In a cathodic enviroment all anodes react to a corrosive enviroment and are linked that way they dissolve to protect the metal it is connected to.Any steel hull or shafts etc may be protected by zinc.All ships have most of the protection on the outside which are changed in dry dock every couple of years those fitted on the inside are normally fitted in the ballast tanks.In leisure use on boats under 50ft annodes are normally changed every year as they are smaller and easier to access(outside of the hull)
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