BLACK-STRAKES, a range of planks immediately above the wales in a ship’s side: they are always covered with a mixture of tar and lamp-black, forming an agreeable variety with the white bottom beneath, and the scraped planks of the side, covered with melted turpentine or varnish of pine, above. All the yards are likewise daubed with this mixture, which not only preserves them from the heat of the sun and the weather, but gives them a fine gloss, which makes a good appearance contrasted with the white varnish on the masts. BLADE. See the article OAR. BLOCK, _poulie_, a machine known in mechanics by the name of pully, and used for various purposes in a ship, particularly to increase the mechanical power of the ropes employed in contracting, dilating, or traversing the sails. The ends of these ropes, being arranged in certain places upon the deck, may thus be readily found whenever they are wanted. The blocks, which are for these purposes disposed in various places upon the masts, yards, and sails, and amongst the rigging, are also of various sizes, shapes, and powers, according to the effect they are calculated to produce. They are single, double, or treble, being so denominated from the number of wheels they contain. There are even some of five, six, and seven fold, but these are only employed to raise or move some very weighty bodies, and are not used about the yards or sails. We shall begin by describing the most simple, and afterwards proceed to those which are more complicated. A common single block is composed of three parts; the shell, the sheave, and the pins. The shell, _arcasse_, approaches nearest to the figure of a long spheroid, somewhat flatted in the middle. Between the two flat sides it is hollowed so as to receive a narrow cylindrical wheel called the sheave, _rouet_, formed of lignum vitæ, or other hard wood; and thro’ the centre of this sheave is bored a round hole, to admit of a pin, which is driven through two corresponding holes in the middle of the shell, perpendicular to the hollow space within. The pin thus becomes the axis of the wheel or sheave, which completes the wooden work of the machine. Thus formed, it is bound with a sort of rope-ring, which is closely fitted to a notch passing round the surface of the shell, and over both ends of the pin: and by this ring, or wreath, which is called a block-strop, they are suspended upon the masts, shrouds, &c. The complicated blocks, or those which contain a number of wheels, either have all the wheels to run upon one axis, (see plate I.) or have their shells so formed that the wheels are one above another. In the former shape they approach nearest the figure of a cylinder, and in the latter appear like two or more single blocks joined together endways.