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.
SS. “Scotia,” 1860
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.