Page 177 



CONTROL AND SIGNAL BUILDING 



2836 



secured to the upper end of the lanyard, the anchor cable may be detached from the buoy by removing 

 the iron rod with a boat hook, the light lashing breaking easily. This allows the buoy to float free, 

 to be picked up later, and makes it possible to hoist the anchor cable and anchor on board before the 

 buoy structure is weighed. 



2836. Anchoring to Reduce Scope 



If buoys are used in a large-scale survey of a shoal area, the swinging of the buoy 

 around its anchor must be minimized in order to reduce as much as possible any im- 

 certainty of position. This is difficult to accomplish, for it is usually inadvisable to 

 reduce the length of the anchor cable and thus risk draggmg the anchor. 



The swinging radius of a buoy may be entirely eliminated by mooring with two 

 or more anchor cables. Buoys used by the Coast and Geodetic Survey are rarely 

 moored because the scale of the survey in which they are used is generally compara- 

 tively small and because of the additional work and material required in the duplicate 

 anchors and cables. A satisfactory mooring with two anchor cables may be effected 

 if the two anchors are placed in line with the direction of the prevailing current, as 

 illustrated in ^A, figure 49. The method of mooring with two cables is described in 2851. 



r^CSL 



DIRECTION OF CURRENT 



T 



B 



Figure 49.— Buoys anchored so as to reduce scope. 



A simpler method of reducing scope which is satisfactory for most purposes is 

 illustrated in B, figure 49. A weight (65 to 100 pounds), attached to the anchor cable 

 about 2 or 3 fathoms above the bottom, acts as a buffer to reduce the effect of surges 

 on the cable and permits the use of a shorter length of cable. The weight also aids 

 in keeping the buoy structure more nearly upright and over the anchor position. 



465382—44 13 



y 



