John Knowles: An Inquiry into the Means which Have Been Taken to Preserve the British Navy, 1821

Iron, from its superior strength, and the cheap rate at which it can be obtained, compared with other metals, was cheifly used on ships where metallic fastenings were introduced, until the year 1783, at which time the copper sheathing of ships' bottoms became a general practice; it has been dicovered by the partial trials previously made, that where the two metals came in contact, and the operation was aided by sea-water, that a speedy corrosion of both took place; and the government then ordered that all bolts under the line of fluitation [sic], should in the future be of copper. In the use of iron bolts some disadvantages were experienced; when corrosion first took place, either by the gallic acid in the oak, by sea-water, or the combination of both, its volume increased, but after some time had elapsed, the metal became diminished, the fibres of the wood through which it had passed injured by the oxide, and the ships were leaky, or what are termed "bolt-sick".

Copper bolts have also their disadvantages, as the oxidation injures the timber, though in a less degree than iron, the volume of the bolts decreases, and the verdigris, which is formed by the action of the acid of the oak on the metal, prevents the adhesion of the bolts to the wood; hence the ease with which a copper bolt may be displaced by percussion, and the partial leaks generally observable from bolt boles, where these fastenings are used.

Mixed metal* bolts, (copper and tin in the proportions of four of the former to one of the latter, with sometimes a little zinc added thereto) have been employed to fasten the bottoms of frigates built of fir; these were in the shape of large round nails, which were denominated, on account of the brittleness of the metal not admitting of their being clenched, "bolt nails;" these from the rough surface that they presented, and their not being so liable as copper to oxidation, held well, and did not injure the wood. The brittleness of mixed metal is, however, an objection to its general use for this purpose.

To save expense, hollow copper bolts have been tried; they required a socket punch to be used in driving them, and much difficulty was experienced in forming a clench over a ring, for which reasons they have not been introduced into ships.

Hollow screws, (to be used instead of tree-nails and bolts,) made of mixed metal, were recommended in the year 1808, by General Bentham; the mode of passing them into the wood, was by means of a key; and when in place, the hollow core was to be plugged up. Solid screw bolts were also used, by directions from that gentleman, on some vessels built after his plan in the year 1796, but were not found to answer. It is, however, considered, that copper bolts, well driven and clenched on a ring, are far preferable to any others when used under water.

In the year 1815, Dr. Pellet, proposed to coat iron bolts with zinc, as a cheaper and stronger fastening than those of copper; upon trial, however, it was found, that iron when newly rolled in its black state, would not take the zinc, that it was necessary to file it bright, in order to effect the coating, and that the zinc required to be brought to a great heat, so as to be in part volatilized, before it would adhere to the iron. So much workmanship was required, that the price of the bolts so prepared was nearly equal to the value of copper, and the zinc was displaced from the head, and some other parts of the bolts by driving them; the experiment was therefore abandoned. Bolts formed of zinc were proposed in the year 1816, by a M. Chaulet, who stated, that they had been used with success in France; but no trial thereof was made, as it is known that it is very brittle, more affected by nuruatic acid than copper, and possesses only one-third of its strength.

In the year 1669, about five tons of several kinds of bolts were purchased of a Mr. Kier, by way of trial; some of them iron, covered with a sheath of copper; others a mixture of copper and zinc, usually termed gun metal; and the remainder a combination, as it is supposed, of metals, the names and priportions of which were not ascertained. A considerable quanitity of these were used on the Standard of sixty-four guns, built in 1782; and when that ship was taken to pieces at Sheerness in 1816, the iron bolts which had a covering of copper, and also those of brass, were found to be in a good state; but the bolts, the composition of which the maker did not disclose, presented the most extraordinary appearance. They had not decreased in size, nor was there any alteration in smoothness of surface, but they had so completely lost their tenacity, that the slightest blow was sufficient to fracture them, and when broken, they had all the appearance of brown pottery ware; upon being cut, there were in some places, particles of a red shining metal, resembling copper, but their extreme lightness proved that but little metal remained.

Copper nails of a square form have also been used for fastening the bottoms of ships; in England this practice has been confined to those built of fir. But in France, they have been employed on ships and vessels built of oak; those in use in both countries, after passing through the bottoms, go about five or six inches into the timbers of the ships. The Spaniards use very long nails for the purpose, which pass through the timbers and are turned on the inner lining*; nails have this disadvantage more than other metallic fastenings, that they frequently split the plank of the bottom.

The ends of bolts have had, in some cases, a worm cut on them, and nuts have been placed thereon as substitutes for clenches; these were introduced generally in a French brig of war, La Ligurienne, captured in the year 1800, by his Majesty's sloop Peterel and carried into Plymouth. The use of nuts and screws on bolts has been recommended, under the notion that if the shelf pieces, planking, &c., should not set close to the timbers of the frame, either from the working of the ships or the shrinkage of the materials, theu might be drawn into contact by the nuts. Thus, without examination or trial, would appear feasible, and in some cases might be effected if all the bolts lay parallel, but as this is seldom the case, the screws become useless, and the endeavour to heave them up, only destroys their worms. The adhesion, too, or iron bolts is so great, in consequence of the volume of the metal by oxidation, and by the shrinkage of the fibres of, perhaps, unseasoned wood round them, that in many cases where instruments are employed to extract them, they are drawn asunder. The softness of copper will not admit of a great strain to be put upon any worm cut in that metal; and under any circumstances, if the bolts happen to be bent, it would be found impracticable to move them or the materials through which they pass. The Dutch, in the year 1816, built two brigs of war, and used bolts with screws on their ends and nuts on them, but it is not their intention to continue that practice*.

* The use of mixed metal fastenings in ships is of an ancient date, for, according to Vegetius, brass was used by the Romans instead of iron for the bolts and nails applied in fastening their galleys.

* This method has also been practised in some ships built in the East Indies.

* The author had the information from Mr. Soutimer, the master shipwright of the royal yard at Amsterdam, a gentleman deservedly held in high esteem in Holland, for his practical experience in ship-building, as well as theoretic knowledge. His opinion is, that the use of nuts and screws on the ends of bolts was found by practice not to justify the expectations formed of the plan; for in carrying on the building of the vessels in question, it was proved, that good work could not be effected by them.

John Knowles: An Inquiry into the Means Which Have been Taken to Preserve the British Navy from the Earliest Period to the Present Time, Particulary from that Species of Decay, now Denominated Dry-Rot.
Winchester and Varnham, London, 1821. p 68.

Transcribed by Lars Bruzelius

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