

91 



604 



- 



Block. 





.)' *Vii 



BLOCK, 



Is the name given to a pulley, or system of pulleys, 

 mounted in a frame or shell, but considering them 

 as detached from the ropes which run through them. 

 When speaking of the block with its rope, the seaman 

 uses the phrase of a tackle of single or double blocks ; 

 hence the term block is applied to the pulley or pul- 

 lies, with its frame or shell, and its band or strap. 



The ship's block consists of its sheaves or pullies, 

 which are circular pieces of wood (usually lignum 

 vita;,) or sometimes brass or cast metal, with a groove, 

 turned on its edge for the reception of the rope ; and 

 in the best blocks, called coaked sheaves, the sheave 

 has a brass bush fitted into the centre, with a hole 

 through it to receive the pin on which the sheave re- 

 volves. The pin is made of lignum vitse, cocus, or a 

 West India wood called green heart ; but the best 

 blocks have iron pins. The pin is supported by pass- 

 ing through the sides of the shell of the block, which 

 is made of elm, ash, or other tough wood, with a 

 hole morticed through it to receive the sheave, and 

 confine it to revolve steadily though freely upon its 

 pin, and at the same time keep the rope from getting 

 off the groove in the edge of the sheave. When the 

 block contains two or more sheaves, as many mor- 

 tices are made. Sometimes the same pin serves all 

 the sheaves j and at other times, the sheaves are placed 

 one above the other, having of course separate pins. 

 The strap is a rope, or, in some cases, a band of iron/ 

 encompassing the shell of the block, in a notch or 

 scoring cut round the block to receive it : The strap 

 terminates in an eye of rope, or hook of iron, by 

 means of which one of the blocks of a tackle is at- 

 tached to the object upon which it is to act as a me- 

 chanical power, while the other block is suspended 

 from some fixed support. The former is called the 

 running block, and the latter the standing block. 



The blocks in use among shipping are so nume- 

 rous, having different names according to the pur- 

 poses to which they are applied, and the manner in 

 which their straps and tackles are fitted up, that a 

 mere enumeration of all their names would take con- 

 siderable room. They may, in general, be divided 

 into single, double, triple, and four-fold blocks, ac- 

 cording to the number of sheaves they contain. The 

 shells of very large blocks are made of separate pieces 

 of wood, as the cheeks of the shell, its partitions, &c. 

 These are called made blocks. The shell is formed 

 of several pieces of elm plank, suited to the thickness 

 of the cheeks, sheave holes, and partitions, and is 

 strongly bolted together by three bolts at each end, 

 driven through and riveted with a washer at the 

 points. 



Blocks are again divided into thick and thin blocks ; 

 the former being intended to receive large ropes, and 

 the latter smaller ones. The following may serve as a 

 general idea of the mode of making any of the common 

 kinds of blocks in the old way, before the introduc- 

 tion of machinery. The shells being sawn to their 

 length, breadth, and thickness, the corners or angles 

 are sawn off. The workman then gauges or marks 



out the size of the sheave hole in the middle, one six- 

 teenth larger than the thickness of the sheave, and ' 

 once the thickness longer than the diameter, for a 

 single sheaved block. In blocks of two sheaves, the 

 partition is kept in the middle, and is one sixth less 

 than the sheave hole ; each sheave hole is gauged on the 

 two opposite sides, and in the same manner for blocks 

 with a greater number of sheaves. The blocks are 

 then jambed up edgewise with wedges In a clave or 

 frame, and the sheave holes are made in this manner ; 

 the length and breadth are first gauged out, and 

 holes are bored half way through the block, along 

 the part gauged out, with an auger of the size of the 

 sheave hole ; then the sheave hole is gauged, and 

 bored on the opposite side in \A>e same manner, so at 

 to meet the opposite holes. Blocks from ten inches 

 and upwards have one hole bored at each end, and 

 cut through with a chisel, and the wood is sawed 

 out with a rib saw. All blocks have the sheave 

 holes cleared through by chisels, and by burrs at 

 the corners. Blocks that are to have iron straps 

 should have the strap fitted on before the wood is 

 cut out of the middle. The hole for the pin is bored 

 through the middle of the block, one-tenth less than 

 the diameter of the pin. The outsides and edges of 

 the shell are next rounded off by the stock shave, 

 and neatly finished by the spoke shave. In the royal 

 navy, blocks are left thick upon the edges of the 

 cheeks ; but in the merchant ships, the edges are 

 somewhat thinned off to a small square, and some- 

 what rounded off. The scores, which are the grooves 

 to receive the strap, are gauged out along the out- 

 sides of the cheeks, and tapered in depth, from no- 

 thing at the pin to half the thickness of the strap at 

 the ends of the block for a single score, and the same 

 on each side of the pin for double scores, which are 

 made when the block is to have double straps. The 

 scores are gauged down across the breast of the block 

 to half the size of the strap, in order to allow for the 

 serving. After the score is cut, the sheaves are fit- 

 ted ; they are one- tenth thicker than the diameter of 

 the rope intended for running on them, and five 

 times that thickness in diameter. The hole for the 

 pin should be bored through the centre of them by 

 a bit fixed in the mandrel of a turning lath, or with 

 a stock an"d bit, and opened out with an auger one 

 sixteenth larger than the pin, that it may easily turn. 

 They are then put in a lath, and turned smooth, and 

 the outer circumference hollowed one-third of its 

 thickness, that the rope may embrace it closely. 

 The diameter of the pin is the thickness of the sheave, 

 and is turned in a lathe, except its head, which is left 

 octagonal to prevent its turning in the block, and the 

 pin is driven through the holes in the block and 

 sheaves. After the sheaves are fitted, the inside of 

 the sheave hole, at one end of the block, is gauged 

 hollow to admit the rope, and correspond with the 

 sheaves ; and a small neat chamfer is taken off the 

 edges. The following articles will explain some of 

 the different kinds of blocks used in shipping ; 





Block. 



