226 LOGGING 
swinging. The standing line either is stretched between a head 
spar and a tail tree with the ends anchored to stumps, or it leads 
from a drum on the engine to a block on the head spar and thence 
to the tail tree, behind which it is anchored to a stump. When 
the latter method of supporting the standing line is used, a block 
purchase is needed to relieve the strain on the engine. 
The standing line ranges in size from Ij to 1^ inches, 
depending on the length of span and the maximum size of the 
logs handled. A Ij-inch line has proved large enough for 
spans of 1500 feet and for logs containing 2000 board feet. 
The trolley has two 14-inch sheaves, with a clevis on the lower 
end to which the skidding line is attached. This line usually 
is 1-| inches in diameter and its length is dependent both 
on the length of span between the head spar and the tail tree, 
and on the distance logs are yarded on either side of the standing 
line, which may be from 150 to 200 feet. 
The haul-back or trip line is |- or |-inch in diameter and 
passes from the drum on the engine, through a block on the head 
spar, then through blocks placed on the edge of the skidding area 
to a corner block near the logs which are being yarded, thence 
to a fall block placed in a bight of the skidding line. The corner 
block is so placed that the fall block, to which both the haul- 
back line and the butt chain are attached, can be drawn to any 
point where a log is to be secured. 
The engine used most successfully with this system is similar 
to that for the MacFarlane. The usual capacity of the skidding 
line drum is 2700 feet and that of the haul-back line drum 
3500 feet. The yarding speed is 600 feet and the return speed 
for the haul-back line about 1500 feet per minute. 
Duplex Aerial System.^ — This is used both for yarding and 
for swinging. Two separate engines, niounted tandem and 
combined in one unit furnish the power. The forward engine 
operates the skidding, haul-back and straw-line drums, and the 
rear engine operates two sky-line drums on which the ends of 
the overhead line are reeled. The sky-line and skidding drums 
have two speeds which can be changed instantly and the haul- 
back line also is geared to a high speed so that the machine can 
be operated faster than ground systems. 
The sky-line consists of a double cable on which the trolley 
» See Figures 71 and 72. 
