214 



SUBMARINE CABLE LAYING AND REPAIRING. 



scale in tons and cwts. corresponding to the various positions 

 it may take up. 



The picking-up dynamometers on repairing-ships are designed 

 to register from 5 cwt. to 15 tons for shallow- water work, or to 25 

 tons for deep-water work, for a span of 12ft. between the two 

 guide sheaves. Fig. 125 shows the general arrangement of 

 these machines. Graduated scales are provided for different 

 ranges of strains suitable to the weights used. 



The strains encountered in grappling are very variable, 

 suddenly rising as pieces of rock are lifted and turned over, 

 and as suddenly dropping again when the obstruction falls 

 free. Such variations are quite distinguishable from the 

 steadily rising strain when cable is hooked. The dynamometer 

 block is attached to a plunger working in a cylinder containing 

 oil and water, and the speed of lift can be regulated by the 



Fig. 125. — Arrangement of Dynamometer. 12 Feet Span. 



bye-pass valve V (Fig. 126) on the pipe connecting the ends 

 of the cylinder. By this means sudden temporary strains are 

 eased down on the machine, while it is free to indicate steady 

 strains. V is usually a single-way cock and there is also a 

 boss and cock on the top bend of the pipe (not shown) for 

 filling. 



For deep-sea work extra weights are attached to the lifting 

 sheave, so that the machine indicates heavier strains and on a 

 different scale. When doing lighter work or grappling the 

 weights are removed, so that the lightest strains are indicated. 

 Messrs. Johnson & Phillips have patented a form of machine 

 having an internal spring which comes into compression as the 

 sheave descends. This gradually reduces the effective weight 

 ■of the moving part, thus allowing very low as well as very high 

 strains to be registered without adding or removing weights. 



