5*1 



SHIPBUILDING. 



SHIPBUILDING. 



522 



that, on a horizontal plane, the proper curvature of the extremities 

 may be obtained. The rib-timbers above the surface of the water are 

 nearly rectilinear, but below that plane they are made with various 

 curvatures. About the middle of the ship they have at bottom nearly 

 the form of a semicircle, while towards the head and stern they form 

 curves of contrary flexure, uniting on the keel with their lower con- 

 cavities towards the exterior of the ship. 



It may be observed that the keel of a ship is not horizontal, or 

 parallel to the plane of floatation when the ship is in still water, but is 

 made lower towards the stern than it is forwards, in order to allow 

 greater length to the rudder, and thus increase the power of the latter 

 in giving a direction to the ship's motion. 



The keelson, e e, jig. 3, is placed longitudinally above the floor- 

 timbers, and immediately over the keel, and it is united to the latter 

 by bolts which go through both, and through the floor-timbers : its 

 transverse section is represented at , firj. 4. In large ships two addi- 

 tional keelsons, t, t, fij. 4, about thirty feet long, are bolted to the 

 floor-timbers sufficiently near one another that the step (foot) of the 

 mainmast may rest upon them ; they serve to relieve the bottom of 

 the ship from the pressure of that mast, and strengthen it against the 

 upward action of the water. The timbers E and F, fy. 3, called the 

 stemson and stemson, are also attached interiorly to the stern-post and 

 stem-post, in order to increase the strength of the fabric. 



The whole assemblage of rib-timbers is covered on the outside, and 

 either wholly or partly on the inside of the ship, with planks of oak 

 from three to six inches thick ; and in order to make the latter bend 

 so as to lie close to the curve surface of the ribs, they are, previously 

 to being applied, moistened by steam : the exterior planking appears 

 in the section, Jig. 4. The planks are fastened to the ribs both by 

 bolts and trenails (plugs of oak from one to two inches diameter), 

 which pass quite through the ship's side, and are tightened by wedges 

 driven into them at each extremity. 



When the ribs do not join closely side by side, it is recommended 

 that, before the planking is applied, the intervals both on the exterior 

 and interior sides of the ship should be filled up with pieces of wood, 

 as long as the curvature of the ribs will permit ; the lines of junc- 

 tion with the ribs being well caulked. Sir Robert Seppings, however, 

 proposed that for ships of war, where there are intervals between the 

 principal rib-timbers, there should be introduced in those intervals 

 other ribs extending from the keel up to the orlop or lower deck, since 

 by this construction the lower part of the ship will be one compact 

 man of timber. He observed that the filling up of the spaces between 

 the ribs not only adds to the strength of the ship by causing its bottom 

 to have a solid thickness, but it tends to preserve the health of the 

 crew, since those openings become receptacles for dirt, by which the 

 air within the ship is vitiated. Channels, or water-courses, may be 

 cut down the ribs at their interior lines of junction, and covered by 

 planks or battens ; by these channels the water is able to descend to 

 the limber passage along the keel, and pass to the pump-well. For 

 merchants' ships Sir Robert Seppings recommended strakes, or courses, 

 of thick planks to extend longitudinally through the ship along the in- 

 terior aide* of all the ribs, and to cover the abuttiugs of the f uttock- 

 pieces in each alternate rib : such strakea appear at n, o, p, in Jig. 4. 

 He considered that no other interior planking would be required, but he 

 recommended that batten* should be fastened over the junctions of the 

 ribs in the vertical planes. 



A ship being a vast fabric consisting of comparatively short pieces 

 of timber connected together by scarfing, and the principal parts of 

 the frame-work, the ribs, the longitudinal timbers, and the planks 

 being nearly at right angles to one another, it must of necessity happen 

 that when the ship is not supported in its whole length and breadth, 

 it will bend by its own weight. This will take place not only in the 

 event of being lifted up by a wave under some place in its length, or 

 pi muil unequally by the force of a wave acting obliquely upon one 

 bow or quarter, but even while floating iu still water, from an excess 

 of the weight in one transverse section over that in another. In this 

 last case it has occurred, a horizontal line having been traced from 

 head to stern by means of a spirit-level while the ship was on the 

 stocks, that immediately upon the ship being launched the two ex- 

 tremities were observed to sink as much as three or four inches ; the 

 ends of the planks separating in the upper part of the structure, while 

 the timbers below were in a state of compression, and the whole body 

 of the ship becoming curved in a vertical direction. M. Dupin has 

 shown ( ' Phil. Trans.,' 1817) that the strain is greatest at that transverse 

 section of the ship which divides the whole length into two parts, in 

 each of which the weight of the displaced fluid is equal to that of the 

 corresponding part of the ship and its loading. To counteract the 

 tendency to arch or bend was the object of Sir Robert Seppings in the 

 application of diagonal braces to the interior side of a ship. 



Trussing ships to prevent arching was used on the Continent as 

 early as 1759 ; and the Swedish architect Chapman, who describes the 

 manner of placing the trusses, speaks of the practice as being generally 

 followed. The method consisted in setting up three parallel rows of 

 fir-pillars from one end of the ship to the other ; the middle row rested 

 on the keelson, and the others on parallel longitudinal timbers, fastened 

 by bolts to the ribs of the chip, one on each side of the keel ; on the 

 heads of these pillars in each row, and under the lower deck of the 

 ship, was placed a longitudinal timber like an architrave ; 'and diagonal 



braces were placed from the head of one pillar to the foot of the next 

 in each of the three rows. It is evident that such a disposition of 

 braces, if well executed, would serve to prevent or diminish the arching 

 of the ship ; but it is far inferior to the method now followed, because 

 of the interference with the loading, and the liability of the pillars to 

 be displaced in consequence of a violent movement of the ship. 



In order to understand the construction of a ship and Sir R. Sep- 

 pings' s application of the braces, let Jty. 5 represent a part, near the 



Fig 5. 



mainmast, of a longitudinal section through a large ship of war. In 

 this figure ee is the top of the keelson ; h h and k k are timbers ex- 

 tending through the whole length of the ship above the ribs, which 

 are supposed to be close together, and not covered by an interior 

 planking; m m, &c., are the principal timbers of the braces; n n, &c., 

 are the trusses to those timbers ; x x is a longitudinal shelf, on which 

 rest the beams of the orlop deck, and the section shows how it is sup- 

 ported on the braces m m, &c. ; y y is a like shelf, on which rest the 

 beams of the lower gun-deck. The beams which support the upper 

 decks rest likewise upon longitudinal shelf-pieces, which appear at w w 

 and z z ; and these lie upon chocks or upon pillars placed against the 

 sides of the ship at intervals between the decks : the same shelf-pieces 

 appear at x, y, w, z, in Jig. 4. Through these and through the ribs pass 

 the bolts by which the iron knees r r r, Jig. 4, are attached to the body 

 of the ship. In small vessels the beams are not always fastened by 

 iron knees, but are merely coaked and bolted to the shelf-pieces : two 

 or more iron knees are however usually placed under the beam near 

 the main and fore masts. The shelves just mentioned constitute as 

 many hoops connecting the ribs of the fabric together longitudinally ; 

 they are fastened by trenails and bolts to the ribs and to the beams of 

 the decks : p P, &c., fj. 5, are the ports, and the dispositions of the 

 braces between them are shown at ! v, &c. 



The connection of the two sides of the ship with each other is 

 effected by means of the beams which extend under the decks from 

 ride to side. The tops of the iron knees are fastened to these, near 

 their extremities, by bolts passing through them ; and the lower parts 

 of the knees are joined to the ship's side by bolts passing quite through 

 the planking, the ribs, the chock-pieces, and the knees themselves. 

 The beams of the principal decks iu large ships are usually made in 

 two pieces which abut end to end, and are connected together by 

 having a strong middle piece scarfed and bolted to them. The planks 

 of the gun and upper decks are recommended to be laid obliquely 

 above the beams, and their outer extremities enter into a rebate 

 formed near the interior side of the ship in certain longitudinal pieces 

 which are channelled for the purpose of carrying off the water from the 

 decks : the diagonal position is given to the deck planks, in order that 

 they may increase the strength of the ship in a transverse direction. 

 The exterior planking of the ship is laid on the ribs in longitudinal 

 directions as nearly as possible parallel to the surface of the water ; 

 and at the extremities of the ship bolts pass obliquely through them 

 and through the stem-post, the stern-post, and the adjacent rib- 

 timbers. 



The oblique timbers, or diagonal braces m m, &c. (fiijs. 4 and 5), 

 which are about six or seven feet asunder, cross the ribs at angles of 

 about 45, and are placed in contrary directions from the middle of 

 each side towards each extremity of the ship. Their upper ends abut 

 against the horizontal shelf under the lower gun-deck, and their heels 

 or lower extremities against the keelson, or against the horizontal 

 timber on each side of it. These braces are attached to the timbers of 

 the ship by cylindrical coaks and bolts, and the lower ends are con- 

 nected with the keelson by iron straps. The timbers h h, k k, which 

 are of fir, are attached to the sides of the diagonal braces ; and the 

 truss-timbers n n, &c., are placed diagonally across the rhomboidal space 

 formed between the principal braces and the longitudinal pieces, in 

 order to prevent the former from becoming bent by the compression 

 which they may sutler endways from any strain which the ship may 



