216 SUiJMAEINE CABLE LAYING AND KEPAIEING. 



dynamometer gives reason to believe that the cable is hooked. 

 It happens occasionally that the cry of " Stop the ship ! " is 

 given when some jerk or strain occurs which turns out not to 

 have been caused by the cable. Eocks, beds of coral, and deep- 

 sea growths all impede the steady travel of the grapnel along 

 the ocean bed, and cause heavy strains to be indicated at times. 

 Owing to irregularities of depth it is necessary from time to 

 time to prove that the grapnel is on the bottom. This is 

 ascertained by the system of weighing the grapnel, which, by 

 the way, is also a very good system for taking soundings. If the 

 grapnel is on the bottom, the dynamometer only indicates the 

 weight in water of the suspended rope, excluding slack, and if 

 not on bottom it shows the weight in water of grapnel, chain, 

 and rope together ; then, knowing the length of rope out, it is 

 easily seen what this weight ought to be. Six-by-three grapnel 

 rope weighs 2 cwt. per 100 fathoms, and an ordinary centipede 

 grapnel and length of ^in. chain about 5 cwt. in w-ater. There- 

 fore if the dynamometer showed 25 cwt. when 1,000 fathoms of 

 rope were out it would be evident that the grapnel was not on 

 the bottom. If the weight showed 22 cwt. when 1,300 fathoms 

 were out it would be known that bottom was reached, as the 

 total weight would be 31 cwt. (rope 26 cwt., grapnel and. chain 

 6 cwt.). The depth would also be known, namely 22 ^ 2 = 1,100 

 fathoms. It is usual to stop the ship while weighing, and, if 

 necessary, heave in the grapnel rope a little to get it taut and 

 vertical. Then if the weight shown on dynamometer is equal 

 to the weight of rope out, the grapnel and chain are just on the 

 bottom, and a few turns more are wound in to see the extra 

 weight of grapnel and chain appear on dynamometer. This 

 proves that all is right below, and the rope is slacked out again. 

 If the dynamometer shows less weight than that of the actual 

 length of the rope out, there must be a considerable length of 

 slack below, due to a rising in the bed of the sea. This is taken 

 in until matters become the same as before. If, however, the 

 dynamometer shows the full weight of grapnel, chain, and length 

 of rope out, it is plain that the depth has increased and the 

 grapnel is not on bottom. When this is the case several fathoms 

 more are paid out, and the whole weighed again, and, allowing 

 for the weight in water of the extra rope paid out, the 

 disappearance of 5 cwt. off the dynamometer reading will 



