Baloo
03-09-2003, 10:35 PM
Is it possible to have too much zinc anode protection? I have a 35 ft timber ex trawler and last time I slipped I put two 2.4 (5 lbs) anodes on the boat, which is twice what I would normally put on. I put two on because when I come out after 12 months the single anode is virtually gone and I did not want to run the risk of being unprotected.
Now I have a real problem with shell (barnacles) build up on the copper sheathed areas and to a lesser extent the prop, in fact after just six weeks I have a 1 inch thick layer of shell on the copper sheathing and absolutely none on the timber. I have copper sheathing on the docking strip, a bit on the stem and covering the timber joins where the deadwood is built up (several layers of 6 inch by 6 inch spotted gum), copper strips about 2 inches wide just over the longitudinal joins. The shell build up is noticeably greater on the copper sheathing than bronze (ie the prop, skin fitting screens etc).
There is absolutely no shell on any timber so I beginning to think that the copper is reacting with the (copper?) active ingredient in the anti foul paint. As I said the paint is working fine on the timber, a little less effectively on the bronze and almost seems to promote shell growth on the copper sheath. It would seem some sort of electrolysis reaction is occurring, hence my original question because the only thing I have changed is the amount of zinc.
I have to swim and clean the boat of shell every 4 weeks, which is fine while the water is warm but a little less appealing when winter comes around. I have to use a metal paint scraper to remove the shell and of course this also damages the paint finish (by removing the paint).
Have I over protected?
Now I have a real problem with shell (barnacles) build up on the copper sheathed areas and to a lesser extent the prop, in fact after just six weeks I have a 1 inch thick layer of shell on the copper sheathing and absolutely none on the timber. I have copper sheathing on the docking strip, a bit on the stem and covering the timber joins where the deadwood is built up (several layers of 6 inch by 6 inch spotted gum), copper strips about 2 inches wide just over the longitudinal joins. The shell build up is noticeably greater on the copper sheathing than bronze (ie the prop, skin fitting screens etc).
There is absolutely no shell on any timber so I beginning to think that the copper is reacting with the (copper?) active ingredient in the anti foul paint. As I said the paint is working fine on the timber, a little less effectively on the bronze and almost seems to promote shell growth on the copper sheath. It would seem some sort of electrolysis reaction is occurring, hence my original question because the only thing I have changed is the amount of zinc.
I have to swim and clean the boat of shell every 4 weeks, which is fine while the water is warm but a little less appealing when winter comes around. I have to use a metal paint scraper to remove the shell and of course this also damages the paint finish (by removing the paint).
Have I over protected?