Blister antifouling thru hulls electrical event??

[robert sailor]

OK I need some guidance from the electrical boys on my problem. I have a British boat with all thruhulls bonded to a central zinc just in front of the shaft strut. The 12 volt system has a separate ground not connected in anyway to the bonding. I have the bottom paint blistering and separating from the hull around all the thru hulls behind the keel. I believe it is an issue coming from my SSB which is grounded to a slicon bronze plate as the problem really started when I started to use the sideband. Have any of you had a similar experiece? Any ideas on fixing this? Cheers, Robert

[fstbttms]

Pix pleez