POWER SKIDDING 239 
Operators using this method frequently log only one or two 
runs from each line at a given set-up, pulling at approximately 
right angles to the track. The distance between set-ups along 
the track is about 200 feet when the above practice is followed 
and the machine, therefore, skids from 5 to 7^ acres before 
moving. A self-propelling machine can be moved from one set- 
up to another and the lines readjusted, when the stand is fairly 
open, in about twenty minutes. When the brush is dense and 
the straw line must be pulled out by hand instead of by a horse, 
it may require one-haK hour. The crew for operating a 4-line 
re-haul skidder consists of from seventeen to eighteen men, and 
in addition one horse for pulling the straw line out to the ends 
of the runs when lines are being placed in position. 
The daily capacity of a re-haul skidder in southern yellow pine 
forests ranges from 100 to 125 logs, 25,000 to 35,000 board feet, 
per line. 
Ground yarding. — This method, in which the lines follow the 
general ground level from the yarding machine to the tail blocks, 
is in use chiefly in the Northwest and in the Inland Empire. 
Ground yarders are used both for yarding logs direct from the 
stump to the railroad and also as an intermediate system of 
transportation between the yarding engine and the railroad where 
it is not practicable to place the railroad within reach of the 
initial yarding unit. In some cases the logs may be relayed 
two or more times before they reach the loading point. 
Yarding engines are mounted on a steel frame and have a ver- 
tical high-pressure boiler which ranges in size from 48 by 96 inches 
to 80 by 153 inches; a two-cylinder engine ranging in size from 
9 by 10, to 13 by 13 inches; and three drums driven by compound 
gears. The skidding line drum has a capacity of 1500 feet of 
cable, the haul-back line drum from 3300 to 3500 feet, and the 
straw line drum about 3500 feet. The machine, with a water 
tank at the rear, usually is mounted on a sled which has two 
runners about 3 feet in diameter and from 35 to 60 feet in length. ^ 
The machine is moved for short distances under its own power, 
being dragged over the ground on the sled by means of cables 
which run from the machine to trees or stumps in the line of 
proposed travel. When long moves are made it is placed on a 
* Yarding engines often must be moved up or down slopes and over a bad 
bottom. A sled provides .an admirable base for this purpose. 
