210 



SUBiJAKIXE CABLE LAYIKG^ AND KEPAIEING. 



and means about seven tons' strain on the grapnel rope when 

 cable is nearing the surface, equivalent to five tons per square 

 inch on the cable itself. Beyond this there is a margin of two 

 or three tons per square inch before breaking strain is reached -^ 

 but, as the cable gets older, this margin diminishes. 



Sometimes on a repair circumstances necessitate putting in 

 a piece of intermediate in too great a depth. In lifting this- 

 again on any subsequent repairs in the same spot the straia 



Fig. 121. — Grappling. Dynamometer Showing Heavy Strain. 



will be unusually great. Suppose a length of type B laid in 

 the moderate depth of 700 fathoms. In raising this the cable 

 would be put to a strain of four tons per square inch, or about 

 9 tons on the grapnel rope. The proper size cable of type I> 

 laid in this depth would only be subject to two and a-half 

 tons per square inch, or about three and a-half tons on the 

 grapnel rope. 



Buoying a Bight. — It is sometimes necessary to buoy the- 

 grapnel rope if it is found in lifting cable that the strain be- 



