Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

nitude, it is true, and its defects have probably grown in the same proportion. We see, in the finest constructed ship, little more than congregated logs of heavy timber, inartificially placed beside each other, each pulling by its own weight a different way; the beams thrusting out the sides, the sides bolted to the beams to prevent their tumbling in, the overhanging stern tearing itself from the body of the ship, and the body struggling to fall in pieces, in spite of the distorted plank wbich binds it together :--no two parts, in short, giving mutual support:-still, however, it may be suited to the element in which it is intended to move; the equal pressure of this fluid binds all together, and the fragility of the machine is only put to the test when in contact with the ground; then, indeed, the whole fabric resolves itself into its constituent parts, scarcely any two of them remaining in adhesion. The act of launching seldom fails to break a ship—that is, to alter the line which was straight before launching, to a curve of six or seven inches when floating in the water. This strain loosens, to a certain degree, every fastening in the machine; yet, according to the present practice of putting a ship together, her existence almost wholly depends upon the fastenings;-but this is a subject to which we shall hereafter have occasion to advert.

We cannot omit the present opportunity of noticing the able and judicious remarks of the commissioners for revising the civil affairs of the navy, on the theory and practice of ship-building. In speaking of that mixture of theory and practice which enables us to build better than the French, at the same time that it may lead to other effects that are hurtful, they observe,

• Where we have built exactly after the form of the best of the French ships that we have taken, thus adding our dexterity in building to their knowledge in theory, the ships, it is generally allowed, have proved the best in our navy; but whenever our builders have been so far misled by their little attainments in the science of naval architecture, ás to depart from the model before them in any material degree, and attempt improvements, the true principles on which ships ought to be constructed (being imperfectly known to thein) have been mistaken or counteracted, and the alterations, aecording to the information given to us, have in many cases done harm.

. From the same cause there has been infinite variety in the alterations made, and in the forms which have been adopted. The alterations being founded on no certain principles, no similarity in the form of the ships could be expected, and they have the appearance of having been constructed on the chance that, in the multitude of trials made, some one might be found of superior excellence. While, therefore, our rivals in naval power were employing men of the greatest talents, and most extensive acquirements, to call in the aid of science for improving the construction ships, we have contented ourselves with

groping

groping on in the dark, in quest of such discoveries as chance might bring in our way.

. Nothing certainly can be more surprizing than that, in a nation so enlightened as this is, and whose power, importance, and even safety, depend on its naval superiority, matters so essential to the preservation of that superiority should so long have been neglected.

As a remedy for this great evil, it has been proposed, that the ships of each class or rate should be constructed in every particular, according to the form of the best ship in the same class in our navy; of the same length, breadth, and depth, the masts of the same dimensions, and placed in the same parts of the ship, with the same form and size of the sails.'*

The Commissioners farther observe, that the French have been so completely convinced of the disadvantages arising froin this variety, that they have, from time to time, ascertained by ordinances, the forms on which the ships of each class or rate must be constructed. We do not understand, however, that either the example of the French, or the intelligent observations of the Commissioners of Revision, have yet had the effect of changing the old system founded on no fixed principles. With the exception of a lot of seventyfour gun ships recently built in merchants'yards, and which, as far as we can learn, have not turned out well, the plans of all our ships of war continue, as heretofore, to be determined by the predilection of some professional Lord of the Admiralty for some ship which he may have commanded; or by the prejudices of the surveyors of the navy in favour of some chance draught which may have succeeded; or by the encomiums lavished on some prize ship by the officer who inay have captured her, &c. All this is perfectly natural, and, if it stopped here, might not be much amiss;-but the mischief follows: each, in turn, suggests some change in the figure of the ship, by which she is to become a paragon of excellence; for instance, a little more sheer,-a little more breadth of beam,a little more height between decks, &c. without considering how small a deviation from the original draught will alter the line of flotation and affect her sailing; change the center of gravity and affect her stability; and, instead of improving, destroy every good quality which she before possessed. The disadvantages arising from such a variety of models are of serious importance. When Lord Nelson was off Cadiz with 17 or 18 sail of the line, he had no less than seven different classes of 74 gun ships, each requiring different masts, sails, yards, &c. so that if one ship was disabled, the others could not supply her with appropriate stores.

One part, however, of the Report of the Commissioners, and a

* Third Report of the Commissioners for revising the Civil Affairs of the Navy.Page 194.

success.

very important one, has been adopted with the most promising

By the King's Order in Council, September 20, 1809, a superior class of ship-wrights' apprentices has been established at the dock-yard of Portsmouth. It consists of twenty-five young men of liberal education, who, before admittance, must be examined by the professor of the Royal Naval College and the , instructor in the theory of naval architecture. Their mornings are passed in the study of mathematics and mechanics, and in the application of them to naval architecture ; in drawing the different parts of a ship, and making complete draughts and plans. The remainder of the day is employed under the master shipwright in the mould loft, and in all the various kinds of manual labour connected with ship-building, as well as in the management and conversion of timber, so as to make them fully acquainted with the detail of the duties of a practical shipwright. The last year of their apprenticeship is to be served at sea, to afford them an opportunity of acquiring some practical knowledge in the steering, sailing, trimming, and ballasting of ships, &c.—during which, the order directs,

they shall mess with the officers, and be treated in all respects as gentlemen.'

Nothing can be more judicious than such an establishment; and we understand that a number of young men of the highest promise have already been entered; among whom we may hope for future

surveyors of the navy, who will excel the French in the science of naval architecture as much as our shipwrights at present surpass theirs in the practice of the art. It is to this part, however, that the animadversions of Mr. Pering are chiefly directed.

By the present mode of ship-building, that noble structure, a firstrate man of war, becomes useless, from premature decay, in five or sir years, and the average duration of the navy itself may be said to be limited to eight years -a short lived existence indeed, when we reflect on the immense expence and importance of our fleets !

This is indeed a gloomy prospect! but is it a faithful representation of the fact? We are inclined to think it is not, and that we shall come nearer the truth in stating that, except in some particular cases, the period of ten years may be assigned to ships of war built in merchants' yards, and fifteen to those built in the king's yards, and that twelve years and a half may safely be taken as the average duration of a fleet of modern built ships. Even this is sufficiently discouraging, when compared with the duration of ships in earlier periods of our naval history. The Royal William, for instance, a first rate, was built at Portsmouth in 1719, was among the ships sent to the relief of Gibraltar in 1782, and, at the age

of near a century, bears the flag of the port admiral-at Spithead.

The

The Queen Charlotte, a first rate, was launched at Deptford in 1810, sent round to Plymouth under jury masts in 1811, found too rotten to be sca-worthy, and is now undergoing a repair which, we imagine, will cost at least £20,000. These, we admit

, are extreme cases of durability and decay; but we could easily furnish a hundred instances of the superior quality of ships built in former days to those built in our time. The Sovereign of the Seas, afterwards named the Royal Soyereign, was built at Woolwich in 1637, and stood 47 years service. The Barfleur was built at Chatham in 1768, is still a good ship, and now under repair for further service. The Montague was launched at Chatham in 1779; after undergoing several repairs, she now carries the flag of Admiral Dixon at Rio de Janeiro: whilst the Ocean, the Foudroyant, the St. Domingo, the Rodney, the Ajax, the Albion, and many others, were falling to pieces within five years after launching, and some of them in less than three. The principal cause of this extraordinary difference in their duration may, we think, be ascribed to the rapid manner in which ships have recently been run up, with timber not properly seasoned, or with a mixture of different kinds of timber; to which may also be added Mr. Pering's complaint of slovenly workmanship, and an injudicious mode of fastening.

It is well known that when timber, not duly seasoned, is put into certain situations, and more especially in those where there is much warmth and where a free circulation of air is wanting, it contracts a disease known, improperly enough, by the name of the dry-rot, the effect of which is a complete decomposition of the vegetable fibre, and consequently a privation of all strength. It is altogether different from the common rot, of which indeed Mr. Pering seems aware, though he constantly confounds the two processes of decay. Neither do we believe that the professed dry-rot doctors liave accurately distinguished the one from the other; we shall therefore submit the ideas which have occurred to us on this important subject.

The common rot in wood is a gradual decay of the fibre, inore or less accelerated by the alternate action of wind, heat, and moisture on the surface; its progress internally being greatest when the wood is constantly exposed to the alternations of wet and drought, as exemplified in the rapid decay of that part of a post which is close to the surface of the earth, while all above and below is perfectly sound :-and least, when constantly soaked in water, or constantly kept dry-when exposed to a free current of air, or excluded from all air.

The dry-rot, on the contrary, is a disease which commences its ravages internally, and is but little affected by any external circumstance, excepting that of heat. The application of a strong heat will kill the disease, but at the same time injure the wood; a moVOL. VII. NO. XV.

derate

[ocr errors]
[ocr errors]

of

derate heat seems to be necessary to bring out the symptoms of the disease:-in dwelling houses, for instance, the dry-rot generally makes its approaches in the kitchen, or in a close warm cellar. At first, its appearance is that of fine fibres running on the surface in endless ramifications, resembling the nervous fibres of leaves; presently the interstices are filled up with a spongy or leather-like substance, assuming the character of that order of cryptogamous plants distinguished by the name of fungus. It is well known that if a piece of green wood be laid across a fire, the air within, expanded by the heat, will drive out, at each extremity, a viscous fluid possessing the property of disposing itself on the surface in reticulated filaments. The same appearance of nervous foliation is not uncommon in the intermediate spaces the concentric layers of the alburnum of wood; and the core or heart of trees, and particularly of the pitch-pine, after its passage in the heated hold of a ship, is often enveloped with a membranous corticle like that which lies immediately beneath the bark. All these appearances are certain indications of the dry-rot; and they point out, with sufficient clearness, that the sap, or principle of vegetation, brought into activity, is the cause of the disease; the effect, though infinitely more rapid, is the same as that of the common rot. It is still a problem in what manner this sap circulates; but there is no doubt that the tubes and cells of the alburnim, or sap-wood, are filled with it in the spring of the year, and that they are empty in the winter; that it is organized matter, developing itself by beat in all the various forms of new bark, leaves, and branches. The stem of a tree cut down will, on the return of summer, make an effort to push out leaves; a more feeble effort of this organized sap ends in the production of fungus only.

These facts and appearances suggest an obvious preventive of the dry-rot:-either by desiccation, or driving out the sap by artiticial heat--by destroying the principle of vegetable life inherent in the sap, by some chemical impregnation, or--by gradual seasoning. In all cases, the process will be considerably expedited upon timber felled in the winter months. There is reason to believe that our ancestors were particularly attentive to this point. They not only never allowed a piece of green timber to be put into a ship, but were equally attentive to the time of felling, and the place of growth. The Sovereign of the Seas, already mentioned, was built of timber which had been stripped of its bark while growing, in the spring, and not felled till the second autumn afterwards; and it is observed by Doctor Plot,* in his discourse on the most seasonable time for felling timber, written by the advice

* Philosophical Transactions for 1691.

of

« ΠροηγούμενηΣυνέχεια »