TRACTORS 211 
When logs are loaded from a yard, a gin-pole may be used, while 
logs that have not been assembled at one place often are loaded 
by means of a crosshaul or by rolling them by hand methods upon 
the vehicle over skids. Animal power is used chiefly for oper- 
ating the gin-pole and crosshaul, although some tractors are 
provided with a loading winch. The use of a tractor for loading 
is seldom as profitable as some other method because the greatest 
efficiency is secured from the machine when it is kept running 
continuously over the roads. 
The rolling resistance of a given road varies widely with its 
quality and condition and the load which the tractor can move 
may be influenced greatly by the type of vehicle, if any, which 
is used to support the logs. Thus on smooth hard roads, a tractor 
can haul two or three times more volume of logs on wagons than 
it can drag on the ground, while the reverse may be true on an 
uneven or wet bottom because of the inequalities of the ground 
surface and the sinking of the wheels in the earth. 
There are so many types of tractors used by loggers and the 
period for which they have been used has been so comparatively 
short that reliable standards of average output are not available. 
The following table, however, will give an approximate idea of 
the maximum loads in tons which tractors can move under given 
conditions. 
The average speed of crawler tractors when hauling timber, is 
approximately 3 miles per hour while the speed without a load is 
from 4 to 6 miles. On long hauls tractors may cover from 
35 to 40 miles in 10 hours when not delayed at the yard landing. 
The daily mileage of tractors on short hauls, especialjly in skidding, 
is much less than on long hauls due to the increase in the time 
lost at the loading and discharging points. 
The relative efficiency of tractors as compared to animals 
depends on many factors.^ Other conditions being equal, the 
horse has advantages over the tractor in work which is not tire- 
some and which only occasionally requires a short and powerful 
effort, while the opposite is true on long hauls and on continuous 
adverse grades. As compared to a tractor, animals are handi- 
1 See Tractor Skidding in the Inland Empire by Frank J. Klobucher, The 
Timberman, July, 1922, pp. 114, 116, and 118; also Tractor and Horse Skid- 
ding in tlie Inland Empire by James W. Girard, The Timberman, Nov., 
1922. pp. 66, 68, 70 and 72. 
