THE MiKINE ENGINE.] 



APPLIED MECHANICS. 



875 



MARINE EXGINE. Fig. 209 represents the ar- 

 rangement of a condensing marine engine suited for 

 driving paddle-wheels. A the slide-jacket supplied with 

 steam from the boiler. B the cylinder fitted with piston 



Fig. 209. 



and rod. C the piston cross-head, from the ends of 

 which, side rods descend on each side of the cylinder to 

 the extremities of two side beams D. H the condenser, 

 supplied with injection-water, by the injection-pipe and 

 cock I, passing through the ship's bottom. K the air- 

 pump, worked by side rods from pins in the side beams 

 D, and discharging into the cistern-head L, whence the 

 supply of water for feed is drawn, and from which a 

 discharge-pipe conveys the waste water through the 

 ship's side into the sea. E the cross-head of connecting- 

 rod, connected by side rods at each end to the beams 

 D. F the connecting-rod, causing the revolution of the 

 crank G, on the shaft of which are fixed the paddle- 

 wheels. M is a parallel motion for constraining the 

 cross-head C to move in a straight line. The feed-pump 

 is generally placed on one side of the air-pump, and a 

 bilge-pump (for emptying the bottom of the vessel of 

 water leaking into it) on the other, both being worked 

 by the cross-head which moves the air-pump bucket. 

 The general arrangement of the marine engine is such as 

 to keep the principal weight at as low a level as possible, 

 lest the stability of the vessel should be endangered by 

 too much weight above the floating line. These engines 

 are generally in duplicate, placed side by side longi- 

 tudinally in the vessel, the crank-shafts working the 

 paddle-wheels being laid transversely.* 



A great variety of arrangement has been adopted in 

 marine paddle engines, so as to secure compactness, 

 simplicity, and lightness, consistently with the great 

 strength required to sustain the shocks to which sea- 

 going vessels are subjected. Among these arrangements 

 we may instance the oscillating engine, to which we have 

 already alluded (page 866), and a remarkably compact 

 engine, called the Annular Cylinder Engine, represented 

 in the annexed plate. In this engine, the cylinder a 

 contains an inner cylinder 6, open at top and bottom, 

 and the piston c is of a ring or annular form, working 

 tightly between the inner and outer cylinders. Two 

 piston-rods d d, passing through stuffing-boxes in the 

 cylinder cover, are firmly fixed to the opposite ends of a 

 cross-head e, which is double, having two thicknesses 

 with a space between them. The lower part of this 

 cross-head extends downwards into the inner cylinder 6, 

 in which it is fitted to slide. To a pin /in this sliding 

 part the connecting-rod y is jointed, and also to the 

 crank-pin h ; i is the crank fixed on the main paddle- 

 shaft, which revolves in bearings in strong framing, 

 secured to the wooden beams that extend across the 

 See ante, p. 859. 



vessel, and tied to the cylinder and foundation-plate by 

 strong wrought-iron bolts or columns. It may be readily 

 seeu from the drawing that this arrangement permits the 

 use of a long connecting-rod well guided at its lower 

 end /, and a stroke of piston of con- 

 siderable length, even when the height 

 allowed for the engine is very limited, 

 as is usually the case in vessels, especially 

 \ such as are of light draught of water. 



The condenser is the box or hollow 

 foundation on which the engine stands, 

 and m is the air-pump, which is worked 

 by a small double beam I, mounted on the 

 framing, and receiving its motion from 

 rods j, connected to the lower part of the 

 cross-head at /. The feed and bilge-pumps 

 are fixed at each side of the air-pump 

 m, and are worked by rods connected to 

 the same cross-head as that which works 

 the air-pump rod, to which they serve 

 as guides. The alternations of the steam 

 to and from the opposite ends of the 

 annular cylinder are effected by a long 

 hollow D slide, which is worked by an 

 eccentric from the main shaft. For stop- 

 ping, starting, or reversing the engines, 

 the eccentric-rod, having a gab end, as 

 described (page 861), is thrown out of 



gear by a small lever, and the slide 



worked by a cross-handle, so as to make 

 the required change of direction in the movement of 

 the piston ; and on this being effected the gab of the 

 eccentric is again dropped into gear, and the motion of 

 the engine continues. 



The conditions of a marine engine suited for driving a 

 screw-propeller, differ considerably from those of the 

 engines we have hitherto described. The shaft of the 

 screw-propeller is necessarily at a low level, and lies longi- 

 tudinally in the vessel to which it is fitted, and it must be 

 made to revolve at considerable velocity. When this 

 system of propulsion was first tried, it was usual to employ 

 ordinary marine engines placed transversely in the vessel, 

 and to fit on their shaft a large cog-wheel, driving a 

 pinion on the shaft of the screw-propeller below it. By 

 this arrangement the low level of the latter was secured, 

 as well as its high velocity ; but the weight, bulk, shake, 

 and noise of the toothed gearing were found objection- 

 able. Screw-propeller engines are generally made now 

 with very short stroke, so that the number of strokes 

 made in a given time is much greater than in ordinary 

 engines of equivalent power. The cylinders are arranged 

 horizontally ; and the piston-rods act on the cranks 

 placed at a low level, without the intervention of side- 

 beams. 



The annexed plate represents the transverse section of 

 a screw-steamer, with the engine placed in the lower 

 part of its hold : g is the cylinder placed horizontally, 

 and supplied with steam from the boiler by the steam- 

 pipe m. The piston-rod / works a cross-head, which 

 moves in horizontal guides, and acts by the connecting- 

 rod e directly on "the crank-shaft d, which is extended 

 horizontally to the stern of the vessel, and projects 

 through a stuffing-box into the water near the stern- 

 post, carrying on it the screw-propeller, indicated by thd 

 dotted circle . For working the air-pumps of screw 

 engines, seve.-al different arrangements are employed. 

 In some cases the air-pumps are placed horizontally, 

 like the cylinders, on the opposite side of the vessel, 

 and worked directly by the piston-rods, which are ex- 

 tended in length for that purpose. In the plate, another 

 method of working the air-pumps is represented. A 

 second or counter-shaft i ia worked by gearing c from 

 the main-shaft d ; and this second shaft, by means of 

 cranks and connecting-rods j, works the pistons of ver- 

 tical air-pumps L In order to secure, in a height so 

 limited, a greater length of connecting-rod, and at tho 

 same time to furnish a guide to resist the transverse 

 strain resulting from the obliquity of its action, the 

 piston of the air-pump is made with a trunk or tubular 



