It is evident that this equation of "A. B." is not at all fitted for logarithmic calculation, requiring, as in the first case, three sets of tables-and, according to his own showing, four distinct casesto determine whether the required side be acute or obtuse. I here beg to inform the tyro in spherical trigonometry, that. all that is required to be geometrically demonstrated is this fundamental equacos. a-cos. b, cos. c sin. b, sin. c which it follows that tion, cos. A= cos. b-cos. a, cos.c ; from and cos. C = cos. ccos. a, cos. b ; where sin, a, sin. b A, B, and C are the three angles, and a b c the opposite sides. No farther aid is required from geometry, all the cases being made out by the analytical method, the analyst taking care that his theorems are well adapted (when it is possible) for logarithmic calculation. The inventor of the logarithms, the illustrious Napier, has shown how this is to be done. Indeed, little has been discovered on this subject since his time. It may, however, be stated, that the application of versed sines may be sometimes applied with good effect. Thus, by solving "A. B.'s" fourth question by this method, we have ver. sin. b=ver. sin. (a−c)+sin. a, sin. c, ver. sin. B. Here a = 112° 54′ 42′′, b = 77° 27′; .. a-c=35° 27′ 42′′, and B=96° 48'. a=112° 54' 42" c= 77° 27' 0" sin. 9.964310 sin. 9-989497 B 96° 48' 0" ver. sin. 10.046772 66 THE GREAT BRITAIN," AND SCREW PROPELLING. 151 Hence b-100° 46′ 18′′, the time as before, nearly. The above appears longer than the first; but it requires only one set of tables, and is, on that account, really sooner done. KINCLAVEN. DESCRIPTION OF THE GREAT BRITAIN IRON STEAM SHIP, WITH SCREW PROPELLER; WITH AN ACCOUNT OF THE TRIAL VOY AGES, BY THOMAS RICHARD GUPPY, ESQ. C.E. [From the Proceedings of the Institution of Civil Engineers.] The Great Western Steam Ship Company originated with a few directors and proprietors in the Great Western Railway Company, who entertained the idea, that, on the completion of the railway from London to Bristol, a direct line of communication, by means of steam-boats, to New York, as the focal point of the New World, might be established with advantage. Hitherto, attention had been directed to the south-western harbours of Ireland, and the nearest ports in America, as the extreme distance between which steam-boats of the great * power then supposed to be practica'ie, would be enabled to carry a sufficient quantity of coal for the voyage; but this company, placing confidence in the opinion of Mr. I. K. Brunel (their engineer), ventured to build the Great Western, a steamer exceeding in size any that had previously been constructed, and with engines of so much greater power, that the predictions of many experienced and scientific men were unfavourable to the project. The Great Western did, however, fulfil the expectations entertained of her by her projectors, in all respects, except in that, like many other moderate-sized steam vessels, so large a part was occupied by the machinery, relatively to that which could be appropriated to passengers and goods, the deficiency of space was soon found to operate disadvantageously in a pecuniary point of view. At first it was intended that their second ship should be of timber, but the superior advantage which the introduction of iron appeared to hold out, induced a very careful comparison, and an investigation into the state of some small steam vessels already constructed of this material, and the result was the abandonment of the previous resolution. As no example of an iron steam ship of sufficient size existed, on which to base any The tonnage, according to the usual mode. of builder's measurement, is therefore, 3,444 tons. The weight of iron used in the hull is about 1040 tons; which is equal to an average thickness of 24 inches. The weight of the wood-work in the decks, fittings, &c., is about 370 tons. And the weight of the engines and boilers (exclusive of the water) is 520 tons. The total weight, therefore, is 1,930 tons; which, at a draft of water of 10 feet 6 inches forward, and 13 feet 7 inches aft, corresponds exactly with the calculation of the displacement of the hull, which is as follows: She will therefore be able to take 1000 tons of coal, and 1000 tons of measurement goods, weighing perhaps 400 tons, at a draft of 17 feet forward, and 17 feet 6 inches aft. The keel plate consists of plates ths of an inch in thickness, by 20 inches wide, which were welded into lengths of 50 feet to 60 feet, and these lengths were joined together, by very accurately made scarphs, 1 foot 6 inches in length, and riveted all over, at distances of 4 inches apart. The end pieces of the keel, which are more liable to touch the ground, are full 1 inch in thickness. The stem is 12 inches deep at the forefoot, by 5 inches thick, and at the 8 feet water mark, it is 16 inches by 24 inches; thence it diminishes gradually to 12 inches by 1 inch. It is welded in one piece 18 feet long. The ribs or frame are formed principally of angle iron, 6 inches by 3 inches by ths inch, at distances of 18 inches from centre to centre, but inclining gradually to 24 inches at the extremities, where, also, angle iron, 6 inches by 24 inches, and 4 inches by 3 inches is used. In that part of the body of the ship which is occupied by the engines, the ribs are doubled, by having a similar angle iron riveted to them, with the web inside, or, as it is termed, "'reversed." The outside plating commences with plates 6 feet to 6 feet 6 inches long, and 3 feet wide, by nths inch thick; of these plates there are four courses; these are followed by several courses of ğths inch thick, which is the strength of the whole of the immersed part, up to the deep load water line. Above that height the same thickness is preserved amidships, but it is gradually reduced to ths inch thick quite high up, and at the extremities, with a view to lighten them. The longitudinal floor sleepers are ten in number; they are 3 feet 3 inches in depth, and inch and nths inch thick. The middle sleepers extend throughout the length of the vessel; those on the sides are level on their upper surface, and consequently are terminated by the rising of the bottom of the ship. These sleepers are tied to the bottom, and are preserved in their vertical position by inverted curves of strong angle iron, which are riveted to the ribs and also up their sides. Along the upper edge of each, there is an angle iron, and over the whole is riveted an iron deck gths inch in thickness. There are two bilge keels, consisting of a middle plate, 1 inch thick, and two angle irons, 5 inches each way by 1 inch thick. These bilge keels are 110 feet long, and their under edges are on the same horizontal level with the under side of the keel, so that in docking the ship, if long baulks of timber are extended across the dock by way of blocks, the weight of the body of the ship (where the boilers and machinery are placed), is supported at given parallel distances on both sides of the keel, all risk of straining it, or the machinery, is avoided, and the vessel is not obliged, in the usual manner, to rest upon her keel, until the bilge shores can be got under. The upper cargo deck forward is made of plate iron, nths inch thick in the middle, andnths inch thick round the sides; it is riveted together throughout, as well as to the iron deck beams, and to the sides of the vessel. The main deck is made of pine timber 5 inches thick, and the planks are cross-bolted at distances of 4 feet apart. As this deck is situated on the load floatation plane of the vessel, where transverse stiffness is of more importance than longitudinal strength, the planks are placed athwartships, and their extremities are firmly bolted down, through two longitudinal stringers of Baltic timber, to the shelf plates, which are 3 feet wide by five-eights of an inch thick, and are very securely fixed to the sides. The middle or promenade deck is also of pine timber 4 inches thick, placed lengthwise of the ship; it has also strong iron shelfplates 3 feet wide by inch thick, and Baltic stringers to attach it to the sides of the ship. The upper deck is of red pine timber, and is also placed lengthwise. As the sides of the vessel at this height, and also this deck, may be considered as the truss, which is to resist longitudinal deflection, or drooping of the extremities, the outside plates are there inch thick, and they have been strengthened by an outside moulding-iron strap, 6 inches by 1 inch, and by additional straps of iron 7 inches by 1 inch, welded into lengths of 60 feet, and riveted to the inner sides of the upper line of plates. The shelf-plate of the deck is 3 feet wide by inch thick, and upon this, outside of the water-way plank, which is 4 inches thick, there is a course or tie of Baltic pine timber 340 inches in section, carefully scarphed and securely bolted to the ribs, and to the shelf-plate, throughout the length of the ship. There are three rows of timber pillars, or stauncheons, which are fixed to the bottom of the ship, passing up between longitudinal ties at each deck, and are secured to the upper one. The beams of all these decks are made of angle iron, 6 inches by 34 inches by inch, and their ends are bent down, and riveted to the ribs on each side. Upon them, the shelf-plates before mentioned are riveted, and thus form a horizontal band 3 feet wide at each deck. A crutch or strut is introduced at each end of nearly every deck beam, which is riveted to it, and to the ribs at about 3 feet from the angle of junction. One of the most important improvements which has recently been introduced in the construction of vessels (particularly those of iron), is the water-tight bulkhead; as in the greater number of cases, when an injury may be sustained in one compartment only, it may absolutely preserve a vessel from sinking; several instances of this have already occurred, and even where it may not suffice for this purpose, it at least separates the leaky and injured from the secure parts, .THE GREAT BRITAIN," AND SCREW PROPELLING. and gives time either to attempt to stop the leak, or to make other preparations. In iron vessels, these bulkheads can be rendered much more effectual than in wooden ones, by their exact contact with the bottom and sides, while at the same time they form admirable ties and stiffeners. In the Great Britain there are five such bulkheads. The first separates the forecastle from the forward passengers' cabin and the hold, and as it is in the forepart of a vessel that injury is most likely to be sustained, this partition is made particularly strong and secure. The next bulkhead divides the forward cabin from the engine-room or more properly, from the fore-hold for the coal and the stokers, at the forward end of the boilers. The third bulkhead is abaft the enginebut in this, there is necessarily a hole for the screw-shaft to pass through; this is secured by a well-fitted collar, and there is also a door, which is so arranged as to be shut and bolted quickly. room, These three bulkheads pass up to the upper deck; there are also two others; one separating the after coal-hold from the after cargo-hold, and another nearly at the stern; both these terminate under the saloon deck. The minute detail of the construction of the hull of the vessel would be too voluminous to be given here, and it would be unnecessary, as it will shortly be published.* It is better, therefore, to proceed to describe the action of the screw "opeller, which has now become an object of such deep interest to all who are engaged in marine engineering, and to the machinery by which it is to be put in motion. At an early stage in the construction of the Great Britain, but not until her sides had assumed the form adapted for paddle wheels, the small steamer Archimedes, belonging to the Company owning the patent of Mr. F. P. Smith for the application of the Archimedean screw, visited Bristol, and amongst other parties invited to make an excursion to the Holmes, on board of her, were some of the Directors of the Great Western Steam-ship Company. The performance of the screw on that occasion induced the author to request permission of Mr. Smith and Captain E. Chappell, R.N., who was officially appointed by the Admiralty to report upon her, to proceed in her to Liverpool. On the passage, enough rough weather was encountered, to show that the screw possessed several good points, and was not so absolutely impracticable as had been asserted; and although far from venturing to In four Parts, large quarto, with forty plates, by Weale, 59, High Holborn. 153 give a decided opinion, on the author's return he wrote such a letter to the Board of Directors as induced them, after some days of deliberation, to decide upon suspending, during three months, the progress of the machinery for paddles, and also of that part of the vessel which might be affected by the change, and to call upon Mr. Brunel during that period to investigate the subject. At the end of the proposed delay, the report which Mr. Brunel made was so favourable, that, undaunted by the novelty and vastness of the experiment, the Directors resolved to adopt this mode of propulsion, of the success of which they have now such cause of congratulation. From that period, until it became necessary to decide on the exact form of screw to be used, all possible means were taken, by experiment and observation, to arrive at the best shape and angle of inclination of the blades, or as it is commonly called "the pitch. Amongst others, the proprietors of Mr. Smith's patent liberally lent the Archimedes to the Great Western Steam-ship Company, for a period of several months, which afforded ample opportunity of trying the performances of the several forms of screws recorded in the Table given in the next page. These experiments were made in the Bristol Channel under circumstances of weather, as nearly as possible similar, and the distances were very carefully measured by two of Massey's Logs, whose accuracy had been previously tested. It will be observed, that the greatest velocity of vessel, 8.375 knots, was attained by Mr. Smith's screw of 5 feet 9 inches diameter, the angle of which was 19 degrees, and the slip was 21 per cent.; that is, the ratio of speed of the vessel to that of the screw, was as 787 to 1. Particular attention is due to experiments Nos. 5, 6, and 7. Reasoning upon the assumption, that the effort of the entering edge of each blade must cause the water to recede, and that each succeeding portion of blade should so increase in pitch as to impinge with uniform force against the water, which was so receding, a screw of this description was made and tried before it was discovered that it was the subject of a patent by Mr. Woodcroft. The first trial served to show, that the curvature or increase of pitch which had been given to it was too great, since the speed of the vessel was greater by 2 per cent. than that due to the mean pitch of the screw, whence it was evident that the entering edge was really retarding, and the terminating portion alone was doing the duty. On the second trial, when a radial strip 3 inches in width had been cut off the after part of each blade, the speed of the vessel was exactly that due to the screw; whence it was also evident, that the front edge still did not assist. On the third trial, after a second radial slip of 4 inches had been cut off the entering edge of each blade, the vessel attained a speed of 8.2 knots, and the ratio of speed of the vessel was as '94 to 1 of the screw. The horse-power employed on this trial, was by indicator, 62.12, and the speed of the vessel 8.2 knots, against 67.1 in the beforenamed trial, with the original screw of the Archimedes, when the speed she attained was 8.375 knots. Although on neither of the trials numbered 5, 6, and 7 with this screw, was so Speed of Horse Power exerted. 95.5 Vessel in Knots. 10.15 In the two cuttings down, this cast-iron screw with three blades, 9 feet in diameter, which was originally very slight, had been so much reduced in substance, that it weighed only 833 lbs. Mr. Barnes, therefore, could not venture to permit the engines to exert their full power, otherwise it is probable that a higher speed would have been attained. The commencing angle is 17°, and the terminating one 1910; the increase of pitch is therefore th, or 8 per cent. The screw of the Great Britain, which is blades. Four wrought iron arms, with 7 08 0 blades, each 2 feet 9 inches long by 1 foot broad. great a speed of vessel attained as on that first named, it is important to draw attention to the fact, that the slip was reduced to a very small quantity. But the horse-power exerted was also much less than in the first trial, arising from some imperfections in the cutting down of the screw and other causes, which would probably have been remedied had there been time to cast a new screw of this description; but unfortunately, just at this period, the Propeller Company required the Archimedes for service, and the experiments ceased. This screw was afterwards tried by Mr. Barnes in the Napoléon, a very beautiful French Post-Office vessel, built by M. Normand, of Havre, when the following result was obtained : Speed of Screw. 11.2 Speed of Vessel to 1. of Screw. 895-10 per cent. of wrought-iron, consists of six arms, formed by placing and riveting together four distinct forgings, or centre pieces, with arms welded to them, each of which is 6 inches thick. Upon the extremities of these are riveted palms of plate iron, which are 4 feet 4 inches long on their circumferential edge, by 2 feet 9 inches in height, and inch thick. The diameter is 15 feet 6 inches, and the pitch or helix of one revolution is 25 feet, which equals an angle of 28 degrees. Its weight is 77 cwt. |