On Naval Timber and Arboriculture

SECTION II. TIMBERS.

Timbers, as before stated, are the ribs of the vessel, spreading out and upward (excepting at the bow and stern) at right angles to the keel and keelson, two large straight logs which form a double spinal support or backbone. The ribs or compass timbers in great public building establishments are sometimes bent by machinery, after being softened by steam or hot liquids8; and for this purpose the {15} cleanest straightest wood is requisite. We, however, do not believe that pieces of great diameter, bent artificially, can have equal strength and resilience as when grown bent-the fibre must in some degree be crippled. We admit that timbers and frames may be built of separate bended pieces of no great thickness, and have all the strength and resilience of natural bend: the strongest and most elastic mode of forming vessels would be to compose them of different layers of plank over each other in diagonal fashion, or at an angle 60°, but the labour and inconveniency of these modes would be great. We will not admit that an experiment between the strength of a piece of coarse cross-grained timber, half naturally bent, half cut out of the solid, and that of a piece of clean timber artificially bent, is any proof on the subject. Let us produce a clean natural bend, exactly fitted to its place, without any section of fibre, and make experiment with it. But at any rate, as this plan (bending of timbers) has never been adopted to any extent in our private building-yards, we must doubt its economy-either {16} that the practice is of no considerable advantage, or that the requisite machinery is too expensive for private establishments, and conclude that fine bent timber still continues a necessary in the formation of at least our mercantile marine.

Of the very ingenious innovations in the structure of vessels contrived by Sir R. SEPPINGS, by which knees and crooked timber might nearly be superseded, we can only say, the practice is not followed, and, at least in private building-yards, not likely to be so;-that the demand for fine crooked timber, comparatively, is, and will continue to be, as great as ever. Should our war navy, from the introduction of steam impulse and bomb cannon, be reduced to fleets of strong gun-boats, the demand for crooked timber, instead of lessening, will greatly increase-the building of frames of straight timber being more expensive, and less suitable, in small than in large vessels; and should war occur, in the hurry of the formation of a new war navy under a different principle, the speediest and simplest mode of construction will be followed.

Nearly two-thirds of the timbers of a vessel consist of the curves and bends a, b, c, d, e, f; the other third is of straighter timber, and easily obtained. {17} All timbers require to be straight in one way-in the plane of their side, and the sides generally to be square. The under measures embrace timbers of appropriate size for vessels from 50 to 500 tons register; it is seldom that merchantmen are required under or above this size. Of course, large war-vessels require timbers of larger dimension. The corresponding timbers of vessels of different size are nearly similar figures, and the length of their respective lines not far from being in the ratio of the cube root of the tonnage-a little deeper and thicker in the smaller vessels. When timbers are formed of larch or pine, they require to be a little more in diameter than when of oak. {18}

Fig. a, Flat floor, from 9?1?/?2 to 18 feet long (that is, 9?1?/?2 for a vessel of 50 tons, and 18 for one of 500), and from 9 to 16 inches deep at middle; thickness 1?/?4th less than depth, the diameter increasing in proportion to the length. When fillings such as s are used, flat floors are cut from straight logs.

b, Rising floor shorter, and same depth and thickness as former.

c, c, High rising floors, from 4 to 8 feet in length of wing, and a little deeper, and same thickness as former. From the difficulty of procuring this bend, the wings are often used of unequal length, according as the timber turns out, the shorter wing to exceed 3 feet, and more when of considerable diameter. Floors are of every rise from a to c, being flattest at midships, and rising gradually as they approach the bow and stern. In all timbers, it is necessary, for strength, that the fibre of the wood extend from one end to the other without much cross grain. See lines on high rising floor, c.

d, First foot-hook, from 7 to 13 feet long, and from 7 to 14 inches deep; thickness 1?/?5th less than depth.

e, Second foot-hook, from 6 to 10 feet long, and from 6 to 13 inches deep, thickness 1?/?6th less than depth. This curve, when of great size, is valuable as, breast-hooks-curved timbers stretching horizontally within and at right angles to the bow-timbers, to support the bow.

f, f, f, Knees, the one wing nearly at right angles to the other; from 2 to 9 feet in length of wing; depth at middle as much as possible; thickness from 4 to 12 inches-generally required about 3?1?/?2 feet in length of wing, and from 6 to 8 inches thick. Knees, when large, suit for high rising floors.

Fig. h is a valuable piece, and easily procured by bending the young plant; when cut, it forms two second foot-hooks.

Figs. a, b, c, d, e, are suitable, though the part cut off by the dotted line be awanting. In good work, this plan is often followed, and a cross-chock put on. (Vid. s, left side of the cross-section of a vessel thus timbered, page 20). By this {19} mode of building, vessels can be constructed from much straighter timber, and the vessels are superior, from being more elastic; but from the nicety and expense of the work and waste of timber, the practice is not much in use.

A first foot-hook alternates with each floor, and second foot-hook, alongside, extending from o to q; and a top-timber, or third foot-hook, alternates alongside of each second foot-hook, and chock extending from q to a. These timbers are bolted together, and constitute a frame or double rib; and the skeleton is composed of a series of double ribs (several inches separate, of course wider above than lower down, as the timbers decrease in thickness), to within a little of the bow and stern, where the timbers are usually placed singly, without framing. {21} In large vessels a fourth futtock is used; thence straighter timber is suitable.

The knees occupy the position at x, stretching horizontally along the inside of the vessel and end of the beams.

Of British trees, timbers are formed of oak, Spanish chestnut, larch, red-wood pine, red-wood willow (the stags-head ozier, Salix fragilis), and sometimes the broad-leafed elm (Ulmus montana) under water.

In Britain, crooked oak for timbers is found chiefly in hedge-rows and open forests, where the winds, casual injury, or overhanging superior branches, have thrown the tree, while young, from its natural balance; or, by the tree, from open situation, or excision of lower branches, parting early into several leaders, which, in receding from each other, form curves and angular bends. On the Continent of Europe, in the natural forest, it is chiefly the tops of old lofty trees which afford the crooks; in consequence, those we import are, for the most part, of a free, light, insufficient quality9. {22}

To procure a sufficiency of excellent crooks, every person who has the charge of young plantations of timber intended for naval purposes, ought, in the more exposed situations not favourable to the growth of plank timber, or timber for bending, when the plants are from 3 to 15 feet high, to mark out the most healthy, suitably formed plants, sufficiently close to fill the ground when of the proper size, say 6 yards apart, and to bend these, as the under figures will illustrate. The dotted portion is the growth after being bent. {23}

The bend of floors requiring to be at the middle, and of angular bend, see Fig. f, young trees of one-half the required length, should have the earth removed from the bulb of the root, from one or both sides, according to circumstances, and the tree and stool partially upset to windward, that is, generally south-west; (the operator, in effecting this, may be assisted by a strong pronged instrument); then fixed in this inclined position, and the earth filled in. This inclination may be given at planting, when the plants are tall.

The best mode of securing the larger plants in their bent position, is by rods, forked or hooked at one end, the other end nailed to a ground-stake;-the upper end, if forked, firmly tied to the bent plant by mat or straw rope. Smaller plants may be secured to the notched tops of stakes by ligatures; and the smallest, particularly larch, pinned down by small stakes with hooked tops. Advantage may also be taken of an adjacent tree of small value, and which would ultimately be required to be thinned out, to tie the bended standard down to the most convenient part of its top or stem, lopping off all above the ligature, if it interfere with the standard, and barking it near the ground, to prevent much future growth. When the workmen comprehend {24} the required...