Sivut kuvina
PDF
ePub
[ocr errors]

"squarer

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. Z-breadths to body plan. 8. Draw freehand the sections to foregoing. 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

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,
5
Sheer forward

= Sheer aft in inches.
3

and,

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 = 46" sheer at 3rd station forward of lowest
82" X 250 = 201" sheer at 2d station forward of

82' X .0625 = 53" sheer at 1st station forward of and for the sheer aft:

30" X 1.000 = 30% sheer at 4th station = A.P.
30% X .562 = 167" sheer at 3d station abaft lowest
30 X 250 = 71" sheer at 2d station abaft

30" x .0625 = 17" sheer at 1st station abaft 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 4-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 bollow. 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.

7

[merged small][graphic][subsumed][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The length of overhang of course cannot be arbitrarily fixed, but a very fair proportion

for ordinary freighters is zy to z 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-breadthat 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 rail) 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 tabulated 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.

[blocks in formation]

.630 .714 .786 .882 .946 .985 1.000 .989 .934 .820 .594 .358 Stem

.444

.756 .757 .812 .889 .854 .990 .918 1.000 .951 1.000 .988 1.000 1.000 1.000 .991 1.000 .965 .985 .891 .856 .727 .572 .576 Stem

.756 .829 .872 .934 .977 .994 1.000 .994 .965 .877 .619 .366 Stem

.603 .730 .810 .910 .967 .979 1.000 .979 .960 .910 .740 .515 Stem

.603 .691 .772 .875 .955 .995 1.000 .978 .930 .803 .532 .298 Stem

.655 .790 .845 .912 .965 .987 1.000 .971 .944 .884 .666 .404 Stem

6 7

.355

9 91 10

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 of and transferred to the half-breadth plan. Should, however, the line delineated after the spline has be 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 what ever area be cut off at any one point be compensated for elsewhere on the water line, as the offsets taken from the diagram will en close 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 actua load water lines of several types with the coefficients of area o same (a).

Load Line Half-Breadths Standardized.

[blocks in formation]

Post .289 .531 .828 .945 .988 1.000 .976 .881 .670 .357 .180 Stem

Post .448 .770 .980 1.000 1.000 1.000 1.000 1.000 .985 .781 .464 Stem

Post .148 .479 .818 .948 .999 1.000 .928 .793 .578 .328 .150 Stem

Post .382 .642 .884 .977 1.000 .987 .932 .791 .578 .308 .154 Stem

Post Post
.407

.275
.678 .483
.898 .750
.965 .900
.992 .980
1.000 1.000
.989 .900
.955 .760
.830 .550
.537 .303
.282
Stem Stem

Post .333 .631 .892 .977 .995 1.000 .980 .942 .775 .440 .228 Stem

6 7 8 9 93 10

.182

« EdellinenJatka »