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WA\i ^nrnttoM |lUt8tr»tion«. -• BY H. BOWLBY WILLSON, ESQ., OF CAXADA. LONDON : J. D. POTTER, g^bmixaUg €\mi ^gent, 31, POULTRY j AND 1], KING STREET, TOWER HILL. 1863. *:^--^j.^ J. AND I. TIREEUCK, BTKAM rUlNTEKS AND I.ITHOOBArUEUH, MONKW£LL STREET, £.C. ■\ ;'.- r '■ I -I , iPiL'S^'i- ♦ It il INDEX REFERRING TO PARAGRAPHS. 1 Paragraph! Economy in Ship-building . . f . . . . . 2.3 Difference between passenger and freight ^ressels 4.76 The question of form involves knowledge of the laws of nature . . . . 6 The law of Resistance in fluids in reference to depth of immersion . . 6 Performances of " Black Prince" and " Warrior" cited 7 — 9 Reason of greater eflScacy of screw over paddle-WLeel . . . . 10.11 The law referred to, in favour of light draught . . . . . . ..12 Statement of the law as deduced from, oxperimenta . . . . • . 13 . 14 Why the "Great Eastern" fails in speed 16.16 Discrepancy in performances of " Warrior " and " Black Prince " accoimted for .. .. .. .. .. .. .. 17 Failure of Col. Beaufoy and French Academicians to discover law of resistance .. .. .. .. .. .. .. ..18 Effect of depth on Whales and other Marine animals .. .. „ Experiments suggested . , . . . . 19 Rule for estimating horse power calculated to mislead without knowledge of the laws of nature . . 20 — 22 Causes of increase of resistance of all kinds 23 Appearance about a Screw Steamer under high spised . . . . . . 24 Theory of Ocean Waves 25 — 28 Laws limiting height of waves . . . . . . 29 — 31 Great force of waves 32^^9r\' " PREFACE. " Himalaya," before she came into the possession of the Govern- ment, — ^is obtained at a far greater outlay, both in first cost and current expenses. Although the public are kept very much in the dark as to the actual cost of building and operating such high speed vessels; enough is known to warrant the assumption, that they can only be maintained by large government subsidies. This circum- stance is of itself sufficient to illustrate the unsatisfactory state in which, what is now considered, high speed ocean navigation remains. So long as the Government of Great Britain alone pays a million of pounds pension money to support ocean steam navigation, the subject ot it cannot be regarded as in a healthy condition. These subsidies must be viewed in the light of a national tax, paid to support a systematic violation of the laws of nature, which we have not even taken the means to fully comprehend. We pay more for the carriage of an ounce letter across the ocean, than the mer- x?,hant does for the transit of a hundred pounds of merchandize. If Govern rnent would change the system, and allow a penny or two pence for every letter, and a half-penny for every newspaper of the minimum weight carried, — I will not say by eveiy transient ship, but by every steamer forming part of a regularly-established weekly or fortnightly line, which will undertake to deliver such mail matter within a specified time, — then we may hope for a sounder system of ocean mail service. I am aware that there are a great many men, at the present time, whose minds like my own have been at work in endeavouring to master the problems I have ventured to discuss, and into whose hands this little treatise may fall. Some of these may have arrived at conclusions different from niy own; but I think that the 'tendency in the development of mechanical and theoretical science is in the direction I have pointed. At any rate, I have the large and valuable experience of the American and Canadian Lakes to fall back on in support of many of my views. It may be remarked as a singular circumstance, that several of the most important scientific discoveries have been preceded by strong presentiments shared in by thousands of the approaching PREFACE. XI \ events which such impressions foreshadow. Lamartine, in alluding to the existence of such prevailing sentiments just prior to the discovery of America, says, " There seem to be ideas floating in the air — a species of intellectual miasma, which thousands of men, without concert, breathe at once." Our present necessities demand a class of vessels that will reduce the voyage between Europe and America to an average of one-half the present time, and at a cheaper rate. I have en- deavoured to indicate how, I think, this may be accomplished, and trust that my ideas may be regarded by the enterprising Merchants of this country, if not by the Admiralty, as worthy of considera- tion. If the thousands of intellects at work on this problem did not believe that it was susceptible of a solution, it would indicate a species of wide-spread monomania. I simply believe that lt thfi deep by '' sounding" as the sailcu ^ term it, ^t to have su^^'^gested the propriety of cxpciimentalizing on the lower strata of water. It had > before then, boon remarked by naturalists, that fish and other marine animaln, accuHtomed to feed in and inhabit tlio di ner regions of the sen, were formed with greater strength, and moved with less speed than those living and feeding near the surface. Cases are related where whales, after being slightly wounded, have sounded so deep, that when they rose to the surface they have been so exhausted as to be readily approached and killed with lances without a struggle. Other cases have been related where they have been killed outright by the enormous resistance they have encountered in their rapid course through the lower depths of the sea. Nor is this surprising when we consider that the pressure on the body of an ordinary man, at a depth of 3? feet, is equal to 20,000 lbs., a pressure which only powerfully-constituted divers are able to bear. 19. Any experiments instituted to determine the ratios of increasing resistance at different velocities, should be made on a scale sufficiently large, and under circumstances calculated ^o afford accui'ate results. The great Lakes of Canada, from their depth and freedom from tidal ^nd other currents, present unusually fiLVorable field* tj obtaining accurate data. There are often weeks togoi-iier when some of these great inland seas are scarcely moved by a ripple, cx'»f»pt when the refreshing evening breezes spring up durin;^ ^\e hot months. Valuable experiments might be mad.: i i ''.ho following manner : — constn^ct a flat bottomed boat of some light and strong material, V SCIENCE OF SHIP-BUILDING. 11 of Kufficient length — say ^^ feet, with a " slip" keel box, eight or ten feet Ijng, and also a similar box placed at right angles with the kee^ As coriHiderublo strain will come on these boxes, lot thom bo 8U|>ported by two upright pieces of scantling, stayed by small chains or wires, passed over cross trees af the top, and s^^cured to the stem and stern post. These scantling will serve as slide gi .iges for the implements to be used. Then con- eti A 1 a Up keel of boiler plate — say 30 feet long, so as tio admit of being dropped down 20 feet below the boat's bottom. Let this thin plate of iron, made sharp at the edges to avert head resistance, be divided into a scale of inches and feet, so as to tell at a glance the amount ot immersion. Attach the stem of the boat by a Ine to a well-constructed dynamometer, or instrument for measur- ing the rate of resistance, which has been made ^ast to the stern of a steamer. First ascertain the readings of the instrument with the sliding keel up, at different velocities. The drawings of such an apparatus as I have described, will be seen by reference to Fig 2 — Plate II. It will now be easy to note the amount of frictional resistance exerted at each successive stage of immer- sion of the scale, and by comparing the different sums of resistance with each other, to establish the ratio or law of increase. In like manner, the law of increased resistance under different velocities, at the same depth of immersion, may be ascertained. Such experiments would require to be repeated a great number of times, and with a number of instruments, to correct each other, in order to arrive at an accurate result. Head resistance might be iscertained by means of a scale to which bodies of different forms and sizes may be attached, and im- r-^ 12 SCIENCE OF SHIP-BUILDING. I' I ! mersed through the cross section box, and be towed horizontally through the water at different rates of speed and at various depths, in the same manner as described in respect to friction. There are no doubt many other devises, which an ingenious engineer, accustomed to study the subject, may avail himself of. But experiments made in the way I have mentioned will give results that will surprise those unprepared for them, particularly in respect to friction.* 20. I will now proceed to apply the law I have laid down to the rule generally used by scientific ship-builders in estimating for horse power. That rule assumes that the resistance to similar forms, is as the square of the velocity and the horse power as the cube. As to the manner in which this rule is worked out in practice, I will quote the words of Mr. Scott Russell, who is a great authority on all subjects connected with ship-building. 21. Mr. Russell says, " he had ascertained that at ten knots per hour, with a vessel of proper form (?), of * It may be interesting to mention some experiments which I made with a small boat, which I had constructed in 1860, either to sail or row. It drew about 6 inches, light, and had a sliding keel — arranged to drop 1, 2, or 3 feet below the bottom; three feet wide, and made of thin boiler plate. I found that In smooth water, uninfluenced by wind, I could pull this boat, with the kesl up, a given distance in 15 minutes. When it was one foot down, exposing on the two sides six feet for frictional resistance, I perceived a decided difference in puliiug it through the water with the oars ; and after many trials, I found it took me a full minute longer to pull the distance between the two marks. On lowering the keel another foot, instead of finding the time increased to 17 minutes, I discovered that fully 18 were required. "With the keel fully down, exposing 18 feet on the two sides, the time was increased to 21 minutes ; whereas, if each foot of immersion en- countered a uniform resistance, the boat being pnllod with the same amount of effort, should have been retarded only 18 minutes. SCIENCE OF SHIP-BUILDING. 13 1,500 tons burthen, the head resistance of a ship could be reduced to 50 lbs. per square foot. He had also as- certained how much a similar vessel could be propelled with, by engine power alone, including the loss due to the working of the engines, and he had found that whilst the direct resistance to a ship going ten knots per hour, was only 50 Ibb. per square foot of midship section, including all loss from communication by paddle wheel, air pump, and other sources, except the slip, this resis- tance was not more than 65 lbs. per square foot of midship section. Thus they could calculate confidently to a quarter of a knot, as he had done for years past with his peculiar shape of ship, the amount of steam power necessary to propel a given ship at a given speed — as for instance, where a speed often knots per hour was desired, he provided for 50 lbs. per square foot of midship section, for the resistance of that ship ; and when he had to over- come the resistance of the machinery also, he made that up to 65 lbs. per square foot." 22. Now it will be seen that, without taking into account the surfaces exposed to frictional and negative resistance, and the draught of the ship and the law of increased vertical resistance, this rule must be attended with great inconvenience. If the engine power of the Great Eastern was predicted on the data obtained from a vessel of 1,500 tons, and drawing only 15 or 16 feet, her failure to realise the expectations of her designers will now be understood. 23. The law in question being established, we must endeavour to find out the cause. The increase in the density of the water by the superincumbent weight of the upper strata, can scarcely be supposed to have much 14 SCIENC!E OF SHIP-BUILDING. to do with it. The experiments made on this head show that water is only compr(^ssed -^is at 500 fathoms, which would be about ytj W at five fathoms. In case of frictional resistance, it is probably due to the increase of pressure on the ship's skin, as the immersion increases, which, as already mentioned, at 32 feet deep, is equal to 20,000 on the body of an ordinary man. Head resistance, or displacement, must, I think, be sought in the power required to raise each cubic foot of water lying in the ship's path, a certain height in a given time, according to her velocity. In the case of a steam ship going at a high speed, the work that the engines have to do, is to raise above the surface a quantity of water equal or nearly so in bulk to the whole mass lying in the way of her largest immersed midship cross-section, and to overcome the friction on her exposed surfaces, as well as negative resistance and of the engines themselves. 24. In respect to these labors, in ocean road making, the great facility with which particles of water move amongst each other, as well as the readiness with which solid substances are moved through it in any direction, or in other words, its great fluidity, has possibly led to much misconception on this point.* *It is not many years since the doctrine prevailed, because of this facility of movement on the part of solid bodies under water, that a body surrounded by any liquid was destitute of weight, and that the particles of liquids did not gravitate on each other. The fallacy of this opinion was at length shown, by suspending an exhausted glass bottle to one arm of a balance, so that its neck was wholly immersed with weight sufficient on the other arm of the balance to keep it in equilibrium. When the water was let into the bottle by means of a stop-cock, it waa found that it required the same amount of weights to be added to the opposite end of the balance to make it niaintain lis equi- librium, as the contents of the bottle weighed in the air. To draw a tin or J^if-r-i-ti^nf^n-i SCIENCE OF SHIP-BUILDING. 16 \ Mr. Scott Russell has so admirably described the manner in which a ship, by the power of her engines or sails, exca\'ates for herself a passage, and has so well informed us what she does with the water, and how she fills up the passage behind her, that little can be added. I wish, however, to state what I have observed, both in deep and shallow water, and what in a small degree may be seen almost every day on the Thames, by close observation, to be the appearance of the water im- mediately surrounding a rapidly-moving steamer. The best point for observation is the deck of another steamer of the same speed moving in the same direction and at such a distance as to make the angle of view about five degrees. If the water is smooth and unrippled, and the steamer under view be a screw, the appearance will be very striking. The moving vessel will seem to be placed in an elongated movi: g basin, scooped out of the water, and she will be seen to keep her place at a fixed distance from the rim, being always nearer to the end in front of her, which her cut- water will touch. If the steamer have a very fine entrance, the edges of the basin, on the two sides will appear higher than near the ends, and the horizontal shape of the rim will be that of versed sines. See Plate II., Fig. I. This rim is formed partly of the displaced water and partly of other water acted on or pressed upward by it. The wave of translation spoken of by Mr. Russell, docs not in the case of such a vessel in iron bucket from ;i deep immersion in a well, or in the sea at a considerable velocity, requires more power at the commencement then when it nears the surface, that is, the power required to maintain a uniform velocity diminishes as the depth of immersion decreases. Some advantage may be gained by having this experiment nicely tested. ■-r T.)-»* -^--T ■'■'^- f »- -.-^"i", 16 SCIENCE OF SHIP-BUILDING. the open sea take a course directly ahead of her, but nearly at right angles to the water lines of her respective bows, and the rollers or waves which follow and which are the result of negative resistance form an obtuse angle to each other having its point next the ship. If, however, the vessel have a bluff entrance and a fine run, the wave of translation will be largest ahead, thereby impeding the progress of the ship, which will rise at the head and sink by the stem, and seem to be labouring up hill. 25. The remarks just made, it will be seen, have a direct bearing on the FORM of the ship, which will presently come under notice (60). Prior, however, to discussing this most important question, which is the main one to be mastered, it will be necessary to consider that of ocean waves, and their effects on ships and other solid bodies. I now speak only of waves produced by the action of the atmosphere on the surface of the sea. The wind to which they are imputed is merely an incident of the atmosphere and one of the processes by which it produces wave motion. 26. The properties of the atmosphere which enables it, when set in motion by changes of temperature acting on vast fields to produce waves, are its elasticity and weight. The qualities of water which render it susceptible of being thus acted on are its fluidity and elasticity — the latter a quality once denied by philosophers. But how- ever small it has been demonstrated to be, there could, I think, be no wind-made waves without it. 27. We have now before us the body to be acted on and the agent ready to aot, and know the peculiar qualities of each required to produce a given result — namely, ocean- waves. But there is yet another requisite, ■ '^^^w^^-Tja^- SCIENCE OF SHIP-BUILDING. 17 but without which there would be no result. I speak of the law of gravitation. We will now see how these combined agencies perform their work. 28. Suppose the surface of the sea to be perfectly smooth, and that a current of atmospheric air, or wind springs up, the first thing that will be noticed, will be innumerable ripples on the face of the deep. This is the commencement of wave-making — the process is begun. As the wind or elastic current of air bearing down on every square foot, with the force of nearly a ton, pushes the water up into these ripples, gravitation pulls it down again. Each time a little wave is thus raised and drawn down, it increases in size, by absorbing its lesser neighbours. It will thus be clearly perceived, that the two agents, which create the waves, are the atmosphere with its peculiar quality of elasticity acting from above and horizontally, and attraction of gravitation, acting from below on a semi-elastic fluid. 29. The waves thus commenced go on increasing in magnitude, so long as the wind increases in force, until they reach the limit imposed by the laws which create them. This law, on the part of the atmosphere, would limit their height to 32 feet, or the height of a column of water, the weight of which is equal to that of an entire atmosphere. But there is another law to be sought in the water itself, which imposes a much smaller limit on the height of waves. That law I am inclined to believe, will be found to be the extent of the elasticity of water. Great exaggeration has prevailed in respect to the altitude of ocean waves. Even learned writers, until very recently, continued to speak of their rising* 40 or 50 feet high. In November, 1840, I encountered during a c 18 SCIENCE OF SHIP- BUILDING. I voyage fiom New York to Barbadoes, in a small barque, one of the severest hurricanes of the present century. It was one of those great cycloidal storms, reported on by the late Colonel Reid, which swept down the whole length of the Carribean sea, and turning with the gulf stream, followed the coast of North America to Newfound- land, and finally crossed the Atlantic to the shores of England. Owing to the ignorance and stupidity of the captain, we received the whole force of the storm for four days, almost under bare poles, when, by changing the course of his ship, he might have run out of it in a few hours (as I endeavoured in vain to convince him). When we reached the middle of the gulf-stream, where the current was three knots an hour, off the Capes of Carolina, we had the wind at its greatest force from the north, almost in an opposite direction to the current, thus raising the waves to what people delight to call, in poetic language, '' Mountains high." Being a good sailor, I mounted the mast to get a better view of the terrible desolation which surrounded our little barque, and to measure the height of the waves. I was quite surprized, when I mounted about 30 feet, to find that I was on a level with the crest of the waves, when the ship was at the bottom of the ''troughs." I therefore arrived at the conclusion that they never rise above 16 or 18 feet above the ocean's level when at rest. The violence of the waves was such (as we found when we came into port) that nearly one-third of the copper was torn from the ship's sides and bottom. This was the commencement of my observations on ocean waves. 30. The law of water (whatever it may be) which limits the height of waves much below the power of the .-.> -«.■ "T" '"-v.; / s SCIENCE OF SHIP-BUILDING. 19 V in atmosphere, no doubt, limits the downward wave motion, which would otherwise extend to the bottom in the deepest parts of the sea. The complete elucidation of these interesting topics, connected with the subject under discussion, will bring to light the law which says to the sea, *' thus far shall thou go, and no farther." 31. The idea that the particles of water in waves advance, is simply an optical illusion, although on the surface, there may be, and probably is, a slight onward movement, counterbalanced by a counter current under- neath. 32. Although the particles themselves do not move forward, the effect of waves on ships is in many respects the same as if they did. To illustrate this fact, let a great ocean-wave encounter an unyielding obstruction, such as a rock rising out of deep water, which would prevent the undulation from passing under it, and the wave will then act in a horizontal direction, with enormous force — ^the force being proportioned to the velocity and size of the undulation. The bearing of this fact on our subject, will hereafter be seen (35, 36). 33. The waves thus formed are simple undulations moving in the direction of the wind, without advancing the particles which form them. These particles we have seen oscillate vertically, or as some allege, in parabolic lines or columns. As they rise and fall in long lines, or in masses, they give the peculiar forms assumed by waves — some being long regular swells and others tumulose in shape. The advancing movement of the undulations, is caused by the graduated rising and falling of these coulmns or masses of particles — the rising lines being always in advance of the falling ones. Thus all the i ^ 3a SCIENCE OF SHIP -BUILDING. particles near the surface occupy alternately the crest and trough of the waves. A well drilled army of* soldiers, formed in lines, might be so manoBuvered, as to produce the effect of ocean waves, by causing the men to fall to their knees and rise in lines in the manner described, without moving a step. 34. A ship, or floating immersed body of any kind, displaces a certain quantity of the particles forming a passing wave. It might therefore, be expected that a ship would conform exactly to the motions and angles ot the wave, where it happened for the time to be. This is certainly what happens to a perfectly flat body, floating directly on the surface, such as a detached portion of a ship's deck, or a raft made of spars or timber. In the case of a ship it is, however, different. The rising and falling lines or masses of particles, act unequally and with different forces on different parts of her, according to their depth of immersion. 3.5. The rolling of a ship is produced by a two-fold action of the waves : namely, first, by the rising of the particles on one side of her, whilst they are sinking at the other, or by the slope [of the wave ; and, secondly, by the forward motion of the undulation, which has fm^ther and faster to travel at the surface than at the ship's keel, where the motion begins rapidly to diminish.* * Mr. Froude in his paper on '* the rolling of ships," read before the Institution of N.A. (Vide Trans. I.N.A., 1861) takes quite a different view from that here expressed : — He assumes that there is no sensible difference between the parallelism of wave undulations at the surface and at the depth of immersion of even the largest vessel. Va'-lous experiments which I have made, however, sustain my opinions. Besides, it is the greater velocity of waves at the surface which causes them to break where they encounter no ouposing solid body. Ill SCIENCE OF SHIP-BUILDING. n If, therefore, a ship sinks so deep into the water as materially to impede the passing undulations, it is 6b\ ais that she will roll more and receive a heavier shock, when a wave breaks against her, than one drawing less. Nay, more ; such a ship will often cause a wave to break, which would have passed under her unbroken had she drawn but a little less water. This will account for such accidents as that which befell the Great Eastern, and caused the loss of her paddle-wheels in 1861, and no doubt many a gallant ship has foundered at sea from this cause. 36. The violence of breaking waves, whether on the sloping strand, or against the more yielding sides or decks of ships at sea, is, under high velocities, enormous, and points out the danger of giving ships too deep an immersion in the less yielding strata of water, so as to interfere seriously with the passing undulations. During the great West India hurricane of 1780, cannon that had lain long buried in the sea were driven up high and dry by the waves, and were still shown when I was there in 1840. 37. A learned writer on waves (jEw. Brit., 1840), lays down the following law with regard to the depth of wave undulations: " The depth of the water to which the agitation of a wave extends perceptibly, never bears a very large proportion to the dimensions of the wave, either in breadth or heiglit, the motion diminishing in geometrical progression as the depth increases in arithmetical ; and at a depth equal to the breath of the wave, the motion is diminished to a 534th part of that at the surface." Whether tliis rule be correct or not, we find a very marked difference between the motion of an 22 SCIENCE OF SHIP-BUILDING. 5. »;.;■ ordinary Atlantic wave, (of say 15 feet from the hollow to the crest), at the surface and at 20 feet below it. If, therefore, a ship draws more than that, she will receive a severer shock and a heavier roll than one drawing less. 38. As already observed, a flat bottomed boat or raft floating immediately on the sm'face, conforms more readily to the angles of the waves than a ship. But there is another peculiarity connected with the rolling of ships. It is the acceleration in the velocity of the motion. This phenomenon consists in the gradual accumulation of angle during several successive rolls, until such accu- mulation reaches a maximum force, when a gradual sub- sidence commences, and the ship comes to rest to begin a new series of rolls. The worst rollers are those in which this peculiarity is most developed. 39. The form that will roll most — the adjustment of weights being the same — is that which apDroache > nearest to a circle, in the cross sections which aiJbrd the greatest amount of buoyancy, because a circular form does not widen its base at the water line as it changes position. The form that will roll least, other things being equal, such as the adjustment of weights, &c., is that of the parallelo- gram and angle combined, the comers being rounded in order to give a more gentle deflection to wave oscillations, as seen at Fig 6 — Plate III. The reason of this is that the latter form gives less draught, and conforms to the peculiarities of waves as already described, and conse- quently receives their action more equalbly on the lines of flotation. It also widens its base of flotation on the least change of position. Every one who has made a voyage in the Great SCIENCE OF RHIP-BUILDINO, 23 Eastern, has had to remark the extraordinary rolling of that vast ship. i When she was building, it was predicted of her that she would neither roll, nor pitch, or at least only in a slight degree. The drawings at Plate I. — Fig 1, and Plate III. — Fig. 4, represent the great ship, and show how nearly she conforms to a circle, although she in reality has consider- able level floor. This great tendency to roll, taken in connection with the accumulation of force, is calculated to lead to serious evils, to say nothing worse, should the ship encounter a real hurricane. The danger arises, in such ships, from the accelerated roll outrunning the periodicity of the waves, so that the ship comes to act in an opposite direc- tion to them, when she will occasionally meet the crest of a great wave half way, thereby adding to its force, and frequently causing it to break over her. The forms of the Resistance, Defence, and the Warrior, approach even nearer to that which, according to my de- ductions, is the worst — though they partake of the triangle ; whilst that of the Great Eastern is in the nature of a parallelogram, with the lower corners too much rounded. See Plate III. — Fig 7. By reference to Plate II. — Fig 3, the acceleration in the rolling of a ship may be traced in her different attitudes and degrees of angle, as you run your eye from right to left, the waves being supposed to be moving in an opposite direction. But most vess,els roll when running before a following sea, as badly as when going in the troughs. When the subject shall be properly brought to the test of experi- mental science, I think it will be found that both kinds 24 SCIENCE OF 8HIP-BUILDIN0. of rolling depend on the same circumstances, and that whatever mitigates the movement in the one case, will do so to the same extent in the other. In both cases, the primary cause of a ship's oscillation, is the unequal action of the disturbed water on the lines of buoyancy or floata- tion. A ship running before a gale, as she rises over each wave, and pitches into the hollow of the next, is de- tained sufficiently long in each position, with her entrance and run deeply immersed, and her midships in a corres- ponding degree immersed, to cause her to incline or fall over to one side, or the other. When the wave reaches the midship sections, where the greatest buoyancy exists at the greatest distance from the axis of motion, the chief action of the water is suddenly changed from the ends to the body, and the vessel is violently righted, and car- ried in an opposite direction by the acquired momentum. If at this instant she has reached a similar position on the opposite slope of the wave, she will acquire an increase of angle. Should these conditions be continued for several successive waves, as I have witnessed, a ship may have her safety seriously imperilled. In such cases, a slight alteration of course, or an easing of the engines, even for half a minute, will check the evil. So very important is this question, it is to be hoped the government of some country will take it in hand, and cause a regular system to be adhered to in every public ship, with the view of collecting data, and determining the best means to obviate this unpleasant and dangerous characteristic in ships. I shall hereafter refer to the effect of the distribu- tion of weights on the rolling of ships (66). 40. An interesting and useful experiment may be made, at a very trifling cost, to show the varying action SCIENCE OF 8HIP-BUILDINO. 25 m of to in )U- be r»Ti of waves, on solid bodies at different degrees of immersion. Take, say throo small spars of the same diameters and of the respective lengths of 15, 20, and 25 feet. Attach bags or sand, or other weights to the lower ends of each, just sufficiently heavy to cause them to float vertically, leaving five feet of each above water. They will then remain immersed respectively 10, 15, and 20 feet. Then drop them into a rolling sea from a boat, or a ship stopped for the purpose, after the subsidence of the wind, and observe the effect. In a few minutes the spars will all be oscillating and swaying backwards and forwards with different periodicities. The experiment, however, will be deficient in not showing the effect of momentum possessed by ships. 41. The next quality belonging to water, and other fluids, to be noticed in connection with this subject, is friction. No accurate measurement of its power ot resis- tance to a ship has yet been made. Wlien a solid of any kind is immersed in water, a quantity of the particles attach themselves to every part, or as we say, it becomes wet. When the body is set in motion it is those particles which cohere to its surfaces that rub against the sur- rounding masses of particles, which press against the body with a force proportioned to the depth of immersion, and not the actual rubbing of those particles against the surfaces. 42. Frictional Resistance, according to the facts adduced, is at its minimum at the surface of the sea, and its maximun at the deepest parts of immersed bodies, moving parallel with the surface, and it increases in proportion to the pressure from above — that is, in an arithmetical ratio ; or the same, as my limited experi- 26 SCIENCE OF SHIP-BUILDINO. ments have led me to ascribe to the combined Resistances from all causes (13). But as the skin of a ship can only receive one half the pressure on each square foot, or inch, I think we can only estimate for one half. In other ■words, referring to the experiments suggested by means of the slip keel, the pressure on the two sides must be considered in the light of a single sum. But, whatever it may be, it demonstrates the great importance of the draught of a ship, when regarded in relation to this kind of resistance. It also demonstrates, the desirability of at once determining by experimental science, the respective degrees of friction, exerted on the surfaces of the various materials, used for forming the outer skins of ships. Those the least porous, or which absorb the least water, and which are susceptible of receiving the highest polish, will be found the best adopted to mitigate the effects of friction. If any of the enamels invented for this purpose, prove efficacious, and are capable of resisting the effects of sea water and barnacles, a great boon will be conferred on the world. 43. I have already suggested (19) a method for ascer- taining the laws of frictional resistance. The same appa- ratus will serve to test the best materials to be used for the outer skins of ships, in reference to the diminution of friction. 44. Some years ago I made an experiment worth re- cording. I was the owner of a small pleasure boat, or yacht, of less than three tons, and a severe contest having arisen between myself and the owner of another and considerably larger boat, in regard to speed, I resorted to the following fc^HJ^ftr.™^ [ flrr Vfr*----^'^'^'' ■*> SCIENCE OF SHIP-BUILDING. 27 \ re- M, sen bly ing expedient, No more sail could safely be added, so I took my boat out of the water, and after she was dry, gave her sevcrul coats of marine varnish, which resists fresh water, and made her skin as hard and smooth as enamel. The next time I encountered my rival, both of us were immensely surprised, that, witii precisely the same sail, I was able to beat him at all points of the wind. In a moderate breeze of six, or seven knots an hour, I found I had added at least a mile to the speed of my little boat, by this simple expedient. In a large steam-ship such an addition of speed — caused by the abatement of frictional resistance, would no doubt amount to two knots per hour, or an economization of 20 per cent, in coals. Mr. Smith, naval architect of Glasgow, has mentioned to me a case where a steamer having 500 tons displacement and 165 H.P., drawing 7J feet, had her speed improved 1^ miles per hour by coating her immersed surfaces with black lead. 45. To experiment on oblique surfaces and curved lines, would require differently-constructed implements. But it will be seen hereafter (54 and 55), that for the sake of acciu'acy and convenience, I purpose to treat such sur faces as opposing only the same frictional resistance as those moving parallel to the ship's keel, charging the difference to the account of head resistance. Neverthe- less, the ends of science would be promoted by making a large number of experiments to ascertain the value of ciu'ved lines, as auxiliaries to the power of the wedge. 46. Until the laws I have laboured to elucidate shall be correctly established by experimental science, ship- building must be regarded as deficient in some of the most important characteristics of a scientific pursuit. The 28 SCIENCE OF SHIP-BUILDING. admissions of the greatest authorities, as already observed, prove that we are still in the infancy of the art. Much of what we do know must be regarded, rather as the re- sults of happy guess work and accident, than of regular scientific investigation. At the present moment, the records of the Patent Office, and the drawings and models at the International Exhibition,* afford nothing but a vast mass of contradictory evidence and conflicting theories. Many of the most learned and scientific men are wasting their time and energies in trying to erect an edifice, by beginning at the top and working downwards, whilst others of the same class have commenced in the middle, and are working both ways, with no better chance of success. When we have begun at the bottom on a safe foundation, then may we hope to erect a perma- nent structure. 47. There is one other kind of resistance to be noticed. The two former, for convenience, I have termed POSITIVE, or head, and FRICTIONAL resistance. The one I now propose to consider is what I have de- signated NEGATIVE resistance. It is caused by the cohesive qualities of fluids, and requires a real and effec- tive force to overcome it. Its effect may be illustrated by the effort required to lift any floating body having a flat level surface underneath — such as a board, perpen- dicularly from the water, when a slight lateral movement will greatly mitigate the resistance. This resistance, I think, cannot be wholly due to atmospheric pressure ; because by retaining the board in a perfectly horizontal position, after it has been lifted from the surface of the * This treatise was written in October, 1882, whilst the Exhibitioa was still opeu. SCIENCE O' SHIP-BUILDING. 29 water, it will be found that quite a mass of water will continue to be suspended underneath, until by giving the board a slight tilt, it will run off in the direction of incli- nation. 48. If the assumption in favor of this kind of resis- tance can be sustained, and a distinction drawn between it and frictional resistance, it may in like manner be reduced to a law. Its bearing on the form of a ship will hereafter be pointed out (60). 49. Acting on the light of my own investigations, limited as they have been by the want of appliances, I shall venture to suggest a theory deduced therefrom, Taking the principles I have imperfectly laid down, as being well founded, we shall have something to guide us in the right direction. 50. The first question, then to be sol^red, is how little draught can be given a ship, without infringing other indispensable conditions and qualities ; and secondly, what form will most diminish the sum of resistance? The second proposition is no doubt largely involved in the answer to the first. The form that will give the least depth of immersion, it might be argued, would do most to mitigate resistance of every kind. But as there must be some depth of immersion, and a corresponding resist- ance, the questions must be considered as separate pro- positions. The question of form is indeed, a complex one, and involves many compromises of principle, if I may so term it, as well as of power. 51. To make this clear, we will next refer to the means, by which a ship is best enabled to perform the work she has to do. That work, as I have alreadv said, in the language of a high authority, is to excavate a ■ -TSf* -(I ^jw?tl^_-^*«^3^r' 30 SCIENCE OF SHIP-BUILDING. passage through the water equal in depth and breadth to her largest midship immersed cross section, and extending the whole length of her journey. To do this she is sup- plied with two kinds of powers — ^nrst the wedge or PASSIVE power ; and secondly, the steam engine or sails, which are the active powers. 52. The wedge being the only mechanical power applicable to ocean road making, the question to deter- mine is, what is the best shape or angle to give it ? In Mechanics, the law of the wedge is, that its power increases as its angle diminishes, or in proportion to the fineness of its taper. In applying the rule to the entrance of a ship, the extent to which it can be carried, must be deter- mined by other indispensable requisites, such as con- venience, strength, and breadth of beam, which gives light draught and stability. 53. By the adoption of the hollow water line, or as it is called in this country, the wave line, a happy combination of principles is effected. But it can only be regarded as coming in aid of the wedge, which after all is the real passive, or mechanical power. I may here mention that this form has been in almost universal favor, on the Western Lakes of America, for 30 years. Those, however, who have used it, have been ignorant of the reasons of its efficacy, in economizing power. An unfounded idea exists, that it derives its efficacy from a supposed re- semblance to certain kinds of waves. The simple fact is, it obtains its virtue from the convenience it affords in fining down the point of the wedge, or the commencement of the ship's entrance, to an almost minimum amount of frictional and head reti stance, thereby increasing its power. The entrance of a ship is thus enabled to cleave the water to the best advantage. SCIENCE OF SHIP-BUILDING. 31 The water is then deflected in a current in the direction of the increasing angle, until it reaches the widest part of the vessel, where the versed sine dies away in the straight lines ofleastfrictional resistance. To illustrate this, let Fig 1. — Plate III., represent the entrance and run of a ship having hollow water lines, and AA., particles of water towards which it is approaching, and BB., CO., DD., EE,, andGG., indicate several sections of the entrance, the exteriors of which are at the respective angles with the keel of, say, 2^, 5, 7J, 7J, and 5 and 2J degrees. When the ship reaches the particles AA., they will be deflected two and a half degrees from the line of her keel, until she advances to BB., (we are supposing the sections to be vertical and to have straight, instead of curved lines), when they will receive a further deflection of 2|- degrees, and at CO., still another deflection of 2 J degrees, when the entire deflection from the line of her keel will have reached 7 J degrees, at which they will remain, until the progress of the vessel brings them to EE., where the angle of deflection begins to diminish. It will then continue to diminish until it dies away in the straight lines of the ship's body, at which the frictional resistance is at its minimi' in. By this it will be seen, that the particles of water come in contact with each approaching section at the same angle. Or, if we suppose the ship to be at anchor in a stream, or current, the great fluidity of water, assisted, perhaps, by its elasticity, causes it to follow the curvilinear course, it is at first gently made to take, and which is gently continued, by the increasing angle of the curve or hollow line, to the ship's keel. But the wave line has its limit of efficacy, and I have seen it carried so far, on the Oana- r I'M I ^„_!.'- 32 SCIENCE OF SHIP-BUILDING. dian lakes, as to cause the water to break at the round- ing of the convex lines, at AA., Plate II. — Fig 3. 54. It will, I think, be obvious, in considering the increase of frictional resistance occasioned by oblique sur- faces — ^whatever that increase may be in comparison with that on surfaces moving through the water parallel to the ship's keel, that it can only be regarded in the light of head resistance, or that of displacement, of which it, in fact, forms a part. It cannot therefore be treated as a separate quantity to be added to the general sum of re- sistances, but is in reality a part of positive, or head resistance. 65. Instead, therefore, of experimenting to find out the increase of frictional resistance, caused by different angles of the wedge, or of oblique surfaces, we must as- certain their value as passive powers in mitigating the sum of resistances. In fact, what we have to do, is to deter- mine the unit of power of the simple wedge, by experi- mental science, to which must be added the value of curved lines, as far as that can be ascertiiined (53) ; that is, we must find how much a wedge of given angles miti- gates or diminishes the sum of resistances when it is driven through the water at a given velocity, and then by calculation determine what the value, or power of wedges of other, or greater, or less, angles will be at the same, or at different velocities. 56. Since then, wo are to regard the increase of Mction arising fi:om the oblique surfaces of a ship, as belonging to the sum chargeable to head resistance, we must treat the whole of the skin as offering only minimum ratios of friction, or, as if the whole immersed surfaces were moving in lines parallel with the ship's keel. SCIENCE OF SHIP-BUILDING. 33 67. But, it may be objected to this method of dealing with the question, that it will be troublesome, if not impracticable, on account of the infinite variety of forms and curves used by ship-builders. 58. Such an objection, however, can only be regarded as a begging of the whole question under discussion, since the very object is to establish, by experimental science, what is the best form for a ship, in order to adhere to it, when ascertained. Like the watchmaker, who knows the exact amount of friction to be overcome, and the scientific proportions to be observed between every part of the machinery of a watch, and is thus enabled to find the necessary power to keep the whole in motion at uniform velocities, the ship-builder must learn to deduce from ascertained laws, the proper length, breadth, depth, angles, and curves — that is, such a com- bination as most to mitigate resistance without detriment to other necessary qualities, and then determine the horse power required to produce a given speed. Mean- time, this very multiplicity of forms, brought up in objec- tion, must be taken as a proof of what I have already remarked (46) on the unsatisfactory state of the science of naval architecture.* * Since this work was written, I have visited a large number of the ship- building yards of the Thames, the Mersey, and the Clyde, and examined a great number of ships on the stocks and afloat, as well as the models and drawings of many of the eminent builders, and have come to the conclusion that little, or no advance has been made in the designs and forms of ships during the last ten years. In the construction of marine boilers and engines, some eco- nomization has probably been effected, as well as in the vapious processes of construction. In respect to the best form to overcome resistance, and miti- gate rolling and pitching, we are just where we wore ten years ago, when the performances of the Himalaya first excited public attention. n 34 SCIENCE OF SHIP-BUILDING. . 59. Having deduced from natural lay. s and principles, what is the best entrance for a ship, we will next proceed to the clearance, leaving the body to be dealt with last. Some builders have gone so far in their indifference about this part of their vessels, as to propagate a sort of axiom, ** take care of your ship's entrance, and the run will take care of itself," or in other words, '* find the best way to get the water out of the ship's track, and it will find its way back, without the aid of your skill." Such ideas are simply the result of ignorance of those laws I have been endeavouring to elucidate. 60. The clearance of a ship must be formed in refer- ence to laws to be established on the subject of negative resistance, (47 and 48) and to the duties it has to perform. The same reasons that favor the wedge and the hollow, or wave line form, for the entrance, apply with equal force to the ship's clearance. But what relieves the ship-builder from the necessity of fining down the clearance of his ship to the same degree as the entrance, is the effort which the displaced water makes to regain its equilibrium. Being elevated above the surface, it falls with greater force towards the ship's wake, than that rising from below. See Fig. 1, Plate II. A current is thus formed which detaches the cohering masses. Hence the hollow or curvilinear form of clearance acts in mitigation of negative resistance, whilst a convex form, such as that given to the Great Eastern, under a wrong notion as to the replacement of water, aggravates it.* Great lean- * A farther illustration of negative resistance is to be seen m the effect produced on the wake of a ship of a very full and convex run. Such a vessel, when sailing in a smooth sea, draws after her so much water, that a small boat will almost " tow '* without the aid of a line. Nevertheless, this form SCIENCE OF SHir-BUILDING. 35 nG33 of cloaranco Is a fault as much to bo guarded against as the reverse. By abridging the lines of flotation in this part of a ship too much, we throw a larger amount of weight on distant parts, whose st.tj.igth is taxed for its support. This is particularly the case with modern ** Screws," and all such formed vessels arc more liable to hog, than whero an opposite principle is kept in view. What is called a high run, it will thus be perceived, is not a desirable quality. A vessel with two sharp ends, resembling an Indian's bark canoe, may not be considered quite " Ship Shape," a term witliout any meaning, and which has led to the squandering of untold millions of money; but, never- theless, it is surprising how soon wc; accustom ourselves to new forms, and ultimately find beauty in adaptation. The present generation feels a sense of pride and superi- ority, in compearing our graceful modern built ships of war with the '' Seventy-fours" of a hundred years ago, when those vessels were regarded as models of perfection, as compared with a line-of-battle ship of the days of the Virgin Queen. An American thinks his lake, or river steamer, a marvel of elegance, whilst an ** old Salt" spurns it as a mere " floating hotel." Such a clearance, as I have described, is shown at Fig. 1 . — Plate III. HH., and also at Plate IV. A A. 61. We will next proceed to the *^ mid-ship" or inter- mediate portion, which has to support, not only the engines, fuel, and cargo, but frequently, from want of judgment in the builder, a large amount of unnecessary weight added vo the entrance and clearance. It requires no reasoning to prove that this part of the ship, the skin of run still predominates in sailing vessels, as every one who visits the Docks at Liverpool or London, will perceive. 36 SCIENCE OF 8HIP-BUILDIN0. of which moves parallel wth her keel, can encounter but one kind of resistance — namely, tliat arising from friction. 62. A certain length of body is necessary to obtain capacity for flotation and cargo. The question then arises, in what ratio must the horse-power be increased, for each additional foot rf midship, in order to maintain the same, or to obtain a higher speed ? Instances are cited, where a positive gain in speed has been efiected, by cutting a ship in two parts and adding to her body, without increasing the horse-power. The cases of the **Europa," *'Candia," and ** Alliance" are cited in proof of this observation. Where such results have followed, it affords evidence that the ship was originally too short in that part to maintain a proper proportion, or else she has, by the addition, been made to draw less water. After reaching the limit of speed, attainable with a given power, it is obvious, that in calculating for increased horse-power for additional length, we have, as already observed, to take cognizance only of frictional resist- ance at its minimum ratios. 63. It may be a waste of time to lay down a rule founded only on present information. I will, however, state that some American lake builders act on the hypo- thesis, that after a steamer has been modelled to the maximum length at midships, to attain a given speed with a given horse-power, the increased horse-power required to maintain the same speed, for any additional length put into her body, will only be in the proportion of one-fourth of that already estimated for. That is to say, if the horse-power was in the ratio of one horse to four tons, it need only be for the tonnage added to that SCIENCK OP SHIP- BUILDING. 87 part of the vessel having straight fore and aft lines, as 1 to IG. 04. To still further illustrate my meaning, we will suppose that a steamer of two thousand tons, actual burthen, can afford to carry a full cargo across the Atlantic at £ 1 per ton, by adding 2000 tons more to her body, she can do the whole work at a cost of 12s. 6d. per ton. In making tliis estimate, I have not considered the additional weight of the ship. Tliis exampie points out the importance, after we have gone to the expense of excavating a passage for a ship, of sending as much freight and as many passengers through it as possible. 65. We will next briefly consider the ship's beam and the shape of her bottom. And here it may be observed, that, as we proceed from one part to another, we shall discover, that each possesses an importance of its own. It is generally believed that broad vessels roll and pitch more than narrow ones. This impression, I think, is erroneous, particularly where they have a good lengtli of floor, and has arisen from a misconception of the causes of ships' rolling. I might cite the instances of nearly all the Ocean Screw-steamers as evidence of a contrary nature. These vessels are generally built narrow and deep, in order to give immersion to their screws, and they are the worst of rollers. Where a wide vessel has been found to roll badly, it must not be charged to her breadth of beam per se, but we must find the reason for this in another direction. The immersed portions of a ship occupy the exact position, and are subject to tlie same laws as the body of water displaced, and the whole ship and cargo weigh exactly as much as the water, whose place the immersed portions of her occupy. If, 38 SCIENCE OF SHIP-nUILDING. / therefore, we do not wish to produce a condition of things at variance with the laws of nature, which I have eo often referred to, we must endeavour to so model our vcs^^cls and adjust the weights of all kinds in them, as to make them confomi to those laws. 66. The question of rolling, beyond the simple yield- ing to the slope or angles of the waves, is so largely affected by the arrangement of the weights of the ship and cargo or armament, that I think I may safely say, if a vessel can be so built, and have her weights so dis- tributed, as to cause her to conform exactly to the slope of the waves, she will roll less and easier than under any other conditions. The average slojie of a wave 30 feet high and 600 wide — that is, 300 from the centre of the trough to the crest — is about 6 degrees ; whilst most vessels roll from 20 to 40 degrees — the '' Warrior" 39. Compare the angles of roll of a flat body, shown at Fig. 4. — Plate II., with those of the ship at Fig. 3. A ship loaded with iron, stowed on her lower floor, rolls too quickly and heavily, and often endangers the masts. If the centre of gravity of the weights fall at or above the surface, she will have too little stability, if below the centre of gravity of buoyancy, too much. Now, as a wide shallow ship naturally stows a larger pro- portion of her cargo nearer to licr lower floor than a deep narrow one, to say nothing of engines and coals, she is more likely to roll more and heavier. A wide vessel, therefore, having her weights distributed in reference to the centre of gravity of displacement or buoyancy, may be made to roll less than a narrow one. The builder should be able to inform the merchant how much of his cargo should be stowed above, and how much below SCIENCE OF SHIP-BUILDING. 39 a given line, according as liis vessel is partially or fully freighted. Regard must also bo had to the horizontal position of the weights, for after the due stability of the ship has been secured, the nearer each ton of weight can be made to conform horizontally to each ton of water displaced, the better. 67. In this case the quantity and weight of matter that must pass the centre of motion of the ship with each oscillation, will bo greater in a deep narrow ship than in a wide one, proving exactly the converse of the popular prejudice on this subject. This will appear by reference to Figs. 3 and 4., Plate III, which represent midship cross sections of ships having the same displacement. B. and B. are the respective centres of displacement and motion ; AA. and CC. respectively represent equal angles, formed by the lines of the ship's inclination, with the line of gravitation when at rest ; and DDDD. are the respective water lines. If we require any further evidence of the fallacy about broad vessels rolling more than narrow ones, we have only to press the argumentum ad absurdmn. Will a plank float steadier on its edge than on its broad side ? 68. Breadth of beam, therefore, at and below the water line, gives stability, due regard being paid to " trim." It follows, that the more wo can widen a ship's base, the greater will be her stability, and she will also draw less water, and encounter le^s resistance in her passage through it, and from wave motion. But breadth of beam, like length, has its limits, which must be determined by the exercise of sound discretion. On this subject I shall have a few words more to sav, when alludingi ^to ships of war. L I i J J 1 " /.» J 40 SCIENCE OF SHIP-BUILDING. 69. In speaking of rolling, the forms of ships' bottoms were incidently discussed (39), so that little is left to be said here. I remarked that the form of the paral- lelogram -with the lower comers slightly rounded, and the lines next the keel curved downwards, in conformity with the doctrine of the hollow or wave line, which gently deflects the water, was the best to meet the peculiar action of wave motion, and to avert rolling. See Fig. 6. — Plate III. ; also the cross sections in Plate IV. Colonel Beaufoy's surface-experiments led him to the conclusion that a triangular-shaped body, moving in the direction of its largest axis, met with less resistance than any other form. This was a wrong conclusion, as will appear evident by reference to Fig. 5. — Plate III., where AAA. is an equilateral-triangle and BB. a parallelogram of exactly equal superficies, and of course having the same exterior dimensions exposed to frictional as well as head resistance. But the difference is in favor of the parallelogram, because all its parts will float nearer the surface, or place of least resistance in fluids. 70. It may be objected that such a form as I have laid down for the cross sections of a ship in the body, or part of greatest buoyancy, will not do for a sailing vessel. I reply that it is the best possible forni for a sailing vessel, due regard being paid to the adjustment of weights, and the centre board, or sliding keel, being substituted for the standing keel. The hollow lines near the centrnl part of the ship's bottom or bilge, will assist in giving efficacy to the centre board, or to a standing keel, should that, in compliance with ancient tradition, be preferred ; and will help to keep the ship up to the wind, and prevent lee way. Yachtmen often designate fast SCIENCE OF SHIP-BUILDING. il sailers having long, flat floors, "sailing machines," in contempt of a class of vessels they find difficult to beat, or rather which often beat those costly sea toys — modem yachts. 71. Vessels with centre boards, and level or nearly level floors, are better sailers in every wind than those having standing keels and triangular bilges. When- ever the wind is abaft the beam, the centre board can be wound up with the windlass or winch, and a material gain is experienced as regards friction. During the last six years, a large number of this description of sailing vessels have crossed the Atlantic, with cargoes, and have very generally beaten the ocean built ships (though the latter were twice, or thrice their size) by several days. Necessity, '' the mother of invention," obliged the Canadians and Western Americans to build broad shallow vessels, with centre boards, so as to navigate their rivers and canals, and now they find them the best on the sea. The form given at Fig. III. — Plate III. is that almost universally adopted on the great lakes of America for sailing vessels. It wants the curves in the bilge to adapt it to ocean navigation. 72. In considering the comparative merits of broad shallow, and deep narrow vessels, we should endeavour to arrive at the average effect of all the forces on the im- mersed portions. To accomplish this, it becomes neces- sary to ascertain approximately the form which will repre- sent an average of all the cross sections. It must also be borne in mind, that in order to maintain the same fine- ness of lines in the entrance and run, the same proportions of length and breadth must be preserved. Where these proportions are all carefully adhered to, it is obvious that 42 SCIENCE OF SHIP-BUILDING. the forces acting on the several portions of the respective vessels will bo equal and subject to the same laws. 73. To make myself more clearly understood, I beg to refer the reader to Plate I., showing in comparison with a midship cross section drawing of a ship marked ** form of least resistance," those of several noted vessels. Th© dotted Ihies may be assumed to be approximations to the average forms of some of these ships. The other dimen- sions of my ship will be seen hereafter (77). But as all these ships — and more particularly the " Great Eastern," draw more water than tiie one suggested by me, and have so much more pared off the outer angles of their bilges, the average form of their cross sections will doubtless give sharper angles than those represented by the dotted lines. 74. If the cross sectional lines in the body of a ship ap- proach a right-angled triangle, as they often do in yachts, and then run rapidly into the vertical, as they recede towards the two ends, it will be seen that the average e£fect will be something near that of an equilateral triangle. See Figs. 6 and 7. — Plate III., for an illustration. By carrying the level floor well fore and aft we not only obtain increased displacement, but we are able to preserve a better form for the support of all the weights. I might leave the subject here for more practical men to elaborate, but I feel that it would be incomplete, and that some things I have said may be mis-interpreted, unless I describe my own view of the best class of vessels to meet the demands of the laws of nature. 75. The size of a ship has much to do with economical working. But this must be made to conform to the par- ticular trade for which she is intended. On long routes, fiitid between great' centres .oi commerce^ perhapa the "-~'-\'-!-- -.-r-itt-'. SCIKNCK or HI I IP-BUILDING. 4:J only limits imposed are those dictated by convenience of management and strength. On the American route, stramcrs of six or eight thousand tons, exclusive of engines and coals, may not bo found too large ; and will, if built to float on the surface, instead of being deeply immersed, prove tlie most economicid. 70. The only dift'erenco required to be observed between the form Jind construction of steamers intended for passengers and light freight, which require high speed, and those intended wholly or principally for freight, for which only moderate speed is recjuired, is in the power of their respective engines. To insure safety, the hulls of both kinds must be equally strong. The shapes of t]i< -nmersed portions, being designed on scientific prin f <'>, deduced from ascertained laws, cannot bo varied to suit different rates of speed without a violation of those laws. Mr. Russell, who has contributed so much to the growing science of naval architecture, has, in this particular, fallen into an error. He says, 'Hhere is a form for every speed ;" that is, a vessel intended to have a speed of ten knots must be made of a different form to one intended to go twelve. This would be to keep the question of form just where it is — an open question, incapable of bjiug brought to a scientific solution. I reverse his axiom, and find there is a speed for every form. That is, the best form, with equal power and tonnage, will have the greatest speed. I think it must be admitted that the form offering least resistance — ^wliich is the essence of economy, at high speed, will likewise oppose least resistance at low speed. 77. For tlie Anierican trade, which every year in- creases, I think steamers, 500 feet long, sixty or seventy ■/'\ 44 SCIENCE OF SHIP-BUILDING. feet wide, and drawing from 10 to 15 feet, according as they are intended for passengers or freight, and from 20 to 30 feet deep, will lo found the bcit. I'heir capacity would range from 5000 to 8000 tons. The drawings of such a steamer are given at Plate IV. Fig. 1. shows the deck, load and bilge lines. Fig 2. is a side view of a steamer 25 feet deep, drawing 15 feet, with a cargo, and coals for a voyage on board. Fig. 3 is a ver- tical longitudinal section, showing the ''backbone" or mode by which I propose to obtain the necessary strength, and which will, at the same time, act as a counterpoise to the weight of the ship's sides, and thu3 cause her to conform to the centres of gravity of displacement. In using the term " centres of gravity," I am supposing the ship to be divided into a number of cross sections, to each of which the expression is intended to apply (65, QG, and 67). Figs. 4, 5, and 6, are midship transverse sections, of three classes of merchant steamers, referred to hereafter (89). The longitudinal drawings represent a ship whose entrance is 200 feet, or four-tenths of her whole length — her clearance and body being each 150 feet long, or three- tenths of her length each, at the load water line. By body, I mean that part having straight fore aiid aft lines, which oppose only frictional resistance. 78. This backbone may either be made of truss work, or of plates secured in the sarnie manner as those used in the outer skin. In large ships the latter would be pre- ferable — ^thus dividing the ship vertically from stem to stem, or so far as may be requisite to obtain the neces- sary strength, into two water-tight compartments, from the keel to the main deck. If by reason of shallowness in the hold, additional strength is required, it can be , ,^- f ^~, SCIENCE OF SHIP-BUILDING. 45 obtair^ed by springing an arch above the deck, in the manner showi) in the drawings referred to. 79. By this method, the ship's keel will become the basis of strength for the whole structure, both longitu- dinally and transversely, instead of looking to the outer walls, as is now done, for the main support. 80. If we now divide the ship into four or five water tight cross sectional compartments, we shall have a com- bination of qualities never yet attained. The speed, strength, safety and comfort of such a ship, though only a fourth the size of the Great Eastern, will far surpass those of any now on the ocean, and it will probably not cost so much to build as ships of the '* Persia'' and '' Scotia" class. 81. In designing so large a vessel, the architect should not overlook the importance of providing steam machi- nery for loading and unloading. This I have found from observation, has not been properly regarded in the " Great Eastern." No ship of any magnitude should carry grain in sacks, as I have remarked to be the case with the great ship — a method requiring from four to six times the time and expense in the handling, as when it is carried in bulk, and loaded and unloaded by steam power. 82. By adopting the backbone principle, no class of ships will gain so much as armour-plated vessels of war. In order to prevent that violent and heavy rolling ascribed to the •''Warrior " — a characteristic that will be found to be common to all of the same class and build, there must be some means adopted to adjust the weights of the ship and armament more equalbly, so as to make them conform to the laws of nature bearing thereon (67). Here W8 have the best means, as I conceive, yet devised, because 46 SCIENCE OF SHIP -BUILDING. < m i I? we are at the same time enabled to add immensely to the ship's strength. I will venture to assort that the appli- cation of bilge ''boards" or keels, as in the case of the ''Warrior," "Resistance," "Minotaur," "Agincom-t," and other ship.^, if any appreciable eifect has been produced by them, it has only been to cause the ships to roll quicker and more violently, by interposing at a leverage distance from the keel serious obstructions to the passage of wave undula- tions, and the rising and falling of the columns or masses of water, which constantly act in opposite directions on the two sides of the ship. The use of the centre board in sail- ing vessels is only the toleration of a necessary evil ; that is, we are compelled to violate a law of nature to prevent the occurrence of a greater evil — namely, leeway. In steamships, no sucL reason can be pleaded in extenuation of either class of keels. By the adoption of the backbone principle, which is a proposal neither more nor less, than to construct a vast iron girder on the line of the keel, we shall also avert that enormous strain which, according to newspaper reports, caused the '- Warrior" on her first voy- age to Lisbon to "leak at every butt." Besides, it will afford, in conjunction with proper timber mortar-beds, an immovable basis for towers (as shown in the draw- ings), capable of carrying and sustaining the recoil of heavier artillery than have yet been forged, and ol the largest mortars. See Plate V. 83. Wlien I commenced this treatise, it was my intention to have avoided, altogether the discussion of questions connected with the peculiarities and details of ships of war. The importance of high speed in such vessels, however, is so momentous, that the question cannot be lightly passed over in any v/ork intended to SCIENCE OF SHIP-BUILDING. 47 point out the indispensable requisites to its attainment. As light draught is one of those requisites, I have ven- tured to suggest how the necessary strength may be obtained by the application of the back bone, or central girder principle. But light draught acts i reduction of the efficacy of the screw, as a propelling apparatus, in two ways. 1st. It limits the diameter of the screw; and, 2nd, it raises it nearer the surface, where the fulcrum against which it acts, or from which it acquires its power, is diminished, and is also more liable to be thrown out of the water by the rolling and pitching of a long and wide ship. 84. There is, however, one advantage gained which must be set off against the drawbacks referred to. The Motion on the screw blades, which must be very great, is mitigated. But light draught for the ship is a gain which far outweighs the loss of power of the screw from the causes assigned (11). I submit for con- sideration the practicability of applying two or more screws to ships of war, as well as to merchant steamers, where high speed is sought.* * Nearly a month after this little work had been nompleted, namely, on the 8th of November, the Times gave an account of the complete success which had attended the double Screw Steamer " Flora." The " Flora" is 22JLfeet wide. 160 feet long, and 15| deep, and has two screws of 7 feet diameter each, placed under her quarters. Her speed, on her trial trip, was 14-16 knots per hour, with a nominal power of 120 horses. Her tonnage is 400. Several experiments of this kind we^'e tried many years ago, on smaller vessels on the lakes of Canada, but as screws are chiefly used on these lakes for the carriage of freight, where high speed is not sought, the practice has not been followed up. Vide note to Paragraph 11. The delay that has taken place in the publication of this paper enables me to quote a further instance of the complete success of the application of two screws. The '* Kate," built by the same firm, Messrs. Dudgeon, Brothers, 48 SCTENCE OF SHIP-BUILDING. 85. By the adoption of two or more screws, masts, sails, and sailors may all be dispensed with. These accessories to a ship of war are her greatest drawbacks, when regarded in the light of an engine of war. If we can perform the work at present exacted partly fi-om steam and partly from sails, wholly by the former, we shall do it with more mierring certainty, and vastly greater effect. When the age of iron and steam shall have fully arrived — the "jolly tars" and '^ wooden walls" will have passed away together, and the nation will save some millions annually thereby. We shall only want steersmen, navigators, and stokers to work our ships, and gunners and marines to fight them. In order to get rid of pre-conceived ideas about the forms and requisites of ships of war, which hang like a nightmare on the progress of national ship-building, it is absolutely necessary that we should simply regard them " as engines of war," adapted to the indispensable re- quirements of navigation and rapidity of movement. ^Q. I have ventured to make some drawings sugges- tive of steam *^ rams," armour plated, carrying broadsides. of Liraehouse, performed her trial trip on Saturday, the 28th February, and the Times, of the following Monday, says : — '* The trial trip proved to be a great success, for by the working of the two screws, one each side of the dead wood, a perfect steering power was obtained, with the ship going either ahead or astern, without any assistance from the use of the rudder ; and by reversing the screws — that is, working them in opposite directions— the ' Ka'vP' turned round upon her centre as upon a pivot, after the manner of a luj e. She was also very fast under steam, with engines only a little Tior> .?.n one-fourth horse-power to tonnage — great capacity of hold, and i ^^- ;i ji'.t of water." The " Kate" is an iron vessel of 500 tons capacity of hold, is 165 long, 22| beam, 131 deep, and drew on trial 7 feet 2 inches ; is flat in the floor, and without keel : speed not given. SCIENCE OF SHIP-BUILDING. 49 and having turrets, as recommended by Captain Coles, and now so extensively used in America. The object aimed at being light immersion, great strength and high speed combined, I propose the use of four screws. Fig 1. — Plate V. shows the deck, water and bilge lines of such a vessel, intended to go in either direction. Figs. 1 and 4, at a scale of 50 feet to the inch, represent a ship 500 feet long, 70 feet wide, and 35 feet deep. Without wishing to enter into details, I have shown the manner in which the screws may be worked and the vessel steered. In so large and costly a ship, there may be two steering apparatuses (one at each end), to guard against the risk of accident. With four screws, however, a ship might be worked almost without a rudder. (See note to paragraph 84). At scales of 40 and 30 feet to an inch, these drawings (1 and 4) will represent vessels of the respective lengths of 400 and 300 feet, and 66 and 42 feet beam each. Thus, after the suggestion of Mr. Scott Russell, I propose to have three classes of war ships, which may be used as rams with turrets, or to carry broadside, or both combined. 87. Figs. 2 snd 3. — Plate V. exhibit midship cross sections of first and second classes, showing their relative sizes, and also how beds of timber may be used to miti- gate the recoil of very heavy mortars and guns. It must not be inferred from the illustration, that I propose, except in extreme cases, such as the use of the 36-inch mortars at Woolwich, to fill the entire midship cross-section with baulks as suggested. The planning of details for the construction and work- ing the turrets are not within the scope of this paper. Fig. 4 shows a side elevation of such a ship, having both £ I 50 SCIENCE OF SHIP-BUILDING. ; broadsides and turrets. AAAA. are gun turrets, and BB. mortar turrets. CC. are wheel houses, and DD. are lifting rudders, nearly counterbalanced by weights, so as to be easily raised into chambers, when not in use. These chambers may be so constructed, that in case of accident the rudders may be unshipped and replaced by spare ones. This, however, may be regarded as an unnecessary precaution, as their position and mode of arrangement place them almost beyond the risk of acci- dent of any kind, whilst the vessel liaving them may, by a well directed blow or shot from a heavy gun, disable an enemies' rudder. A ship built on the pi an I have sug- gested, even if she drew 20 feet, could float with her rudder down, wherever the " Warrior" can float ; and if perchance she got into shoal water and her rudder touched, it would readily rise into its chamber^ without injury. In such cases the vessel must be steered by her screws, which would also be available in ascending rivers or turning in emergency. The two rudders acting in aid of the four screws would give the most complete and ample control over the vessel in action, that can possibly be desired.* Another important advantage is claimed for this kind of rudder. By being placed below the ship's keel near the end, the blade of the rudder will always be acted on uniformly by the water, which must be admitted to be a very great desideratum. Fig. 5 is merely sugges- tive of some details, and has been supplied by a practical friend who approves of my plans. • The reporter of the Times in giving a description of the performances of the " Kate," on the 28th of February, 1863, speaking of the importance of applying two screws, says, " In fact, the whole question has such an important bearing, look at it in what light we may, whether as a power of steering ships of commerce nnder steam, when threading tortuous rivers, or ships of SCIENCE OF SHIP-BUILDING. fit 88. The question as to the best mode ot applying four screws — whether so as to drive them by separate and unconnected engines, or by long shafts made to connect and disconnect at pleasure in midships, is one on which I cannot offer an opinion. In ships of great length and breadth, the rolling may so diminish the dip of the screw as to render a connection of the shafts on each side de- sirable, in order that when one screw is rolled or pitched partially out, the other may receive the power of both engines. The conditions of such a vessel, as I suggest, may be summed up ap, follows : — 1. — A displacement of 10,500 tons to be disposed of as under : — Weight of Hull - - - Ditto of Engines, &c. - Armour Plating, &c. Armament, Stores, &c. - Coals Total 10,500 Tons. 2. — ^Ability to carry thirty 100 pounder guns in broad side, and six 500 pounders, or four such, and two large mortars in turrets. 3,500 Tons. 1,300 >> 1,350 J) 1,350 >j 3,000 j> war when engaged ^\ ith the enemies' ships or forts, that the great interest that has been displayed by the Admiralty and many naval and scientific men., in the trials of the two vessels, the 'Flora,' in November last, and the * Kate,' on Saturday, is fully accounted for." The drawings, exhibiting the details and mode of working lifting rudders, having received the warm approval of two experienced and practical Naval Architects — the one an English, and the other a French gentleman, have been made the subject of an application for a patent. Hence they are not here given. The principle is not claimed as new, but the mode of applying it, so as to afford the utmost degree of efficiency and command over the vessel. 62 SCIENCE OF SHIP-BUILDING. 3. — Tho power to more with equal facility and speed either end foremost. 4. — A draught of water (with full armament and stores for a year's ordinary requirements, and 3000 tons of coals, at commencement of voyage) not to exceed eighteen feet. 5. — 18 Nantical miles per hour under full steam, or 432 per day, on a consumption of 200 tons of coals giving a supply for 15 days, and a run of 6450 knots. With two screws working at full power, she would make 15 knots per hour, 360 per day, consuming 100 tons of coals, and giving a run of 1 0,800 knots in 30 days. Under half steam , with two screws, her speed may he set down at 12 J knots per hour, 300 per day, with 75 tons consumption of coals — to last 40 days, and giving a run of 12,000 knots. One screw* at full speed, consuming 50 tons of coals per day, would give about lOJ knots per hour, (the ''Great Eastern" drawing 27 feet, made 11 J knots with her screw alone), 250 per day, and coals for a run of 15,000 miles in 60 days, and under easy steam something more. These estimates are founded on the experience of Lake steamers of light draught, such as the '' City of Buffalo." 6. — Ability, with 1000 tons of coals to ascend rivers and hold towns in subjection wherever the draught of water is 17 feet. 89. The following table exhibits the relative dimen- sions, power, estimated speed and economy of tlu-ee classes of merchant steamers, to which is added some particulars of the " City of Buffalo," American Lake vessel. • The " Kate" and ** Flora" steered as 'well with oue screw in motion as with two. SCIENCE OF SHIP-BUILDINQ. 53 (Foet) ut. 1 and. 400 8rd. OUT of 3alfUo. Length 500 800 340 Breadth \ »» / 70 56 42 40 Depth to bottom of keel \ ** ) 30 25 20 16 Load draught V »» / m 15 12i 10 Ditto to underside flat floor V »» ) 15 13 11 16 Engine power (Nominal Horse) 1250 1000 650 500 Speed (estimated) (Knots) m lOJ 14i 19 Displacement ( . ) 10500 6100 2650 Weight of Hull, &c. (Tons) 3600 2750 1200 Ditto Engines, Boilers, &c. ( » ) 1150 850 600 Freight capacity ( . ) 5000 2000 500 1000 Coals per voyage, Liverpool to Quebec (2500 m.) ( » ) 750 500 3f' 250 Time (estimated) (Days) 6 7 8 H Coals per ton of freight (Lbs.) 336 555 1600 560 as It will thus be seen that 10 third class ships would be requii'ed to carry as much cargo as 1 first class, and 4 to carry as much as a second class. The " City of Buffalo" would not compare so favourably, either in speed, or economy, if made strong enough for an ocean steamer. 90. Before concluding, I wish to - >iT 3r some remarks suggested by reading Mr. Andrew Murray^s recent and valuable work on ship-building. At page 54, Mr. Murray sums up the preliminary knowledge which a naval architect ought to possess, as follows: ''Before a naval architect lays down the lines of a vessel, he is aware of the purposes for which she is intended. He knows the armament, cargo, &c., which it is intended she shall carry. These being known as well as her weight at launching, since the specific gravity of the materials of 54 SCIENCE OF SHIP-BUILDINO. which she is composed is known, the first requirement is to make the total weight and corresponding displacement, when ready for sea, agree with the required draught of water. " We know that the displacement depends on the product of the three dimensions, length, breadth, and depth. The naval architect therefore proceeds to form a rough design, probably in comparison with some well known ship of the same class, and he will then proceed to adopt this design, as far as practicable to his own calculations, at least as far as necessary."* 91. These suggestions, coming from a scientific architect, in the service of the Admiralty, and the author of a standard work on ship-building, in my judgment, show conclusively the necessity of another step being taken towards the establishment of scientific data, from •\;7hich to deduce more certain and fixed principles respecting the designs of ships. Being thus armed, the naval architect should be able to calculate, from re- cognized rules, the best form and proportions of a ship of * This method of designing a ship is according to the " rule of thumb," on which the Rev. J. V/ooliey, in his able paper on " the present state of the Mathematical Theory of Naval Architecture," read before the Ins. N. A., 1860, remarks as follows : — ** Construction by the rule of thumb means, I apprehend, the adoption of some approved lines, with little or no luodification. Those designers who resort to this mode are pretty safe, and may generally calculate on producing a good vessel ; but they make no step in advance of existing practice^ they add nothing to existing science ; and whenever the majority of designers are of this class, and persist in all their ships in perpetuating some received model, refusing to accept improvements, because unable to judge of their real merits, the practice of ship>'huilding mmt on the whole be stationary, and the country, where this stale of things exists, must be content to see her ships surpassed by those of another country. ' SCIENCE OF SHIP-BUILDING. 55 on I a given tonnage, without reference to any other ship. The best form, according to my theory, is that which opposes the least resistance, and consequently requires the least power and least expense to propel, and which also rolls the least, and this form I have endeavoured to deduce from the laws of nature, so far as they relate to the questions connected with ships. Mr. Murray, however, proposes to deduce the forms of his ships some how or other, from " a rough design made in comparison with some other well known ship," &c. 92. Again, at page bQ^ Mr. Murray states that " the actual, or absolute resistance per square foot of surface, or of midship section, remains undetermined on account of our ever varying forms, given to the bodies of ships, be- fore and abaft the midship section." Nevertheless the rule to estimate for horse-power is based on this uncertain and unsatisfactory knowledge (2 1 ). See also my remarks at 52. 93. At page 58, Mr. Murray further remarks : " It has before been shown that calculations founded on the angles of incidence at the bows of a ship, to determine the exact resistance, do not correspond with the rosults obtained by experimental researches, or with practice." How could this be otherwise, when such experiments have been made either in ignorance, or disregard of the most important laws of nature relating to this subject ? Not even an allusion has any "where, that I can discover, been made to the rapid increase in resistance of all kinds opposed to bodies (moving horizontally) at each foot — aye, each inch we descend below the surface. Perhaps I have over-rated this ; but even if I have, its importance •rarill V»o fmiTi^l ir% V»ft VArv rrrpn+.. 94. "Attempts are still being made" says Mr. Murray, 56 SCIENCE. OF SHIP-BUILDING. 'S' ■ " to determine the exiict resistance to ships of different forms, moving at different velocities, and valuable addi- tions to our knowledge in this respect may be looked for. But the subject is one beset with difficulties." These difficulties, Mr. Murray goes on to specify, as being the state, or qualities of the immersed surfaces, inasmuch as a vessel has been known to have her speed decreased 20 per cent, by foulness of bottom — and besides this, there will be imperceptible variations in form. 95. Mr. Mnjray speaks of a narrow ship as having an easier roll than a wide one — without noticing the question of centres of gravity and adjustment of weights, on which the question of rolling mainly hinges (67 and 82). 96. I have been led into making these observations on Mr. Mm-ray's valuable work, or rather on his sugges- tions to Naval Architects, as to the best means of obtaining a starting point for their designs, because they . embody the latest, and hence it may be presumed, most approved ideas on the subject. Mr. Scott Russell, aUliough leading the van in the revolution that is taking place in Ocean Steam Navigation, as well as others of great eminence in scientific investigation, has made similar suggestions. 97. The present method of relying wholly on data, obtained from the results of numerous steam ships, may lead to improvements in the models and construction of future ships, hut it can never establish a new system based on scientific principles. To do that, we must find out the laws which bear on the qiu^stion, irrespective of any particular vessel already in existence. We may then avail ourselves of such acquiied data for purposes of I'easoning and comparison. SCIENCE OP SHIP-BUILDING. 57 5> 98. In my judgment, it remains for the governments of the great maritime nations to initiate the necessary experiments to build up a new and truly scientific School of Naval Architecture.* The saving that will thus be effected will be immense. The economization in inter- national and other maritime commerce will lead to results as important as those produced on inland traffic by the general introduction of railways. In other words, what railways have done on the land, the more rapid and cheap navigation that will ensue from the new and improved system of ship-building and propulsion, will accomplish on the tracklefej paths of ocean. * Since the nomination of Mr. E. J. Reed to the Chief Constructorship of the Navy, it has been stated that the Admiralty, on his recommendation, have decided to constitute such a board of reference and examination, to relieve themselves of the labour of deciding on the numerous applications made by inventors and others having plans to submit. A board of this sort, properly constituted, and having for its object, in connection with its other duties, the conducting of a series of experiments to ascertain the laws of nature, as they bear on the science of ship-bnilding, would, no doubt, prove of the utmost advantage in every way. It is submitted that the better plan will be, to have this Board attached to the Patent Office, and charged with the duty of examining all applications for patents — giving the power to i*eject such as are not novel, or may be merely fanciful and useless. The Board should be clothed with all the necessary powers of a Judicial Tribunal in respect to taking evidence, &c. From this " Inventor's Court" an appeal might be granted to the higher Tribunals of the country, where parties feel agrieved. In a Bill prepared by the writer for the Canadian Government — and which he hopes soon to see substituted for the present wretched patent law of the Province — he has provided the machinery for a Tribunal of this kind. The advantage of having the Board of Referees and examiners attached to the Patent office, will be that applications to other Government departmenis, for the adoption of new patented, or unpatented invent'ons, may, in like manner be referred and reported on to the proper authorities. :j. ADDENDUM. E'B!! The sheets containing my observations on Ocean "Waves, the Rolling of Ships, &c., had gone through the press before I received the third volume of the transactions of the Institution of Naval Architects, containing some learned papers on these subjects. I do not, however, see that they add much of practical value to the previous stock of information. Still more recently I have had the pleasure of attending the meetings of that Institution, at its session for the current year. At one of these, Mr. Scott Russell delivered a very able discourse on the Wave and Rolling questions. At the opening of his address, he alluded to the observations formerly made by Dr. "WooUey, which I have quoted in the preface, respecting the want of accurate knowledge of the laws of nature, and congratulated the association on the progress since maae in their discovery. It would be presumption in me to gainsay the correct- ness of this assumption. Indeed, the theory respecting wave motion, to which Mr. Russell has given his adhesion, is so beautiful, and explains so much that required explanation, that I hope future experiments may fully establish its correctness. But the subject is so deen and complicated, that I shall not attempt to offer any obser- r.vj;.,.' y>:jr~'-'r'^X'"i^'' SCIENCE OF SHIP -BUILDING. 59 vations on Mr. Russell's views, until his paper shall appear in print, which I hope may be at an earlier period than that to which the publication of the transactions of the Institution are usually deferred. I will, however, venture to express the opinion, that before these questions engage any further mathematical elaboration, the suggestions I have made, and which it has been my chief object in publishing this paper to make known, should be acted on. It is, I think, unde- niable, that the basis for all reasoning on these subjects, must be sought in the laws of nature ; and these can only be ascertained by numerous and well-conducted experi- ments. On this point, I take the liberty of again quoting from Dr. Woolley's admirable paper before referred to. He says, ^' The mathematical expression, for the time of rolling, affords very little clue to the behaviour of a vessel. Ships in which this element is nearly, if not quite, the same, according to calculation, are as wide as the poles asunder in their actual performance at sea ; so that while one, in a heavy sea, rolls with considerable ease, another is so uneasy, as seriously to endanger her masts. One cause of this may be, as has already been observed, that, in order to bring the case within the grasp of mathematical analysis, so many assumptions and limitations are necessarily introduced, as to ignore the form of the vessel, except just above the water line." Now, in view of such an important admission from a great mathematician, and seeing also (liat Mr. Scott Russell and Mr. Froude, two others equally great in scientific lore, " differ as widely from each other" — to use X. T» yj\jx±\s Vow vivio do i/iic UO XV o\^v/xxiK3 \j\j xxic;, i/iiau before wasting more time in these learned discussions, it 60 SCIENCE OF SHIP -BUILDING. i;, f- r will be wise tn fird, in the discovery of the laws of nature, a starting p^ji'x, that shall enable all scientific men to arrive at a coniiiion solution of every problem connected with the motion and resistance to ships. I was rather surprised to hear Mr. Froude state his experience of the rolling of the " Great Ejisterr," w'thout noticingthe direction of the ship inrelatioi? tothe movement of the waves which caused it. He said that t\\e worst rolling fit she liiid during his voyage in her to Quebec, was in a comparatively smooth sea — a circumstance ({uitein accord with my <>\tm experience In the same ship. lii iiiy case, I remarked tliafc we v/ere running, as nearly as possible, in the direction of iiiy wa^xs, and the cause of this seemingly unriauiral .s\ate of things I have endeavoured to expiiiin at pages 23 and 24, On one of these occasions, I went down to the wheel-platform, the better to observe the height of the waves, and their action on the vessel. riie undulations, which were unrippled, for we had no wind at the time, and which vere scarcely noticeable from 'he high decks of the '' Great Eastern," I estimated to be fully eight feet high, from hollow to crest. I now leave it to Mr. Froude, and the other learned writers on the subject, to sr^y whether I have given a satisfactory solution of this phenouienon, so often noticed by ocean travellers, as well as of the best mode to check the accumulating roll. Had the ship been steaming longi- tudinally with the waves, or, indeed, in almost any other direction than the one she happened for t^- lime to hold in reference to them, or had she bee > oing faster, or slower, the nchronism which p od ed the In making these observations, I must pleao' i;^i arance ^^Jn SCIENCE OF SHIP-BUILDING. 61 arance of the mathematical processes adopted by Mr. Froude to establish the amount of stability of ships. Much of his reasoning is locked up in a language which I once imperfectly understood, but which has, for want of practice, become Hebrew to me. But I think their value muse be much lessened when we hear Mr. Scott Russell, equally learned, taking direct issue with his brother mtihematician on the most prominent points of the subjects under consideration. Another more practical member of the association, no doubt, remarked, that it had always been found when theory and practice dif- fered, the latter was right. Of course, this must be the case if the theory be merely hypothetical, or good guess work. But practical men ought not to despise science, or sneer at scientific experiments; nor should scientific men lay themselves open to the censure of practical men, by offering theories deduced from uncertain premises, which are always liable to be impugned, or overthrown. I offer no opinion on the controversy between Captain Coles and Mr. Reed, about the comparative merits of their respective plans for fighting heavy guns in cupolas or in concentrated broadside batteries; but will simply express it as my belief, that Mr. Reed's ships building at Deptford, will be deficient in the necessary speed to make them formidable opponents. Before two years pass away, there will be many ships in foreign navies, whose speed will come up to my estimates. But I entirely concur i^ Mr. Kus >eiFs opinion that both Mr. Reed's and Captr. a Cole's plans are worthy of trial, and will produce vessels of great value for particular services, where high speed, lonsr vovaares, or heavv armaments are not re- quired. My principles relate mainly to the conditions 6^ SOJENCE OF SHIP-BUILDING. ^ necessary to obtain these latter indispensible requisites as well as economy, and are applicable to every class of steam vessels — without reference to the method of armament, or manner of fighting it. High speed and ecomomy are the first and most important objects to be attained. This was fiiUy conceded by the Naval Architects at their late meeting, and the damage done by the Alabama, against which a whole fleet of war vessels had been sent without being able to capture or destroy her, was cited in proof of it. With regard to the proper position for the centre of gravity of a ship and her weights, the general opinion seemed to favour the assumption that it should be in or near the water line, though no definite reasons, or data were given for it. In the '< Warrior " it was stated to be two feet below the water line ; but as she rolls unusually heavy angles, in consequence of the momentum im- parted by the great weight of her armour plating acting at a leverage distance from the centre of motion, no useful conclusion can be drawn fi-om such data. The question must therefore still be regarded as an open one, to be ascertained by future experiments. In my jutig- ment, much will be found to depend on the distribution of the weights horizontally, even in the same form of vessel, as well as in vessels of different forms. I conse- quently assume that the centre of gravity of vessels must be raised, or lowered within certain limits to meet the conditions imposed by the horizontal distribution of the weights, armament, and cargo, (66) and that no point can be definitely assigned, as being applicable under all circumstances. I was unfortunately absent from the Institution when SCIENCE OP SHIP-BUILDING. 63 Mr. Russell read his paper " on the education of Naval Architects in England and France," but came in in time to hear the discussion on it. The general impression seemed to favour the early establishment of a school for this purpose, at Portsmouth or Greenwich, under the auspices of the institution. This will be a step in the right direction, provided the school is placed under the control and professorship of men competent to take a large and unprejudiced view of the whole science of naval construction. Otherwise, it will only serve to perpetuate old falacies and stop the way to actual im- provements. The lectures might be open on certain conditions to all who may choose to attend. J. & J. 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