On Naval Timber and Arboriculture. Patrick Matthew
leaders; they do not form a proper junction with the stem, by reason of the wood, as it swells, not being able to throw up the bark out of the narrow angle; thence the bark of both stem and branch is enclosed in the confined breek, and the wood never unites6, thence disease is {10} liable to be generated between them, or the branches are subject to be torn down by the wind; and should they ultimately come to be removed, being then of considerable size, and the section from their perpendicular position being partly horizontal, as the sides of the wound swell up, the rain lodges in the centre, and generates rot. These nearly perpendicular branches generally originate from improper pruning, springing out where a large branch has been cut away.
Lop off all branches, which, by taking an irregular direction, incline to rub upon the more regular; also remove all splintered, twisted, and diseased branches.
Do not cut away any of the lower branches (feeders) till they become sickly or dead. By pruning these prematurely, you destroy the fine balance of nature, and throw too much vigour into the top, which in consequence puts forth a number of leaders. You also diminish the growth of the tree by the loss of healthy feeders; the timber of the tree increasing in proportion to the quantity of healthy branches and foliage (the foliage being the stomach and lungs {11} of the plant). You also, by diminishing the number of feeders, increase the comparative size of those remaining, which throws the upper part of the stem into large knots, improper for plank, and renders then future excision dangerous, as large feeders, when circumstance or decay require their removal, or, when they are rifted off by winds or snow, leave wounds which often carry corruption into the core of the tree.
After the tree has acquired a sufficient height of bole for plank, say from 20 to 60 feet, according to circumstance of exposure, climate, &c., and also as many branches above this height as may be thought necessary to carry on advantageously the vital functions, as the superior head will now sustain small injury by being thrown out into large branches and plurality of leaders, (if it be oak it will become more valuable by affording a number of small crooks and knees); it will then be proper, in order to have timber as clean as possible, and regularly flexible, to lop clean off all the branches on the stem as far up as this required height. From the early attention to procure very numerous feeders, and to prevent any from attaining large size, the wounds will very soon be closed over, leaving no external scar, and as little as possible of internal knot or breaking off of {12} fibre. There are many salves, panaceæ, and pigments in use for covering over the section of removed branches, which in ordinary cases may occasion no injury, but they are unsightly. In wounds of beech trees where the cut tubes are so prone to die downward a considerable way into the stem and to generate rot, an antiseptic quickly-drying pigment might be beneficial. This and the time of the season for pruning, at which the cut tubes or fibres are least liable to die inward, deserve attention. We consider the spring the least dangerous time. Should a number of small shoots spring out in consequence of this last pruning, they may be swept down if good plank be desired; if not, they may remain, as their presence will not greatly injure the plank, and they occasion the stem to thicken considerably faster where they grow: yet it is probable that, in doing this, by obstructing the flow of the sap downwards, they may interfere with the natural enlargement of the roots, and ultimately be injurious. Some varieties, or rather some individuals of oak, are much more prone to this sprouting upon the bole after pruning than others; where the disposition exists in a great degree it ought to be encouraged, and the tree set apart for the construction of cabinet work. {13}
This system of pruning—encouraging numerous feeders and one leader while the tree is young, and of allowing or rather inducing the branches, after the tree has acquired sufficient height, to spread out into a horizontal top, is in harmony with, and only humouring the natural disposition of trees, and is therefore both seemly and of easy practice7. The perfection of naval forest economy would consist in superadding (according to instructions to be given on training of timbers) a top of which every branch is a valuable bend or knee, though in consequence of the situation the timber will be fragile, and of light porous texture.
In pruning and educating for plank timber, the whole art consists in training the tree as much as possible, and with as little loss of branch as possible, to one leader and numerous feeders, and to the regular cone figure which the pine tribe naturally assumes. This can be best and most easily performed by timely attention—checking every over-luxuriant, overshadowing branch and wayward shoot on its first appearance; so that none of the feeders which spring forth at first may be smothered, till {14} they in turn become lowermost; and by the influence of rather close plantation, which of itself will perform in a natural manner all that we have been teaching by art, and will perform it well. This closeness must, however, be very guardedly employed, and timeously prevented from proceeding too far, otherwise the complete ruin of the forest, by premature decay or winds, may ensue, especially when it consists of pines. Of course all kinds of pines require no other attention than this (well-timed thinning), and to have their sickly moss covered under branches swept clean down.
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