There are few scientific subjects which present so many objects of interesting and useful inquiry as Naval Architecture. The forms of ships best adapted to answer the different purposes for which they are designed, the materials of which they are built, and the best methods of combining those materials, all require from their importance the most careful investigation. What can be of more consequence, either personally or nationally, than the security of that machine in which a man ventures his life, and a nation its honour?
It would be an inquiry of considerable interest, to ascertain the practice of ship-building by the ancients; but it is to be regretted how little has been handed down to us on the subject. The magnitude of the ships of ancient Greece and Rome is but little more than conjecture, exaggerated by some and depreciated by others; of their forms still less is known than of their magnitude; and of the methods of purring them together, and of their fastening, there are scarcely any records remaining. It is stated by Vegetius, that brass was substituted for iron in his time; and by Athenæus, that such was the practice as far back as Nero. A galley, supposed to have belonged to Trajan, said to have been buried 1300 years in the lake Ricco, was discovered, which had a sheathing of lead on her bottom, fastened with copper nails; this vessel had also been caulked and doubled. These slight accounts afford the most important part of our knowledge of the connexion of an ancient vessel.
It is not, however, now proposed to enter into the more general question of the mode of fastening ships, but rather of the materials which have been used to preserve the connexion when the parts are brought together.
Of the early modes of fastening, it is probable that ligatures were the first used for this purpose, as is seen even at the present day: boats of considerable dimensions, in the East Indies, being fastened by coir (the cordage made from the outside husk of the cocoa-nut), and the intestines of animals in some uncivilized countries, being made to answer the same end. Wooden pegs were probably the next step, after that iron, and lastly brass and copper.
Our modern fastenings are generally bolts, nails, and treenails: and these again consist, the bolts of iron and copper; the nails of iron, mixed metal, and copper; and treenails of various sorts of timber, cut into a cylindrical shape.
The excellency of a material for ship fastening appears to consist in its being strong, durable, not having a tendency to decay those parts of the timber which come in contact with it, and in its being cheap.
The material which has hitherto been found to answer these conditions best is copper. Iron began to be discontinued in the bottoms of ships in this country1 about 1783; at which time copper sheathing began to be generally used in our navy. It was found that the iron fastenings in the neighbourhood of the copper were so rapidly oxidized, that copper fastenings were of necessity put into the bottoms of ships to ensure their safety.
The advantages of copper are, that it is strong, although not so much so as iron. It is durable, only a very small portion of its weight being lost after very long service; and it also possesses the third property we have mentioned to a great extent: for although the wood is deteriorated in its neighbourhood, yet it is so trifling in degree, as not to make it a material objection. It however wants the fourth property, it is of great cost; and when it is considered that the weight of copper put into a 74-gun ship, under present circumstances, amounts to about 35 tons, at a value of about 3000l., it must be seen that the expense would be enormous, if it were used to the exclusion of the more general fastening of treenails and iron. It is evidently, therefore, a great desideratum to find some substitute of less value. Were it not for this, there could be no doubt that a ship fastened wholly with copper bolts, to the exclusion of both iron and wood, would leave nothing more to be desired.
Nails are but little used in modern ship-building in this country, at least in the more important parts of fastening. The metal nail, from its taper shape, is not to be depended on where there is any strain, since, if it 'give' at all, it evidently becomes loose immediately. The iron nail, while it retains its strength, is a much more effectual fastening, since the corrosion, which almost immediately takes place, sets it so firmly that there is little danger of its starting. This corrosion, however, in a few years reduces its strength to almost nothing; and if exposed to the action of sea water, it may be expected to be reduced to a mass of oxide long before the timber is decayed. Notwithstanding this, nails of an immense size and length are used by the Spaniards and Portuguese, and in the East Indies, as the general fastening of their ships' bottoms: being driven through the bottom, and four or five inches of the point turned on the inside, making indeed an effectual clinch, but having an exceedingly clumsy and unworkmanlike appearance.
With regard to mixed metal as a fastening, little need be said: it is too brittle to allow of its being clinched; and without this security, there is not much confidence to be placed in bolts either wholly or partly composed of copper. It is now but little used, except as nails in the weather decks. The dumps or bolt-nails into which it has been also cast, are seldom used to any great extent, except in fir, where treenails are considered of too great diameter in relation to the scantling of the timbers, and are also found to be very injurious to the wood.
We now come to that important instrument the treenail2. Of this the opinions that have been expressed are so opposite, that they are for that reason both likely to be far from the truth; one party affirming it to be the "worst fastening that could possibly have been devised," and the other extolling it as the best possible fastening. We shall take a middle course: its utility is proved by its universal application; its inadequacy is apparent from the necessity there exists of using metallic fastening in its aid. Perhaps we cannot do better than try it by the properties we have deemed essential in ship fastening. And first, as to strength: here its deficiency is manifest, for although made of a diameter as large as can be prudently used, without wounding too much the plank and timbers, it is found quite unable to resist the strain of the caulking-iron without the due support of metallic fastening, it having been constantly found, that where a ship has been much caulked the treenails were upset or broken, where metallic fastening has been either altogether omitted or too sparingly employed. As to durability, it is to be apprehended that a shorter period must be assigned to treenails than they have even hitherto attained. This duration must of course depend in some measure on the quality of the timber of which they are made; but there is yet another condition generally admitted to be essential to the duration of timber; that pose parts which are brought into close contact should be as nearly as possible composed of the same substances, otherwise the chemical process of decomposition may be greatly accelerated. This is remarkably apparent in the decomposition caused by the contact of oak timber with teak. On this account the contact of pieces of different species of wood is to be avoided as much as possible. At the present day, when, from the scarcity of English oak, woods of various kinds are resorted to as substitutes for that valuable material, of whatever kind the treenail may be, it is impossible to comply with this condition, since if it pass through a plank of English oak, it is probable the remainder is driven into a timber of A[f]rican oak, &c. On the other hand, an English oak timber is covered by a plank of English or Dantzic oak, fir, elm, beech African, &c. Still as a sufficient quantity of English timers and plank is not to be procured, we must hope that the extraordinary precautions of seasoning, ventilating, roofing, and other salutary measures, will counteract the ill effects which might otherwise reasonably be expected to ensue.
With regard to the treenail, as a mere fastening, experience justifies a high opinion while it remains sound. Its shape enables every part of it to hold firmly, while its elasticity allows it to be driven with a drift, which ensures a contact almost perfect, and which the swelling of the treenail, from the moisture it imbibes after it is in the water, makes still more certain; so that it is much more common to see a well-driven treenail leak through its substance, than between it and the timber. As a further proof of the goodness of this fastening, while sound, we appeal to the professional man, who must have frequently remarked the trouble which a single treenail will sometimes occasion in the breaking up of a ship; resisting by its tenacity and toughness the efforts of the workman to clear it, and only yielding at last to his saw. But the same plank will also furnish examples of treenails of scarcely greater strength than so much pottery, and of other so decomposed that a shell in the hole is all that is left, the remainder being completely decayed.
The third condition, that fastening shall not decay the timber around it, has been in some measure noticed in what has been said of the durability of treenails. It may be necessary however, to state more distinctly that the plank in the neighbourhood of treenails is sometimes in nearly as bad a state as that round iron; with this difference, that the decay takes place on the outside of the plank in the latter case, and on the inside in the former- This fact may be thus accounted for: the head of the bolt is naturally first acted on by the water or atmosphere, and a mass of oxide is quickly formed there, which produces its pernicious effect on the outside of the planking. The treenails on the contrary absorb the moisture from the head, a part of it is naturally deposited in the joint between the timber and plank, and decay on the inside is the consequence3. But here it may be remarked, that nothing can be more varied than the result of observations on the decay of timber: in one case the treenail is entirely rotten while the timber is perfectly sound around it; in another part the treenail is as fresh as when put in, and the timber may be picked out with the fingers. Indeed the results of our experience on timber altogether are most unsatisfactory, the fact of to-day contradicting the observations of the past year, and that of to-morrow the theory of half a century's formation. There is no chance of its being otherwise till experiments are made in a systematic manner, conducted with care, and recorded with exactness, but above all registered and remembered; so that the result may not be lost or forgotten. Till this shall be the practice, experience will be but a mass of isolated facts, without combinations or benefit; and serve but too often to prop an erroneous theory, or foster a pre-conceived opinion.
The treenail possesses our fourth qualification in an eminent degree: it is the cheapest fastening we can apply, and there it will require some modification of other materials before it is likely to be superseded. Treenails of African timber have lately been introduced, but not with complete success; although perhaps the best substitute for English oak treenails hitherto used. It is not a wood that can be cleft; they are therefore sawn, and then mooted; consequently, from the nature of the wood, the treenail frequently breaks off in driving, although, when the grain is straight, it drives like a bolt. There is a material objection, however, to any of these hard woods for the manufacture of treenails; that unless they are driven very tight, they are likely to leak; and if they are driven tight enough to prevent that, they endanger splitting the planks into which they are driven, from the want of elasticity.
Iron bolts, as a security for the outside planking, are now used only on the topsides, at some distance above the loadwater line. Its strength is considerably greater than that of copper, while it is specifically lighter. It is also very cheap, for these two reasons, therefore, it is extensively used for fastening above the water.
The great drawbacks on the use of iron are its want of durability from corrosion, and the great effect it has in destroying the timber around it. The corrosion is such, that in eight or ten years it is no longer to be depended on; and in some cases, where it has been used on the bottoms of ships which have been long in existence, planks have actually fallen off, when the vessel has been taken into a dock.
There have been many methods proposed of rendering the iron fastenings more durable: viz., by casing or washing them with tin or copper, but as yet it would appear, from none of of [sic] them having been adopted, with but indifferent success. The causes of failure seem not to have been sufficiently recorded, for we know little of these experiments except that they have been made.
There is now, however, a very important experiment going forward for this purpose. The plan is under the direction of Capt. weny, R.N.; but we believe the discovery or invention is due to Dr. Rivere, an intelligent American, who after an immense number of experiments, arrived at the following mode of application. The protecting metal is a mixture4 of zinc and copper, cast into rings or plates; the bolts being driven as usual, but having a ring of this metal at the head and point. After the bolt is driven, a piece of the protecting plate is let in over the bolt-head, which is carefully cleaned, and the plate then well dressed on the bolt, to ensure a complete contact. The only condition prescribed with regard to this metal is that the surface of this protecting metal shall not be less than 5 per cent. of the surface of the bolt to be protected. From the specimens, exhibited by this gentleman, of bolts which have been immmersed in brine, salt-water, &c., and which, after a trial of a year and a half, are still perfectly bright, there is good reason to hope for some success from this mode of treatment.
It is curious that while this experiment was being carried into effect in Chatham dock-yard, another of a something similar nature was discovered in the Terpsichore of 32 guns, whilst breaking up. This was of several iron nails which were used to fasten a part of the upper deck, between the fore and main hatch-ways; this part of the deck was of teak, and had been put into the ship when repaired in India about 25 years before. These nails were tinned, and almost all that were found, were in a ver perfect state, both that part which had been in the teak deck, and that part in the oak beam. Compared with the nails in a plank under similar circumstances, by the side of them, which had not been so protected by thinning, they were in a decidedly better state: but as the latter also were not so much corroded as might have been expected from their long service, in consequence of the dry state of the deck, the ship having been a receiving hulk for the last 20 years, the experiment, though certainly favourable, and bringing to the mind of the writer a conviction of its utility, is yet, from not having been made on the bottom of a ship, not of that decided character that could have been wished on so important a subject. It may be remarked here, however, in connexion with this experiment, that the pins in the shackles of chain cables, to facilitate the taking the cables into short lengths, have for some few years past been tinned; and from the testimony of some intelligent officers on board ship, as well as of the blacksmiths employed in surveying these chain cables when brought to the dock-yard, it has been found decidedly useful, inasmuch as they were quite free from corrosion, except where the head had been battered in driving, and the tin beaten away.
This experiment is of so important a character, that its success or failure involves a remarkable era in ship-building. The expense of copper has been found so great, that the utmost care and economy in its expenditure have been prescribed in the royal dock-yards; should, however, these experiments succeed, we shall have a metal fastening possessing every property that can be desired; combining strength with cheapness, and durability in itself, with that of the material in its neighbourhood.
In order to supply, in some degree, the want of an experiment on the tinning of iron bolts on the bottom of a ship, a piece of green oak was procured, and some bolts, previously tinned, wbout a foot long, and an inch in diameter, were driven into it. One of these was driven out again to ascertain if the tin had been rubbed off by the friction in driving it. It was found as perfect as at first.
The piece of wood was then coppered, and placed in the water of the Medway, where it is intended to remain a sufficient period to put this question at rest.
It has been objected to tinning, that in driving or clinching a bolt, the tin would undoubtedly be removed from the head and point. This is very probable, but as the rings would also be tinned, all the parts in contact with the wood would be protected, and the only effect would be a little reduction of the head and clinch.
It should have been mentioned that the protecting metal of Capt. Sweny, or some medification of it, is also formed into sheets for sheating ships' bottoms; with which several ships in the merchant and India service have been sheathed. It is to be hoped that the owners or some one connected with those ships, will publish an account of the result of this experiment, as from the cheapness of the metal it would be a most desirable substitute for that expensice article, copper. We confess ourselves not sanguine on this point, on account of the oxidation of the copper, being that quality which preserves the bottom free from those animal and vegetable substances which are found to adhere where copper is not used. And this we think also will casue the failure of all those measures, such as painting, zinc plates, iron protectors, &c., which have for their object the preservation of copper sheathing; by destroying one of the principles on which its utility is founded. This was conspicuously the case with the protectors recommended by Sir H. Davy.
There is another mode of fastening, which, though it may be said to have had its day, yet deserves to be mentioned; this is by nuts and screws. There have been various suggestions in order to make this powerful instrument available in ship-building; but as far as we have yet seen, they have almost entirely failed.
It has been the frequent endeavour of many ingenious men, to place them so that wehn any shrinkage takes place, the screw may be employed to bring the parts again into contact, and by means of the nut keep them together. When, however, it is recollected, that for this to take place, every bolt must be exactly in the same direction, and that every bolt must be set nearly simultaneously, it will be seen that there is more difficulty than would at forst be apprehended; and when to this is added the shrinkage of the materials on and around the bolt, the chances that in the working of the vessel it may have been, though ever so slightly, bent, it is hardly too much to say, that it is impossible to answer the sanguine expectations that have been held out in their favour.
There is another abjection to the employement of screw fastening, that the security derived from the nut on the end is much inferior to that of the common clinch.
This would not at first be expected, but was found to be the case in an experiment, in which two bolts of the same diameter, one with a screw at the end and set up with a nut; and one clinched on a plate in the common way, were subjected to the same strain. It was expected that the threads, four or five of which were taken by the nut, would be of greater strength than the mere clinch, in the proportion of the quantities of metal apparently effective. The result, however, was different: two or three trials proved the value of the clinch, since the screw bolt broke in the thread, while the clinched bolt remained undisturbed. The trial was thus made: A heavy hawser being rove through the two ring bolts experimented on, tackles of sufficient power were then bent to this hawser, and by a leading block the angle equally divided. Horses were then put to the fall, and driven till one or the other broke.
This result we imagine to have taken place in consequence of the injury sustained by the fibre of the iron in cutting the screw: on the same principle as a spar will be sprung, where a slight score has been made round it, with much less force than from its diameter would appear to be adequate. On the other hand, the use of the hammer had so tempered the iron of the clinch as to render it capable of a greater resistance than its thickness would lead us to expect.
We have as yet made no mention of an improvement in ship-fastening, which should hardly have been so long passed over in silence, considering its value and importance. We allude to the dowell or circular coak. The coak or dowell has long been used in masonry, but for its introduction into shipcarpentry we are indepted to General Bentham, about 1802 or 18035. Its present extended employment, however, is due to Sir Robert Seppings, who has availed himself of its valuable properties wherever it can be usefully applied; and its situation above and below the buts, in the tick strakes of the planking, in the scarphs of the shelf, &c., must have a powerful effect in preventing longitudinal extension. Its great value, however, is in its preventing the possibility of bad workmanship, to which the operation of tabling, which it has superseded, was perculiarly liable. To those who are not conversant with these details, it may not be superfluos to explain that a dowell is a cylindrical piece of wood or other material (now prequently iron, hollow, and filled with cement), of a certain diameter according to the magnitude of the timbers to be connected. The dowell engine may be considered as a large centre-bit fixed in a brass frame, of the same diameter exactly as the dowell to be used, and having a small spindle in its centre. The timbers to be dowelled having been brought into contact (fayed), a small auger, the size of the spindle, is put through at the place where the dowells are to be placed. The timbers are then separated, and the spindle of the dowell-engine inserted in the auger hole; the mortice of the dowell is then made in each piece, and necessarily, by means of the spindle, exactly in the proper direction; and from the dowells and the engine being of precisely the same diameter, a perfect fitting is ensured. It should be observed, that whatever number of coaks there may be in seating (fitting surface), they must be precisely in the same direction, otherwise, it is evident, the surfaces could not possibly be brought together.
In taking leave of this subject, it is impossible for a shipwright not to feel impressed with its importance. In the first place, fastening, if not properly applied, is worse than useless, it is weakening that which it is intended to strengthen, and throwing away the time and labour of the workman and the cost of the materials. Again, fastening, although properly placed, if not well-driven, is useless and deceitful: compromising the safety of the ship and the lives of the crew.
1 See Knowles on the Preservation of the Navy.
2 They are supposed to be coeval with our navy, mention being made of them as early as 1560.— Knowles on the Preservation of the Navy.
3 This was very remarkable in the Terpsichore, of 32 guns, lately broken up at Chatham, where there were holes round the treenails on the inside of the plank in the bottom, 1½ inch within the other parts of the surface.
4 The specific gravity of this mixed metal is only 6950, while that of copper is 8788, and zinc 7191.
5 Knowles, on the Preservation of the Navy.
Transcribed by Lars Bruzelius
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