Messrs. John Hall and Sons, of Dartford, also experimented on these two patents, and from this the tubular condenser was called Hall's Condenser. I think the boat it was first tried in was called the 'Dartford.'
Trevithick's difficulties in urging so many and great changes in marine propulsion may be estimated by the acts of other engineers.
"Mr. Rennie was engaged for many years in urging the introduction of steam-power in the Royal Navy. In 1817, we find him writing to Lord Melville, Sir J. Yorke, Sir D. Milne, and others on the subject. In July, 1818, he laments that he cannot convince Sir G. Hope or Mr. Secretary Yorke of their utility, but that he is persuaded their adoption must come at last. On the 30th May, 1820, he writes James Watt, of Birmingham, informing him that the Admiralty had at last decided upon having a steamboat, notwithstanding the strong resistance of the Navy Board."[208]
So that Mr. Bennie, as professional adviser of the Navy Board, had to persuade for three years, with a knowledge of Trevithick's prior experiments, before active steps were agreed to; for twelve years had then passed since Trevithick's nautical labourer and iron steamboat had been tried on the Thames, and five since his experiments with the screw-propeller.
An article in 'The Times' gives in strong contrast the relative value of screw and paddle-wheels as propellers. The 'Syria' was originally a paddle-wheel steamer, having oscillating cylinders worked with steam of 25 lbs. on the inch, and Hall's tubular condenser; after a time the paddle-wheels were removed for a screw-propeller, driven by two steam-cylinders side by side, of different diameters, the high-pressure steam exerting its full force in the small cylinder, and then expanding in the larger cylinder. All the leading features in this improved steamboat of the present day, such as high-pressure expansive steam in one or two cylinders, with tubular condenser and screw-propeller, had been publicly proved by Trevithick fifty years before.
PLATE 18.
COMPOUND MARINE ENGINE, 1871.
London: E.& F. N. Spon, 48, Charing Cross. Kell Bros. Lith. London.
"Screw against Paddle.—An interesting and important trial trip has recently been made, which serves to exhibit the advantages of the screw over the paddle as a means of propulsion for ocean-going steamships. In 1863, the steamship 'Syria,' of 1998 tons, was built for the Peninsular and Oriental Company by Messrs. Day, Summers, and Co., and fitted with paddle-wheel engines of 450-horse power. The 'Syria' then attained a speed of 13·038 knots per hour, and the consumption of coal was at the rate of 45 tons per diem. The builders have lately converted her into a screw-steamer (for carrying the mails between Southampton and the Cape of Good Hope), who, without in any way disturbing the configuration of the hull, have fitted the 'Syria' with compound inverted engines of 300 nominal horse-power. These engines have two cylinders, respectively of 36 in. and 72 in. diameter, with a stroke of 4 ft. 2 in. On Monday last the 'Syria' attained an average speed of 12·637 knots, with a consumption of coal equivalent to 18 tons per diem; thus showing a difference of only 0·401 knot per hour, with a lessened power of 150 horses, and a saving in consumption of coal of 27 tons per diem; while the carrying capacity of the ship, arising from the economy of space in the engine-room, has been enormously increased, as she can now stow 1200 tons of cargo against 500 tons previously."[209]
Mr. Husband, of the firm of Harvey and Co., of Hayle, has obliged me with the annexed sketch (Plate XVIII.) of a modern high-pressure steam expansive compound marine engine, with surface condensers, on which the grandsons of Trevithick are now working, to be placed in the 'Batara Bayon Syree,' an iron yacht for an Indian Rajah, embracing the modern improvements of direct-action compound engines, and illustrating the principles which governed the constructors of the 'Syria.'