“The necessities of the screw propeller after its general adoption demanded a much greater increase of engine revolution than constructors in the early days, or for some years after, deemed it prudent to adopt. Thus a great variety of design, including beam, steeple, oscillating, and other forms of machines were used, all with gearing between the engine and the propeller. But a few direct-acting engines appeared very early, and gradually, as engineers gained confidence, the latter type became universal, and assumed the form of the inverted cylinder in the so-called steam-hammer engine which was the universal type for mercantile purposes until the end of the century.
“John Elder we may look upon as the father of multiple-expansion engines. He, together with his partner Charles Randolph, was trained in the marine school of Mr. Robert Napier, Vulcan Foundry, Glasgow. In 1852 they commenced business, and by 1856 had constructed several four-cylinder compound engines. Randolph, Elder and Co. entered into a contract for a set of engines, the coal for which, on trial, would not exceed 3 lb. per indicated horse-power per hour. The trial ... worked out at 2¹⁹⁄₂₀ lb.” In regard to coal consumption, the Pacific Steam Navigation Company’s boats Callao, Lima, and Bogota, after being brought home from the Pacific coast to be re-engined, all showed a consumption of from 2 to 2¹⁄₂ lb. (per indicated horse-power) of best Welsh coal. The Bogota’s speed with the old engines was 9·75 knots and the coal consumption not less than 38 cwts. per hour. On her outward voyage with new engines she “gave a mean speed of 10·47 knots with 19 cwts. of coal per hour.” The steam-pressure was 22 lb. and the horse-power was about 950 indicated.
“These early fathers seemed to see into the future. Walter N. Neilson, in his Presidential Address (1859), refers to the ‘three grand requirements (of marine engines) as—a safe and suitable boiler for 100 lb. and upwards; a good arrangement of engine to receive the initial force of the steam without shock or liability to derangement, and carry out expansion to the greatest practical limits; and, lastly, an efficient surface condenser.
“John Elder was among the first to adopt the surface condenser and the cylindrical boiler, and he thus in the ’fifties brought to a successful issue these three grand requirements. We must go back to these early days to realise what it meant to make a boiler which would be safe for 100 lb.; steel plates of the present day weighing tons were then represented by puddled iron plates weighing hundredweights. This led John Elder to try a water-tube boiler, practically the modern Yarrow boiler, also a spiral tube boiler, but probably none of these was successful owing to the salt-water difficulty, evaporators not being introduced till many years afterwards.”
As the adaptability of iron for constructional purposes became more generally recognised, it led to the proposal that steamers should be built on the longitudinal principle instead of with an ordinary keel and a series of transverse ribs. The use of iron also enabled shipbuilders to increase the safety of their vessels considerably by means of transverse bulkheads, the number of these being increased until, even as early as 1838, the iron steamers then being built for the Glasgow and Liverpool line were each divided into five sections, any three of which were estimated to be sufficient to keep the steamer afloat if the other two should become waterlogged through collision. Several vessels were constructed on modifications of the longitudinal system, the chief among them being the Great Eastern. In 1853 James Hodgson of Liverpool issued a circular on the advantages of iron sailing ships, in which he pointed out not only the greater strength obtained by using iron but the comparative cheapness of construction. The circular stated that a wooden ship of 1000 tons would cost £16 10s. per ton, and an iron ship £13 10s. per ton, both fitted for trade to the East. The wooden ship would not carry more than 1500 tons, whereas an iron ship built from the same external lines would carry 1800 tons, and this difference at £5 per ton out and home, added to allowances for insurance, depreciation, and interest, would make a difference in favour of the iron ship of £2295.
The “Sarah Sands,” 1846.
What was true of sailing ships was equally true of steamers, and Hodgson had shown this some years before the publication of his circular, when he built the Sarah Sands.
The Sarah Sands afforded an excellent example of the strength of iron ships if well and substantially built. She grounded on the Woodside Bank in the Mersey when carrying 1000 tons dead weight, and remained high and dry until the tide flowed again, during which time she did not sustain the slightest damage. She experienced several mishaps at one time and another, which demonstrated not only the superior manner in which she was put together, but also the superiority of iron ships over wooden ones, for it is difficult to suppose that a wooden vessel would have withstood all these casualties without sustaining serious damage. The Sarah Sands was built in 1846 at Liverpool; she was 182 feet between perpendiculars, 33 feet beam, 32 feet deep, and of 1400 gross tonnage. Her engines were of 300 indicated horse-power and were built by Messrs. Bury, Curtice, and Kennedy of Liverpool. She had two oscillating cylinders of 50 inches diameter and a stroke of 3 feet, working upwards to the crank shaft, and a still greater novelty was the application of a direct coupling between the crank shaft and the screw shaft. Her boilers were of the wet-bottomed type, and had six furnaces besides return tubes, the steam pressure being 9 lb. She was four-masted and heavily canvassed, carrying courses, topsails, and topgallant sails on the main and mizzen masts, while she was fore and aft rigged, including topsails, on the fore and jigger masts; her head sails included a large fore staysail and two immense jibs.
She made her first voyage from Liverpool to New York in January 1847, in connection with the Red Cross Line, and remained in this service until the end of 1849, when she was transferred to the American coastal route between Panama and San Francisco, being probably the first iron screw vessel to go round South America. The discovery of gold in Australia caused her to be sent to Sydney with a crowded passenger list of gold-seekers, and she was thus the first iron screw steamer to cross the Pacific to Australia; she afterwards came back to Liverpool and was again placed on the New York trade, and in 1854 was sent to Canada and was the first iron screw steamer in that trade also. On her return passage she struck the rocks in the St. Lawrence, near Belle Isle, and remained fast four days and nights. When she returned to Liverpool it was found that she had not started so much as a rivet, which says a good deal for the strength of her construction. This was destined to have another unnecessary proof, for as she left the graving dock she capsized owing to her ballast having been removed and not replaced, but again she was none the worse. Next she was employed as a transport for troops to India in 1857, and caught fire in her saloon, but as the hull was of iron the fire was subdued and she put into Mauritius with the whole after-part burnt out. This ended her career as a steamer, for she returned to England under sail and was converted into a sailing ship, and in the following year met with a disaster which even her tough frame could not withstand; she struck on the rocks near Bombay and went to pieces.