Another Paper was read on this interesting subject in March 1863, by W.J. Hay, Esq., F.C.S., Admiralty Chemist, at the Institution of Naval Architects, J. Scott Russell, Esq., Vice-President in the Chair. Mr. Hay said—
"Although I most cheerfully comply with the request of your Secretary to read a Paper to this Institution, yet I feel much diffidence in doing so, least I should not sufficiently do justice to so comprehensive a subject, it being one of national importance with regard to economy, and of the highest interest to the mercantile marine.
"I shall endeavour to give, as briefly as possible, the various proposals and plans which have been suggested and carried out from time to time for sheathing ships and other vessels.
"I will first allude to the fact that wood sheathing was used in the 15th century for two purposes, viz., to keep the soft caulking formed of oakum and tallow from coming out and to prevent the destructive action of the different species of sea worms.
"Experiment was next made to a considerable extent with lead sheathing; and in 1670 an Act of Parliament was passed granting to Sir Philip Howard and Francis Watson the exclusive privilege of manufacturing milled lead for this purpose. Twenty ships were sheathed with lead fastened with copper nails; and it was not wholly discontinued till 1770, when the "Marlborough", on examination at Sheerness, was found to have lost all the sheathing, except a small portion on the bow knee and the rudder.
"In a work on Naval Architecture by Leon Battista Alberti, and which was written in the 15th century, it is stated that, 'Lead sheating was used in the 2nd century, and that while he compiling his work, Trajan's ship was weighed out of the Lake of Riccia where it had lain sunk and neglected for above 1,300 years.' He observed, 'that the pine and cypress of it had lasted most remarkably. On the outside it was built with double planks, daubed over with Greek pitch and caulked with linen rags; and over all there was lead sheathing fastened on with little copper nails.'
"After the examination of the "Marlborough", wood sheathing was generally used. Experiments were made with copper sheathing. Several methods of rendering it more durable, as well as of checking the growth of sea weeds, were adopted, such as filling the sheathing with nails so as to form almost an entire metal sheathing, and paying them over with Composituions suggested by different persons. In 1737 several Compositions were tested at Portsmouth, and ultimately, one made of pitch, tar, and brimstone, was deemed the best adapted for the purpose, and was generally used for graving.
In October, 1761, the Admiralty determined to try copper sheathing for the Navy, and ordered that H.M.S. "Alarm" should be sheathed with thin copper. This vessel proceeded to the West India Station, and after a sufficient time had elapsed for the result of the experiment to be determined, she was examined. The sheathing was then found to have answered well in keeping the bottom comparatively free from the adhesion and growth of barnacles, &c. It thus appears that the first ship coppered was the "Alarm" in the year 1761, the second was the "Aurora" om 1765, and the third the "Stag" in 1770; four more were coppered in 1776, nine in 1777, and in the course of the three following years the whole British Navy was coppered — an event which may be considered as forming an important era in the naval annals of this country.
"Some few years after copper sheathing became general, it was discovered that through the connection of the copper sheathing with the iron bolts in the bottom, and the pintles in the rudder, oxidation had taken place to a great extent; and from careful examination it was discovered, that within a period of three of four years, the iron fastenings were injured so much as to render the ships unfit to be sent on foreign service. A mixture of pitch and tar, called soft stuff, was put over the endds of the bolts, and other ironwork in the bottom, to prevent the contact of the two metals; but this entirely failed in protecting the iron. The injury to the fastenings assuming such a formidable aspect, the Navy Board contemplated, in 1783, discontinuing copper sheathing, but a suggestion of the use of bolts of mixed metal instead of iron for fastenings for the lower parts of the ships was approved of and adopted for a time; but before the end of that year, copper, instead of iron bolts, were ordered to be used in all the ships.
"In the latter part of the year 1823, the Board of Admiralty sought the advise of the President and Council of the Royal Society, as to the best mode of manufacturing copper sheathing, or of preserving it, whilst in use, from the corrosive effects of oxidation. Sir Humphrey Davy undertook the investigation; and, as in order to determine what conditions of copper were requisite to its durtability in sea water, it was necessary to ascertain to what action the waste in the meatl was owing, he proceeded first to examine the chemical changes which took place in sea water whilst a strip of copper was immersed in it. The phenomena which that experiment presented formed the basis of reasoning that resulted in a discovery of the means by which copper sheathing might be protected from the destructive action of sea water. Sir H. Davy had already ascertained that chemical attractions might be exalted, modified, or destroyed by changes in the electrical state of bodies; and, by a consideration of the changes that he witnessed both in the copper and the water which had been in contact, he arrived at the conclusion that, as copper was but 'weakly positive' in the electrochemical scale, and that it could act upon sea water only when in a positive state, if it could be rendered slightly negative it would not be susceptible to corrosion in that fluid. His experiments fully established the truth of this supposition.
"The principle having been fully established that the waste of copper sheathing was the result of electro-chemical action, it had next to be ascertained what proportion of negative metal would protect the copper from the destructibe action of sea water. This was determined by another series of experiments, of which the following were the results:— When the metallic protector was from 1-20th to 1-100th of the surface of the copper, there was no corrision or decay: with smaller quantities, such as from 1-200th to 1-400th, the copper underwent a loss of weight, which was greater in proportion as the protector was smaller; and as a proof of the universality of the principle, it was found that even 1-1000th part of cast iron saved a certain proportion of the copper. In the course of thse experiments it was proved that cast iron, a substance which is cheaper than zinc, and much more easly procured, was likewise equally fitted for the protection of copper, except in sulphurous waters. It ´lasts longer than malleable iron or zinc, and the plumbaginous substance whichis left by the action of sea water upon it, retains the original form of the iron, and does not impede the electrical action of the remaining metal.
"On the 7th June, 1824, the Navy Board issued an order that the surface of the protectors in contact should be 1-80th part of the surface of the copper. The form in which the protectors were applied was in bars 6 inches wide at their base, 8 inches in thickness at their centre, and, in outward form, represented the segment of an extended circle placed horizontally amidships, about three feet below the water line.
"Dr. Paris states that, after a trial of the protectors, which lasted several weeks, the surface of the copper sheathing became coated with carbonate of lime and magnesia, and that under such circumstances weed adhered to the coatings, and marin insects collected upon them; but that when the proportion of cast-iron or zinc was below 1-150th, the electrical power of the copper being less negative, no such depositions occurred, and that although the surface had undergone a slight degree of solution it remained perfectly clean. He considered this a fact of great importance, as it pointed out the limits of protection, and made the application of a very small quantity of the oxidable metal more advantageous than that of a large quantity.
"Whilst, however, the agnecy to which the principal waste of copper sheathing was owing was thus satisfactorily determined, Sir H. Davy directed his attention still further to the causes of destruction in copper sheathing, as he had been led to suppose there must be a mechanical as well as a chemical action contributing to the general effect; and from the experience he acquired during his voyage to Denmark and Norway he concluded that on the most exposed part of the ship, and in the most rapid course, the loss, owing to mechanical action, was to that resulting from chemical action, in the proportion of nearly 2 to 4&middledot;55. I shall have occasion to refer to this point hereafter, as much of this action depends upon the character if the copper under trial. The value of these discoveries can hardly be over estimated, as they have constituted the most important indications in all subsequent inquiries. It is known that the application of Sir H. Davy's protectors led to the rapid fouling of the bottoms of ships by the adhesion of weeds and zoophytes; and that, in consequence of this unexpected disadvantage, they were abondoned at an early stage in the experience of protection. This abandonment of a principle because of a concomitant difficulty certainly does not meet with the approval of scientific men. But whether there was propriety or not in such a course, the result of it has been that no effectual means have been employed for the protection of copper sheathing; nor until within the last few years was anything done towards investingating the destruction of sheathing. This may be attributed to the loss of a man, who, although not unexposed to the jealousies and comments of different parties, had the full confidence of the Navy Board.
"The health of Sir H. Davy was such as to prevent his further investigations of this subject; or the same powerful mind that suggested and carried out the requirements of the Admiralty, viz., the preservation of the copper, would very soon have overcome the fouling. Others followed out his beautiful design, and, at the same time, taking advantage of the results of his experiments with perfect and imperfect conductors, have to a certain degree realized his unborn views of regulating protectors by the partial interruption of the current; for he pinted to this fact in his experiments with different numbers of sheets of paper, which have led to the interposing of a porous material — canvas, wood, or earthenware — between the positive and negative pair; whilst protection has been afforded, and at the same time, a clean surface preserved. These proposals, however, emanated without the acknowledged reputation of a Davy: hence they have not met with any encouragement except in Sweden.
"The late Admiral Sir Edward Owen considered that the iron cables and the iron paddle.wheels of steamers acted like Davy's Protectors, and caused the copper to foul. He was perfectly correct with reference to the paddle-wheel as regards the fouling; and the decay of the spurs of the paddle-wheels by galvanic action in contact with the copper sheathing was very great. That removed from the 'Elfin' was nearly decayed through its mass; and that of H.M.S. 'Penlope' was reduced from its original size — 4½ inches, to 2½ inches.† Some of the incrustation — the coraline matter from 5 to 8 inches in length — with which H.M.S. 'Geyser' was entirely covered, will shew the state of her copper when she was docked at Portsmouth.
"For several years after, efforts were commenced by those in the Service to ascertain the cause of the increased wear of copper sheathing: the various conditions of its use were supposed to have more to do with the wear than the intrinsic state of the metal. This opinion was also entertained by the late supervisor of metals, who stated that the superior durability of copper sheating must be sought elsewhere than in its composition; and that it must be sought less in the properties of the copper than in the conditions of its use. This has been refuted by many facts: first, general exerience did not support it: secondly, there had not been such chenages in the conditions of its use as to hustify the supposition: and, thirdly, practical facts were directly opposed to that opinion. The placing of different descriptions of copper in the same condistions has shewn that they are subject to variations of wear to a remarkable extent in accordance with what might be expected from the physical condition of the metal.
"In all the attempts which have been made to improve the protection of copper sheathing, it has been practically admitted that, from whatever cause the deterioration may have resulted, the excess of wear is a consequence of its increased suspectibility to electro-chemical and chemical action. The accidental conditions of wear, which have frequently been the object of attention, were not though of before the quality of the sheathing was impaired.
"Instances have occurred in the Navy of the very rapid destruction of sheathing about the water-line of ships, whilst other portions have not suffered wear in proportion. It has been supposed by some who have given opinions on the copper question, that such excessive wear resulted simply from atmospheric influences, without implying a fault in the condition of the copper itself. This opinion does not, however, appear to be verified; but it rather seems that the rapid wear at the water-line is strictly relative to the general quality of the copper, and that that copper which will best resist the combined influence of air, water, and friction.
"The loss sustained in copper sheathing has always been considered a serious expense; but the protection of the bottom from destruction by the teredo, and fouling by weeds animalculæ, fully compensate for that expense. Experiments have as yet failed to show that any of the improved kinds of sheathing are superior or equal to ordinary wearing copper. Eighteen vessels in Her Majesty's service have been sheathed with Muntz's yellow metal, and from the reports it has appeared to wear well. Some few sheets have proved brittle, but on the whole, the results have been equal to what had been expected from it. But for the purpose of the Government, copper should be of that durable character, that all ships sheathed and lying in the harbour should be in such a state as to require nothing but cleaning before proceeding to sea.
"Hall's patent copper is on trial on sixteen ships. One only has yet has been examined — the 'Alert' which was sheathed September 1856; in December 1857 it was removed. It was then found to be eaten through in some places, the loss being greater than with ordinary Chatham copper, a sample of which was on the same ship, and the loss on which was 5½ ounces per sheet. A very limited trial has been made with copper prepared with phosphorus, which seemed to be a desirable addition; but whether due to the presence of the phosphorus, or to that substance producing a species of refining by ejecting all oxygenm remains to be proved. It will be seen by the results of the experiments with phosphorized copper sheathing that it is desirable to apply chemical agents to improve the copper used for sheathing.
"Dr. Percy of the Government School of Mines, and one of the most talented metallurgical operators, at the meeting of the British Asociation at Swansea in 1848, through alluding to the effects of certain foreign bodies upon copper, such as sulphur, phosphorus, &c., induced Colonel Sir H. James, of the Royal Engineers, at that time associated with Portsmouth Dockyard, to express a desire to test some specimens with which Dr. Percy had furnished him in sea water. The results of thses experiments with copper containing phosphorus were so satisfactory, that Sir J. James obtained permission from the Admiralty to have it tried. The trial was made although on a limited scale, and the report was in favour of the copper containing phosphorus.
"Although in the earliest preparation of sheathing for the Navy the application of chemistry to the process of its manufacture was not well understood, yet what it was deficient of in schience was, in a great measure, supplied by practical skill in refining and purifying the metal. And further, whilst the durable sheathing manufactured in those times was often alloyed with foreign elements, the more complete fusion to which the metal was subjected in the furnace brough the alloys into such a state of combination with the copper as to render it beneficial.
"refining and alloying are entirely chemical matters, and the durability of sheathing depends on the perfection of these operations; but without analysis of the copper before, during, and after the manufacture, the different physical conditions brought about either by chemical process, or otherwise, will fail to give that insight into the subject which it is so desireable to have. Again, the nail experiments, numbering upwards of one hundred, and which have been in progress for years, have proved that the irregular wear and loss sustained on sheathing is due, in a much greater ratio, to chemical than to electro-chemical action.
"In conclusion, I will quote the opinion of Dr. Percy on the subject. He says:— 'With regard to the deteriotation of the composition of the copper employed as sheathing, it cannot be expected that any results of much preactical value will be obtained except by very expert chemical analysists.'
"I will now only observe that in whatever respect the advantages of improving the copper sheating may be looked at primarily, public economy is the ultimate point towards which it necessaily tends. The value of the copper on the ships' bottoms, and its annual cost would scarely be credited by any one not conversant woth such matters; and until chemical supervision is combined with the process of manufacture, nothing definite can be insured; and chance and irregularity must continue.*
* N.B.— The quantity of copper sheathing required for metalling a First Rate is 4750 sheets, or about 18 tons; and for a Frigate 3300 sheets, or about 13 tons, at a cost to the Government of at least 1s 3d per lb. placed — or say £2500 and £1800 respectively, including labour, nails, &c.
Transcribed by Lars Bruzelius
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