13-i BULLETIN 711, IT. S. DEPAETMENT OF AGRICULTURE. 



obsolescence, also the time the skidder can be used by an operator 

 before it has to be disposed of, have a direct bearing on the amount 

 that should be written off annually for depreciation. Conserva- 

 tively, for the purpose of timber appraisal, the efficient life of a 

 skidder should be placed at 10 years, with a scrap value of 10 per 

 cent of the original cost. (See discussion of depreciation on ground 

 yarding engines.) 



MACFAELANE SKT-LINK SYSTEM. 



The MacFarlane sky-line sj^stem differs from the Lidgerwood sys- 

 tem in that no slack-pulling line is employed, the main cable upon 

 which the carriage travels being raised or lowered when the system is 

 in operation, Tlie first step in the evolution of this system was taken 

 in 1905. In that year Mr. C. E. MacFarlane was confronted with the 

 problem of moving logs about 900 feet down a steep slope to the 

 Kalama Eiver, the elevation of the bench above the river amounting 

 to 600 feet, with the slope in places so steep that it was difficult for a 

 man to climb up. To move the logs down this slope on the ground was 

 not practicable and there was not enough water in the river to permit 

 the use of a chute. It was decided that some inexpensive overhead 

 method would have to be used. The trip drum of an ordinary 8^ by 

 10 inch gi'ound yarding engine, set at the top of the slope, was fitted 

 with a double brake. A 1-inch plow steel cable was made fast to a 

 stump on the opposite side of the river, led up the hill, and passed 

 through a block suspended to a properly giiyed tree about 60 feet 

 from the ground. A ^-inch line ran from the main drum, through 

 a block attached to the end of the main or overhead cable, and thence 

 back around a stump, thus providing a purchase for raising the main 

 cable. A five-eighths-inch trip line was strung about 150 feet to one 

 side of the overhead cable and led through a block to the carriage. 



In yarding a log, say, 150 feet from the main cable, the trip line 

 pulled the carriage and main line over to the log, permitting the log 

 to be hooked on ; slack was then taken out of the main cable, thus ele- 

 vating the log, by reeling in the ^-inch purchase line on the main 

 drum, and the log was lowered down the hill by letting out the trip 

 line. When the log reached the river the main cable was lowered, 

 permitting the load to be unhooked. The device constituted an over- 

 head snubbing sj'stem, since it relied on gi-avity to pull the logs in. 



The cost of yarding logs by this sj^stem was considerably less than 

 it would have been if a ground-yarding method had been used, the 

 operator finding that the steep ground was logged as cheaply as some 

 moderately level ground with the ground method. The logs ranged 

 from 600 to 1.500 feet in volume. 



