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Originally appearing in Volume V24, Page 977 of the 1911 Encyclopedia Britannica.
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LONER EDGE T position; but the process of copying the frame lines on it is one of measuring on battens the ordinates of their intersections with water and diagonal lines, and is the same in either case. All of the frame lines are shown on the scrive-board, and the complete section of the frame surface for both sides of the ship is shown at each station. To avoid confusion of lines, either a separate board is used for the fore and after bodies, or•they are drawn on the same board with their centre lines parallel and a few feet apart, and one of the two bodies inverted. All the lines already referred to as having been laid off in the body plan on the mould loft floor, including the lines of outer edges of all transverse frames, the inner edges of all in the double bottom, and the upper edges of all floor plates outside the double bottom, the projections of plate edges of inner and outer bottom, arm of longitudinal frames and main longitudinal bulkheads, projections of beam at side lines for all decks, and of the intersection of the beam surface of the protective deck by the plane of each frame, are copied on the scrive-board and rased in on its surface. The scrive-board thus gives complete information of the shape and dimensions of every part of each transverse frame. To completely define the frame the " bevelling " is required in addition, that is the angle between the two flanges of the angle bar on the edge of the frame connecting it to the outer or inner bottom plating. The bevelling is usually given at the plate sight edges; but any other convenient bevelling spots may be chosen and their positions marked on the frame lines. To obtain the bevelling at any spot a normal is drawn to the frame line in the body plan at the spot; the distance from the frame line is measured along this normal to its intersection with the next frame line .towards the midship section, and this distance is set up as one of the sides containing the right angle in a right-angled triangle of which the frame space is the base. The angle of this triangle opposite the base is the supplement of the bevelling of the frame at the spot considered. When the curvature of the bottom in the plane normal to the square station at the bevelling spot considered is sensible in the length of a frame space, the normal distance measured is that between the two frame lines on either side of that at which the bevelling is to be obtained, and the base of the triangle is made equal to twice the frame space. The bevellings for each frame are marked on a bevelling board, the angles between the straight lines marked on the side of the board and the straight edge of the board representing both the bevelling and its supplement. In the frame bars there is no doubt as to which of these two angles the workmen are to regard as the true bevelling, since the flanges of the frames are all turned towards the midship section, so as to make the true bevelling always greater than a right angle, or " standing " as it is usually expressed, in contradistinction to " under " bevelling, which is less than a right angle. Special bevelling frames are used in marking the bevelling boards, by which the construction of the triangles is reduced to setting off the normal measurement between the frame lines and drawing the hypotenuse directly on the bevelling board. The flanges of the angle bars on the inside edge of the frame, or the " reverse " frame bars, usually point the same way (that is towards the midship section) as the flanges of the frame bars, throughout the double bottom, in order to facilitate the construction of the bracket frame. Where the breadth of the longitudinals is constant, therefore, the bevelling of these angles on the inner bottom is the supplement of that of the frame angles. But throughout the double bottom neither bevelling differs much from a right angle. When the longitudinals taper in breadth separate bevellings must be taken for the inner angles by a method similar to that already described for the frame angles. Outside the double bottom the reverse angle, or inner part of the split zed bar, is either unconnected to anything but the floor plate, or else connects to a horizontal flat, and does not require bevelling. The bevellings of the short angle bars which connect the bracket or floor plates of the transverse frames to the longitudinals are also obtained by measuring in the body plan at the middle of the inter-section of the longitudinal surface with the plane of a frame station the normal distance to its intersection with the plane of the next frame station, and setting it up as one side of a -right-angled triangle of which the frame space is the base. To check the spread of the transverse frames during their erection, half-breadth staffs and height of breadth staffs are issued from the mould loft, or their lengths may be taken off the scrive-board. These give the co-ordinates of the ;intersections of the longitudinal sight edges with the frame fines, referred to the middle line of the body plan and a level line through the underside of the keel at each station. The frames are brought to and held in their correct positionsas shown by these staffs by shoring them in the vicinity of the longitudinals. Shoring ribbands are not universally employed, the longitudinals at some shipyards being relied upon to keep the transverse frames in their correct relative position while framing the ship. Shoring When they are used, one is usually placed a few inches ribbands. below and parallel to each deck edge and longitudinal sight edge. For the ribbands under the deck edges, the beam at side line is projected into an uncontracted half-breadth plan, a flexible batten is bent to the line, and on it are marked the positions and directions of the ordinates representing the traces of the planes of the frames. The ribband batten is then used to mark the positions of the frames on the ribband itself, generally made of pitch pine about 6 in. square in section. The position where the upper edge of the ribband is to come is marked on the scrive-board and the marks transferred to the frame angles when they are bent. When the frames are erected at the ship they are brought into their correct positions as shown by the marks on the ribband, the upper edge of which is kept to the marks on the frames. The frames and ribband are temporarily secured together, until the plating is fitted, and the whole kept in its. proper position by shores. The ribbands under the longitudinals lie for practical purposes in diagonal planes, which must be rabatted in order to get the positions and directions of the frames correctly marked on the ribband battens. The ribbands are marked, secured to the frames and shored, similarly to those under the deck edges. A beam mould is prepared for each deck, the upper edge of the mould showing the round down or camber of the longest beam in relation to a level line marked on the mould. The mould Deck is applied to the body plan on the mould loft floor or on beams. the scrive-board in its correct position at each frame station and the ends of each beam are marked on it, the ends being short of the frame lines by an amount which varies with the nature of the frame, but sufficient in any case to clear the inside of the flange of the frame bar. Bevelling-boards are supplied showing the angle at each frame station between the upper edge of the beam and the frame line for guidance in forming the beam arm, which is usually two and a half times the depth of the beam, and the form of which is shown by a separate mould. When placing the beams in position at the ship their height is given by the beam end lines shown on the scrive-board and transferred to the frames when bent to the lines on the scrive-board. The beam mould for the armour deck shows the length of the sloping part and the shape of the knuckle, with only a short length of the middle horizontal part. On the horizontal arm of the mould vertical lines are drawn at a given distance from the middle line at each frame station. It is essential that the shape of the longitudinal frames should be obtained with considerable accuracy, especially when half-breadths and heights measured to their sight edges are Longilargely relied upon for keeping the transverse frames to tudiasis. their designed spread during erection. As already stated, the longitudinal surface does not much differ from a surface generated by the normal to the ship's surface as it travels along the curve of the longitudinal sight edge. The surface generated by the normal is developable provided the sight edge is a line of curvature, which is approximately ensured by the method of drawing it, and it is found by experience that no error of practical importance is involved in developing the surface of the longitudinal by the following approximate method. Fig. io8 shows part of the body plan in which the frame lines are numbered I to 7, the projection of the longitudinal sight edge is shown by a b c d e f g, and the projections of the traces of the longitudinal surface with the planes of the frames are shown by the straight lines al aa2, bI bb2, ci cc2, &c. The curves al bl el di el fl gi and ¢2 b2 c2 d2 e2 f2 g2 both cut all the traces at right angles, so that they are involutes of their envelope. Their positions are chosen at convenient distances beyond the inside and outside of the group of frame lines, which defines the length of longitudinal which is to be developed in one operation. Farallel straight lines A1G1, A2G2, the distance between which is equal to the normal distance between the two involutes in the body plan, are drawn in any convenient position on the floor, and perpendicular ordinates, I, 2, 3, 4, 5, 6, 7, drawn between them distant the frame space apart. The longitudinal is developed in this plan on the assumption that when its surface is unrolled the involutes al la gi and as b2 g2 will coincide with the straight lines A1Gt and A2G2 respectively. Taking gigs in the body, represented by G1G2 in the plan, as the fixed end of the longitudinal from which the surface is to be unrolled, the lengths glib glee, &c., are measured along the curve of the involute and set off along the lines 6, 5, 4, &c., in the plan giving the points Fs, Es, &c., which represent with sufficient approximation the true positions of points of the line al bt c, d, el fl gi in space relatively to a straight line through gi rpendicular to the body plane. A batten is bent through the points t Fs Es Ds Cs Bs As thus obtained, and the positions of the points marked on the batten, which is then allowed to spring straight along the line G1A1, the points Fl El D1 C1 Bl Al being marked from the corresponding marks on the batten. The points F2 E2 D2 C2 B2 As are obtained from the other involute in a similar manner, and the straight lines F1F2, ElE2, &c., obtained by joining corresponding points are regarded as the expanded positions of the traces of the longitudinal surface with the planes of the frames. The distances G2G, F2F, E2E, &c., are then made equal to g2g, f2f, e2e, &c., in the body, and the curve G F E D C B A through the points so found is the expanded sight edge of the longitudinal. The distances GGo, FFo, EEo, &c., are then made equal to the depth of the longitudinal in the plane of the corresponding frame stations, when Go Fo Eo Do Co Bo Aa will be the expanded shape of the inner edge of the longitudinal. The method described above is sufficiently accurate to lay off a whole longitudinal in one length, if it is not abnormally twisted. A modification of this method, in which the involutes al bl gi and a2 b2 g2 are replaced by straight lines perpendicular to the trace, from which the longitudinal is to be unrolled, may be used; but, without affording any substantial simplification of the work, its accuracy is so much less than that of the method described above, that it is not safe to lay off more than two or three plates of the longitudinal in one length by it. When the longitudinal is much twisted, as, for example, when the longitudinal surface at its end is to be made continuous with a deck flat, which is not normal to the surface of the ship, it is generally desirable to use the more laborious but reliable method of " mocking up" In fig. 109 the curves numbered to 6 are projections of frame lines in the body plan. a b c d e f is the projection of the sight edge of the longitudinal breaking into the projection of the edge of a deck flat at a, and at bl cl d,. el ft is the projection of the inner edge of the longitudinal. The edges of the longitudinal are faired so that the traces of the longitudinal with the planes of the frames shall turn uniformly from the horizontal position of the deck flat at aa1 to the position of the main part of the longitudinal normal to the frame lines at 6 and beyond, the depth of the longitudinal in the planes of the frames being kept constant. LL is the trace of a level plane drawn conveniently near to the sight edge in such a position that it is entirely below all the traces df the longitudinal with the planes of the frames throughout the length which is to be mocked up. Trapezoidal frames made of four straight battens nailed together at the corners, such as X Y E E in the figure, are made to show the relative position of the traces of the longitudinal surface and of the level plane with the plane of each frame. The outer and inner ends of the trace of the longitudinal surface are marked on the upper batten of each frame as at e, et, and a point Ot, fixing the lateral position of each batten frame relatively to a convenient straight line perpendicular to the planes of the ship's frames, is marked on the lower batten. A diagonal plane such as DD can be used instead of the level plane LL for convenience in allowing smaller and better-shaped batten frames to be used; and the process is precisely the same. The batten frames are then erected on their bases XY in planes perpendicular to the floor, parallel to one another and distant the frame space apart, with the points 0 in all the frames lying in one straight line perpendicular to the batten frames. The upper edges of the upper battens then define the true shape of the longitudinal surface in three dimensions, and a fair curve through the pointse, &c., marked on the battens represents the outer edge, and through points el, &c., the inner edge of the longitudinal. Whether the shape of the longitudinal has been obtained by development on the floor or by the mocking-up process, batten moulds are made to the outline of each plate, the butts being arranged to come in the middle of a frame space allotted to them in the drawing, giving the shift of butts of bottom plating and longitudinals. Cross battens are fitted to mark the position of each transverse frame, and diagonal battens in each frame space to stiffen the mould, and to carry marks or figures indicating the shape and dimensions of the lightening hole, which occurs between each pair of frames in non-watertight longitudinals. These moulds are used by the workmen for marking off the shape of the plates and the positions of the rivet holes in them, the size and spacing of the rivets being given by the specification. No moulds giving the twist of the longitudinal are required, as that is so small that the plane plate can be pressed down into shape on the ends of the parts of the transverse frames, which must be already in position when the longitudinal is erected at the ship. The external sectional shape of the bilge keel in a sheathed ship consists of a single steel plate in the middle of the section covered over by wood trimmed to shape. The plate lies in Bilge keel. a diagonal plane and is readily laid off by rabatting the diagonal plane. This gives the true form of the intersection of the bilge keel plate with the surface of the frames, and the outer edge of the plate is obtained by setting out from the inner edge the specified width of the keel plate plus an allowance for the thickness of the shell-plating. In an unsheathed ship the bilge keel is of triangular section, as shown in the body plan in fig. 99, and is formed by two steel plates riveted together at their outer edges and connected to the shell-plating by angle bars at their inner edges, the space between the plates being filled with wood. In this case the middle plane of the keel is a diagonal plane, as shown by 2D in the figure. The depth of the bilge keel at each frame plus the allowance for shell-plating is set out from the frame line along the diagonal, giving the vertex of the section of the keel at each frame station. A triangular mould is then made to the section of the bilge keel shown in the midship section drawing and is applied with its vertex coinciding with the points on the floor found as described above and with its centre line coinciding with the diagonal, and the traces of the sides of the keel are drawn by it at each frame station as ab, dc, in the figure. The surface of each side of the keel is then developed in the same way as the surface of a longitudinal except that in this case, since all the traces are parallel, the involutes used in the case of the longitudinal become straight lines, and the development is strictly accurate. A mould to each plate of the bilge keel, similar to the mould for a longitudinal plate, is prepared from the expansion on the floor and issued for the guidance of the workmen. A triangular batten mould, made to show the angle between the diagonal plane, in which the centre of the bilge keel lies, and the horizontal, and having marked on it a point to be set at a given distance from the middle line plane of the ship at the height of the under side of the keel, is also issued to enable the position of the centre line of the bilge keel to be sighted-in on the bottom plating of the ship. The remaining information issued for the erection of the ship is mostly in the form of drawings, which are largely descriptive rather than dimensioned, inasmuch as the frames and beams of larawinga the ship being once erected all other principal parts have to conform to them in shape, even where a slight difference may occur between their shape as erected and as laid off on the mould loft floor. All the drawings of the structure and of the fittings must be pushed on and issued to the shipyard in good time. Very much of the success achieved in actual building will depend upon the efficiency of the drawing office, and the rapidity with which the various detailed working plans can be supplied for guidance. These plans must be accurate and complete, and must be ready as soon as required. The drawing-office staff has the oversight of weights actually worked into the ship, a careful record of which should be kept. Each firm has its own system of work in these departments, but experience shows that the more thorough and systematic the work in the drawing office and its adjunct, the mould loft, the better the general result. Another important record is the cost of materials and labour. In all shipyards careful account is kept of workmen's time, whether employed on piece or by the day. Many different systems are in vogue; but whatever the system, the aim is to record the cost of the labour in each trade, and the detailed cost of various parts of the ship. While the work connected with laying-off and obtaining materials, &c., is going on, the shipwrights, assisted by Laying handy labourers, prepare the ground for the keel blocks, keel lay the blocks at the proper height and inclination, and blocks. secure them against being floated away by the tide or being accidentally tripped while the ship is building. The blocks consist of several pieces of tough rectangular timber, 4 to 6 ft. in length, and laid on each other to the height required. The top block is called the cap-piece, and is of oak or other hard wood. The blocks are spaced about 4 ft. apart for ships of medium size, and somewhat less for ships of large size. They are usually placed upon a longitudinal bed of timber, which remains embedded in the ground for successive ships: the ground should be hard, or very well piled, otherwise the blocks may sink when weight becomes concentrated over them during building, and difficulty arises from the keel, or the propelling shafts, drooping from a straight line. The upper surface of the blocks must be at such a height from the ground that men, especially riveters, can do their work with facility under the bottom of the vessel, that the launch can be fitted, and that when launched the vessel may move down into the water without striking the ground. The last-named is a most important consideration; and thus it comes about that the first thing to be settled, before the blocks are laid, is how the vessel is to be launched. The tops of all the blocks are accurately adjusted to a plane surface sloping about a in. in a foot from bow to stern. The shipwrights at the same time prepare the uprights for the staging, and erect them around the building berth in suitable position with the first line of staging, which will be required at an early period in the ship's construction. The platers and angle-smiths begin to prepare the keel, framing, bulk-heads, &c., as soon as the material is delivered and the laying-off and mould-making are sufficiently advanced for the purpose. The actual building generally dates from the first work of this character. The keels of small vessels usually consist of a stout flat bar placed vertically and attached to the garboard strakes by through Keel and rivets. Occasionally the keel consists of a vertical centre Kemal. through-plate, with side bars at its lower edge. In large merchant ships, and in war vessels, the keel usually consists of a wide horizontal plate running along the centre line of the bottom, the sides being turned up as necessary to follow the shape of the bottom (see figs. 118 and 119, Plate XIV.). The framing varies very considerably with the size and type of the ship, as already described. In small vessels a frame usually consists of an angle bar, called a frame bar, extending from gunwale to gunwale, to which is riveted a bar, also continuous from gunwale to gunwale, called a reverse bar, in such a way as to form a built-up Z-bar, and between these floor-plates are introduced across the bottom, to give the required strength when resting on the ground or on the blocks. Sometimes the frame consists of a Z-bar, in which case the reverse bar is not required in the vicinity of the floor-plate. Sometimes angle bulbs are used for frames, as in the case of oil steamers, where internal ceilings are not required. The process of constructing a complete frame of angle bars and plate is as follows: From the scrive-boards the shape of the section at the frame is transferred to the bending blocks or slabs, the outline being drawn in with chalk; the necessary preparation is made, and the frame bar is drawn from the furnace, and while hot bent to its shape and given the required bevel. The reverse bar is prepared in the same way, except that the inner edge of the frame and floor must be worked to. The floor-plate has to be cut to shape. In large ships the frame bars, reverse bars and floor-plates will be in two, or even in three, pieces; in this case the butts are kept some distance from the middle line, and are shifted in alternate frames, so as not all to lie in the same fore-and-aft lines. The butts of both frame and reverse bars, as well as those of the floor-plate, are butt-strapped, to maintain as much as possible the strength of the structure. The frame bar, floor-plate and reverse frame bar all being set, they are placed together in their respective positions over the outline of the frame on the slabs or scrive-boards, the final adjustments made and rivet holes marked and punched, and the work secured together and riveted up. When the keel is in place, and as far as possible riveted, the frames, bulkheads and beams, which have been made ready by the iron-workers, are brought to the building slip and got into position by the shipwrights. They are held in place and faired by means of shores and ribbands. The latter are made from straight-grained timber of considerable length, sawn out in long straight pieces of square transverse section. They hold the frames in position until the outside plating is riveted. Upon them are marked the lines at which they must be crossed by each frame, and they are bent round and attached to the frames in a fore-and-aft direction at certain heights, which are marked on the frames at the scriveboards. Some four or more ribbands are used each side of the ship. As the work proceeds, the positions of the frames and ribbands are checked continuously, their positions being maintained by shores from the ground, or some structure prepared for the purpose. Except in small vessels, the beams are not attached to the frames before they are erected, but are hoisted into place as soon as possible afterwards. The bulkheads are put together on some convenient flat surface, sometimes on the scrive-board or a similar platform constructed for the purpose. If of large size, they are transferred piece by piece and erected at their proper positions in the ship; but when-ever possible, they are rivited up and hoisted into position complete. The stem and sternpost are obtained from the forge or foundry and erected at an early stage of the work. The part of the stern abaftthe transom is sometimes framed separately on the ground before being erected in the ship. The centre keelson is generally worked intercostally between the floors, but it has continuous parts, usually angle bars, above the floors. Each intercostal plate is secured by angle bars or flanged edges to the floors and to the flat keel plate. Sometimes it is continuous, especially in large ships and in war-ships. The frames are then cut by it, and the floor-plates are attached to it by short angle bars. After the centre keelsons, the side keelsons and side and deck stringers are fitted. The steel pillars are substituted for the shores supporting the deck beams, being riveted at their heads to the beams and at their heels to the keelson, inner bottom or tank top. While the work is proceeding, the shipwrights make the stages, put up gangways and ladders for carrying on the work, fit extra blocks and shores, or remove and replace them as may be required. They line off all plate edges on the frames, the overlap being usually painted in with white paint, ready for the platers. They also erect the stem, sternpost, rudder and shaft brackets, or struts in twin-screw vessels. In a ship fitted with an inner bottom the procedure is somewhat more complicated, as the transverse frames cannot be lifted into place as a whole. There are many varieties in the arrangements in such cases; one frequently adopted is shown in fig. iii in which the inner bottom extends out to the turn of the bilge. This figure also shows the general construction of the vessel, including the framing at a bulkhead and elsewhere, the bulkhead itself with all its stiffening bars and attachments to the sides of the vessel, and the inner bottom. At the centre line, immediately over the flat keel plates, there is a vertical girder, the full depth of the double bottom, connected to the flat keel plate and to the centre plate of the inner bottom by continuous double-angle bars. This centre girder may or may not be water-tight, according to the desired tank arrangements. The transverse frames are in four parts: the two lower extending on either side from the centre girder to the margin plate of the double bottom, which is a continuous girder of special construction; and the two upper, from the margin plates to the top-sides. The lower parts consist of a floor-plate with angle bars at its edges for attaching it to the outer and inner bottoms, the centre girder and the margin plate. At the bulkheads these floor-plates are solid, and the angle bars are united and made water-tight; elsewhere they are lightened by holes, and the angle bars at their upper and lower edges and ends are separate pieces. The two upper parts of the transverse framing consist of a frame and a reverse bar, each having a deep and a shallow flange, and are riveted to one another along their deep flanges, with their shallow flanges standing the reverse way to one another. The shell-plating is attached to the shallow flange of the frame bar. Between the centre girder and the margin plate on each side of the ship there are two intercostal girders, the plates of which are connected by short angle bars to the floors-and to the shell and inner bottom plating; and between the margin plates and the lower deck on each side there are three stringers, consisting of intercostal plates attached by short bars to the outer plating, and three continuous angle bars riveted to part of the intercostal plates which extend beyond the reverse bars. In the course of erection, after the flat keel plate is laid upon the blocks, and the centre girder placed upon it, the two lower parts of the frames, which have been constructed alongside, are put into position, their outer ends being carried by ribbands shored from the ground. The intercostal girders and margin plates are then fitted. The lower edge of the margin plate is brought close to the outer edge of the frames, and is connected by a longitudinal angle bar to the shell-plating, while its upper edge is flanged for the purpose of being attached to the inner bottom plating. The ship at this stage gives the impression that a flat pontoon is being constructed. When the margin plates are up and faired and, as far as desirable, riveted, the upper parts of the frames on each side are erected and the fairing proceeded with as before. The beams are now got into place, also the side and deck stringers. As will be seen, the margin plate cuts completely through the transverse frames, and special brackets are provided to maintain the transverse strength. The chief advantages derived from cutting the frames by the margin plate are the cheapness with which water-tight work is secured, and the rapidity with which this part of the work can be proceeded with. As soon as the keelsons and stringers are riveted, and the ship by their means sufficiently stiffened, the outside or shell plating is commenced. The plating squad is supplied with a drawing ll r showing the disposition of the butts in each line of plates; S heoutsido e light wooden moulds or templates are then made, giving l t s e the exact shape of the edges and butts, and the positions p of all the rivet holes in the frames. From these moulds the edges and butts and the holes are marked off, the holes are punched, and the edges and butts sheared and planed. The plates are then rolled to shape, furnacing being resorted to only when the curvature is too extreme to be obtained with the plate cold. The usual arrangement of the plating is that of inside and outside strakes alternately (see a, fig. 79). The inside strakes, which are worked first, are templated off the ship, and lie directly on the flanges of the frame bars. The outside or overlapping completed at as early a period as possible, and painted, so the work on the squads plates are then worked, and are templated from the place they are in a smith's fire is required. It is usual to defer the painting of intended to occupy on the ship. They are kept at the proper I certain parts of the steel structure of a ship as long as possible, so distance from the frames by liners or slips of the same thickness as the adjacent inside plates. Towards the ends of the ship the number of strakes of plating must be reduced, as the girth along the frames is much less than over the midship portions. Stealers are introduced for 1P011 this purpose; they are single plates, which at one end _, receive the butts of two plates, and at the other the butt of only one. By them two strakes are merged into one. Th Thbflii b fd ill ee numer o pates requrng toeurnaces sma in comparison with the whole number, but there are always IMF it some at the after end of the ship, especially in the neighbourhood of the boss (for the stern tube) and the counter, and a few at the forward end of most ships. As each plate is got ready, it is taken to the ship, hoisted into position, and temporarily secured by the platers by means of bolts and nuts. As the work of plating proceeds, and the weight~~. of the ship increases extra shores are put into place and ~= ~,,\-bilge blocks erected by theshipwrights,tokeep thestructureI to its shape and prevent local and general "" unfairness. The shell-plating in way of the intended bilge blocks is it r. a, ,. _.I~_~~I~A=111! of riveters are engaged on the deck-plating and internal work, such as the bunkers, engine and boiler bearers the , shaft tunnel, casings and, in the later stages, the hatches, houses on deck, &c., and as much as possible of the light. lght. A s the s the is wo rk is rk is before completed the sbyhellthe platers, out the day-for nternal work done ters, it is ready the riveters and caulkers; and these trades follow on I r- d ~~/'~~~~~~r~i~~~~ without delay, except in some parts of the casings an decks in way of the machinery, which are left portable, and taken down after the launch, to allow the machinery to be put in place. The platers usually work in squads, composed generally of three platers, a marker-boy and a number of helpers or labourers, the number of whom depends on the size and weight of the plates, and the nature of the work to be done on them, and also on the facilities of the yard for hand-ling such material. On the work of a large vessel many of these squads would be employed. The riveters also work in squads, a squad consisting of two riveters, one holder-up and one heater-boy, with sometimes a catcher, i.e. a boy to pass on the heated rivets when the distance from the rivet-hearth is great. Pneumatic riveting has not made great progress in Great Britain. Hydraulic riveting to a limited extent is adopted, especially in the case of work that can be taken to the machine, such as frames, beams and other parts; but in shipbuilding the large proportion of the riveting is done by hand. In the Royal dockyards platers' work is done by shipwrights, and riveting is not considered a trade; though regarded as skilled labour. Shipwrights also lay the blocks, erect the ribbands, shore and fair the ship, but labourers construct the stages. Drillers' work consists in drilling by hand or by portable electric or pneumatic drills holes which it is not convenient or possible to punch or drill before erection ; they also rimer out and countersink punched and drilled holes when this is necessary. Portable electric or pneumatic drills are used when possible in some ship-yards, and three-cylinder hydraulic engine drills are employed for some purposes, such as in cutting armour bolt holes in thick plating behind armour. The caulkers follow closely upon the riveters, and generally work singly. A very important part of a caulker's duty is water-testing. In the large oil-tank steamers possibly 8000 tons of water are used for testing one ship alone, and about the same amount for a large war vessel. This water is pumped from the sea or river into the compartment to be tested. In the case of an oil vessel, each compartment is filled right up, and a pressure put on by means of a stand pipe, carried .for a considerable height above the highest part of the tank; any leakage found must be made good by the caulker, and the tank retested until it is perfectly water-tight. The double bottoms of merchant ships, and the smaller compartments and double bottoms of war vessels, are filled up and tested by a head of water rising a few feet above the load water-line. It is not usual to fill all the larger compartments, such as boiler and engine rooms in war vessels, or the machinery compartments and cargo holds in merchant ships; but water at a high velocity is played on the bulkheads by hose, to test the water-tightness and the strength. An occasional test, however, is made by filling a typical large compartment with water to a height of some feet above the load water-line. Angle-smiths form beam knees where that ordinary red rust may form and dislodge the black mill scale these are welded, and generally all angle-bar work where heating ` which is answerable for a great deal of corrosion in steel ships, as 0 g 81Q 0 FIG. III.—British Cargo z 4 s a - so that when once the bilge blocks are in place they need not be disturbed until immediately before launching. While Steamer; midship portion, in perspective. in certain circumstances it forms a galvanic couple with the steel plate. For warships the British Admiralty requires the removal of this scale from these parts by immersing the plates in a weak solution of hydrochloric acid. Red and white lead, oxide of iron and oxide of zinc form the bases of most of the paints used on steel ships. Structural Arrangements. The following are particulars of ships recently built at New London (Conn., U.S.A.) on the longitudinal system: " The great centre girder, which in all vessels prior to these has been in the form of an I girder, is formed of a double II or box; that is, these vessels have two vertical keels instead of one. The girder is of the same depth as the double bottom (6 ft.). On each side of this girder there are several other vertical longitudinal members, having the plating on the top, forming the tank top, and the shell-plating below, forming the bottom of the tank. This tank or double bottom is 6 ft. deep for the greater part of its length, and is increased at the extremities, where it merges into the fore-and-aft peaks at the collision bulk-heads. The whole of this space can be filled with water when desired, to sink the ship to a suitable draught when making a voyage without a cargo or with a very light one, at the same time allowing the ship to keep afloat whenever the outer shell or skin has been pierced by rocks or by colliding with other vessels. This bottom girder or double bottom forms the ' backbone' of the ship, from which the great frames spring or extend up to the weather deck, about 6o ft. above the keel. The frames are made of channel steel spaced 30 in. apart, but as they near the extreme ends they are spaced closer, and are
End of Article: LONER

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