Читать книгу Reminiscences of a Liverpool Shipowner, 1850-1920 - Forwood William Bower - Страница 4

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.

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.

The turbine, invented by Sir Charles Parsons in 1897, has effected a revolution in the engines of large size. The principle is simply to allow steam at a high pressure to impinge upon blades fitted to a rotor which it revolves on the principle of the syren. The steam is afterwards used expansively in a second rotor working directly upon the screw shaft. The advantage of a turbine engine is its simplicity – few working parts and a saving in weight and space; its disadvantage is that a separate turbine has to be employed to obtain sternway. Recently, geared turbines have been introduced which are lighter, slightly more economical in fuel, and are sweeter running machines.

It is noteworthy that whereas gears were necessary in olden times with engines working at a low pressure to speed up the propeller shaft, with turbines gears are used to reduce the revolutions.

Meantime, greater boiler efficiency was being obtained. The “Britannia” worked with a pressure of 12 lbs. This was gradually increased to 30 lbs. in boilers constructed in 1868, and this was practically the range of pressure during the period of single-expansion engines. The salt water used in these boilers caused them to become quickly salted up, which not only diminished their efficiency but shortened their lives, and it was not until the compound engine was invented by John Elder that cylindrical boilers, working at a pressure starting at 60 lbs. and increasing to 190 lbs., were introduced. These proved a great success. By the use of fresh feed water and replenishing it from the condensers, salting was prevented and the life of a boiler greatly increased.

No further great improvement in the boiler has taken place. The water-tube boiler is still in an experimental stage, and attention is now being directed to oil fuel, which will reduce the engine-room staff, ensure greater cleanliness and quicker despatch.

The result of these improvements in marine engines and boilers has been to reduce the consumption of coal from 4 lbs. per indicated horse-power to 1.4 lbs., which cannot be considered otherwise than a great achievement. The future high cost of coal is sure to stimulate invention, and we may at no distant date expect developments in internal combustion engines adapting them to high powers which may open up a new and great era for mechanically-propelled vessels, and again entirely change the world’s outlook. We have also always before us the probability of further discoveries in electricity; the recent developments in wireless telegraphy teach us that we are only on the threshold of discoveries which will bring this mighty but mysterious power more and more into the service of man.