Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

The use of timber of the first year's fall we should most peremptorily prohibit; the vital principle, like that of seeds, will, we suspect, in every species of timber, make an effort to develop itself the first returning spring.

No discovery has yet been made, that we know of, of a speedy method of seasoning timber by artificial means, though numerous experiments have been tried with that view ; such as charring, burning, stoving, burying in unslaked lime, or sand, coating with paint, tar, and compositions of various kinds, the effects of which have generally been found pernicious, by tearing the fibres asunder-or favourable to the progress of decay, by driving the moisture into the interior parts of the wood and preventing its escape.

Various attempts have also been made to destroy the principle of vegetation, by impregnating timber with some chemical preparation, as solutions of green vitriol, arsenic, acetate of lead, alum, &c. infusions of galls, common salt, &c. all of which have failed. We know not if corrosive sublimate has been tried; but we are sure, at least, that it is destructive, both of animal and vegetable life. It is well ascertained by those concerned in alum works, that the timber used in them acquires not only a great degree of durability, but becomes nearly incombustible. All processes, however, by impregnation are likely to prove too tedious and expensive to be applied ou so large a scale as is required for the timber employed in ships of war. Add to this, that all acid impregnations would be destructive of iron, which is but too liable to corrosion by the acid of the woods in their natural state.

Experiments, we understand, are now making at Woolwich, on the speedy seasoning of timber, by stowing some hundred loads in a close kiln, and introducing, by means of a retort filled with sawdust, an oleaginous substance, which, by insinuating itself into the pores of the timber, as the aqueous or sappy particles are driven off by heat, prevents the fibres from being torn asunder and preserves the logs from cracking. The idea is ingenious, but we augur no useful results from the experiments themselves. It has not been discovered, from the closest inspection, that any artificial process was adopted in seasoning the timber of the Royal William, or any other of our most durable ships; while, on the other hand, the sound state of timber found in old cathedrals, churches and mansions, after many centuries, affords the most ample proof that nothing more is necessary to secure its durability than proper seasoning, exclusion of wet and damp, and exposure to the common air. The beautiful roof of Westminster Hall is as sound and perfect as on the day it was erected. It is for those concerned in the management of timber to de: termine (what indeed ought not, at this late period, to be a subject of inquiry) in what mode the seasoning by a natural process may best be

C 3

effected,

THE

effected, whether by piling it in stacks, or placing it on-end under sheds, or strewing it horizontally on the ground; by siding or squaring the tree when it is felled, or by leaving the outside or sap, as it is called by the workmen, to protect the more central part from cracking

It is not enough, however, that the timber which enters into the construction of ships be thoroughly seasoned; it should be kept as much as possible free from moisture. The alternate exposure to water and air, to heat and cold, will sow the seeds of decay in the best oak how well soever it may be seasoned. It would be vain therefore to expect any very protracted period of duration in ships which, while building, have been exposed for four, five, or six years to all the vicissitudes of the weather. Yet this exposure, water-soaked at one season, split by the heat of the sun at another, and the crevices filled with ice at a third, is called seasoning! We should call it AN ADMIRABLE INVENTION FOR DESTROYING OAK TIMBER BY THE common rot IN LEAST POSSIBLE TIME ; and the fact is that some of the timbers which have been set up the first year, are found so far gone, in the third or fourth, as to make it necessary to replace them with others less seasoned.* Instead of six years exposure on the stocks, with the bottom of the ship water-soaked in the cavity called the slip, and the upper part splitting in the sun, or cracking with the wind, sir months would be more than sufficient to complete the machine, when the necessary quantity of dry and duly seasoned timber was collected and prepared on the spot. This, however, is not the practice; trees which have been felled a dozen years, and trees which have scarcely left the forest half as many months, greet one another in the same machine. These timbers are closed

up

with plank of many inches thick which must necessarily be soaked with wet, in order to bend it to the frame of the ship; and which, as it becomes dry, sbrinks from its work. Mr. Pering therefore suggests the propriety of building ships under cover. This is not a new idea. The Swedes build all their ships of war at Carlscrona in covered docks. The slips in the naval arsenal of Venice are roofed; and the French have a covered dock at Brest. England, the first naval power in the universe, and equal to all the rest united, is most deficient in proper accommodations for its navy. Her dock-yards have risen from small beginnings to their present state, by a succession of expedients and make-shifts. The navy which they have created has altogether outgrown them; they are wanting in extent, and in the conveniences due to so magnificent

In the Nelson, a first-rate building at Deptford, some of the timbers have rents in thein six feet long; these receptacles for rain and ice will probably before next summer be increased to twelve feet.

a fleet.

6

a fleet. The expense of a covered dock would be doubly saved in the first line-of-battle ship built in it. The workmen would perform their work sooner and better, because no kind of weather would interrupt their progress. The ship would be caulked, and painted, and coppered when dry, to the exclusion of partial leaks, suffocated damps, and oozing drip.'

But the premature decay in our ships of war is not to be ascribed solely to the state of the timber employed in their construction, nor to their being built in the open air. It is frequently owing to the mode of fastening by treenails, ' a mode,' says Mr. Pering, so objectionable that I defy all the shipwrights in the kingdom, or the art of man to invent a worse instrument for confining the planks of a ship to her side.'* Though not so decidedly hostile as Mr. Pering to this instrument, provided it be made of good sound oak of the same seasoning as the pieces which it is meant to bind together, yet we agree with him in considering it as a very imperfect species of fastening, and highly approve of the substitute which he proposes, namely, a copper bolt, of about seven eighths of an inch in diameter. Its advantages consist, in the first place, in giving a less wound to the plank and timbers, and thereby allowing a reduction of the scantling or size of the timbers; and, in the second, in giving more security, firmness, strength, and, consequently, durability to the machine. The increased expense, supposing it to amount to £2000 or £3000, or even twice as much, in a line-of-battle ship, is of very little moment, when set against the increased durability of the ship, and, above all, the increased security of her crew.

As we look on the proposed substitution as matter of no inconsiderable importance, we have endeavoured to obtain some accurate information on the subject; the result of our inquiries is as follows: that taking the number of treenails required to fasten a 74 gun ship at thirty thousand, the value of them will be about £800. The weight of copper bolts required to replace them, may be about 45,000 pounds, which, at fifteen pence the pound, would amount to £ 2,862. This additional weight, which would sink the ship in the water little more than one inch, would neither impede her sailing, nor injure her stability, as it would be principally below the line of flotation. When the ship, so fastened, is worn out, the original value of the copper cannot be reduced more than a fourth, so that the new ship, to which they may afterwards be applied, will

* Treenails, as the word implies, are pins of cleft vak, from an inch to an inch and a half in diameter, and from a foot to nearly four feet in length, used for fastening the inside and outside planks of a ship to the upright timbers. They have recently been made of American pitch pine, a wood more liable to dry-rot, and decay than oak, and consequently very improper for the purpose.

be

be fastened with copper bolts at a cheaper rate than with treenails. There is already a complete establishment at Portsmouh for remelting and rolling copper sheathing. I wish they had tried it on one ship,' says Mr. Secretary Peps in bis MS. memoirs, when copper was first proposed for sheathing ships. They did try it near a century afterwards; and though it succeeded beyond expectation, yet such were the prejudices of the surveyors of the navy, that there was but one coppered ship in the whole tleet under Admiral Keppel. “We wish,' in our turn, that our more enlightened surveyors could be prevailed on to try copper bolts“ on one ship.'

The bolts used for fastening the knees, beams, &c. are now generally of copper. The bolts of the knees and hooks and the nails of the decks are recommended also to be of copper instead of iron, upon the exposed parts of which, the sea air and salt water act with great power, while the acid of the wood acts still more powerfully on those that are buried within it. Whether of copper or iron, the common practice is that of clenching them by battering the ends of the bolts over metal rings. If a clench, in the first instance, could bring all the work tight together, consisting, as it sometimes does, of three or four pieces, and from three to sixteen or eighteen feet thick, which must of course be the length of the bolts, it could not remain tight for any length of time. It would be as endless as useless to cut off the clenches and endeavour to harden up the bolts; and the ship must become more loose and leaky from day to day ; as was the case with the Ocean and the Bulwark before they had been twelve months at sea.

* Let a coachmaker,' says Mr. Pering, build a coach, and fasten it together in the same way as a shipwright fastens a ship, hy driving in bolts, and then clenching them on the wood; how long will that coach run over the stones in London, or on the turnpike road? But he resorts to a different mode, which is the strongest in the world, that of compressing wood into wood by means of a screw, instead of a clench; by this all racking is done away, for a certain time, till the wood shrinks, on the observation of which the carriage is driven again to the coachmaker's, and the fastenings are hove up. Now, let any man in the world, whether he be a mechanic or not, decide which is the best mode of fastening--a clench or a screw.'- - No bolt was ever yet driven into a ship that performed the office it was meant to do. In the first place wood is never compressed to wood by a clench; in the next, the shrinking of the wood gives play to the bolt-suppose the pieces forming a mast to be fastened by bolts, and the hoops left off, how long would it stand? It is the compression alone that gives it strengthpp. 31 and 32.

The last cause of premature decay in ships, mentioned by Mr. Pering, is the mode of caulking their seams. The usual practice is to begin from the upper part of the ship's side and proceed downwards. A fixed number of threads of oakum must be driven into every seam, be the width of it what it may; if too narrow to admit the quantity, the reaming iron is applied to open it; the consequence of which is, that the whole strain falls

downwards.

upon

the plank immediately below the iron, the treenails are upset, the lower edge of the plank is forced over the upper edge of the next inferior one, like the wooden shingles of a root; the plank starts from the timbers, the caulker dabs off the projecting edge to make an even surface for the copper sheathing, and all is right! Can such practices, we ask, be familiar to Mr. Pering, and escape the observation of the master-builder of the yard? Are they known to the surveyors of the navy, and continued from a dislike to innovation? or, has Mr. Pering selected an extreme case and given it a general bearing? In a natter of such vital importance to the navy, it ought not, and cannot, escape inquiry. The surveyors of the navy or the masterbuilder of Plymouth yard, or both, are imperiously called upon, either to justify the practice, or to contradict the description of it.

The whole of Mr. Pering's new mode of ship-building is thus

summed up.

• Convert the timbers, set up the frame, and finish the ship out of the way, without at all caring whether the timbers are green or not-let her stand to season, but by no means let a caulking-iron approach her side for two years at least-no more of her bolts should be driven, than may be sufficient to hold her together, as every aperture should be left open for the circulation of air ; no treenails should be used on any account, but the work should be fastened with copper alone wherever it is practicable. The advantages are, that the timbers, plank, bulk-heads, and all other parts of the ship would be equally and properly seasoned together; and the caulking of the ship to be done just before she is put into the water, when her plank has so shrunk as to be likely to shrink no more. Every part of the ship would thus be as dry as possible; no fungus, no drip, no unwholesome damp would arise, to endanger the health of the ship's company; the sides of the vessel will be both windtight and water-tight; the plank swelling upon the oakum will unite with it and form one solid body. When the seasoning is deemed complete, then let the screws on the ends of the bolts be hove up, so as to bring wood and wood together in the closest contact. The ship would now be as tight as a drum, water-proof, and healthy throughout.'-pp. 59–61.

We now take leave of Mr. Pering. If his censures are just, we know not in what terms to convey our indignation at the insufferable negligence and indifference which must prevail in our dock-yards: it is fitting, at any rate, that an immediate investigation should take place. The mode which he proposes for putting a ship together has plain good sense to recommend it, and is, in our opinion, highly deserving of being put to the test of experiment.

Confident

« ΠροηγούμενηΣυνέχεια »