122 BULLETIN Til, U. S. DEPARTMENT OF AGEICULTURE. 



tainty, and the results secured so far give distinct proniise of further 

 improvement. 



One operator has come to certain tentative conclusions with regard 

 to the use and adaptability of overhead systems in coast timber, 

 ■which may be summarized as follows : 



(a) That overhead systems have little advantage over ground 

 yarding systems in level or slightly sloping country and that they 

 are not so satisfactory as the high-lead system on short hauls. 



(5) That overhead logging can be successfully and economically 

 emJDloyed on almost any kind of ground, provided the quantity of 

 timber justifies the necessary expenditure for proper equipment. 

 Some rough mountain sides have been logged from railroads at 

 their base, and numerous other types of rough country have been 

 logged at moderate expense that could not have been logged at all 

 with other systems, practically considered. 



(c) That the length of overhead line which can be successfully 

 employed depends on the support which can be given the line, the 

 weight of the load to be carried, the size of the line, the grade of 

 the line in operation, and the deflection of the line. Wire rope is 

 constructed to withstand certain pulls and stresses. The stress or 

 tension on a cable suspended between two points is entirely different 

 from that of any other type of rope application, and as a rule much 

 greater than the stress expended by the suspended load. Too often 

 conditions necessitate the use of an overhead cable with little sag 

 or center deflection, and sag governs in a large measure the length 

 of the cable. Putting it another way, the greater the deflection that 

 can be secured the longer the cable that can be used. 



(d) That machinery designed and built for ground logging is 

 not adapted for overhead logging. Ground logging machinery 

 is built for power and to withstand strains. Furthermore, there is 

 no elasticity in its make-up. Under certain stresses the engine or 

 the line may break. Overhead logging engines, on the other hand, 

 should have high-speed drums and be so constructed as to refuse 

 to handle any load in excess of that allowed by the factor of safety 

 in the overhead line. Under certain conditions excessive strains on 

 the overhead cable can be prevented by the arrangement of the 

 other lines. Engines adapted for both ground yarding and over- 

 head or high-lead yarding can now be purchased. These have two 

 speeds — one for ground yarding, the other for overhead or high-lead 

 yarding. The slow-speed pinion can be shifted in one-half hour's 

 time, the result being that a high-speed engine adapted for over- 

 head logging is converted into a slow-speed engine for ground 

 yarding. 



The bases of these conclusions are to be found in the peculiarities 

 of the system. A wire hung between two supports along which the 



