Summary of The Development of the Steamship - 1887 - Part 7 of 7
As the ship's speed is increased the spaces between the crests of these lengthen in unison with the speed, and it has been shown that when the speed is such that a wave-crest would be at the middle point of the after body (or quarter) the wave-making resistance is least, and that it is greatest when the hollow appears at this point.
A ship must therefore be of a length that depends largely upon the length of wave which at a high speed she will tend to produce in order that she may be driven at such a speed without an expenditure of power disproportionate to the effect produced. This length, if very high speeds are desired, is best wholly taken up in fining the entrance and run, leaving no parallelism of middle body, and broadening and deepening the ship to keep the necessary displacement.
The wave-action at several speeds is well shown in the illustrations (frontispiece, pages 524 and 527), which are from instantaneous photographs, showing the Chilian cruiser Esmeralda at her full speed of 18 knots, when on her trial off Newcastle-upon-Tyne, the Giovanni Bausan, of the Italian navy (almost a sister ship to the Esmeralda), at a moderate speed, and H.M.S. Imperieuse, at about 16 1/2 knots. The following are the principal details of the Esmeralda and Impérieuse :
The eddy-making resistance is greater or less, of course, as the form is blunter or finer, and there is less resistance with a blunt bow and finely formed after-body than were the two reversed. Our practical towing friends will be glad to know that Mr. Fronde substantiates their oft-reiterated assertion that a log tows more easily butt-end foremost.
In the Merkara, a merchant ship built by Mr. Denny, of 3,980 tons, 360 feet length, 37.2 feet breadth, and 16.25 feet draught, this resistance is, at all speeds, about eight per cent. of the surface friction, which at the maximum speed of thirteen knots, at which she was intended to be run, still formed nearly eighty per cent. of the whole resistance.
The Giovanni Bausan, of the Italian Navy. (From an Instantaneous Photograph)
A very wonderful result of these experiments has been to show (in the words of Mr. Fronde) " what an exceedingly small force, after all, is the resistance of a ship compared with the apparent magnitude of the phenomena involved. Scarcely anyone, I imagine, seeing the new frigate Shah (of 6,250 tons displacement) steaming at full speed (from sixteen to seventeen knots) would be inclined, at first sight, to credit what is nevertheless a fact, that the whole propulsive force necessary to produce that apparently tremendous effect is only 27 tons—in fact, less than one two-hundredth part of the weight of the vessel—and of this small propulsive force at least 15 tons, or more than one-half, is employed in overcoming surface friction simply."
Of course, very small vessels, as torpedo-boats, have been driven at very high speeds, but the power necessary is in enormous disproportion as compared with the above, a development in 135-foot torpedo boats of from 1,000 to 1,200 horse-power and more being not uncommon.
The acceptance of the results of Mr. Froude's deductions has naturally led to an increase in the beam of fast ocean steamers ; we find all the later-built to be much broadened, and there is a still increasing tendency in that direction. It is needless to say how much this means in many ways to the passenger ; the gain in safety by affording greater subdivision which will come with double screws will not be the least : "
With single screws you cannot possibly divide your engine and boiler space into compartments so as to render the ship safe against sinking by collision even with small vessels. With twin screws you can carry a water-tight middle line bulkhead right through both engine and boiler compartments, and you can, as at present, divide the engine-room from the boiler-room by a transverse bulkhead, and also, if necessary, subdivide the boiler space by an extra transverse bulkhead " (Mr. W. John).
Collision will and must remain the great and really almost the one danger which the North Atlantic traveller need fear. He can rarely hope to cross in the usual steam route without experiencing a run of some hundreds of miles through fog, especially on leaving or approaching our coast. So long as the Gulf Stream and the cold in-lying current from the north move in juxtaposition as they do, so long will the fog be almost always present upon the border-land dividing them.
How easy it is for a great ship to be sunk was shown in the case of the Oregon. A blow from a pygmy schooner not more than one-tenth her size, and a hole was opened through her side which unfortunate circumstances combined to make fatal, and the great vessel, a triumph of human skill in hull and machinery, is lying in a few hours upon the bottom of the sea, with a million days of skilled labor, as represented by ship and cargo, in this moment made valueless. Who can overestimate the care and responsibility upon the man who commands such a ship ? In what other calling are they found as such a constant part of daily life ? And how illy they are paid for it !
The only remedy for such an accident as that which befell the unlucky Oregon seems to be a subdivision to a greater extent than has heretofore been attempted in a merchant ship ; and that this will come in a degree which will make the finer passenger ships practically unsinkable, unless under most exceptional circumstances, would seem quite sure.
How wonderful has been the scale upon which this great industry of carriage by steam vessels has grown can only be shown by tables of statistics.
The steam tonnage in the United States, Great Britain, France, and Germany, beginning with 1840, was as follows :
This statement, showing our steam tonnage registered for foreign trade to be 6,000 tons less in 1885 than in 1870, is not an encouraging one, especially when taken in connection with the fact that the percentage of our imports carried in American vessels has steadily dwindled from 75.2 per cent. in 1856 to 66.5 in 1860 ; to 35.6 per cent. in 1870 ; and to 15.98 per cent. in 1886. Even during the civil war it never fell below 27.5 per cent.
The amount of steam tonnage built in the United States and in Great Britain at intervals of five years from 1855 is as follows :
|United States||United Kingdom|
The largest number built in any one year between 1870 and 1885 was, in the United States, in 1882-being 502, with a tonnage of 121,843 ; and in the United Kingdom, in 1883-being 1,028, with a tonnage of 744,126.
The smallest in any year in this interval was, in the United States, in 1877 -being 265, with a tonnage of 47,415 ; and in the United Kingdom, in 1876-being 354, with a tonnage of 136,932. The startling steam tonnage of 1883 (nearly three-quarters of a million tons) built in Great Britain, of which 134,785 were built at Glasgow, 125,870 at the Tyne ports, and 117,776 (Note 541-A) at Sunderland, has been followed by a great depression. In 1884 but a little over half that of the preceding year was built (415,095 tons) ; and in 1885 this was again almost halved, the output falling to only 221,918 tons, and the average size also falling off from 724 tons in 1883 to 456 in 1885.
Nearly or, practically, quite all of the vast fleet represented by these figures are of iron or steel ; the tonnage of the wooden steamers generally falling in later years in Great Britain to a total of 1,000 tons or less, and this made up of vessels averaging not more than 30 tons each.
The rapidly advancing use of steel in the United Kingdom is shown by the following table, which excludes steamers built on foreign account :
|Iron Steamers||Steel Steamers|
Or whereas but ten per cent. of the total was of steel in 1880, it exceeded the iron-built tonnage in 1885 by twenty per cent. It may be taken for granted that, hereafter, no important steamer will be built of any other material, until something different from that now at command shall be developed.
How small our own expansion in the iron and steel ship-building industry has been, in comparison with that elsewhere, is shown by the fact that in the sixteen years 1870-85 we have built but 397,363 tons of iron and steel vessels, out of a total of 1,359,700 tons of steam tonnage built in that period. One would think that this immense yearly addition of steamships represented in the foregoing tables would soon go beyond the world's needs, but the almost incredible losses from wrecks, casualties, and other reasons for disappearance from the register, must be considered.
Though we had built 522,802 tons of steam vessels in the years (each inclusive) 1881-85, there were on the register but 229,919 tons more in the last of these years than in the first, showing that 292,883 tons had disappeared in that time. In Great Britain an average of 173,061 tons of steam vessels has disappeared yearly from the register in the five years 1881-85, or the enormous total of 865,326 tons.
Of her whole tonnage, sail and steam, of 7,387,208 tons (comprised in 23,230 vessels, of which 4,803 are steamers above 50 tons, representing a total of 3,932,296 tons), Great Britain lost by wreck alone, in 1885, over three per cent., and this was much below the usual average. In the nine years 1875-83, 6,107 British vessels, representing, 2,095,252 tons, were totally destroyed by wreck. Of these, 5,160 were sailing vessels, of 1,455,023 tons ; and 947 were steamers, of 640,229 tons.
In the face of these tremendous figures the ship-builder need not despair —he need only wait ; a few slack years and the gaps in the ranks become so great that building of necessity must re-begin. The lives of ships are indeed more precarious than those of us mortals. They perish at the annual rate of about 30 in the 1,000, whereas our general chances are one-third better.
But these losses of ships carry with them the lives of many brave men ; with the wrecks above enumerated, 14,878 seamen were lost, and 1,242 passengers. In this bald statement what vistas of suffering, incapacity, carelessness, negligence, misfortune, and heroism are opened up !
In looking over shipping statistics, nothing is more curious than the variations in sailing tonnage built—always a more variable quantity than steam, and especially so in Great Britain. In that country in 1880 but 58,065 tons were produced ; but it gradually mounted to 219,094 in 1885, nearly equalling the steam of that year if the 36,626 tons, steam and sail, built for foreigners be reckoned, and exceeding it by nearly 12,000 tons if that built on British account only be taken. Sail, however, has again fallen off in 1886, but the vessels turned out have been of a much larger class than in 1885.
In our own country the steam tonnage built in 1885 for the first time (excepting in 1880, when they were about equal) surpassed in amount the sail, though it must be said that the latter in this year showed a very great falling off (60,000 tons) from the amount built the preceding year.
This sudden development of sailing vessels in Great Britain in the last few years is a rather unexpected and interesting phenomenon. It is due mainly, no doubt, to the very great depression in trade and freights, whereby it was made impossible for many steamers to continue in use without great loss ; while at sea, at least, the sailing vessel is not running up a large coal bill, and if laid up there is less capital idle and less deterioration on account of machinery.
It must, too, be recognized that while steam has been advancing with such rapid pace on the highway of economy the sailing vessel has followed closely in its wake.
While the wind continues to blow we may of course look for sails upon the sea to take advantage of it, but with the decrease of coal expenditure to one and a half pounds per horse-power per hour, and with the fruition of some of the newer developments, so many of which are promised, we can fairly reckon upon the part to be played by sails in commerce as one of constantly diminishing importance—though long may some remain to nurture the true seaman, who can never be developed in the cavernous depths of a stoke-hole, or on the attenuated masts of a modern steamship !
Less steam tonnage has been built in the last three years, no doubt, on account of the great uncertainty of the engineering mind as to the outcome of the great changes since 1881. Many fine ships launched within this period have come to be considered obsolete before they were finished, and owners have hesitated to order until they felt that something like fixity for a few years, at least, should be arrived at.
Triple and quadruple expansion engines, forced draught, twin screws, new arrangements of screws, newer types of boilers, etc., are a few of the things which have had to be considered, and it is not to be wondered at that there should be a desire to settle slowly upon a design which was to cost possibly in many cases a million or more of dollars.
There is, however, one certainty—the compound engine is relegated to the past as was its predecessor of the single cylinder. Still higher pressures, still greater expansions, are probable, though in the next five or ten years we can hardly hope for such an economical advance as in the last six.
Much the same remark, however, has been made at each great step in steam, and, learning from the experience of preceding prophets, it would perhaps be better to say that expectancy is the safest attitude of the mind in such a question.
It is well, however, that these changes should not come too frequently : the ship-owner should be allowed a little breathing time, and not be continually oppressed by a nightmare of obsolete ships.
Let us hope that now we have built 150,000 miles of railroads, we may have enough to satisfy the country's demand for some little time, and that our designing talent and our capitalists' dollars may again be turned toward that field in which for fifty years we were foremost.
A fair chance, however, must first be given the owner ; the grip of Legislation which has throttled our shipping industry for so long must be relaxed, and we must recognize that laws dealing with shipping which had their birth in England in 1652 are not necessarily suited for America in 1887.
Source: SCRIBNER'S MAGAZINE.
VOL. I. MAY, 1887. No. 5.
Copyright, 1887, by Charles Scribner's Sons. All rights reserved.