26 APPENDIX. 



The boilers, on the whole, are certainly less exposed than the cylinders, but, from their 

 greatly reduced thickness, they transmit the heat more readily. 



When one boiler only is employed, the side next its neighbour, by giving out heat 

 thereto, is another source of loss. The side of either of the ' African's' boilers has 123 feet 



square surface. Then, as before, 3 ' 4 cw r t- x 123 S( *- f< " = 8'48 cwt. of coals expended 



oU sq. tt. 



in maintaining the temperature of the contiguous boiler. I think this falls short of the 

 actual waste by this channel in 24 hours. 



' Dee ' steam-frigate, 200 horse power ; area of jackets, 162 feet square ; external surface of 

 boilers and steam-chests, 1783 square feet. Now, the actual waste by her jackets per day, 1 



as before estimated, is 11'24 cwt. of coals; and U ' 24cwt - x 1783 sq. ft. = 123 . ? cwt Qr 



lb'2 sq. ft. 



6'18 tons of coals loss in 24 hours by radiation from the exposed surface of the boilers; 

 the surface of the bottoms being included. 



Again, the area of the sides of one set of boilers opposed to their neighbours in the same 



vessel amounts to 263 feet square. And H ' 24 cwt ' x 2 3 8q ' ft ' =a 18-25 cwt. of coals 



162 sq. ft. 



loss in 24 hours from absorption, when one set of boilers alone is employed. If the above is 

 considered as a fair estimate of the loss from radiation in 200 horse vessels, it must of course 

 be proportionally greater in vessels of double the power. 



35. ECONOMY IN THE EXPENDITURE OF COALS. In order to obtain a correct idea of 

 the number of days' fuel which a vessel can carry, an important consideration in vessels of long 

 voyage, it should be estimated what amount the boilers consume at full speed in still 

 water, (the greatest expenditure takes place under these circumstances,) making allowances 

 for clearing out fires alternately, after having been some time under weigh : under every other 

 circumstance, the consumption is rather less than greater. During strong gales the con- 

 sumption may be very considerably reduced : I have seen seven days' fuel protracted to 

 eleven, by working such of the furnaces only as were adequate to the wants of the 

 engines. 



I subjoin one or two extracts from my journal of a Mediterranean voyage, which will show 

 to a certain extent the advantages of this practice, labouring under the drawbacks of radiation 

 before detailed. 



1st Experiment. 10 hours with Welch coal. Consumption, 9^ bushels per hour with 4 fires. 

 Revolutions, 25 per minute. Speed of vessel, 7 knots per hour by log. Vessel deep ; smooth 

 water. 



2nd. Strong winds a-head. Put out one fire, and closed the furnace-mouth. Consumption, 

 8 bushels per hour with 3 fires. Revolutions, 18| per minute. Speed of vessel, 5 knots. 



3rd. Strong gales a-head. 2 furnaces, or one boiler only employed (being robbed now by 

 that in disuse). Consumption, 6 bushels per hour. Revolutions, 11 per minute. Speed of 

 vessel, 4 knots. 



These extracts of actual work will give the best idea of what might be further gained by 

 a better arrangement than sea-going steam vessels are usually prepared with. 



36. SWEEPING FLUES, &c. Persons not practically acquainted with the working of 



1 The steam pipes were clothed. 



