Figure 7. Sinker blocks housing cathodic protection units with coiled 

 cables prior to laying of system. 



The potential profile of the cathodically protected mooring was made 

 using a portable field meter and two 50-foot leads. A silver/silver chloride 

 reference half-cell was attached to one of these leads and a steel pick to the 

 other. The instrument was read at the surface while a diver made electrical 

 contacts with the pick at the mooring chain; the half-cell was held 1 foot 

 from the point of contact. The readings received are listed in Table 1. 



The potential of the control buoy was found to be -680 mv at the 

 time the potential profile of the cathodically protected buoy was made. The 

 potential of the ground ring was -665 mv, and the potentials 10 feet down 

 the two painted and one bare leg were -675, -690, and -680 mv, respectively. 



The control heads of the cathodic protection system were not 

 functioning properly, and the supplier was unable to make the alterations 

 necessary for their proper operation. Thus, it was decided that the system 

 should be modified by replacing the magnesium anodes with ones of zinc 

 which require no control head for regulating the potentials. 



