Chapter X: X. The rails of the head

Y. The knee of the head, or cutwater.

Z Z. The cheeks of the head.

a a. The cat-head.

M ⊕ C. The rising line of the floor.

_k_ _u_ C. The cutting-down line, which limits the thickness of all the floor-timbers, and likewise the height of the dead-wood afore and abaft.

⊕ _u_ U W. The midship-frame.

_a_, _b_, _c_, _d_, _e_, _f_, _g_, _h_. The frames or timbers in the fore-body of the ship, i. e. before the midship frame.

1, 2, 3, 4, 5, 6, 7, 8, 9. The timbers in the after-body, or which are erected abaft the midship-frame.

As the eye of a spectator is supposed in this projection to view the ship’s side in a line perpendicular to the plane of elevation, it is evident that the convexity will vanish, like that of a cylinder or globe, when viewed at a considerable distance; and that the frames will consequently be represented by strait lines, except the fashion-piece abaft and the knuckle-timber forward.

It has been already observed, that the plane of projection may be defined a vertical delineation of the curves of the timbers upon the plane of the midship-frame, which is perpendicular to that of the elevation. It is necessary to observe here, that the various methods by which these curves are described, are equally mechanical and arbitrary. In the latter sense, they are calculated to make a ship fuller or narrower according to the service for which she is designed, and in the former they are drawn according to those rules which the artist has been implicitly taught, to follow, or which his fancy or judgment has esteemed the most accurate and convenient. They are generally composed of several arches of a circle, reconciled together by moulds framed for that purpose. The radii of those arches therefore are of different lengths, according to the breadth of the ship in the place where such arches are swept; and they are expressed on the plane of projection either by horizontal or perpendicular lines; the radii of the breadth sweeps being always in the former, and the radii of the floor sweeps in the latter direction. These two arches are joined by a third, which coincides with both, without intersecting either. The curve of the top-timber is either formed by a mould which corresponds to the arch of the breadth-sweep, or by another sweep, whose center and radius are without the plane of projection. The breadth of the ship at every top-timber is limited by an horizontal line drawn on the floor-plane, called the half-breadth of the top-timbers. The extreme breadth is also determined by another horizontal line on the floor-plane; and the lines of half-breadth are thus mutually transferable, from the projection and floor-planes, to each other.

The necessary data by which the curves of the timbers are delineated then are, the perpendicular height from the keel, the main or principal breadth, and the top-timber breadth: for as a ship is much broader near the middle of her length than towards the ends, so she is broader in the middle of her height than above and below; and this latter difference of breadth is continued throughout every point of her length. The main breadth of each frame of timbers is therefore the ship’s breadth nearly in the middle of her height in that part: and the top-timber breadth is the line of her breadth near the upper ends of each timber. It has been already observed, that as both sides of a ship are alike, the artificers only draw one side, from which both sides of the ship are built: therefore the timbers abaft the midship frame are exhibited on one side of the plane of projection, and the timbers before it on the other.

Plane of PROJECTION, Plate I.

A. The keel.

B C. The line which expresses the upper-edge of the keel, from which the height of each timber, and height of its different breadths are measured.

B D and C E, perpendiculars raised on the line B C, to limit the ship’s extreme breadth and height amid-ships; or, in other words, to limit the breadth and height of the midship-frame.

A F. A perpendicular erected from the middle of the keel to bisect the line of the ship’s breadth in two equal parts.

F * 9. The half-breadth line of the aftmost top-timber; being the uppermost horizontal line in this figure.

Note. The seven lines parallel to, and immediately under this, on the right side of the line A F, are all top-timber half-breadths, abaft the midship-frame; the lowest of which coincides with the horizontal line D E.

The parallel horizontal lines nearly opposite to these, on the left side of the line A F, represent the top-timber half-breadths in the fore-body, or the half-breadths of the top-timbers before the midship-frame.

G, H, I, Q, R, S, T. The radii of the breadth-sweeps abaft the midship-frame; those of the breadth-sweeps in the fore-body, or before the midship-frame, are directly opposite on the right side.

⊕ A ⊕. The midship-frame, from the extreme breadth downwards.

1, 2, 3, 4, 5, 6, 7, 8, 9. The out-lines of timbers abaft the midship-frame, in different parts of their height.

_a_, _b_, _c_, _d_, _e_, _f_, _g_, _h_. The outlines of the timbers before the midship-frame, in different parts of their height, h being the foremost, or knucke-timber.

K _i_. The wing-transom, whose ends rest upon the fashion-piece.

L. The deck-transom, parallel to, and under the wing-transom.