KEEL. The principal piece of timber of a ship, usually first laid on the blocks in building. If we compare the body of a ship to the human skeleton, the seems to resemble the backbone, and the timbers the ribs. It is generally com posed of several thick pieces of wood placed lengthways, which, after being scarfed together, are bolted and clenched upon the upper side. Keelage signifies the duty paid by a ship on coining into port.
The keel is generally elm, except the after-piece, which, on account of its wet and dry, is sometimes oak, especially when the ship is expected to be a great while in building. The num ber of pieces in the keel is not very ma terial, so that it gives good shift to the keelson and the mainmast. The keel is scarfed with a book in the middle, which should lay very close, it being designed on purpose to bear the strain of calking the butts, that the bolt in the scarf may not be strained. The keel should not be tapered much, either forward or aft at the upper part, and from thence it is to be bearded away at the lower edge ; for, when the dead-wood is trimmed, espe cially abaft, being frequently very thin, it is with much difficulty that the dead wood can be securely bolted.
The speed of a vessel does not depend so much upon the form of the bow as it does on the depth to which it is hn mersed in the water. In the case of a frigate drawing 17 feet water, and ano ther frigate of the same burthen drawing 11 feet, the last will have a body of six feet less fluid to penetrate, to make her hold a good wind, while the first has six feet perpendicular depth of her hull de pressed, being about one-third of her real size. Therefore, she has a body of water to displace, and to force herself through, equal to the difference between 11 and 17. The resistance of the fluid also increases in proportion to the depth. Vessels in the coal-trade draw one-third less water than any other of British con struction; yet, when employed as trans ports, they sail as fast as any others and, before the wind, in ballast, or half loaded, frequently beat the royal navy. When closed hauled on a wind they drop to leeward ; but if they were furnished with eliding keels, they would be superior to all the other English vessels. The Dutch have vessels built almost flat, but all these have lee-boards, by the assistance of which they sail as fast as any that navi gate the North Sea.
Ships, or vessels of the larger classes, should always be so constructed as to sail on, or nearly on an even keel,—that is, so that when the ship is trimmed for sailing, she should have her keel parallel to the surface of the water ; therefore, as much as the effort of the wind on the sails and mast, in forcing the ship through' the water, has a constant ten dency to depress the bow, so much should the ship be properly trimmed at the stern.
A sharp-built ship sinks under its car go so fast, that by the time it comes to its bearings, it is frequently not loaded. Those and long floors, on the other hand, `Sink slowly ; and after hav ing taken in the quantity they measure, will have, frequently, plenty of room, and remain high out of the water. The only objection to the latter is, the unfit ness of a flat-floored vessel to hold a good wind, but this difficulty is removed by the adoption of sliding keels. The same principle, which causes flat-floored vessels to sail faster before the wind, to carry a larger cargo, and draw less water, operates with equal force in rendering then' easy at anchor. Their form, with the fulness of their body fore and aft, enables them to rise and fall, according to the lift of the sea, while sharp and clean-built ships pitch with the utmost violence, frequently with such force as to endanger the masts ; to say nothing of the strain which the tremendous jerks give the hull and the injury of the an chors and cables.
The use of sliding keels is known, by actual experience, to be of the greatest importance. In fresh breezes, or in light winds, it is totally immaterial how much sail is set, or how it is disposed ; since the act of raising or lowering the keels will immediately counteract the inconve nience that might otherwise arise from carrying too much, sail, either forward or aft. The most trifling practice will ren der the navigators perfectly acquainted with their use, and the easy steerage of this ship will convince him of their ad vantage. In a gale of wind it is neces sary that the main and fore-keels should be hauled close up, and the stern-keel let down to such depth as shall be found necessary to make the vessel steer per fectly easy.