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THE GREAT EASTERN, OR LEVIATHAN: THE WAVE PRINCIPLE.
THE most gigantic example of naval engineering yet constructed is, at the same time, the latest development of three systems of investigation, the latest response to three problems-What is the form of ship that will pass most rapidly through the water; what is the size of ship that can be worked most profitably by steam in long oceanic voyages; and what is the construction of ship that will give the most strength with a definite quantity of material? Any description of the mighty Great Eastern, at all worthy of the subject, must take account of these three phases of inquiry.
It is now about a quarter of a century ago that Mr. Scott Russell first began those experiments which led him to the recommendation of the wave principle for the form of ships—that is, the adoption of a certain similarity between the curves of a ship's hull and the curves of a wave. The forms of ships had long been an object of attention among scientific and practical men: seeing that it is to the interest of every shipowner and every navigator that his vessel shall speed on her voyage with as little obstruction as possible. The form of least resistance' to the waves has often been diligently sought. More than half a century ago, Colonel Beaufoy, in a spirit at once scientific and patriotic, expended a sum little short of 30,000l. in an elaborate series of researches on this subject; but unfortunately the results were not commensurate with the time, money, and ingenuity employed; for the forms of the models constructed did not comprehend such as were actually required for the purposes of naval construction; nor was the state of science at that time such as to warrant, with any degree of certainty, a deduction from the resistance of oné form to that of another.
Mr. Scott Russell had his attention drawn to this subject by a scheme of some of the canal companies for the establishment of swift boats, that might con pete with stage-coaches for passenger traffic. He studied the shapes of the bows or heads of ships; he observed that the duck's-breast' bow, a favourite among seamen, raises a large wave immediately in front of the vessel, which retards its velocity; he noted that when a vessel passes through the water at a great velocity, the high wave raised in front, falling again, forms a hollow, by its pressure, immediately behind it; and he found that the water is afterwards sent out with great force on both sides of the vessel. In short, he ascertained that much power is unprofitably spent during the forcing of a passage-way for a ship through the water, when of the ordinary build. Soon after the establishment of the British Association for the Advancement of Science, Mr. Russell communicated the results of his canal experiments; and consequent thereupon, a Committee was formed to carry the investigations further, under the auspices of the Association. The Committee was formed of Mr. Russell and Sir John Robinson, but the task of conducting the experiments was chiefly undertaken by Mr. Russell. Three series of inquiries were instituted :-To determine the nature and laws of the different kinds of waves; to find the nature of the connection
existing between the motions of waves and the resistance of fluids to the motion of floating bodies; and to ascertain the shape that ought to be given to a ship to insure the greatest speed with the least expenditure of power. Almost every year's proceedings of the Association, down to the last Dublin Meeting in 1857, brought forward valuable information touching the progress of these important investigations. A few of the principal results may be here noticed.
It was found that waves present very different properties according to their mode of production-especially one called by Mr. Russell the Great Solitary Wave, or Primary Wave of Translation. He found that, in this wave, the particles of water do not move continuously and rapidly forward, as unscientific persons usually imagine; nor are their movements limited to an up-and-down motion, as men of science formerly believed; they perform a succession of leaps in an upward curve, called by mathematicians a hemi-cycloid. The particles of water perfectly at rest before the approach of a wave, are by that approach lifted up, translated forwards, and deposited, perfectly at rest, in new locations: the length of the leap, the height of the wave, and the depth of the water, all being connected by certain relations. It was next found that this curious movement of the particles of water in a wave has much to do with the motion of floating bodies. Mr. Russell contrived apparatus by which small models of ships could be drawn or driven, with various degrees of velocity, through troughs or channels of water; and when high speed was attained, some of the results were very novel and important. Two general principles were established:-That when a vessel passes along the surface of water with high velocity, it produces a Wave of Translation, moving with a velocity depending in some degree on the depth; and that whenever the velocity of the vessel becomes greater than the velocity of the wave, the vessel is carried along on the top of the wave with diminished resistance. This last-nained result was most unexpected; it seemed to say that the faster we go the easier it is to go. Steam-ship owners had been accustomed to believe that a small expenditure of fuel, and a low velocity, were more economical than the opposite conditions; and therefore they did not attempt high speed, unless the nature of the passenger-traffic absolutely called for it. It was now found, however, that this theory required a new examination. Some of the steam-ship companies had observed, equally to their surprise and satisfaction, that by using higher power, and attaining higher speed, they in certain cases saved fuel and money. Mr. Scott Russell gave a definite form to this fact by announcing, at the Birmingham Meeting of the Association in 1839, this general proposition :-That in a voyage by a steam-vessel in the open sea, exposed to adverse as well as favourable winds, there is a certain high velocity, and high portion of power, which may be accomplished with less expenditure of fuel and of room than at a lower speed with less power. It was only in long voyages, made in the storm-tossed ocean, that this principle was considered to apply. Mr. Russell adduced an example of the performance of a ship under four conditions-two variations in weather and two in steam-power; showing how, in some circumstances, a bright quick fire will consume
ess coal than a dull slow fire in doing the same work-using the word 'fire' not only figuratively but literally. It was a ship of 1,200 tons, worked at one time with 400, and at another with 500 horse-power. The results may be thus tabulated :
One ton of Coal per hour.
Fair Weather :- -400 horse-power, 9 miles an hour, 216 miles per day, 2,160 miles in 10 days, 240 tons of coal. Adverse Weather :-400 horse-power, 5 miles an hour, 120 miles per day, 2,160 miles in 18 days, 436 tons of coal.
One and a quarter tons of Coal per hour. Fair Weather:-500 horse power, 10 miles an hour, 240 miles per day, 2160 miles in 9 days, 270 tons of coal. Adverse Weather :-500 horse-power, 6 miles an hour, 162 miles per day, 2160 miles in 13 days, 395 tons of coal.
The result may be thus collected that if this ship of 1,200 tons had made a voyage of 4,320 miles, with an equal proportion of fair and adverse weather, she would have saved about 6 days of time, and 11 tons of coal, by using 500 horse power instead of 400-a result equally pleasant to owners and to passengers.
Having thus ascertained, partly by observation on existing ships and partly by experiments on models, that there is a particular velocity for every steamer, more profitable than any lower velocity, Mr. Russell proceeded to combine with this the results of his researches on the proper forms of ships. When a vessel is passing over the sea, she displaces a certain amount of water, depending on her size and draught, and then the water closes in behind her to fill up the vacated space. The experimenter found the waves of this water to have a peculiar form; and he arrived at an opinion that the lines,' or curvature of the bow of a ship ought to resemble the curvature of a Wave of Translation; whereas the stern should resemble the curve of the Wave of Replacement. This peculiar form was named by him the Wave form, and was recommended as being the 'solid of least resistance.' To test this theory in every possible way, Mr. Scott Russell, aided by Sir John Robinson, and Mr. Smith of Jordan Hill, applied to many eminent shipbuilders for information on the points most needed, and also on those concerning which the shipbuilders themselves were most in doubt. More than a hundred models of vessels were constructed, from 3 to 25 feet in length; and delicate apparatus was invented, by which these models might be drawn along a surface of water, varying from 30 to 2000 yards in length, at various degrees of immersion, and with various velocities. The object, in every trial, was to determine what combination of conditions insured the swiftest motion. The transverse section, the bow-lines, the stern-lines, the place of greatest breadth, &c., all were studied in the same way. It sooon became apparent that ships might be made fuller than usual at some parts, and finer at others, with advantage. The enormous number of 20,000 experiments were made, embracing
not only the models already adverted to, but existing ships up to 1,000 tons burden. A striking proof was adduced of the value of almost imperceptible changes of form in changing the velocity of vessels. Four boats were built, about 25 feet long each, exactly alike in depth and in breadth, in weight and in capacity, in midship area and in-draught of water; all good sea-boats, and all having their respective admirers in regard to shape-differing in nothing but the slight curvatures of the hull; and, nevertheless, they cut through the water with very different velocities, although propelled with equal powers. The boat which performed the best was on the wave principle; and, moreover, this was found to be the driest, easiest, and best sea-boat. All the experiments tended towards one general result-the desirability of assimilating the form of a ship in certain parts to the shape of waves. In practical navigation the great point is, how to obtain a passage for a ship by removing or displacing the particles of water as quietly as possible, and to no further distance on either side than the greatest width of the vessel. On one occasion, Mr. Russell caused a model boat, 75 feet long, to be drawn by horses along a canal at a very high speed, and made the head pass between two oranges floating on the water: these oranges, intended to represent on a large and visible scale two particles of water, were observed merely to touch the sides of the vessel until they got amidships, where they remained quiescent until they closed in behind the stern. To produce this gentle displacement in the proper degree, it was found that the stern must be much fuller than the bow, and that the broadest part of a ship ought to be some distance behind the centre, say at three-fifths from the head and two-fifths from the stern.
During the course of Mr. Scott Russell's experiments, the late Dr. Scoresby made an independent series of observations on the waves of the Atlantic, during two passages in 1847-8. Navigators and marine-painters, poets and novelists, have delighted to represent ocean waves as being 'mountains high;' but the veteran arctic navigator lowered the ambition of those waves considerably. He found that, during a very heavy gale, the height of the waves, from crest to hollow, varied from 24 to 36 feet, or 12 to 18 feet above and below the mean level of the sea. During a raging storm the height is known to reach 45 feet occasionally-a scene of terrific grandeur, but still far within the limits which fancy has given to waves 6 mountains high.' It was further found that the waves, during what sailors would call a 'fresh sea,' are from 100 to 150 feet across from crest to crest; that in a moderate gale' they may reach 300; that in a great storm' they extend to 600 feet; and that waves of this last-named breadth move onward with a speed exceeding 30 miles an hour. One result of this discovery (if discovery it may be called) is the demonstration that a ship 600 to 700 feet long would always rest on the crests of two, three, or more waves, unless in a storm of unusual severity; she would ride on the waves, and would have too many supports under her to break her back -a catastrophe often prophesied for long ships when the breadth of waves was not fully known. The researches of Russell, Robinson, and Scoresby have gradually produced fruit. It was observed, as a curious and instructive fact,
that yachtsmen, pirates, smugglers, and slavers-all interested on various grounds in the maintenance of a high speed at sea-had long adopted forms of vessels bearing some analogy to the wave form; they had adopted it for its swiftness without knowing why it is swift; but science came forward to show that the shape of waves themselves determines the matter. Ships soon became laid down purposely on the wave principle. In 1839 the Fire King was built, a pleasure yacht, very roomy, and yet swifter than any other vessel of the day in Great Britain. After this the Vanguard, built on the same principle, was found to be the swiftest steamer on the Dublin and Cork route; and the Great Britain, a wonder in its day, although since eclipsed by larger steamers, was laid down on lines of the same principle. At the Southampton Meeting of the British Association in 1846, Dr. Phipps described two yachts that had been built in Ireland on the wave plan, surpassing, in speed and other qualities, any yachts on those stations of similar size; one of them, of only 45 tons, attained a speed of 11 nautical miles an hour, when close-reefed and in a rough sea. It was at the same time stated, on the authority of Captain Fishbourne, of the Flambeau steamer, built on wave lines, that the superiority of that form becomes more marked in bad weather -just when a trustworthy ship is most needed. Of eight steamers on the Holyhead and Dublin route in 1848, it was found that those which attained the greatest speed, 15 to 18 miles an hour, had been constructed in more complete conformity than the others with the wave principle. When shipbuilders and steam companies found that the length of a steamer ought to depend on the speed wished to be attained, and that the breadth need bear relation only to the amount of accommodation required for the machinery, cargo, and passengers, they gradually availed themselves of this knowledge, either in building new vessels or in altering old ones. In many instances, engines were taken out of old vessels, and placed in new iron steamers, built on wave lines, with a great increase both of speed and of cargo-space, without any increase of working cost. The Americans, alive to what was going on in England, gradually adopted the wave form. The English Admiralty, distrustful of novelties in shipbuilding, held aloof. The prevailing opinion in the Royal Navy was that, owing to the fineness of the bow-lines on the wave principle, it could not be possible for such vessels to carry the same amount of heavy ordnance calculated to fire in a line with the keel, as in vessels of the ordinary construction. To disprove this, Mr. Scott Russell undertook the construction, for a foreign government, of two iron war-steamers that would stand these tests-to carry double the armament of any war-steamer of the same tonnage and power, and to go two knots an hour faster than any war-steamers then afloat. Mr. Russell announced, at the Ipswich Meeting of the Association in 1851, that the vessels in question fully stood these tests. Many of the splendid clipper-ships built within the last half-dozen years are on wave lines; but there is no public announcement of the fact; the British Association has made a free gift to all the world of any advantages derivable from experiments made under its auspices; and shipbuilders find themselves at liberty to adopt any or all parts