SCIENCE AND THE SEA 



were perfected for varying usage, depending on location. The ordi- 

 nary deep sea type cable is only one inch in diameter and weighs 

 about 2 tons per mile. Such cables, brought up after more than 40 

 years in deep water, have shown but insignificant signs of deteriora- 

 tion. A cable laid near the shore or on shoals has added protection 

 against damage by ships anchors and trawling gear. The shore end 

 of a cable may thus be up to three inches in diameter and weigh 30 

 tons per mile and have a breaking strength of 12 tons or more. By 

 far, the most common source of damage is fishing trawls. Damage 



caused by underwater slides and volcanic action can be extensive but 

 fortunately it is relatively rare. 



The theory of how fouling occurs is based largely on conjecture 

 since there are no witnesses and few reports are made. Experiments 

 have been made proving that a well constructed and maintained otter 

 board can cross a cable laying on the bottom hundreds of times with- 

 out fouling. Snagging frequently occurs as the trawler ends the tow 

 and swings around to heave in the catch. This maneuver allows the 

 trawl boards to flatten on the bottom and when the trawl is raised 



A trawl ridden submarine cable showing a kmk 



64 



