20 APPENDIX. 



projecting above the decks, in vessels which cannot conceal them beneath ; but when the deck 

 is sufficiently above the boilers, projections of hatches and scuttles should be avoided, the 

 deck being more easily kept tight by being often wet, and occasionally caulked. 



WATER-WAYS of marine boilers, to economise space, are often made much too narrow; so 

 that the crust, in falling from the sides of the flues, is intercepted with other matters left in the 

 boilers by oversight or neglect ; thus forming convenient shelves on which the calcareous 

 matters repose and continue to accumulate. It is then inevitable, that the side plates will be 

 "drawn" or bent towards each other by the fire, in its passage through the flues: not 

 unfrequently, in such cases, the flues are so obstructed as to become impassable. The fire in 

 its zig-zag course now attacks the bends or extremities of water-ways, which turn its direction 

 into the joining flues ; cracks and openings are soon made, through which the water and non- 

 conductors are forced; in these places, patches are with difficulty fitted, and, from their 

 situation, are exposed to be speedily injured from the increase of mass. Water-ways in no 

 instance should be less than four or five inches wide, and in those between the fire-places some- 

 thing more ; the ebullition being so rapid here, that the water is more likely to be repelled, and 

 the plates exposed to injury, which a sufficient quantity of water would obviate to a certain 

 extent. If it be found convenient to make the spaces six, seven, or even eight inches, which 

 is more than necessary in the largest boilers, no increased expense of fuel will be felt in 

 practice, after the bulk of water is once heated: this fact is quite established. Too much space 

 beneath the flues, in the lower class of vessels having little depth of hold, is not necessary; it 

 ta.kes away from the room above, requisite for scaling, and adds to the gross weight un- 

 necessarily, by the increased stowage of water. A rectangular trunk or trough, extending the 

 entire length of the bottom of each boiler, with a man-hole at both ends, is the plan most 

 desirable ; and being fitted between the sleepers, it descends beneath the other portion of the 

 bottom, and becomes a receptacle for all the scales which may fall from the tubes. From 

 the bottoms of these trunks the blow-off pipes, well protected by a grating, should proceed : 

 thus the necessary space is gained, without too great an increase of weight or height. 



Boilers that have been much incrusted, and the water-ways in many places choked, have in 

 some instances, when blowing off could at all be effected, been perfectly clear beneath the flues ; 

 that is, the scales have not combined into a mass : therefore, the space in addition to the trunk 

 need not be much more than that pointed out for the water-ways between the flues, except in 

 large vessels, where a space beneath the entire bottom of the flues is desirable for repair ; 

 and for the purpose of affording means of keeping the bottom of the shell perfectly dry when 

 not employed, a very necessary precaution on a foreign station. The accumulation between 

 the tubes is much to be guarded against; to meet which a sufficient number of 'man-holes 

 should be cut through the upper parts of the boilers, so as to permit a due ventilation for the 

 men employed in scaling the boilers, (a material object in a warm climate,) 1 as well as 

 to afford convenience of repairing fire-places, and removing the scale, which I am persuaded 

 has been often negligently permitted to fall between the tubes, by the people employed in 

 scaling, to avoid the increased labour imposed by neglect of proper arrangements for removing 

 the same, it not being at all times in the power of engineers to look after them : much time 

 will be gained, as well in repairs as in cleaning, by anticipating these difficulties. 



1 Keeping the safety-valves open greatly assists in cooling the boilers. 



