Anode/Antifoul reaction

[kevinandbarb]

Has anyone out there experienced the following problem:

We lifted the boat after 8 months (last November) to spray off and check anodes on Maxprop and bowthruster. Anodes doing their job properly but was horrified to find that the antifoul had been eaten away in patches around the new through-the- hull anode (fitted March 2005). The eaten away area extends to roughly 18in in circumference. The boat was completely stripped of antifoul in 2002 and recoated with VC 17m, but last year we changed to VC Offshore which we understand has a higher copper content. Fouling on the hull was minimal, so we were pleased with that but instead of having a beautifully smooth hull resembling a Teflon saucepan, we now have these patches! It seems as though the anode is reacting with the copper in the antifoul. We have disconnected the anode until we find out what is going on, but obviously this is not a very good idea. Have since fitted a galvanic isolator.

Have been in touch with International and MG Duff but neither has the answer! Has anyone else had this problem or can anyone offer advice? We want to stick with VC antifoul and don't relish the idea of another strip off.

 

[TJAGAIN]

yes very strange, i had exactly the same problem last year, fitted new anodes and when i took her out an area of maybe 2-3 sq feet of antifoul had parted company with both my bilge keels. the year before no problem but i was using ALU anodes,don't know if it makes a difference or indeed why it happened at all.any ideas?

 

[VicS]

This sounds like the same problem that people have with anodes on wooden boats, at least the cause is the same. The current flow through the water between the anode and the bits it is protecting in effect liberates a little sodium hydroxide (caustic soda) at the anode. In wooden boats this can have a devastating effect on the wood and is a well known phenomenon. I suspect the same thing is happening to you but the effect is that of a faily effective paint stripper being applied contiuously in the area around the anode. I don't think it is related to the copper content of the antifouling.

It sounds as though there is rather a high current flowing perhaps the anode is closer to what it is protecting than it need be. Perhaps you would be better off with more than one anode. Maybe it's just that the antifouling is not stuck on as well as it might be. I have often wondered how a second layer of Teflon AF sticks to an existing layer of nonstick coating!

 

[VicS]

Sorry I should have said welcome to the forum.

It might be a good idea to talk to International yachtpaints

The best place (correct place!) to ask for practical advice is the Reader to reader forum.

It would be nice if tou could put a bit more detail in your profile, but only as much as you are happy with.