MARINE BOILERS. 



32. There cannot be a more striking proof of the ignorance of 

 ..general principles which prevails, respecting this branch of steam 

 engineering, than the endless variety of forms and proportions 

 which are adopted in the boilers and furnaces which are con- 

 structed, not only by different engineers but by the same 

 engineer, for steamers of like power and capacity, and even for 

 the same steamer at different times. Thus the original boilers 

 of the Great Western, built for the New York and Bristol or 

 Liverpool voyage, were of the common flue sort. They were 

 subsequently taken out and replaced by tubular boilers. The 

 dimensions and relative proportions of these two sets of boilers, 

 thus supplied to the same vessel for the same voyage, differing as 



completely one from the other as if they had been designed for 

 different vessels and different voyages. 



On contemplating engineering proceedings, such as are exhibited 

 in the preceding table, it is impossible to deny that practical men 

 in such cases are groping in the dark, without the slightest benefit 

 r from the light which they ought to derive, from the present 

 -advanced state of physical science. 



33. Tubular flues have been in many steamers adopted in 

 preference to the flat and longer flues already described. In the 

 second set of boilers of the Great Western above mentioned, the 

 tubes were eight feet in length and three inches in diameter. In 

 the boilers of the steamer Ocean, which are also tubular, the 

 following are the principal dimensions : 



Boilers : 



Number . . 3 

 Length . . . 14 feet. 

 Breadth . .194 feet. 



Furnaces : 



Length . . 9 feet 



Diameter . . 3| inches. 

 Cylinders : 



Number . . 2 



Diameter . 56 inches. 



Number . . . 7 Stroke . . 54 feet. 



Length . . 7 feet. ! Pressure of steam above 



Breadth . . . 2 T ^ feet. atmosphere . 4 Ibs. per in. 



Tubes : 



Material . . Iron. 

 Number 378 



Consumption of coal 

 per hour . .18 cwt. 



Among the more recent specifications of the machinery of marine 

 engines submitted to the Admiralty, are some in which the boilers 

 ,are traversed by nearly 2000 tubes of 3J inches external diameter, 

 and five feet in length, giving a total heating surface of about 

 9000 square feet. 



34. ( A formidable difficulty in the application of the steam- 

 engine to sea voyages has arisen from the necessity of supplying 

 the boiler with sea water instead of fresh water. The sea water 

 ds injected into the condenser for the purpose of condensing the 



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