Rotation of the wire rope is a function of its helical con- 

 struction, and the direction in which it rotates depends upon the 

 direction in which the strands are laid. Length of cable and weight 

 of loading determine the degree of rotational stretch which will be 

 produced. 



TEST PROCEDURES 



Conducting a study at sea to gather the information sought in 

 this evaluation would require operation of a test vessel with in- 

 strumentation which would be prohibitively expensive. The manu- 

 facturers of wire rope and cable were not able to supply directions 

 for such an investigation, and since no A.S.T.M. standards or 

 guide lines were available, the test procedure to be described was 

 developed empirically at NEL. 



NEL towers were used to support a length of cable. Gener- 

 ally 120 feet of cable was used so that one end could be secured in 

 the tower. The working length was 100 feet, suspended to within 

 5 or 6 feet of the ground. A drag or brake system was used to 

 regulate the twist, from unwind to rewind, to the speed at which 

 it was estimated the cable would be turning in the sea, and to sim- 

 ulate the drag it would encounter in sea water. Count was made of 

 rotational turns from unwind to wind. Other tests were made, on 

 longer lengths of cable, by securing sheaves at different levels in 

 the tower and, by means of a winch from a tractor, raising and 

 lowering the weights to distribute a load over the required length 

 of cable (figs. 1-6). To determine the amount of stretch for any 

 given load, the cable length was measured before addition of a 

 weight and again after it was completely "relaxed" under the addi- 

 tional load. 



Each cable was tested under these conditions to determine 

 the elastic stretch and rotational effect when known loads were 

 applied to a given length of cable. The test results are summa- 

 rized in tables 2-15 which indicate the amount of elongation 



10 



