All the elements insuring the qualities that embody a wellshaped boat of the particular type contemplated and at the same time a stable ship having been thus determined, the lines may be commenced with the certainty that no unnecessary alterations will be required. The freeboard will be calculated from the legal tables given and explained herein, but in any case the limiting draught consistent with the block coefficient determined on as the maximum available for the required speed should be taken advantage of. After carefully drawing the center and other construction lines, and marking off the ten or twenty ordinates that it is proposed to use, it will be well to have a definite routine or method in which to draw down the various views comprising what are embraced under the general term "lines." To this end the following will prove a good sequence: 1. The "dead flat" section on body view. 2. Rail sheer line. 3. Contour of stem and stern in profile. 4. Rail half-breadth. 5. Load water line half-breadth. 6. Bilge diagonal. 7. Transfer L. W.L. and B.D. -breadths to body plan. 9. Trial displacement by planimeter. 10. Sheer heights from profile to body plan. Taking this routine in order: — 1st. The dead flat or midship section should present no difficulties, as the area of this section is pre-determined from the coefficient B. This being so, the height of rise of floor construction line is assigned by giving the easiest bilge consistent with the area of section demanded. In no case should the bilge be "squarer than the demands of this area require, as in full vessels sufficient difficulty is encountered in setting the bilge strake plates and bending the frames without adding further to it. 2d. In most vessels, except yachts and launches, it will be found advisable to make the lowest part of sheer at the half-length amidships, as otherwise correction would have to be made for freeboard and the classification societies' numerals. It is best, then, after fixing the height of bulwark or sheer strake above upper deck to underside of moulding, to run a pencil line parallel to L. W.L. from A.P. to F.P., at which points and above this line the sheer forward and aft should be set up. The amount of sheer will of course depend on the type of vessel, i.e. whether intended for sea or river. In the latter case it is evident the same amount of "spring" would not be required as for over-sea voyages. The standard sheer prescribed by the British freeboard tables will be, however, a good guide, and where this is deemed insufficient or where special cases suggest a departure from these, as in passenger steamers and first class ocean liners, a handy rule and one that gives a very symmetrical sheer is to take one-fifth of the vessel's length in feet, calling the quotient inches which will equal the amount of sheer forward. One-third of this will be the sheer aft, as :Length in feet - Sheer forward in inches, Sheer aft in inches. 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′′ sheer at 4th station F.P. 82" x .562 66 46" sheer at 3rd station forward of lowest 82′′ × .250 201′′ sheer at 2d station forward of = 82′′ × .0625 = 51′′ sheer at 1st station forward of 66 and for the sheer aft: = A.P. 30" x 1.000 = 30" sheer at 4th station 30" x .0625 = 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." 66 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 3-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. |