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Originally appearing in Volume V24, Page 972 of the 1911 Encyclopedia Britannica.
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SNATT SWELL AT 6ECTIONS IN WANE OE DOUBLE BOTTOM position of the palms and the direction of centre of shaft. Guided and the sloping sides form cylindrical surfaces. The straight lines of by these moulds and the detailed drawing, the pattern for casting the A brackets is made. The projections of the plate and longitudinal sight edges are drawn in the body plan on the floor by measuring their distances from the middle line along each frame line in the half- Sight Si in block model, on which they have been already arranged, e he t he body enlarging the measurements to full size and setting them t plan. off round the corresponding square stations in the body. The points so found should lie on fair curves, if the sight edges have been properly arranged on the model, except of course where discontinuities in the curves may occur, as where a plate sight edge crosses a longitudinal sight edge to avoid an acute intersection. The edges of the sunken strakes of plating are drawn parallel to and distant the width of the lap from the sight edges, and as already stated, the breadths of the bottom plates are measured between the lines of plate edges so found and used in ordering the material from the manufacturers. The surface of the inner bottom is defined relatively to the outer bottom by the depth of the vertical keel and longitudinal frames Inner given in the specification. The outline of the vertical keel bottom. is also shown in the sheer drawing, and the general shape of the inner bottom by the midship section, which is often supplemented by a section through the engine-room where the double bottom is locally made deeper. The surface, of the longitudinal is arranged so that its trace with the plane of each square station is approximately normal to the curve of the square station; taken in conjunction with the method of drawing the sight edges so as to cut the frame lines as nearly as possible at right angles, this is approximately the same thing as generating the surface of the longitudinal by the normal to the ship's surface as it moves along the sight edge. The depths given in the specification are depths measured in the plane of the square stations, and, when the longitudinals are fitted on a raised strake of outer bottom plating, are greater by the thickness of that plating than the distance to be set in from the frame line to find the inside of the frame on the inner bottom. The latter is usually worked with the strakes of plating disposed " clinker " fashion, or is sometimes flush with edge strips fitted on the underside. Points in the sections of the inner bottom frame surface by the planes of the square stations are obtained by setting in the depth of the longitudinals, and the surface of the inner bottom is faired by diagonal and water lines in the same way as the outer frame surface. In the engine-room space where the depth of the double bottom is increased, and'where there are usually plane surfaces to take the structure under the engine bed, and a cylindrical recess to provide clearance for the engine cranks, these special features must be faired separately, so also is any bossing of the inner bottom at the after end to allow clearance for the shaft tube and fittings. The plate edges already arranged on the model of the inner bottom must be transferred to the floor and faired in the same way as those of the outer bottom; and the breadths of the plates measured from the floor must be used in ordering the material from the manufacturers. Before and abaft the double bottom the transverse frames may consist of zed bars, split at their lower ends for the insertion of a Inner floor plate. The longitudinals are reduced in depth, ace o1 and are intercostal between the frames until they coalesce sune con- frames. with flats or fore and aft bulkheads, or they are con- fram S. tinued as deep zed bars slotted over the narrower trans- double verse frames. The inner surface of the frames therefore Outside bottom. does not require any process of general fairing; but the upper parts of the floor plates are drawn on the floor, and are faired locally throughout the lengths of the ship where they maintain a uniform character. - The freeboard forward and aft and amidships is generally given in the specification and can be measured from the sheer drawing. Deck Guided by these dimensions and by the deck lines shown lines. in the sheer drawing, the heights of the intersections of the beam at middle with the square stations are marked on the corresponding square stations of the contracted sheer plan and faired, and the intersections with the square stations are then projected to the middle line of the body plan. The round up or camber of the midship beam of each deck is shown on the midship section drawing. The camber line is a circular arc, the round up being the versed sine of half the arc and the breadth of the ship at the level of the beam the chord. A mould is readily constructed to these data and is applied so that the chord is perpendicular to and its middle point coincident with the middle line of the body plan on the floor. When the centre of the arc coincides with a point projected from the beam at middle line the arc cuts the corresponding square station at a point in the projection of the beam-end line. The points in the beam-end or beam-at-side line so formed should lie on a fair curve, which is tested by projection into the contracted sheer plan, and the line is then rased in in the body plan. The shape of the lower protective deck in a battleship is shown in the sheer drawing. Throughout that part of the length of the ship covered by the main armour belt, which rests on this deck, the deck edge usually lies in a water plane. The middle part of the deok also lies in a water plane, except where it is raised up over the engines, the sides and middle part of the deck section are joined ny arcs of circles of uniform radius, and this part of the deck is necessarily fair from the nature of the method of constructing the sections of its surface. At the ends of the ship the beam-at-middle and beam-at-side lines are copied from the sheer drawing and faired on the floor and the beam surface between these points may be faired by one or more bow and buttock lines. The surface of the framing behind the main armour belt in a war-ship, arranged as shown by the midship section depicted, is parallel to the surface of the armour and distant from it the thick- ness Pra of armour and wood backing plus the thickness of andm ping lating plating behind armour, generally a double thickness of behind plating flush jointed. This distance, less the thickness of armour the shell plating already taken off in getting in the frame lines, is set in normal to the surface shown by the lines on the floor in wake of the armoured side by approximate methods similar to those used in taking off the plank and plating, and the projections of the frame lines behind armour in the body plan are thus obtained and drawn in. The frames are usually single zed bars extending vertically from deck to deck and are completely defined by these lines without the necessity of drawing any inside surface lines. Projections of the intersection of the surface of the frames behind armour with the beam surface of the deck at the top of the frames and with the plate surface of the deck at their heels are drawn in the half-breadth plan, and expansion drawings of the frame surface are prepared in a manner somewhat similar to that which will be described later in dealing with the expansion of the surface of each separate armour plate, except that in the present case the whole length of the surface is expanded in two or three z-in. scale drawings. The expanded positions of the frame lines, and of any longitudinal girders which may be fitted behind armour are shown on this drawing, also the approximate positions of the armour plate butts and edges and of the armour bolts. The butts and edges of the plating behind armour are arranged on this drawing and the dimensions of the plates measured therefrom in ordering them from the manufacturers. Thin protective plating beyond the ends of the main armour belt usually projects from the ship's side and is secured without wood backing direct to the shell plating, which is worked in two thicknesses flush jointed in wake of the protective plating. In this case the frame surface of the ship already laid off is the frame surface behind armour, and the disposition of the butts and edges of the plating behind armour and of the armour itself is arranged on the half block model; but only the plating behind the armour is ordered to dimensions taken from the model. It is important that the detailed information giving the shapes and dimensions of the armour plates should be in the hands of the manufacturers as early as possible on account of the time required for the manufacture of this material. As, more-fie over, modern armour plate steel is so hard that it is im- armour of possible to cut it with machine tools, the plates must be $ยต,s hip, delivered of the exact size required, and the information sent to the Manufacturers must be of a high degree of accuracy. For this reason the shapes and sizes of the armour plates are sometime$ obtained by the " mocking up " process, in which the surface of the armour is represented in three dimensions by making moulds or batten frames to the sections of the surface in the body' plan on the floor and erecting them in their correct lateral and fore and aft relative positions. The positions of the butts and edges of the plates being marked on the frames so erected, the moulds for each plate, as described below, can be made with great accuracy, and this process is practically necessary if there is any considerable twist in the surface of the ship where covered by the armour. In general, however, the armoured side is very little twisted and can be treated for practicable purposes as a developable surface, in which case the necessary information can be obtained by a process of laying off as described below, which, though obviously only approximate, is found by experience to be sufficiently accurate for practical purposes. In fig. io7 the portion of the body plan shows sections of the armour surface by planes of the frames, which are generally a ft. apart behind the armour, and the half breadth shows projections of the upper and lower boundaries of the armour surface, and of the joint between the two strakes, which is arranged to lie in a level plane. The armour belt extends from the main deck above to the armour deck below. The upper edge of the armour, therefore, follows the beam-at-side line of the main deck; but is generally allowed to be about in. below it, so as to make sure of getting in the armour, in spite of possible small inaccuracies in building the rest of the structure, which might result in restriction of the space between the two decks. The lower edge follows the armour deck edge, which is usually a level line throughout the length of the belt; but is kept an inch or two above it to avoid making the armour plates with a sharp edge to fit the acute angle between the protective deck and the ship's side; the armour, how-ever, actually rests on the deck as shown by the midship section depicted. The butts of the armour are arranged" brick fashion]," that is, the butts of one strake at the middle of a plate in the adjacent 972 strake, and each butt should be as close as possible to one of the vertical frames behind armour in order to allow the armour bolts to be sufficiently near the butt of the plate. At the same time it is convenient both for manufacturing purposes and for erecting the plates at the ship, to have the butt surfaces as nearly as possible normal to the surface of the plates. The butts are therefore arranged in vertical planes whose traces in the half-breadth plan lie in direction between the normals to the projections of the upper and lower edges of the plate. The lengths of the plates are made as great as possible taking into consideration the capacity of the manufacturer's rolls and of the appliances for handling them during erection at the ship. To lay off any plate such as that of which the projections of the intersections of the planes of the butts with the surface of the armour are ab, cd in the body plan and alb', cidl in the half breadth, a straight line YY is drawn in the body plan so that its direction lies between the directions of the normals to ab and cd at the points where they cut YY, and a straight line XX is drawn in the half-breadth plan similarly lying between the normals to al ci, and bl di and approximately at the centre of the plate. Battens are bent to the curves aYb, cYd, a1Xc1, b1Xd1 and the points named are marked on the battens so as to give the lengths aY, bY, a1X, &c., measured round the curves. A pair of rectangular axes OX, OY are then drawn in any convenient position on the floor and the points a2, b2, c2, d2 found such that the co-ordinates of a2 are Ya, Xal, of b2, Yb and Xbl, of c2, Yc and Xei, of d2, Yd and Xd1. The figure a2b2c2d2 obtained by joining the points so found by straight lines is regarded as the expanded shape of the surface of the plate. A flexible batten mould is made to this figure and is used by the manufacturer to mark the four corners of the plate and thus to get its superficial size. A pair of moulds such as N are made, one to the top and the other to the bottom of the plate in the half-breadth plan, showing the curvature of the edge and the direction of the butts; and another pair such as M, one at each butt, showing the curvature of the edge of the butt plane and the sectional shape of the top and bottom of the plate. The butt moulds are made to the section of the surface of the plate by the plane of the frame, which is indistinguishable from the section by the very slightly inclined plane of the butt. Each of the butt moulds serves for the two plates which join at the butt, but each edge mould refers only to one plate. Female moulds, the backs of which are straight lines which lie in one plane, or, as it is technically expressed, are " out of winding " when the moulds are in their proper position, are also made to fit on the butt and edge moulds as P, Q in the figure. By means of these moulds the manufacturer makes each separate plate to its correct curvature and twist, while the top and bottom " out-ofwinding " moulds for two or more consecutive plates have a common straight line drawn on them as ll in the figure, to fix the relative position of the plates when they are temporarily erected at the manufacturer's works to prove the correctness of their shape. A drawing is also made showing superposed expansions of the back and front surfaces of the armour without any necessity for extreme accuracy, as these surfaces are fully defined by the moulds. The butts and edges of the plates with numbers identifying each plate with its moulds are shown on this drawing.[COURSE OF CONSTRUCTION The specification gives particulars of the dimensions of the bolt to be used and lays down the general principle of their distribution, e.g. one bolt to so many square feet of armour. The bolts are approximately arranged in accordance with this specification on the expansion of the plating behind armour. For the purposes of the present drawing their positions must be definitely fixed sufficiently clear of the frames behind armour to allow space for putting on the nuts. With vertically arranged frames practically the fore and aft position only is of importance from this point of view. The projections of the normals to the plate surface representing the centre lines of the bolts are drawn in the half-breadth plan, and shifted if necessary to give the required clearance of the frames. The positions of the centres on the back of the plates are then measured along the curved sections of this surface in the body and half-breadth plans from the nearest edge and butt, and these distances are indicated in figures on the drawing. The positions of any holes for the fastenings of top and bottom edge covering plates, or of any fittings to go on the outside surface of the armour are also shown by figured distances from the edges and butts of the plates on this drawing. All holes must be drilled and tapped in the plates by the manufacturer before the final hardening process which renders the material unworkable. The drawing also shows the plate in each strake selected as the " shutter in " or last plate to be fitted in place. This plate is not finally completed by the manufacturer until all the rest are in place at the ship and moulds have been made to the space which remains to be filled up. The moulds for screen bulkhead armour are prepared in a similar manner, but the process is usually simpler as the surface of this armour, when not actually plane, is cylindrical with a vertical generating line and therefore accurately developable. For barbette armour nothing more than a drawing is usually necessary, the barbette being circular in plan, the surface cylindrical and the top in a horizontal plane. The information issued from the Mould Loft for the guidance of the workmen in the shipyard has been generally order of passed over in the foregoing work. description, which has been de- voted principally to the information pre-pared for the guidance of manufacturers of material, but it is not intended to imply that all the material is ordered before erection is begun. Much of the information for the erection of the frames and other parts of the structure, including the keel and transverse and longitudinal frames amidships, may be given before the ends of the ship are faired on the floor. Keel battens are provided giving the spacing of the transverse frames through- out the length of the ship, the Keel. lines defining their positions on the battens being marked with the distinguishing numbers by which the frames are identified on all the drawings, moulds and information subsequently issued. The drawing showing the size of each plate and the position of each butt of the flat and vertical keel plating and angle bars, prepared in connection with the ordering of the material, is completed to show all details of the keel and its riveting in accordance with the specification, and serves as information for its erection. Section moulds are made in accordance with the frame lines in the body plan for guidance in shaping the flat keel plates transversely, and on these the edges of the adjacent plates are also marked. The practice, at one time quite common, of making batten moulds to each frame line on the Mould Loft floor for the guidance of the workmen employed bending the angle or zed bars, and Transverse shaping and assembling the parts of the frame, is now frames. almost entirely superseded by the use of the " scrive- board." Such batten moulds, when issued, showed the outline of the frame, or of the part of the frame between two longitudinals, the shape of the floor plate or bracket plates, the position of the plate edges and other bevelling spots, and generally everything necessary for completing the frame ready to go into its place at the ship. The scrive-board is an auxiliary mould loft floor constructed conveniently near the frame-bending slabs, and having copied on it, with certain modifications or additions adapting it to the Scrive- practical needs of the shipyard work, the whole of the board. body plan as laid off on the Mould Loft floor. For con- venience in copying the lines it is sometimes made so that it can' be divided into portable parts and taken to the Mould Loft to have the lines copied on it, and then transported to its proper position and put together again. Otherwise it is a fixture in its proper
SNAPDRAGON, or ANTIRRHINUM (Gr. Fis, ptvbs, snout, ...

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