SAILS; SAIL MAKING. The principal sails of large vessels can be placed at right angles to the direction of the keel of the ship, and this position is given to them when the vessel goes before the wind; in other cases the same sails may, by means of the braces, be placed obliquely to the keel. The sails which are attached to the ship's stays, and the sails of boats or small vessels, are when supine in a vertical plane passing through the keel ; degree of obliquity to that plane may, however, be given to them at their lower extremities, if necessary.
When a vessel is in still water, the pressure of the wind against the sails overcomes its inertia, and motion takes place in some direc tion. The motion goes on increasing by the accelerative power of the wind, as the motion of a descending body is accelerated by the force of gravity ; but at the end of a certain time the resistance In an opposite direction, both of the air against the sails and hull of the ship, and of the water against the latter, becoming equal to the accelerative power of the wind, the ship acquires a terminal or uniform velocity, and in this state (neglecting the resistance of the air) there may be said to be an equilibrium between the pressure of the wind against the sails and of the water against the vessel.
The management of a sail in a ship be longs to seamanship ; but the manufacture of the sail itself is simply an industrial employ ment. The canvas used for sails is a very stout material, woven in England or Scotland from Russian hemp, and purchased in the form of rolls called Lolls, each bolt containing about 40 yards of canvas 24 inches wide. There are six or seven different qualities of this canvas, according to the size and position of the sail to be made ; and each quality has a particular number attached to it, and must have a certain weight per square foot. Thus, in the Royal Navy, a bolt of No. 1 canvas, contain ing 38 yards, must weigh 44 lbs. ;whereas No. 7 weighs only about half as much : the inter mediate numbers having intermediate weights.
As the canvas is only two feet wide, many breadths are required to form a large sail. The mainsail of an East Indiaman contains nearly 700 yards of canvas : while the whole suit of sails for such a ship requires as much as 9000 yards. As the sails vary much in
shape, considerable tact is required in cutting up the canvas so as to avoid waste. The art of the sail maker consists not only in seaming up the numerous breadths, so as to give the requisite dimensions to the sail, but also in strengthening the sail by sewing rope to its edges. The seaming and sewing are effected with large three-sided needles, of seven or eight different kinds, which are threaded with sewing twine having from 200 to 400 fathoms to the lb. The skeins of twine previous to being used are dipped into a trough, contain ing melted tar, grease, and oil, which is after wards dried. The sail-maker has a thumb stall and a palm-thimble, for protecting his right hand. His stitches have a regulated degree of closeness, on which his rate of pay ment in part depends ; there are usually about 100 stitches in a yard. The overlapping of the breadths is an inch or an inch and a half. Besides the seaming, sundry small pieces of canvas are stitched to the sail to strengthen it in various directions; and the edge rope or bolt rope is sewn on with great firmness. So skilfully is the canvas marked out and cut up by.a master sail-maker, that in the 9000 yards for-the forty sails of a large ship, there will not be more than three or four yards actually wasted.
The Storm Sails patented in 1814 by Mr. Archibald Trail aro made in the usual man ner, but are subsequently strengthened by sewing to their surface a number of canvas bands about an inch broad, with cords woven in them, such bands being secured at their ends into the bolt-ropes, or cords forming the boundaries of the sail, and carried diagonally across the surface of the sail at an angle of 45° with the seams, and at a distance of about three feet from each other. Two sets of bands are used, crossing the sail in opposite directions, one set being attached on each side of the canvas. By this simple contrivance the strain is so equalised as to render tearing less probable than with an ordinary sail ; while, if any injury be inflicted, the rent is confined within the narrow limits of one of the diamond-shaped compartments into which the sail is divided by the protecting bands.