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The Berlin and Milan decrees in 1807, having shut us out from the ports of the Baltic, large quantities of oak, and red and yellow pine timber, were imported from Canada, and the use of those woods, it was found, was highly prejudicial to his Majesty's ships.
We give an instance, furnished by Mr. Knowles, of the effect of dry rot, on board the Queen Charlotte, of one hundred guns, in 1811. The keel of this ship was laid in October, 1805; her frame completed in December, 1806, and stood to season till September, 1808: the work was then continued till the 17th of May, 1810, when she was launched: in 1811, she was sent from Sheerness to Plymouth; where, in July, the dockyard officers discovered that her topsides were in a state of rapid decay. Thus in a short space of fourteen months from her being launched, a firstrate ship of war, without having been in commission, was nearly rotten from the topside to the gun-deck clamps—below which there was no appearance of fungus. In the Queen Charlotte were found the following sorts of fungi: Boletus hybridus, boletus medulla panis, boletus lachrymans, xylostroma giganteum, and the auricularia pulverulenta.
The injury was ascribed to the great quantities of Canada oak, and American pitch-pine, used in the construction; but these, though subject to early decay, were not the only causes; the work had been commenced and carried on at improper seasons, and the timbers saturated with rain water had been enclosed, by the planking of the wales. She was also caulked in winter; and perhaps the unseasonable application of fires in the hold, acting on the damp air and water so confined, produced the growth of fungi. The American wood was found much more affected than the British oak. Every defective part was either removed, scraped, or dubbed over, ventilation promoted, the ship kept dry during her repairs, which in 1812 were completed, to the amount of 30,000/. She was then put in commission, and has continued to be kept so to this hour; and the reports from Portsmouth, where she is the flagship, state, that she will last four years longer without any repair.* This report must be a great consolation to those who considered the disorder incurable, and not to be checked by any means; and that every ship in the navy would require to be rebuilt in eight years.
As an experiment, the Eden of twenty-six guns, having the dry rot, was, at the recommendation of Sir R. Seppings, sunk in Barn-pool, in November, 1816, and having been six months in that state, was weighed, commissioned, and sent to the East Indies, where she remained three years; on being opened at Deptford, in 1821, it was discovered that no fungus existed in those parts where it was usually found; but her iron work appears to have been more corroded than in vessels of her age. With all these precautions, we cannot flatter our
selves that the dry rot will ever be effectually eradicated: we have lately seen some melancholy instances of it in ships not more than eight years off the stocks. France has it as well as ourselves: it is more common in large ships than in small ones, and is generally found in the most secluded places, as under the floors of the magazines, or in the wales above water, where the air cannot penetrate.
We add a list of ships built of foreign woods, of which the teak is the most durable, the red pine of America the least: the frigates constructed of the last sort seldom ran longer than four or five years.
There are two ships of thirty-six guns each, now building at Deptford, of timber imported from Sierra Leone, the Andromeda and Alarm; the former from wood called turtosar, the other, conta.
A very considerable change has of late years taken place in the arrangement and connexion of the materials which compose the fabric of our ships of war, and also in the formation of their bows and sterns. It will not be expected that we should give a detailed description of changes of such magnitude; the principle of which is the substituting the triangle for the rectangle, and by so arranging the materials in the hold, that they shall form a diagonal trussed frame, composed of a series of triangles.
The system of trussing is also extended between the ports aloft, though not with equal effect, owing to the shrinking of the wood ; but a uniform strength is generally preserved throughout the fabric of ships so constructed, it being a settled principle with the author of this system, to keep in view these two leading axioms,—" That the strength of a fabric consists not so much in the quantity of the materials of which it is composed, as in the disposition, the connexion, and the security of its several parts." And, "That the strength of a ship, let its construction be what it may, can never exceed that of its weakest part, and consequently, that partial strength produces general weakness,"
The ships constructed on this system, have the interstices between the ribs filled with slips of