To meet the advances in French construction a new classification of rates took place, with French captured ships as models. The capture of the _Foudroyant_, for instance, in 1758, provided us with the form and dimensions of a splendid two-decked 84-gun ship. Our 80-gun three-deckers were thereupon abolished, and no three-decker was thenceforth built with fewer than 90 guns. The capture of the _Invincible_, in 1757, gave us a valuable model for a 74-gun ship, a rate highly esteemed, which bore the brunt of most of this century’s warfare.[25] From her was copied the _Triumph_, and other experimental 74’s, with dimensions varying from those of the _Invincible_, were at this time laid down. All 50-gun ships had already dropped out of the line of battle; they were now followed by the 60’s. No more 60 or 70-gun ships were built; their places were taken by 64’s and 74’s respectively, of relatively large size and displacement. Nor was improvement confined to form and dimensions. Attention was now paid to material. New rules were made for the cutting and seasoning of timber, and for its economical use. Sheathing was tried; in 1761 the frigate _Alarm_ was sheathed in copper for service in the West Indies, where the worm was active. The copper was found to keep clean the hull, but at the expense of the iron fastenings; so when, in ’83, copper sheathing became general, an order was issued for all new royal ships to be copper fastened up to the water-line: an order beneficial on another count, since even without the presence of copper sheathing, iron bolts had always been liable to corrosion from the acids contained in the oak timbers. Ventilation was also studied, more for its effects on the hull timbers than on the health of the crews. The scantlings of all ships were strengthened. Taffrails and quarter-pieces were reduced in size, and the weight thus saved was devoted to strengthening the sterns and reinforcing the deck supports; additional knees and fastenings were provided throughout the structure. Moreover, towards the middle of the century the formation of the sails was gradually altered, first in the smaller rates and afterwards in the larger ships. The old-fashioned spritsail, which had been of greatest effect when going free, but which had also been used with the wind abeam by the awkward expedient of topping up its yard, gave place in our navy to the fore and aft jib, which could be used with the wind before the beam. Later the lateen sail on the mizzen gave place to a spanker hung from a gaff or half-yard. These alterations had a general effect on the size and position of masts and sails.