Mr. James Howden patented a forced draught process by which the incoming air is warmed by the heat (which would otherwise be wasted) in the uptakes and funnels, and then conducted direct to the furnaces; and he claims by this to be able to do with still smaller boilers, besides avoiding the danger to the tubes now sometimes experienced in war ships with closed stoke-holes.
Italian Cruiser Piemonte at Full Speed—22.3 knots = 253⁄4 miles per hour.
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But there still remains the problem of how to feed the furnaces by mechanical methods, so as to save the very large staff now required in the boiler-room of our large steamships. So far all means hitherto adopted with success on shore have proved failures at sea, and at present there is no reason to suppose that any one of them can be so adapted as to prove generally efficient for service. It is necessary for such a purpose that the gear can go continuously for many days, and the coal be small and tolerably uniform, and the supply regular. Such coal is not convenient for passenger ships, and if the demand for the present supply of small coal were increased the price would preclude its use. Some success, however, has been achieved in saving labor in the stoke-hole, and the most noticeable invention to this end is that of Mr. Thomas Henderson, whose now well-known self-cleaning fire-bars do away with the necessity for the firemen raking the fires out to remove the clinkers which adhere to the grates and obstruct the air-passages. By means of this apparatus, the alternate bars having a very slight movement, the coal gradually travels to the back end of the grate together with the clinker, which latter is eventually deposited behind the bridges. Thus not only is considerable labor saved, but the fires are always in such good condition that the full pressure of steam is maintained, and so a better speed kept up by the vessel herself.
On shore the tendency is to substitute gas for solid fuel, or to use the coke resulting from gas manufacture. That something of the same kind might be done on shipboard is possible, although not at present probable. The higher efficiency of the coal when treated in this way would enable still more power to be obtained from a pound of it, and there would be savings in other ways of a beneficial nature.
Then, again, if petroleum, or other liquid of a similar nature, could be obtained at a fairly low price, it might be used on shipboard; and as it has a heating power twenty-five per cent. higher than the best coal, and fifty per cent. higher than some of the commonest kinds weight for weight, the substitution of it would be a means of obtaining better speed. But it is always a question of cui bono, and when it is taken into consideration that the voyage between Sandy Hook and Queenstown is now done in 140 hours, and to do the distance in 5 days would require a speed of nearly 231⁄2 knots, with an increase in power of sixty-two per cent., and in fuel consumption of thirty-eight per cent., the cry must be regarded as a very far one at present. At the same time it is not desirable to believe that there is now finality in the speed of steamships, although by analogy with railway trains that conclusion might be arrived at.