FLOATING AND RAFTING 



357 



one man as no special effort is required, both of which are 

 advantages. 



Logging dams with "bear-trap" gates 80 feet wide have been 

 built and operated in Wisconsin. 



Half-moon Gates. — A dam constructed to store water for log 

 sluices often has a gate of a type called the "half-moon." It is 

 not used for wide sluiceways nor for large heads of water. The 

 gate, which is shghtly curved, fits tightly into the sluiceway with 

 the convex face upstream. It is supported by four arms from 



Fig. 103.- 



Upstream View of a Rafter Dam, showing a Needle Gate. 

 Appalachians. 



16 to 24 feet long, which extend to the lower end of the sluice 

 where they are attached to a beam hung on bearings placed on 

 either side of the top of the sluiceway. A platform erected over 

 the gate supports a drum actuated by a hand wheel with gearing, 

 or by a hand lever. Chains are attached to either side of the 

 gate head and are passed up over the drum, and the gate, which 

 swings through an arc of a circle with a radius equal to the length 

 of the supporting braces, is raised by winding in the chain. 



Needle or Bracket Gate. — Splash dams, especially in the Appa- 

 lachian and Pennsylvania regions, are often provided with so- 



