Although steamers thus gradually increased in size and power, the “Oceanic,” built in 1899 for the White Star Line, may, I think, claim to be the pioneer of the great Atlantic liners. She was 16,900 tons and 704 feet long, and 21 knots speed. She was quickly followed by the “Lusitania” and “Mauretania,” built for the Cunard in 1907, with a tonnage of 33,000, and a speed of 24½ knots. They were again eclipsed in size by the “Olympic,” “Aquitania,” and the “Imperator,” all about 50,000 tons; but the “Mauretania” still holds the blue riband of the Atlantic for speed. It is scarcely safe to say that the last big ship has been built; size is only limited by commercial considerations and the depth of water available in our harbours, as an iron ship, being a girder, her length is limited by the depth which can be given to the girder. The cost of construction may, however, limit the size of ships, at all events, for some years.
Chapter III
THE EVOLUTION OF THE MARINE ENGINE
The steamship as a practical proposition developed slowly, being retarded by the dilatory evolution of the marine engine. The first serious effort to apply steam power to vessels of any size dates back to only 1838-1840, years which witnessed the establishment of the Royal Mail, the Peninsular and Oriental, and the Cunard Steamship Companies. Their first vessels were steamers of 1,200 tons, having a speed of eight or nine knots. Such vessels were not formidable competitors of the old packet ships, except in the passenger trades; their average passage across the Atlantic, occupying from thirteen to seventeen days, not being a great improvement upon the passages of the sailing-packets. The ships of the Dramatic Line averaged 20½ days, and those of the Black Ball Line 21 days.
SS. “Great Britain,” Launched 1843
The advantage of the greater regularity in the passages of the steamer was, however, obvious, and greatly stimulated invention. The improvements in the paddle engine were slow. We were a long time getting away from the side-lever engine, working at a low pressure. The “Britannia,” built in 1840, was 1,200 tons; her engines indicated 740 horse-power, giving a speed of 8½ knots. The “Scotia,” the finest paddle steamer ever built, and the last of the great paddle boats, was built in 1860, and had the same type of side-lever engine, but her tonnage was 3,871, with an indicated horse-power of 4,800, giving her a speed of 13 knots. The most rapid passage made by the “Britannia” was 14 days 8 hours; the most rapid made by the “Scotia” was 8 days 15 hours.
The screw propeller was invented in 1836, but for a long time it was thought to be inferior to the paddle as a means of propulsion, and there was some difficulty in applying the power to the screw shaft. The side lever in various forms was tried, but proved a failure. The “Great Britain,” 3,270 tons, launched in 1843, had engines which worked upward on to a crank shaft, and the power was brought down by endless chains to the screw shaft. This did not prove satisfactory. Then we had oscillating engines working a large geared wheel fitted with wooden teeth to increase the revolutions of the propeller. Then came the direct-acting engines with inverted cylinders, which for years were almost the universal type of engine, and were a very efficient form of low pressure engine.
The compound engine revolutionised the steamship trade, ensuring such economy of fuel as to permit of long voyages being successfully undertaken. The compound engine developed into the triple expansion engine; the object being to get the last ounce of power out of the steam by first using it in a high pressure cylinder at 180 lbs., then passing it into a larger cylinder, using it expansively, and finally passing it into a still larger cylinder at about 8 lbs. pressure, and again allowing it to expand. The triple expansion engine came into general use in 1886.