SHIPBUILDING. 



SHIPBUILDING. 



04 



experience. The diagonal frames, together with the oblique trussing 

 between the ports in the upper work*, not only rwunt the tendency of 

 the *hip to become arched, but the former resist also any pressure 

 which tuay Uke place externally against the bottom <>f Uie ship in the 

 event of grounding ; t the Mine time the exterior planking, the 

 longitudinal timber*, and the oblique planking of the decks bind the 

 whole fabric in one firm body. A cloee contact of the several parU of 

 the dilgonal frame* U evidently of the utmost importanoe, at on it 

 depend* the Mcurity of the (hip against a change of figure. 



The principle on which the diagonal brace* act may be easily under 

 food from the following consideration* : Let * M, A H, Jig. 8, be two 

 principal brace*; r D ami DC, OB and BC, the strut* or trusses inserted 

 between them: then if r be the point of support, and if the parts 

 beyond x and M be those which hare a tendency to link by the weight 

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of the superstructure, it will follow from the 'elements of mechanics, 

 that in this case the braces A M and A x, and the longitudinal timber 

 r o, will be subject to the strain of extension in the direction of their 

 lengths, while the trusses o B and BC.FO and D c, as well as the longi- 

 tudinal timbera D B and M N, will be subject to the strain of com- 

 pression. The effect of braces disposed in the positions A M, A x, in 

 miiUhips. and of others corresponding to them towards the head and 

 stern, will be that the strain arising from the weight of the extremities 

 of the ship, and by which arching is produced, is counteracted by the 

 power of the trusses, in positions corresponding to r t> and c o, to resist 

 being compressed. A contrary effect would take place if the principal 

 brace* were disposed in the directions c r and c o, c being the point 

 supported ; for then the trusses between them, and the longitudinal 

 piece* DB, would become disengaged, and would fall out of their 

 I ;.-. 



Sir Robert Seppings's diagonal braces were first introduced in 1810, 

 and his paper on the application of them is contained in the ' Philo- 

 sophical Transactions' for 1814. They were first applied to the 

 Tremendous; and the success was complete, for after three years' 

 service it was found, by means of lines of sights along the ship, that 

 the gun-deck had not arched in the least, and the upper deck only three- 

 fourths of an inch. 



The introduction of iron knees and braces in wooden ships has not 

 only strengthened them considerably, but ia a great advantage in the 

 saving of space for stowage. The sheathing of ships at first consisted 

 of a second covering of planks applied, on the exterior of the first, 

 over the bottom and sides as far as they were under water. [Sn KATIIIXU.] 

 To save the first expense of copper, a mixed metal called Muntz's 

 Metal, or yellow metal, and composed of 6 parts copper to 4 parts 

 zinc, was in 1832 manufactured at Birmingham under patent, and its 

 use has considerably increased in the merchant service. It has been 

 found that there is a limit to the quantity of copper in this kind of 

 ahmthing, as unless the quantity of copper lie between 50 and 63 per 

 cent., and the zinc between 60 and 37 per cent., the compound will 

 not roll at a red heat while too much copper renders the compound 

 difficult to work, and too much zinc renders it too hard when cold. 

 By this use of metal sheathing shells and sea-weeds are partially 

 prevented from adhering to the sides and bottoms ; the friction of the 

 water against them is diminished, and the damage which would be 

 caused by worms is avoided. 



As further details on the practice of wooden shipbuilding may be 

 obtained from such excellent works a* that of Mr. James Peake, of 

 H.M. Ii.-ky.ir.i. Woolwich, we only add some information on the 

 manner in which various subjects intimately affecting the whole 

 question of naval architecture hive been treated. 



In 1814, Mr. Walters, a civil architect, took out a patent for a 

 method of counteracting the arching of a ship by braces of iron, which 

 be proposed to apply on each side of the ship between the rib-frames 

 and the exterior planking. The braces were to extend obliquely l>oth 

 ways from the upper-deck beam in midships, in the direction of tin; 

 line of nliortest distance on the surface, towards the keel, win < 

 which were nn opposite sides of the ship were to meet under the bows 

 and stem. By this disposition tin - of the vessel could not 



ink without putting all the timbers bctw. n tin- tnisses in a state of 

 compression, and thus all their joints would be kept close together. 



1 Mem. .ire de la StnbiliU- des Corps Flottants,' published in 

 1822 by the Jfcinui Dupin, the stability of a ship as derived from differ- 

 ence of form was considered, and has proved useful to the shipbuilder. 

 In about 1-J7, mime papers, chiefly contributed by the students of 

 the School of Naval Architecture at Portsmouth Dockyard, were pub- 

 lished by Messrs. Morgan and Creuze, formerly pupils of that insti- 

 tution ; and u these embodied several valuable translations from 

 foreign author* on the laws of the resistance of fluids, they n. 

 be read with considerable benefit. The Rev. Dr. Woolley, the late 



principal of that school, and our present great authority in naval 

 mathematics, declared, iu a paper read before the Institution <>f Naval 

 Architects in 1380, that the experiments : ired to were most 



carefully made, and entitled to rank among the most important 

 contributions towards the determination of the theory which have 

 ever appeared. 



In 1851, Mr. Kincham, the muter-shipwright at Portsmouth Dock- 

 yard, published a ' History of Naval Architecture,' which throws much 

 us branches of the science. 



In 1852, Lord Robert Montagu endeavoured, in a small work pub- 

 lished by him on naval architecture, to influence the form of vessels 

 by the dissemination of a new theory affecting the question of the 

 molecular motion of water when di-turbed by an 

 Something similar was also published at New York by Jlr. Cii ; 

 But no permanent benefit to science seems to have been thereby pro- 

 duced ; for, as already mentioned, the theory of resistances is still in a 

 very incomplete and unsatisfactory state. The nearest appro 

 any theory founded on the disturbance of the particles of v, 

 that of the form assumed by the mam of water so displaced, and whieh 

 constitutes the theory announced to the scientific world in I.- 

 Mr. John Scott Hussell. This, as a question of Miiplmildi- 

 paramount interest, intimately connected as it is with that of speed 

 and the various other ! j < ndeut qualifications of a ship, as influ 

 the ready defence of the country. Mr. Russell's tin. i 

 already alluded to undi IT, in the Ilioo. l>i\. 



of this ' i; but an illustration under Siui'iirn.Di.NU may be 



acceptable. 



In devising the form of a ship, ho proceeds, as already explained at 

 fgi. 8 and 4 ; but instead of adopting merely arbitrary changes of area, 

 he arrives at his precise form of midship and load-water curves by the 

 use of a simple and elegant formula, producing thereby curves of con- 

 trary flexure, which are said to facilitate the passage of a solid through 

 a fluid. His experiments have shown that although the straight bow 

 of wedge-like form presents actually the smallest surface to the i 

 of the [articles of water, yet that in this form such particles, impinging 

 upon the bow, rebound or ore driven off at right angles to the 

 line, raising a perceptible wave; while Scott ' 



entrance allows the water to roll along the curve to the side of the 

 vessel without such opposition. To illustrate plainly his theory with 

 all possible brevity, let us suppose that, for instance, the ai> 

 outline curve of the midship leottOO have ::ined : this would 



represent the greatest beam, uot at the centre of the fore and aft line 

 of the ship, but at a point at about two-thirds of the length from the 

 bow. Mr. Scott Russell divides his ship, upon the load water line, into 

 two unequal and dissimilar portions. He considers that tin- length 

 of midship portion (which, according to his theory, ma;, 



it.-il lines perfectly parallel to the keel) does not affect, or .- 

 affects, any other property than the displacement, the additional i 

 of such added midship portion being comparatively trilling. Thus his 

 ship, in its abstract original, is mcivly a bow and a stern ; but 

 curves which form these are, at their junction at the midship section, 

 tangential, and are parallel to the longitudinal axis, they admit of an 

 easy absorption into the general outline curve nf the ship. 



Let the line AD represent two thirds of the whole length of the ship :d 

 the load-water line, ami lie the bow or forward portion. AT representing 

 the half-breadth at her greatest or midship section : join < 11. 

 A c, and from its centre, <>, and with oc as radius, describe the 

 circle on A c, and divide it into any number of e.[iial parts say 



i n also into six equal parts, and draw the- ordinat.es 

 !', h'2', cS', &c., parallel to AC. Then draw 1.1'. 8.8', :'..:!', Ac., 

 parallel to A n. meeting the lirst ordinates at the point* 1', -J', :i', &c. ; 

 then will these points, 1', 2', 3', &c.. be points in the curve whieh Mr. 

 il calls the wave principle, from some analogies whieh he 

 n to exist between it ami the form of waves. It will be found 

 ,- area of the portion r :'.'; will be equal to the ana of ;! 

 Jf'nn, forming an interchange of area without disturbing the amount 

 of displacement or the tonnage of the .-.-hip. 



The following figure will also, by the same rule, show the it 

 Fig. 8. 



the stern portion of the load-water line, the outline curve being drawn 

 in precisely the same manner. 



