The final form of the marine reciprocating engine was of the vertical type using steam in two, three or four stages of expansion
AMONG the finest horizontal trunk engines ever built were those installed in H.M.S. Northumberland, an iron sea-
The engines of H.M.S. Northumberland had two cylinders 9 ft. 4 in. in diameter, with a stroke of 4 ft. 4 in. The trunks extended through the back and front covers of either cylinder. These trunks had a diameter of 3 ft. 5 in which reduced the effective areas of the pistons and made them equivalent only to those with a diameter of 8 ft. 8 in. The bearings or gudgeons carrying the small ends of the connecting rods were housed in the pistons, and the large ends of the rods drove balanced cranks set at right angles. These engines are illustrated in the previous chapter.
THE CONDENSER AND PUMPS of the engines of the Britannic of 1874 are shown in this photograph of a model. The engines were built by Maudslay, Sons and Field, and were 33 feet in height. They indicated a horse-
The valve gear and method of steam distribution to the cylinders of these horizontal trunk engines is of special interest. The steam chest of each cylinder contained a large double-
In addition to the link motion valve gear, the engines of H.M.S. Northumberland were provided with large expansion valves to give an early steam cut-
The propeller was-
The inverted type of marine steam engine, with the cylinders arranged vertically over the crankshaft, was introduced about the year 1850. From about 1860 this form of reciprocating engine became standard practice for passenger and cargo vessels in the merchant service. In the Royal Navy, however, the vertical engine was not at first widely adopted except for a few coastal defence ships in 1872.
The reason for this slow progress in the Navy was the necessity for placing the machinery below the water-
The advantages of the vertical engine over all earlier types include economy in athwartships space. Two sets of engines could be placed side by side in twin-
Vertical marine engines, in the early days of their development, were sometimes arranged to work as “simple” or single-
fourth full size and developing about 15 horse-
The engines comprised two cylinders 5 ft. 6 in. in diameter, with a stroke of 3 ft. 6 in. They drove cranks set at right angles. Each piston had two rods terminating in a long crosshead working between guides. By adopting this method of construction, the total height of the engines was reduced.
The slide valves controlling the steam supply to the cylinders were operated by link motion reversing gear. The links were moved as required by large handwheels from a driving platform built round the engines at approximately middle-
An ingenious device was employed to counterbalance the weight of the main slide valves. To the upper ends of the valve rods were attached pistons that worked in cylinders placed on top of the steam chests. Steam from the chests acted on the undersides of the pistons, thus supporting the weight of the slides and lessening valve motion strain.
Another point of interest in the design of these engines was the unusual position of the condenser. This was of the surface type, with horizontal tubes giving 3,488 sq. ft. of cooling area. The condenser was placed between the two engines, forming part of the framework that supported the two cylinders. At the ends of the engine were turned steel columns supporting the cylinders and steam chests. At either end of the condenser were arranged the air, circulating, feed-
Early Compound Engines
The arrangement of the pumps and their valves was of special interest. The feed and bilge pumps had simple plungers, but the others were provided with pistons working in cylinders. The portions of the cylinders above the pistons acted as air pumps and those below the pistons served as circulating pumps for the supply of cooling water to the condenser. Valve boxes for the pumps were arranged within the condenser, but the valves, of the rubber-
THE TANDEM COMPOUND ENGINES of the Britannic, built in 1874. This photograph shows the control side of the model illustrated above. The engines comprised two low-
These engines indicated 1,427 horsepower at 45½ revolutions a minute, with steam at a pressure of 18 lb. per sq. in., giving a speed of over 13 knots. The A. Lopez had a displacement of 2,665 tons and was 270 feet long with a beam of 38 feet.
Following on “simple” engines of the type described above, came compound or two-
The end standards of the engines of the Carnatic contained the surface condensers. These supported the two low-
The air pumps were combined with the boiler-
The slide valves of each pair of cylinders were moved by a single valve rod operated by link motion reversing gear. This motion was fitted with a handwheel and screw for reversing, assisted by a steam cylinder. The power reverse was rendered necessary by the massive proportions of the component parts. On the back of every high-
The two low-
The after part of the propeller shaft was originally provided with a universal joint so that, it could be lowered with the propeller boss level with the ship’s keel. This arrangement was introduced by Sir E. J. Harland in 1871, to secure greater immersion and so prevent “racing”, or excessive speed of the screw. Racing occurs when a ship’s propeller is lifted from the water by the pitching of the vessel in heavy weather. Sir E. J. Harland’s device affords an interesting comparison with Edward Shorter’s screw of 1800, described in an earlier chapter dealing with marine propellers.
The Britannic had a net tonnage of 3,152 (5,004 tons gross). She was 455 feet long, with a beam of 45 ft. 3 in. and a depth to the main deck of 33 ft. 8 in.
The next step in the development of the marine engine was the introduction of three-
Two sets of triple-
give the required clearance between hull and screws. The diameters of the high-
Steam at a pressure of 180 lb. per sq. in. was supplied by twelve double-
For use in the Navy the triple-
There were six ships of her class. The machinery was of less weight per horse-
The starting platforms were placed beside the central fore-
The introduction of four-
respectively below them. The diameters of the cylinders were 1 ft. 10 in., 2 ft. 6 in., 3 ft. 7 in. and 5 feet. Their common stroke was 3 ft. 9 in. With steam at a pressure of 160 lb. per sq. in. these engines indicated 986 horse-
The modern quadruple-
The surface condenser was placed at the back of the engine and was supplied with cooling water by a separately driven centrifugal pump. The air, feed and bilge pumps were worked by levers from the crosshead of the first intermediate-
An interesting development was the introduction of double-
In a later chapter will be described the development of the steam turbine.
[From part 23, published 14 July 1936]