METHODS OF HAULING IN TUNNELS 59 



loads, and are used only in special circumstances, where the 

 shaft is of small depth, when the amount of material to be 

 hoisted is small, or where for any reason the use of hoisting 

 engines is precluded. The steam hoisting engine is the stan- 

 dard machine for the rapid lifting of heavy vertical loads. 

 Recently oil engines and electric hoists have also come to be 

 used to some extent, and under certain conditions these ma- 

 chines possess notable Advantage*. 



The construction of hand windlasses is familiar to ever}' one. 

 In tunnel work this device is located directly over the shaft, 

 with its axis a little more than half a man's height, so that tin- 

 t-rank handle does not rise above the shoulder line. To develop 

 its greatest efficiency the hoisting rope is passed around the 

 windlass drum so that the two ends hang down the shaft, and 

 as one end descends the other ascends. A skip, or bucket, is 

 attached to each of the rope ends ; and by loading the descend- 

 ing skip with construction materials and the ascending skip 

 with spoil, the two skip loads tend to balance each other, thus 

 increasing the capacity of the windlass, and decreasing the 

 manual labor required to operate it. Skips varying from 0.3 

 cu. yd. to 0.5 cu. yd. are used. The horse gin consists of a 

 vertical cylinder or drum provided with radial arms to which 

 tin- horses are hitched, which revolve the cylinder by walking 

 around it in a circle. The hoisting rope is rove around the 

 drum so that the two ends extend down the shaft with skips 

 attached, as described in speaking of the hand windlass. The 

 power of the horse gin is, of course, much greater than that of a 

 windlass operated by hand, skips of 1 cu. yd. capacity being 

 commonly used. Horse gins are no longer economical hoisting 

 machines, according to one prominent authority, when V 

 (114-20) > 5000, where V equals the volume of material to 

 be hoisted, and H equals the height of the hoist, the weight of 

 tin- i-x< avated material being 2100 llw. per cu. yd. AH a gen- 

 eral rule, however, it is assumed that it is not economical to 

 employ horse gins with a depth of shaft exceeding 150 ft. 



