POWER SKIDDING 219 
Power for operating the cahleway system is provided ])y a 
vertical, high-pressure boiler and a pair of engines mounted on 
a steel frame which is supported on two sets of trucks, each of 
which is pivoted. The machine is moved from one set-up to 
another by means of a locomotive. On arrival at the location 
where it is to be used, the frame is elevated above the rails by 
hydraulic jacks, the trucks turned in a quarter circle, and a 
short span of track placed under each truck. The machine is 
then lowered and shunted off to one side of the railroad by the 
Ski dding Carr iage 
Outfiaul Rope 
Fig. 66. — The Lidgerwood Skidding Carriage, and the Arrangement of 
Operating Cables and Slack-pulhng Line. 
side of the head spar tree, where it is blocked up and remains 
until the next move is made. This leaves the main railroad track 
clear for the operation of logging trains. 
Some steel spar machines move about under their own power 
while others are moved on flat ears of special design by a locomotive. 
In the first case the machine is side-tracked at the set-up so as 
to leave the main line clear, while in the second case the machine 
remains on the main line and is elevated above the track by 
means of hydraulic jacks and each corner is supported on blocks. 
When the skidder has been adjusted in position, the carrying 
cars are pushed to the rear of the machine so that empty log 
cars can be spotted under the loading boom. 
The three main drums on the skidder are arranged in a row in 
front of the boiler. The forward drum handles the slack pulling 
cable, the middle one the outhaul rope and the rear one the 
skidding line. 
In operation, the outhaul and skidding drums are interlocked, 
and when the outhaul rope is wound on its drum, the trolley is 
drawn out towards the tail tree, carrying with it the skidding 
line and the slack-pulling line. The speed of the outhaul line 
usually is from 1200 to 1800 feet, although it sometimes is as 
