and (3) hauling out of the water, inspecting, and rehabilitating the complete 

 mooring assemblies every 3 years where there are adverse bottom conditions 

 and every 5 years where there are favorable bottom conditions. Public Works 

 Center, San Diego follows the 3-year program for both buoys and ground 

 tackle. NCEL studies^"''^ show that properly chosen and applied coating sys- 

 tems can provide mooring buoys with up to 5 years of protection. Although 

 the Public Works Center, San Diego dip-coats their chains with a coal tar 

 coating (MIL-C-18480), there are no coating systems presently available that 

 provide lasting protection to mooring chains. 



Graham^ states that ". . . cathodic protection properly applied can 

 and does inhibit all underwater corrosion on the shell of a buoy, and in addi- 

 tion effects a very material reduction in corrosion wastage in the wind and 

 water area immediately above the true water line." Brouillette and Hanna^'^ 

 state that about half of the tidal area on steel sheet pilings can be cathodically 

 protected. Seabrook^^ found that not only the buoy but also the bridle and 

 swivel could be cathodically protected. He reported that prior to the use of 

 cathodic protection it was frequently necessary to replace the bridle chain 

 and swivel after 3 years of use. 



NCEL tested^"''^ a cathodic protection system on mooring buoys in 

 which no attempt was made to protect the chain. Periodic inspection of the 

 test installation, however, indicated that some of the cathodic protection was 

 being transferred from the buoys down their tight riser-chains. Because the 

 investigation of cathodically protected mooring buoys utilized a system with 

 magnesium anodes, they were also initially tested for protecting the mooring 

 chain. The system was designed, however, for a simple conversion to one 

 with zinc anodes. 



CATHODIC PROTECTION SYSTEMS 



Magnesium Anodes 



Fabrication. A standard Fleet mooring was modified by the Public 

 Works Center, San Diego for in-service testing of the cathodic protection 

 system. The mooring consisted of a Mark 1 1 peg-top buoy with a riser-chain 

 and four ground legs. Each ground leg had a sinker block located 1 35 feet 

 from the ground ring and an anchor located 90 feet from the sinker block. 

 Figure 1 shows the layout of the ground tackle with the location of the 

 anodes and remote ground cables indicated. 



