Page:Proceedings of the Royal Society of London Vol 1.djvu/517

Rh propensity of all large vessels to bend from head to stem when ﬁrst launched, by reason of the great weight of the two extremities, and the little support at these parts in comparison with the centre, which, from its greater breadth, sustains an over-large proportion of the whole pressure.

This defect of the common structure is shown by reference to a common ﬁeld gate, which, without the diagonal piece, or brace, would soon fail at every joint, but, when braced, partakes of the advantage of the triangular structure, the principle of which, when correctly applied, occasions the whole stress to be diverted from the transverse direction of the timbers employed, and thrown into that of their length, in which their strength is greatest.

Accordingly, in the new system of ship-building here described, the object of the author has been to introduce diagonal timbers and planks in as many parts of the fabric as could Well be accomplished.

In the ﬁrst place, a diagonal timber is introduced between the upright timbers in each interval between the ports; secondly, instead of the lining, which it has hitherto been the custom to place within the frame, a diagonal timber-work is introduced, intersecting the timbers of the frame at angles of 45°, and about six or seven feet asunder. with their upper ends abutting against what are called the shelf-pieces of the gunadeck beams, and having their lower ends supported by the timber strakes. Between these are also placed other timbers, equally inclined, but in an opposite direction, so as to present a rhombic net-work, which is dowelled to the original frame, and is itself further strengthened by short pieces placed diagonally from corner to corner of each rhombic compartment.

Beside the addition which is thus made to the strength of the sides of the vessel, these sides are also more ﬁrmly united together by an improved construction of the knees, by which the transverse beams are united to them. A degree of unity and ﬁrmness is also given to the decks by an oblique position of the planks, which, upon the same principle as before, brace the beams and joists, and resist that yielding of the joints which would otherwise take place in their rectangular construction.

The object of the author has been to give as much inﬂexibility as possible to every part of the hull; for in this part he conceives that unbending stiffness is better calculated than any yielding elasticity to resist those forces to which this portion of the vessel is liable; for though a hope has been entertained, that the known weakness of the common construction might lessen the violence of sudden shocks, by allowing each part to yield in some measure to the force impressed, this conception, he thinks, is not founded on any distinct knowledge of principles, and could not be entertained by those who consider that yielding does not imply elasticity, and who observe, that those parts which yield instead of recoiling with equal force, only become progressively weaker, in consequence of the violence they sustain.

In addition to the foregoing means of bracing by oblique position of timbers and decks, Mr. Seppings has introduced another practice,