Читать книгу On Naval Timber and Arboriculture - Patrick Matthew - Страница 5
ОглавлениеPART I. STRUCTURE OF VESSELS.
VESSELS are constructed of wood under two forms, Plank and Timbers; Plank, the out and inside skin of the vessel—Timbers, the ribs or frame which support the plank.
SECTION I. PLANK.
Trees intended for plank ought to be reared in close forest, or protected situation, drawn tall and straight, or what is preferable for a part, with a gentle regular bend, technically sny, Figs. v and x, (next page). It requires to be of clean solid texture, from 12 to 40 feet in length, and at least 8 inches in diameter at small end, or any greater thickness. For the conveniency of transport, oak plank timber is generally squared or planked where grown, and is cut out from 2 1⁄2 to 7 inches in thickness, and from 6 to 18 inches in breadth. Plank is needed of such various dimensions, that any oak tree of clean timber, nearly straight one way, and straight, or with a gentle regular bending, the other, may safely be cut into plank, the section to be in the plane of the {6} curve. Figs. v, x, y, z, represent the most advantageous forms of logs for cutting into plank. The dotted lines shew the section of the saw in planking: the straighter the log is in the plane of the saw, it is the more suitable, as the planks bend sufficiently side-way by steaming; Fig. v, of considerable bend and taper, where the planks, when cut, have a bend edge-way, is the most valuable: this form requires to be very free of knots. In straight planks, Fig. z, cleanness from knots is not such a desideratum.
Figs. z, y, of any length—best long; x, from 25 to 35 feet; v, v, from 12 to 24 feet.
In the above cut, for distinctness, the saw is drawn entering the butt. In practice it enters the top.
When planks are cut out where grown, they are sawn from the round log immediately after it is {7} felled and barked, which not only prevents injury from drought-cracks, but produces also a considerable saving of timber and labour, as the wood is softer when green; and the centre planks can thus be had much broader than after squaring the log. The outer part of the matured or red wood, which is partly cut away in squaring, is also the cleanest for bending. The sap or not sufficiently matured wood, when left on the side of the plank in the vessel, wherever it is not always soaking in water, is only useful to the shipwright, as it decays in two or three years, and demands an expensive repair. When plank timber is squared, it is for the conveniency of carriage and stowage, and where timber is of little value.
Of British trees suited for plank, the most valuable are oak, Spanish chesnut, larch, red wood pine, and sometimes beech4, elm, plane (Acer pseudo-platanus) under water. As no timber decays under water for a considerable length of time, when put in fresh, unless it be devoured by the sea-worm, beech or any other hard tough wood is nearly equally good as oak for outside plank under light water-mark, provided the timber be hastened out of the bush into the vessel, or be kept in pools, either in log or {8} plank, till used, or be planked, and the plank kept dry under cover. One summer on the ground will generally render a beech log in the bark useless.
DIRECTIONS5 FOR TRAINING PLANK TIMBER.
Divide all branches into leaders and feeders; leaders, the main or superior shoots which tend to become stems, A, a, a; feeders, the inferior branches, B, b, b, b.
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Should more than one leader appear from the time of planting the tree till it attain the required height for the plank, shorten all but the most promising one down to the condition of feeders, making the section immediately above a twig, preferring one which takes a lateral or horizontal direction. Vide dotted line crossing a, a.
Should any feeder, below the required height, become enlarged beyond its compeers, such as B, reduce it to equality (vide dotted line), or prune it close off, if this should be necessary to the symmetry of the tree.
Cut off, close by the trunk, all shoots which rise at a very acute angle with the main stem, such as C. There is a triple reason for this: they rise up and interfere with the more regular horizontal feeders, tending also to become 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.
