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COURSE OF

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Originally appearing in Volume V24, Page 966 of the 1911 Encyclopedia Britannica.
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COURSE OF CONSTRUCTION] other See also:

information required for laying the See also:vessel off and making the necessary moulds being usually given on other drawings. The sheer See also:drawing of the " See also:Lord See also:Nelson contains the information usually given concerning the See also:form of the See also:ship and other features of the See also:design required for laying the vessel off, ordering the material for her construction and afterwards erecting the same in position. In these drawings it has been necessary for the See also:sake of clearness to reduce the number of square stations and See also:water or level lines commonly shown in drawings of this See also:character. The number of these lines is fixed in the preparation of the design by the See also:necessity of accurately defining the See also:surface of the ship so that the intentions of the designer as regards form, displacement, and what may be called the geometrical features of the ship may be realised. In a large warship there are usually 21 square stations shown, including the forward and after perpendiculars, the distance between which defines the nominal length of the ship. The water-lines are 3 to 4 ft. apart. Intermediate square stations and water-lines are frequently introduced where the curvature of the surface of the ship is rapidly altering; as at the ends and below the See also:bilge. It is usual, and obviously sufficient in the sheer drawing as well as in the See also:process of laying off, to show only one-See also:half of the ship on one See also:side of the See also:longitudinal See also:vertical See also:plane of symmetry. Thus, in the half-breadth See also:plan only the See also:port side of the ship is See also:drawn; and in the See also:body plan, for greater clearness, the half ship is further divided, the See also:part forward of the midship See also:section, or square station at the See also:middle of the length of the ship, being shown on the right of the middle See also:line of that plan, and the part aft of the midship section on the See also:left of the middle line. Other Drawings.--The See also:profile and plans and the midship section have also been described in this See also:article. The profile and plans of H.M. yacht " Alexandra " are given on plates. Fig.

84, See also:

Plate X., is the profile which shows in sectional See also:elevation all the decks, bulkheads, machinery, living spaces, See also:store spaces, &c.; See also:figs. 86, 93, 94, 95 and 96, Plate X., give the plans of the See also:promenade See also:deck, upper deck, See also:main deck, See also:lower deck and hold respectively with important fittings shown upon them; figs. 88, 89, 90, 91 and 92, Plate X., give sections of the ship showing the inboard See also:works at stations E, D, C, B and A on the profile respectively; and on fig. 97, Plate XII., is given the midship section with all the See also:principal scantlings of the framing and plating. Fig. 98, Plate XIII., also gives the midship section of H.M. battleship " Lord Nelson." Any two of the three plans of the sheer drawing may be taken to represent the " See also:horizontal " and " vertical " planes of Descriptive See also:Geometry, and are theoretically sufficient to define the shape of the vessel completely, but the three plans are practically necessary for the sake of clearness and are always used. In the design sheer drawing the lines may represent the inter-sections of planes with the surface of the framing of the ship, or with an imaginary surface having a mean position between the irregularities of the surface of the ship caused by the See also:system of plating adopted. The former system is the more usual in the drawings of See also:steel-built See also:merchant See also:ships, necessitating an See also:allowance on all measured dimensions used in calculating displacement, &c.; the latter system is usual in warships, in which the surface represented by the sheer drawing of a ship plated with raised and sunken plates strakes as described on p. 962, would be an imaginary surface midway between the outsides of the raised and the sunken strakes. A sheer drawing on this latter system is said to show displacement lines in contra-distinction to the former system which shows " moulded " or See also:frame lines. In the See also:case of vessels with a See also:plank sheathing over the bottom the surface shown on the sheer drawing is the outside of the planking. As the See also:primary See also:object of the laying off of the ship is to ascertain the shape of the frames, the surface of the outside of the frames is always that which is laid off on the See also:mould See also:loft See also:floor.

If displacement lines are given in the sheer drawing a preliminary process of deriving from them the moulded lines is necessary before laying off on the floor. The process, to be strictly accurate, involves setting in the requisite distance along the normal to the surface shown in the sheer drawing. This is easily done at the midship section, where the normal to the surface lies in the plane of the section and coincides with the normal to the See also:

curve of the square station in the body plan, or at the practically vertical parts of the sides of the ship, where the normal to the surface lies in the water plane and coincides with the normal to the water-line in the half-breadth plan. In other positions, however, It would be necessary to See also:rabat a plane containing the normal on one of the planes of reference, set in the required distance along the rabatted normal, find the projections of the point in the frame surface so obtained and of other similar points, and thus obtain the projections of curves on the frame surface, which by their intersections with ordinates and water-lines would give a new set of square stations and water-lines corresponding to the moulded surface of the ship. Such a process, though See also:simple, is more laborious than is necessary in view of the degree of accuracy required, and in practice it is customary to set in normal to each square station a distance slightly greater than the thickness of the plank and plating, the increased distance required being roughly estimated from a See also:consideration of the obliquity of the water-lines, without producing any sensible See also:error. The frame lines having been obtained, it is customary at some shipyards to "See also:fair" the body on See also:paper on a larger See also:scale than that965 of the sheer drawing, before laying off on the floor. This saves a certain amount of labour in fairing the full-sized body on Fairing the floor, the errors in the body as first copied on the floor, which it is the object of the fairing process to correct, being proportional to the increase in scale in first copying. The process is similar to the full-sized fairing which is described below. A straight line is drawn on the floor parallel to a fixed straight See also:batten nailed to the floor a See also:short distance from the See also:wall of the See also:building to represent the load water-line in the sheer and body plans and in such a position that the whole See also:depth of the ship can be drawn with regard to it within the limits on the floor and clear of the batten, the inner edge of which becomes the See also:base-line of the sheer, half-breadth and body plans. The fore and after perpendiculars of the sheer and half-breadth plans are drawn at right angles to this line and the fixed batten in convenient positions near the ends of the floor, the fore perpendicular on the right and the after perpendicular on the left as in the sheer drawing, and so as to allow the extreme outlines of the See also:stem and stern to be drawn upon the floor together with not less than one-fifth of the length of the sheer and half-breadth plans at each end of the ship. A line perpendicular to the water-line and the fixed batten is drawn, usually near the middle of the floor, to represent the middle line of the body plan. The middle line of the half-breadth plan is usually taken as coinciding with the base-line, the inner edge of the fixed batten.

The level or water lines shown on the sheer drawing are drawn in on the floor parallel to the load water-line so as to serve for both the sheer and body plans. Ordinates representing those given in the sheer drawing, which correspond to the sections in the body plan, are drawn in the sheer and half-breadth plans and others are added where desired, so also are additional water-lines between those shown on the sheer drawing and above the load water-line, so that in full-sized drawing on the floor the sections and stations may be sufficiently near for fairing the whole of the See also:

external form of the ship. If, as is usually the case, the ship is too See also:long to be laid off in one length on the floor the midship portions of the sheer and half-breadth plans are drawn superposed over the forward and after parts, and are usually contracted longitudinally as will be described presently. The distances from the middle line along each water-line in the body plan of the See also:original sheer drawing, or of the enlarged body when the process of preliminary fairing has been adopted, to the intersection of the water-line with each section are measured to scale and tabulated. At the lower parts of the body, in the vicinity of and below the " bilge," where the water-lines cut the square stations very obliquely and the points of intersection become somewhat indeterminate, See also:diagonal lines as shown by ID, 2D in fig. 99 are drawn in the sheer drawing in such positions as to intersect as many as possible of the square stations approximately at right angles, and the corresponding diagonal lines are drawn on the floor. The distances from the middle line of the body plan in the sheer drawing along the diagonal lines to their intersections with the sections are measured and tabulated. It is usually desirable, especially in ships with a See also:great extent of practically See also:flat bottom, to draw See also:bow and buttock lines to include this portion of the surface, such as IB in the figure, as the diagonals approach more or less closely to bow and buttock lines and shorter measurements are required in transferring the lines; the heights of their intersections with the transverse sections above the base-line being measured and tabulated. The See also:draught of water of the ship at the forward and after perpendiculars is given in the See also:specification enabling the underside of See also:keel in the sheer plan to be drawn in on the floor between the points where the rise of keel commences at the extremities. The flat part of the keel is generally See also:uniform in width for the greater part of the length of the ship, and tapered at the extremities. The line representing its side must be drawn on the floor in the half-breadth plan. The height of keel-line above the base-line at each station in the sheer plan and the corresponding half siding of keel are the co-ordinates of the lower extremity of the corresponding transverse section in the body plan.

The lower extremities of the sections are at once fixed in the body plan by the intersections of their horizontal and vertical ordinates transferred from the half-breadth and sheer plans For the upper endings of the transverse sections in the body plan a level line is generally drawn on the body of the sheer drawing just above the See also:

projection of the upper deck edge and the sections at the square stations produced to meet it. The intersections of this water-line with the sections are measured and tabulated. The whole of this process of measurement and tabulation is frequently done in the drawing See also:office, and the " loftsman " or See also:person who conducts the laying off on the floor is not supplied with the sheer drawing, but only with these tables of offsets," and similar tables for the lines in the sheer and half-breadth. The process, however, is the same in either case. The tabulated measurements for the sections of the body plan are then set off full See also:size by means of long measuring staffs on the lines on the floor, corresponding to those in the sheer drawing on which the measurements were taken, and thus give points whose co-ordinates are to those of the corresponding points in the drawing in the ratio of 48:1, if the drawing from which they were taken was to a scale of 4 See also:inch to the See also:foot as is usually the case. A suitable See also:wood batten is then See also:bent or " penned " as nearly as possible through the 966 See also:series of points on the several water, diagonal and buttock or bow lines corresponding to each square station, being held in position by nails, specially adapted for the purpose, lightly driven into the floor, the batten in each case being adjusted so as to See also:lie in a fair curve. Usually the batten will not under these conditions pass through all the points found for the curve on See also:account of irregularities introduced or magnified in the process of enlarging to full size, and it must be allowed to take up a mean position passing outside some of the points and inside others. All of the sections i i the body plan are drawn in with See also:chalk in this way. The section where the greatest breadth of the ship occurs, usually at or near the middle of the length, must have the line parallel to and half the moulded breadth of the ship from the middle line for a tangent, and no section must project beyond this line.

End of Article: COURSE OF

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COURNOT, ANTOINE AUGUSTIN (1801-1877) 		[next]
COURSING (from Lat. cursus, currere, to run)

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