In the year 1761 a most important improvement was introduced, which greatly increased the usefulness of ships. This was the discovery of the value of copper plates as a material for sheathing their bottoms. Previously to this period lead was the metal used for sheathing purposes, and even it was only employed occasionally. In other cases the bottoms of vessels were paid over with various compositions, the majority of which fouled rapidly. The first vessel in the navy that was copper-sheathed was the Alarm, a 32-gun frigate. At first the use of copper caused serious oxidation of the iron bolts employed in the bottom fastenings, and copper bolts were substituted for them.
About the year 1788 the dimensions of the various rates were again increased in order to keep pace with the improved French and Spanish ships. In the year 1780 the 38-gun frigate founded on a French model was introduced into the navy, and continued to be much used throughout the great wars at the close of the eighteenth and the commencement of the nineteenth century. The first British frigate of this rating was the Minerva, which measured 141 ft. in length of gun-deck; 38 ft. 10 in. width of beam; 13 ft. 9 in. depth of hold, and 940 tons—figures which were evidently based on those of the Aurore, captured in 1758 (see p. [128]). In 1781 and 1782 two very large French frigates were captured. Their names were the Artois and Aigle, and they exceeded in size anything in this class that had yet been built. The length of gun-deck measured 158 ft.; width, 40 ft. 4 in.; depth of hold, 13 ft. 6 in.; tonnage, 1,152; they each carried 42 guns and 280 men.
Again, in 1790, the force of new ships of the various rates was much increased. The largest line-of-battle ship then built was the Hibernia, of 110 guns. She was the first of her class introduced into the navy. Her dimensions were as follows:—Length on gun-deck, 201 ft. 2 in.; extreme breadth, 53 ft. 1 in.; depth of hold, 22 ft. 4 in.; burthen in tons, 2,508. The armament consisted of thirty 32-pounders on the lower deck, thirty 24-pounders on the middle, and thirty-two 18-pounders on the upper decks, while eighteen 12-pounders were mounted on the forecastle and quarter-deck. It is worthy of remark that, for some time previously, the large line-of-battle ships carried 42-pounders on the lower deck, but it was found that the 32-pounders could be loaded much more quickly, and that a great advantage arose in consequence.
Fig. 56.—The Commerce de Marseille. Captured 1792.
In the year 1792 the first 40-gun frigate, the Acasta, was built. This type of vessel was intended to replace the old 44-gun two-decker. The Acasta measured 150 ft. on deck; 40 ft. 9½ in. extreme breadth; 14 ft. 3 in. depth of hold; with a burthen of 1,142 tons. Her armament consisted of thirty 18-pounders on the main deck, and ten 9-pounder long guns on quarter-deck and forecastle.