156 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



or compound geared. An engine having the gears compounded 

 is always classed as a yarding (skidding) engine (sec' Plate IX.). 



The trip or haul-back is a small wire-rope travelling between, 

 the power skidder and a pulley or pulleys set near the logs to 

 be dragged, and used to return the main cable with tongs^ 

 chokers, or hooks for the next log. 



The choker is a noose of wire-rope by which a log is dragged. 

 It is from 20-30 feet long and has a choker hook on one end 

 and a braided eye on the other. As a rule one choker is used 

 with each log, and one to three chokers are attached to a butt 

 chain. 



The butt-chain or line is a short connection by which chokers 

 are attached to the main yarding line. It consists of the main 

 connecting link, either a heavy steel chain with short links or 

 a wire-rope with eyes spliced in each end, with a hook or 

 clevis on the end which is attached to the main line, and a 

 swivel, a link, and a butt-hook on the other. The swivel in 

 the connection allows the log to roll when being pulled in 

 without twisting the main line. The trip line is usually 

 considered as a part. It is attached to the same clevis as the 

 butt-chain by means of a link, a swivel, and another clevis. 



Yarding engines vary in size and type. They are invariably 

 compound-geared with double cylinders. For mountainous 

 broken country a good type to use is a compound-geared 

 11x13 inch or 12x12 inch, and in fairly level country 

 a compound-geared lox 11 inch or loi x 10^ inch yarding 

 engines. 



The main yarding line varies from i-i| inch in diameter 

 and from 900-1500 feet in length, and is made exclusively 

 from plough steel. "The Wentworth Patent Core-rope," manu- 

 factured by Craven & Speeding Bros., Ltd., Sunderland,. 

 England, is said to be the best wire-rope used in British 

 Columbia. It is claimed for thfe patent core that it prevents 

 the strands from crushing each other and, in consequence, does 

 away with internal friction that wears away and breaks the 

 individual wires of the strands. Jt is claimed for this rope that 

 the breaking-strain is greater by 10-15 % than in ropes con- 

 structed with the ordinary core, it has also greater flexibility. 

 Trip lines are |-f inch in diameter, and about 2^ times as 

 long as the main yarding lines; straw lines are about § inch in. 

 diameter and as long as trip lines. 



