The amount of sheer having been decided upon with the lowest part, say, at the half-length, the quickest and simplest way to run the sheer line, insuring a fair curve, will be to divide the halflength before and abaft the lowest sheer, into four equal parts, and at each of these points set up the perpendicular heights obtained, as under, postulating in this case that the sheer at F.P. is equal to 82 inches, and the sheer at A.P. 30 inches, giving a mean sheer of 56 inches, as per freeboard tables. 82" x 1.000 82" x .562 = = 46′′ sheer at 3rd station forward of lowest = 201′′ sheer at 2d station forward of 66 82" x .0625= 51" sheer at 1st station forward of 66 82′′ × .250 and for the sheer aft: 30" × 1.000 = 30" sheer at 4th station = A.P. 30′′ × .562 = 167′′ sheer at 3d station abaft lowest 30" .250 = 71" sheer at 2d station abaft 30′′× .0625= 13′′ sheer at 1st station abaft 66 By pinning the spline to these spots and adjusting the free ends to the eye, an absolutely fair sheer line may be run in, bearing in mind, however, that in ships with a very full rail line forward, compensation must be given on the sheer to adjust the great disparity in the length of the half-breadth rail line and the same line projected on sheer plan; as, if this be not done, the rail line on model, and of course on the actual ship, will appear as "rounding down." 3d. The contour line of the stem will be very much a matter of individual taste, although above water line it is usual to make it straight unless in special cases. By "straight" is meant "apparently so, as it is customary to give about -inch round on face of stem from where it leaves the top of the forefoot curve to stem head, an absolutely straight line adjoining a curve appearing as slightly hollow. Also, it is not advisable to make the stem plumb, as the illusion in that case is to make it appear as leaning aft. A rake forward of about twice the moulding of the stem head is common. In outlining the stern and counter the same remarks as to taste apply, care being taken that the counter line where it meets the rudder post is carried by an imaginary curve to harmoniously meet the arch of body post. The counter line, from knuckle moulding to stern post, should be perfectly straight - not hollow. A hollow to this line gives the appearance of an overweighted overhang, and a broken sheer, besides making the plating more difficult to set. The length of overhang of course cannot be arbitrarily fixed, but a very fair proportion for ordinary freighters is to of the length. The height of deck or rail at taffrail, or "cock-up," will be dependent on the camber of deck at transom frame (No. 0). The midship camber proportioned to the half-breadth at this frame should be set up and the deck line carried through this spot in a fair curve to taffrail. The height so obtained should be then transferred to body plan, and the deck (or rail line) between No. 0 section and taffrail drawn in as a round of beam curve, from which may be obtained the intermediate spots for deck at side (or ail) on sheer plan. 4th. The rail half-breadth will depend on the particular type of ship being designed. In freighters it will be parallel to the center line for probably half the length amidships, whereas in yachts and other fine vessels it will "round" all the way. It is convenient to have rail half-breadths at hand for various types of vessels for, say, ten ordinates with half-end ordinates or whichever number is adopted as the standard. These should be tabuated with the half-breadth amidships as unity, when, with the aid of a slide rule, the half-breadths for the design may be very rapidly proportioned. It will be found convenient to have these for liners, freighters, sound and river steamers, yachts, etc., from good examples of their respective classes. The contour of rail line around taffrail will require careful fairing into the A.P. ordinate spot, and also at center line, where in no case should it be perfectly straight, the effect of such being a hollow. Neither, on the other hand, should it come to a "peak or point, but carefully drawn as an arc of a circle. The knuckle mouldings, whether they be one or more, may with advantage be delineated by tracing the rail line just drawn and transferring it forward to its exact location. By so doing it will be seen that the stern between knuckle and rail lines will develop with a pleasing gradation from "O" frame to the upper counter line. Table of Rail Half-Breadths for Various Types. 5th. The load water line, as already stated, must circumscribe the area calculated with the aid of the coefficient a. The method of obtaining a has been previously explained. To obtain the form of this water line, and at the same time insure the accuracy of the required enclosed area, it will be found advantageous to prepare a diagram similar to the one opposite, or this one may be used with the aid of proportional compasses. Opposite the value of a for the design in hand half-breadths for ten ordinates may be read off| and transferred to the half-breadth plan. Should, however, the line delineated after the spline has been fixed not meet with the designer's individual taste, or where greater fullness or fineness is required for special cases, forward or aft, it will be a very simple matter to modify the line, at the same time observing that whatever area be cut off at any one point be compensated for elsewhere on the water line, as the offsets taken from the diagram will enclose exactly the area required. Of course the designer may make his own diagram for the number of ordinates he prefers to design with. In any case the run of the line for a few feet forward of the post will require special adjusting when the oxter is being faired. In addition to the diagrain, the following table is given of actual load water lines of several types with the coefficients of area of same (a). Load Line Half-Breadths Standardized. a.857. a.683. a .717. a .797. a.656. a .771. 6th. The construction line for the bilge diagonal is variously drawn from rise line or base line; but the latter is the more useful, being adaptable to extremes of types and unaffected by rise of floor line; i.e., the line should be drawn diagonally across the DIAGRAM OF BILGE DIAGONAL OFFSETS body plan from the intersection of the base with the half moulded breadth line to center line at load water line height. It is evident that the area enclosed by this line must bear a close relation |