LOGGING IN THE DOUGLAS FIR REGION. 87 



metrically around a center core, the strands consisting of wires 

 twisted together symmetrically according to a definite geometrical 

 arrangement. The unit of construction is the strand. While a 

 large number of geometrical combinations are possible, the ordinary 

 practice is to use 1 wire in the center of the strand and to surround 

 it with 6 wires, then sucessively wjth layers of 12, 18, 24, and 36 

 wires, etc., the construction being known as the concentric strand. 

 Six wires around a center wire produce a strand for a haulage rope. 

 A supplementary layer of 12 wires makes a 19-wire strand for a 

 hoisting rope. This strand in turn, when covered by a third layer 

 of 18 wires, makes a 37-wire strand that is used in a special flexible 

 hoisting rope. In strands of uniform diameter the greater the 

 number of wires in the strand the more flexible the rope. The 

 strands, usually 6 in number, are, as a rule, laid together around a 

 hemp center. 



The " haulage rope," 6 strands of 7 wires each, is a relatively 

 stiff rope with large wires capable of resisting external wear. Its 

 use is limited to conditions where there is much abrasion and little 

 bending around sheaves. In the "hoisting rope," 6 strands of 19 

 wires each, the wires are smaller than those in a 6 by 7 rope, and 

 are less able to resist abrasion, but can more easily be bent around 

 sheaves and drums. The "special pliable rope," 6 strands of 37 

 wires each, is composed of still smaller wires than the 6 by 19, 

 possesses greater flexibility, and may be bent around fairly small 

 sheaves. It should not be subjected to much external wear, par-, 

 ticularly in the smaller sizes, as the wires will be worn off quicklj^ 

 The " extra pliable rope," 8 strands of 19 wires each, is more flexible 

 than the 6 by 19, and may be used over smaller sheaves than the 

 latter. It is about as flexible as 6 by 37 construction, but not so 

 strong, owing to its larger hemp center. 



The ropes so far referred to are of the one-size- wire construction. 

 In the making of 6 by 19 rope certain features result from a slight 

 modification of the strands and wires. In Seale construction the 

 center wire of the strand is large, the next layer of 9 wires is 

 small, and the outer layer of 9 wires large. These strands pro- 

 duce a rope somewhat stiffer than ordinary 6 by 19 construction 

 and having a limited number of uses. The strands of another con- 

 struction consist of wires of three different sizes, 7 inside wires of 

 uniform diameter surrounded by 12 wires which are alternately 

 large and small. This combination increases the metallic area and 

 strength by approximately 10 per cent. 



There are two general methods of laying up rope — ^the common 

 type, known as regular lay, and Lang's lay. In the former the wires 

 are twisted in one direction and the strands are laid into the rope 

 in the opposite direction. Most of the rope made in America is 



