396 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



constructed upon the best principle. The boiler is to be so high 

 that a portion of it will be exposed to shot entering the vessel 

 above the water line. It is proposed to protect the boiler by- 

 coal; but the protecting power of coal is very small. A 32-lb. 

 shot has been known to pass through 18 feet of coal. Steam gun- 

 boats should have a high speed, for a short time at least; and at 

 the same time should be economical. We should not -construct 

 vessels like the Collins' steamers to do work which can be done 

 by vessels costing one-fourth as much. We need not construct 

 as large vessels as we should expect to provide in time of peace, 

 for the men who engage to serve in war will expect to work hard 

 and expose themselves to hardships and dangers. We need not 

 build them excessively large, in order that they may be more com- 

 fortable for the officers and crew. He should not think we need 

 to build gun-boats at present larger than sufficient to carry one 

 large gun and from ^0 to 100 men. Such vessels need not draw 

 more than six or seven feet of water. It is a mistaken idea that 

 a low pressure boiler is any safer for a gun-boat. What is 

 required mainly is efficiency, and want of efficiency is in itself 

 want of safety. But the low pressure boiler is unsafe for another 

 reason ; that it must necessarily be more exposed to shot, and the 

 damage from the escaping steam is very great in case of penetra- 

 tion of a shot into the boiler. A locomotive boiler to develop 

 more power than can be developed in the nine foot boilers pro- 

 posed, can be placed within four feet of the floor timbers. It 

 w'ould be necessary to cool the water or to use a surface condenser, 

 but that difficulty has already been efficiently provided for. An 

 equal amount of heating surface in a locomotive boiler will 

 evaporate three or four times as much water as in the boilers 

 usually adapted to marine engines. They are also much lighter. 

 Connected with this is the question of working steam expan- 

 sively. We are now told that there is no advantage in working 

 steam expansively. But, although in engines not properly pro- 

 tected there is perhaps not much advantage in working steam 

 expansively ; yet in those properly clothed there is an immense 

 gain from expansion. A large engine acting slowly, is in itself a 

 surface condenser to some extent. But in gun-boats there is no 

 difficulty at all in keeping the steam dry and cylinders hot ; and 

 if the proper heating apparatus should give out, it can be shut off 

 in an instant and the work can proceed in the old way. Loco- 

 motives have been built by thousands, and are found to develop 



