by the Scotts the fuel consumed in carrying 1 ton of cargo for 100 miles was 224 lb., the expenditure to-day is from 4 lb. to 5 lb. The economy of the steam engine has accounted, as is shown in the Table, for a considerable part of this improvement. But, at the same time, the growth in the size of ships has enabled the normal speed of 10 knots to be realised, with an addition to engine power of much less ratio than the increase in the capacity of the steamer. As to speed, recent progress has been most marked in the Navy, and it is therefore fitting that here we should direct our attention to Naval work.

FOOTNOTES:

[17] Woodcroft's "Steam Navigation," page 20, etc.

[18] Woodcroft's "Steam Navigation," page 54.

[19] Deas' "Treatise on the Improvements and Progress of Trade on the River Clyde" (1873), page 24.

[20] Muirhead's "Life of Watt," pages 428 and 429.

[21] Williamson's "Clyde Passenger Steamers," pages 348 to 351.

[22] James Napier's "Life of Robert Napier," page 21.

[23] This was the second of the name--a favourite one after the Duke of Wellington's great victory, and gave rise to the following poetic effusion:--

And now amid the reign of peace,
Art's guiding stream we ply;
That makes our wheels, like whirling reels,
O'er yielding water fly.
As our heroes drove their foes that strove
Against the bonnets blue;
On every side the waves divide
Before the _Waterloo_.

--Millar's "Clyde from Source to Sea," page 179.

[24] Millar in "Lecture on Naval Architecture and Marine Engineering at Glasgow Exhibition, 1880-81," page 138.

[25] "Greenock Advertiser," August 6th, 1819.

[26] "Steamboat Companion" for 1820.

[27] Millar, "On the Rise and Progress of Steam Navigation." Lectures at the Glasgow Exhibition (1880-81), page 138.

[28] Hodder's "Life of Sir George Burns, Bart.," page 161.

[29] Williamson's "Clyde Passenger Steamers," page 32.

[30] Lindsay's "History of Merchant Shipping," vol. iii., pages 78 to 80.

[31] Weir's "History of Greenock," page 89.

[32] Williamson's "Memorials of James Watt" (1856) page 228.

[33] "Greenock Advertiser," July 5th, 1839.

[34] "Greenock Advertiser," February 5th and May 25th, 1835.

[35] Fincham's "History of Naval Architecture," page 294.

[36] Sir Thomas Sutherland, in the "Pocket Book of the P. and O. Company" (1890), page 15.

[37] Fincham's "History of Naval Architecture," page 235.

[38] Sir John Ross's "Steam Communication to India by the Cape of Good Hope" (1838), page 31.

[39] "Greenock Advertiser," January 22nd, 1839.

[40] Fincham's "History of Naval Architecture," pages 320 and 321.

[41] Lindsay's "Merchant Shipping," vol. iv., page 86.

[42] "Practical Mechanic's Journal," vol. i., 1853.

[43] The number of steam vessels belonging to the United Kingdom in 1849 was only 1142, of 158,729 tons; Sweden, which was second among the nations of the world, had only about one-tenth of this tonnage.--Porter's "Progress of the Nation," page 626.

[44] Holmes' "Marine Engineering," page 74.

[45] Rankine's "Steam Engine," page 502.

[46] "Transactions of the Institution of Naval Architects," vol. xxviii., page 141; and vol. xxx., page 278.

[47] Lindsay's "Merchant Shipping," vol. iv., page 434.

[48] "Proceedings of the Institution of Naval Architects," vol. xi., page 152.

[49] Lindsay's "Merchant Shipping," vol. iv., page 435.

[50] Pollock's "Modern Shipbuilding, and the Men Engaged in it," page 199.

[51] "Proceedings of the Institution of Mechanical Engineers" (1901), page 608.

A Century's Work for the Navy.

The work for the Navy by the Scotts began with the building, in 1803, of a sloop-of-war named _The Prince of Wales_; a photograph from the model of this vessel is reproduced on Plate XIV. Since the construction of this ship the firm have carried out several important Admiralty contracts, including the first machinery manufactured in Scotland for a dockyard-built ship, the first steam frigate built in the North, and several later ships, with their engines; the most recent order being for the machinery of the armoured cruiser _Defence_, of 14,600 tons displacement, and 27,000 indicated horse-power, to give a speed of 23 knots.

The progress demonstrated by a contrast between the small sloop-of-war and this latest powerfully-armed and well-protected high-speed cruiser, is a record of research and invention, not only on the part of the naval architect, but also of the chemist, the metallurgist, and the engineer; the triumph is greater than that reviewed in the case of the Merchant Marine. Great speed has been achieved, notwithstanding that the problems to be solved in its attainment have been intensified by the limitations in the size of the ship in order to minimise the target presented to the enemy's fire, and by the necessity of providing for heavy armour, armament, and ammunition in the displacement weight.

When a comparison is made of the Navy ships at the beginning of the nineteenth century with those of a hundred years earlier, it is found that little progress had been made, either in design or in gun-power. The largest vessel in 1700 was of 1809 tons burden, with a hundred guns. A century later, the size had increased only to 2600 tons, with a hundred and twenty guns.[52] But even this was an exceptionally large vessel. The British ships were, as a rule, smaller, and perhaps slower, than the French ships; but then--as now and always--skill in strategy, courage in combat, and devotion to duty were the most powerful factors in action. No fault in these respects could be found with the work of our Navy in the various engagements which terminated in the epoch-marking victory in Trafalgar Bay.

The peace following the Napoleonic wars was not conducive to advancement, as there was little incentive to pursue the sciences which contributed to the development of destructive weapons. Steam as a motive power and iron as a constructive material were not so readily adopted in the Navy ship as in the Merchant Marine. Progress in the utilisation of iron was not continuous. The first application of steam was belated, and its popularity was not unalloyed.

The Admiralty ordered their first ship of iron in 1839--a small, non-fighting boat for the Dover station--and there followed other vessels for the exploration of the River Niger. But the first iron fighting ship was not built until 1843. In 1848-9 the Scotts constructed the iron steam frigate _Greenock_, the largest iron warship of her day, and the first steam frigate built on the Clyde. The over-all length of this vessel was 213 ft., the beam 37 ft. 4 in., and the depth of hold 23 ft. She was of 1413 tons burden, and carried ten 32-pounder smooth-bore muzzle-loading guns. The illustration on Plate XV. is a reproduction from an old engraving of the launch of the vessel. It is a noteworthy feature that the figure-head was a bust of John Scott, the second of that name. This compliment by the Naval authorities of the time was well merited, as he did much not only for the advance of naval architecture, but also for the development of Greenock.

As a writer of the day put it, this vessel was the _experimentum crucis_ of the principle of constructing fighting ships of iron.[53] By 1850 there were six large iron vessels, ranging downwards from the 1980 tons of the eighteen-gun ship _Simoon_, with eleven smaller vessels; but they were all condemned, because it was found by experiment[54] that the 32-pounder gun at short range could perforate the side of the iron ship, and that the projectile carried its "cloud of langrage" with great velocity into the interior of the ship, so that men could not stand against it. Tests were also made with sixteen wrought-iron plates superposed, to give a total thickness of 6 in., but these also were perforated by the 32-pounder projectiles at 400 yards range; so that the adoption of iron on the main structure of the ship was practically delayed until armour-plates were first rolled in 1859.

The obstacle to the adoption of steam was the unsuitability of paddle-wheel machinery for fighting ships. The wheel was exposed to gun-fire, and the whole of the machinery could not be located below the water line. Moreover, the side wheel limited the number of guns which could be utilised for broadside fire. The first steam craft ordered by the Admiralty was a small vessel of 210 tons and 80 nominal horse-power, built in London in 1820.[55] Several other non-fighting steamships followed. By 1837, the largest steam vessel in the fleet was a sloop of 1111 tons and 320 horse-power.[56] In 1839 five steam vessels were built, and two of them--the _Hecate_ and _Hecla_--were engined by the Scotts. These wooden steamers were the first Naval vessels sent to Scotland to have their machinery fitted on board. They were of 817 tons and 250 horse-power. The paddle-wheels had a diameter of 25 ft. 1/2 in., and there were seventeen floats. The main engines, illustrated on page 29, represent the type adopted, not only in the Naval, but in the Merchant service of this time. The steam pressure was then about 3 lb. per square inch.

On Plate XVI. we illustrate the general arrangement of the machinery in the _Hecate_ and _Hecla_. There were four boilers of the rectangular type, each with two wet-bottomed furnaces at one end and large return flues at the other end. The uptakes passed up inside the boilers through the steam space, uniting in one funnel.

Smith's screw-propeller was tried experimentally in 1837, and Ericsson's about the same time. The comparative trials of the _Archimedes_ fitted with Smith's screw against existing paddle-steamers did much to prove the efficiency of the new system.[57] The screw-ship excelled the performance of paddle-steamers on the service, and the screw-propeller was adopted by the Admiralty in 1845; twin-screws followed twenty-five years later.

The _Greenock_, built in 1848, was the first war vessel by the Scotts fitted with the screw-propeller. We have already referred to her construction in iron, and to her launch. She had a displacement of 1835 tons, and her engines were of 719 indicated horse-power. The speed realised on the trial was 9.6 knots. The _Greenock's_ machinery, which is illustrated on the next page, is specially interesting, as it represents one of the earliest attempts to drive the screw-propeller by gearing. Two horizontal cylinders were fitted, each 71 in. in diameter, with a stroke of piston of 4 ft. The gearing consisted of four sets of massive spur-wheels and pinions, in the ratio of 2.35 to 1, so that 42 revolutions per minute of the engines give 98.7 revolutions to the propeller-shaft. The propeller was 14 ft. in diameter, and was so fitted that it could be detached and raised to the deck. There were four rectangular brass-tube boilers, each with four wet-bottomed furnaces, and all the internal uptakes united in one funnel, which was telescopic, so that when it was lowered and the propeller raised out of the water, the vessel had the appearance, as well as the facility, of a sailing frigate.

As will be seen from the drawings, both the engines and boilers were arranged very low in the hull, to be safe from the enemy's fire. The engine and boiler compartment occupied 72 ft. of the length of the ship--about one-third of the total length--and the seating for the machinery was specially constructed, with a very close pitch of frames which were only 1 ft. apart. For comparison with the drawings of the machinery in the _Greenock_, we give on page 49 a similar drawing of the machinery of the _Canopus_, of 12,956 tons displacement, seven times that of the _Greenock_. To double the speed, the power of machinery had to be multiplied twenty times, and yet the space occupied is only about trebled.

In 1850 the largest of the steam vessels in the Navy[58] had a displacement of 3090 tons, but the most noted was the _Dauntless_, of 2350 tons displacement, with engines of 1347 indicated horse-power to give a speed of 10 knots. It is true that there were three smaller vessels of greater speed, one of 196 tons steaming 11.9 knots; but this was the highest rate reached in the Navy service. By this time some of the fast mail steamers made 13-1/2 knots. These latter were suited for war service, but we have already dealt with them.

Following the adoption of the screw-propeller in warships came the abandonment of gearing for the engines. For many years various forms of horizontal engine were used; first with return-connecting rods, and subsequently with direct-acting rods. Steam pressures steadily increased, largely owing to stronger materials being available. It was, however, not until the 'seventies that the cylindrical boiler, the compound engine, and the surface condenser admitted of an increase to 60 lb. per square inch[59]--several years after these improvements had been introduced in the Merchant Marine.

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.

[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.

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Two Centuries of Shipbuilding by the Scotts at GreenockChapter II: Part 2

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