POWER SKIDDING 245 
as the log reaches a point near enough to the spar to have the cable 
exert a lifting tendency. This cHstance depends upon the height 
of the spar tree and the configuration of the ground but seldom 
exceeds 600 feet. 
A main spar tree from 15 to 20 feet from the center of the rail- 
road track is selected at the proposed setting and the top is cut 
off at a point from 150 to 200 feet above ground. The spar is 
then guyed with from six to nine lines.' In case a suitable tree 
is not available at the setting a spar may be moved to the site, 
although this method is resorted to only under exceptional cir- 
cumstances. 
The yarding engine is placed from 150 to 250 feet from the spar 
tree in order to relieve the strain on the spar. The main cable 
is supported on a high-lead block of special design, which is sus- 
pended under the guy lines at an elevation of from 125 to 175 feet. 
A standard type of ground yarding engine may be used for 
high-lead yarding, but a special three-drum type with higher 
drimi speeds is necessary if the operator secures the full advantage 
of the system. Some operators now mount their yarders on steel 
cars instead of on sleds, and place them on a siding near the spar 
tree, lashing the car to the latter. 
The cables and chokers are similar to those used for ground 
yarding but cables of a smaller size are often used because there 
is less wear on them. 
The crew required to operate this system may consist of eleven 
men, provided the spar rigging is done by a special crew, which 
may rig for two skidding units. 
1 hook tender 1 engineer 
1 rigging slinger 1 fireman 
3 choker men 1 wood buck 
1 signal man 1 wood sphtter 
1 chaser 
The output per crew may exceed that for a ground system operat- 
ing under like conditions by from 15 to 30 per cent. 
SWINGING AND ROADING 
Overhead, ground yarding and high-lead equipment are fre- 
quently used in the Northwest to bring logs from a yarding ma- 
chine to the railroad spur or to some driveable stream or other body 
1 When nine guy hues are used, six radiate from a point near the top of the 
spar, and three from some point lower down. 
