82 SUBMAKINE CABLE LAYING AND KEPAIRING. 



shore-ends, it is chiefly weight and substance that is required 

 to withstand wear. For this purpose galvanised iron wire is 

 largely used of a breaking strain of not more than 30 tons per 

 square inch. 



The sheath of a light intermediate weighing about 2 '3 ton& 

 per naut has a sectional area of 



—=0*25 sq. in. 

 9-1 ^ 



(where 9*1 is the weight in tons of 1 naut square inch of iron). 



This would be composed of either ten wires of No. 7 B.W.G. or 



twelve of No. 8, and the total breaking strain of the sheath 



would be 



0-25x30 = 71 tons. 



The weight of the finished cable would be a little over 3 tons 

 per naut, and the weight in sea water about 30 per cent. less. 



The sheath of a heavy intermediate of say 6^ tons per naut 

 has an area of 



|;^=0-72 sq. in., 



equal to ten No. 1 wires, and of a strength equal to 

 0-72x30 = 22 tons. 



The specific gravity would be about 3-7. 



For shore-ends the sheath is from 10 to 17 tons per naut,- 

 according to depth, the heaviest type being used for laying 

 from the beach to about a mile out. With 10^ tons the area 

 of sheath is 



-^ = 1-15 sq.m.. 



^tnd the tensile strength 



1-15x30=35 tons. 



If single, this sheath would be composed of ten No. 00 or 

 twelve No. wires, and if double, of twelve No. 8 and fourteen 

 No 2 wires. 



For the heaviest type of shore-end the sheath is always 

 double and weighs about 17 tons per naut. For this weight 

 the wires composing the two sheaths would be : — 



Inner sheath, twelve No. 8 wires or ten No. 7 wires ; outer 

 sheath, twelve strands each consisting of three No 4 wires, the 



