ARROGANT AND ENCOUNTER. 



The "Great Britain " is a vessel of 3500 measured tons ; her tonnage by 

 deplacement being 2970, and her draught 16 feet. The diameter of the 

 cylinder is 82^ inches ; the length of stroke, 6 feet ; the nominal power, 

 500 horses ; the diameter of the screw, 154 feet 5 its P itc h, 19 feet > and 

 its length, 3 feet 2 inches.' The screw has three arms or blades, and its 

 shaft is connected with the crank-shaft by a pair of toothed -wheels, which 

 have a multiplying power of 3 to 1, so that for every stroke of the piston, 

 the screw-shaft revolves three times. The ample proportion of 17A square 

 feet of heating surface per nominal horse-power, is provided in the boiler. 



The crank-shaft, being put in motion by the engine, carries round the 

 great cog-wheel, or combination of cog-wheels, which are fixed upon it ; 

 and this wheel acting on smaller ones called pinions, on the screw-shaft, 

 impart to the latter the threefold velocity of revolution just mentioned. 



87. As an example of screw-propelling engines working without gearing, 

 we give in fig. 27 those constructed by Messrs. Penn and Son for H. M.'s 

 screw -steamers "Arrogant" and "EncoTinter." In this case the cylinders 

 are horizontal, and are traversed through the centre by a pipe or trunk, upon 

 which the piston is cast. This trunk is projected through both ends of the 

 cylinder the orifices through which it passes being rendered steam-tight 

 by proper packing. One end of the connecting-rod is attached to the 

 centre of the trunk, the other end being connected with the crank, which 

 is formed directly upon the screw-shaft. The air-pump lies in a horizontal 

 position, is double-acting, and placed within the condenser. A large pipe, 

 called the eduction pipe, leads from the cylinder to the condenser, where 

 the condensation is produced by a jet of cold water, and the warm water 

 resulting from the process is ejected by the air-pump through the Avaste- 

 pipe, and discharged overboard. In fig. 27 one cylinder and one air- 

 Fig. 27. 



pump only are represented, but it must be understood that there are two, 

 precisely similar to each other, placed side by side. The valves by which 

 the water is admitted to the air-pump from the condenser, and those by 

 which it passes from the air-pump to the hot well and waste-pipe, con- 

 sist of several discs of caoutchouc kept down by a central bolt, so as to 

 cover radial slits or orifices in a perforated plate. These valves are found 

 to operate without noise or shock, notwithstanding the high speed at which 

 the engine must work, in order to give the necessary velocity to the screw- 

 shaft without intervening gearing. The diameter of the cylinder of the 

 "Arrogant" and "Encounter" is 60 inches, and the diameter of the trunk 

 24 inches ; the latter being deducted from the former, leaves an effective 



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