breaking strength of the cable can be calculated. The manufacturer 

 usually will test the particular E-M cable in pure static tension for 

 adequate breaking strength and determine the modulus of elasticity of 

 individual armoring wires. From Young's modulus the longitudinal spring 

 constant can be determined for a cable with a specific area and length. 



The other two important mechanical properties, bending and torsion, 

 should be considered and determined for each particular E-M cable as 

 well as the tensile breaking strength. The user must recognize poten- 

 tial flexural and torsional problem areas such as sheave passage, fixed 

 terminations, cyclic loading due to currents and wave action, and ship 

 motions and payload response. If the user has a working knowledge of 

 his entire cable system, then he should be able to predict the allowable 

 limits on the bending and torsion parameters. The resulting design 

 specifications to the cable manufacturer should have details which reflect 

 such knowledge of the system. 



Once the cable is fabricated, a sample should be tested to verify 

 that the manufacturer met all of the design specifications. The tests 

 performed should determine: 



Effect of sheave size (minimum bending radius) 



Effect of sheave groove size 



Effect of fleet angle and level wind 



Bending fatigue over sheaves 



Cyclic loading due to transverse vibrations 



Natural frequency versus length curves in strumming mode 



Load versus rotation curves 



Since most manufacturers make only special order E-M cable, they do not 

 have permanent facilities to perform these tests. The extent of their 

 testing is the determination of the breaking strength and modulus of 

 elasticity. Manufacturers, at a premium cost, can do the tests by 

 setting up the facilities for any particular cable. 



Corrosion of Electro-Mechanical Cables 



Metal wires can have a high strength-to-diameter ratio which, couDled 

 with their flexibility and ease of manufacture, make them ideal candidates 

 for strength members in electro-mechanical cables. However, many metals 

 and alloys are subject to corrosive attack when they are exposed to sea- 

 water. For cable lifetimes of up to six months, such attack is normally 

 insignificant; however, for long-term exposure in terms of years, such 

 attack may be the limiting factor in cable design. 



The information included in this section is not based upon actual 

 exposure of E-M cable to the ocean environment but is based upon an analy- 

 sis of pertinent information gathered in marine corrosion tests on plate 

 and sheet materials and wire rope. 



The most common material presently used for strength members of E-M 

 cable is carbon steel. Referred to as plow steel, improved plow steel, 

 extra improved plow steel and several trade names, this material is in- 

 expensive, easy to fabricate and has a high strength/weight ratio. All 

 types of carbon steel are, however, subject Co uniform corrosion when 



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