Chapter IV: Front Matter (4)

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 23-1/2 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.

Footnotes:

[10] This, however, is not an absolute test of the fineness of the _water-lines_ of a vessel, and it can only be used as such on the assumption that the midship sections of ships are of similar form. The best test of the fineness of water-lines is made by taking the displacement as a percentage of the prism whose length is that of the ship and whose section is the same as the midship section of a ship, assuming, however, that the midship section of all ships is approximately that found in general practice to-day; in speaking of coefficients it will mean the percentage of the rectangular block above named.

[11] More than thirty years ago this matter had been observed by the officers of the British navy, and experiments were ordered to be tried with H. B. M. S. Flying Fish, a 1,100-ton cruiser, her length being 200 feet, breadth 30 feet 4 inches, and her draft of water 10 feet 6 inches forward and 13 feet aft. With 1,290 I. H.-P. her speed was only 11.64 knots, whereas with 577 I. H.-P. it was 9.923 knots, and a speed of 11.201 was obtained with but 878 I. H.-P. A false bow 18 feet long was then fitted, so as to give finer lines forward, or, as sailors describe it, “a better entrance,” when it was found that with 1,285 I. H.-P. a speed of 12-1/2 knots was attained, and with 1,345 very nearly 12-3/4 knots. There is also every reason to suppose that could the stern have been altered in a similar way, the speed would have been still higher, in spite of the ship being larger and with a consequent increase of immersed surface to cause resistance. It has, besides, been observed on many occasions that when steamers have been cut in two and lengthened there has been no diminution of the speed, but, on the contrary, in some cases there has actually been a gain; so that in these two instances there is an apparent anomaly, viz., that with the same power the larger ship is propelled at a quicker speed.

The late Dr. Froude investigated this matter some years ago, and showed that such results were quite possible, independently of any fining of the lines, owing to the effect on the ship of the waves set up when in motion. One very curious illustration of how such waves may seriously affect a vessel is in that of a yacht built many years ago by an eminent firm on the Clyde, which failed to come anywhere near the performances guaranteed owing to the fact that as the speed increased the hollow following the wave formed at the bow increased and approached nearer and nearer to the paddle-wheels, until the water dropped below the floats and allowed the wheels to spin in the air; the propelling effect was thus entirely lost until the vessel slowed down sufficiently for the water to rise again to the level of the paddle-wheels. Such a thing could scarcely happen with a screw steamer; but the very bad steering qualities of certain naval ships is due to the fact that the inrush of water at the stern causes currents to flow _with_ the ship, and therefore to produce quite different results with the rudder from those which generally obtain.

[12] A nautical mile is 6,080 feet, the land mile being 5,280 feet. The knot is a measure of _rate_ of speed per hour. A vessel makes 20 knots when she is travelling at the rate of 20 nautical miles per hour.

[13] The dimensions, speed, etc., of the steamers here referred to, as well as other representative steamers from 1836 to 1890, are shown in the table on page 78.

[14] In the case of river steamers of moderate size there is not the same restriction on the position of the wheel, and as a matter of fact, as in the case of stern-wheelers, it is altogether at one end.

[15] It is now claimed for the twin-screw ship that she is not only capable of entering shallower harbors, but that she is in every way much safer, and it is most unfortunate that, owing to an act of carelessness, this was not conclusively shown in the recent accident to the City of Paris. But there is safety in the twin-screw beyond that which is rendered possible, as in the cases of the City of Paris and Majestic, by the division of the engine-rooms, viz., the fact that if one engine breaks down it is improbable that the other would do so at the same time, and that the vessel, although somewhat crippled in speed, would still be able to pursue her voyage; also, that in the event of accident to the steering apparatus the passage could be continued and the direction of the ship guided by regulating with one or both of the engines. Each of these features is pronounced, and the advantages have been proved on many occasions.

THE BUILDING OF AN “OCEAN GREYHOUND.”

BY WILLIAM H. RIDEING.

THE COST OF AN OCEAN RACER—INTRICATE “FINANCING” OF SUCH AN
UNDERTAKING—THE CONTRACT WITH THE SHIP-BUILDERS—THE UNCERTAIN ELEMENT
IN DESIGNING—GREAT SHIP YARDS ALONG THE CLYDE—THE PLANS OF A STEAMER
ON PAPER—ENLARGEMENT OF PLANS IN THE “MOULD LOFT”—WHAT IS MEANT BY
“FAIRING THE SHIP”—THE “SCRIVE BOARD”—LAYING DOWN THE KEEL—MAKING
THE HUGE RIBS—WHEN A SHIP IS “IN FRAME”—SHAPING AND TRIMMING THE
PLATES—RIVETING AND CAULKING—READY FOR LAUNCHING—THE GREAT “PLANT”
WHICH IS NECESSARY FOR THE BUILDING OF A SHIP—DESCRIPTION OF A
TYPICAL YARD—WORKS COVERING SEVENTY-FOUR ACRES—WHERE THE SHAFT IS
FORGED—THE LATHES AT WORK—THE ADJUSTMENT OF PARTS—SEVEN THOUSAND
WORKMEN.