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Old 09-07-2012, 03:17   #1
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Stray current and antifoul failure/ delamination

Hi All
Has anyone any experience of Antifoul delamination caused by stray current.
I believe that our boat is suffering from the effects of stray current, with anodes showing, what seems to be excessive wear and the fact that the Jotun antoifoul, put on the hull 1 month before relaunch in April appears to have delaminated compleatly down to an earlier coat of antifoul or primer.
while I can understand the effects stray current can have on the anodes can it have an effect on copper based antifoul. I have seen antifoul fail in patches. But I have never seen 2 coats of red Jotun copper based antifoul, painted onto numerous previous coats of the same antifoul compleatly leave the hull.
I have arranged for an extra large anode to be hung over the side while at anchor and in port, that is until someone with more experience can look at the situation. But I'm hopeful that someone in the forum can enlighten me on the problem.
Regards Joe
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Old 09-07-2012, 06:56   #2
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I had an alloy hull that had non-stop problem with antifoul and top coats delaminating. Turned out i had too much anode in the area. Removal of the rudder anode fixed the problem.
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Old 09-07-2012, 07:13   #3
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Re: Stray current and antifoul failure/ delamination

Too much zinc is as bad as not enough. Hanging junk over the side is screwing with your neighbors.
But I never heard of this.
How many" previous coats", a month of drying before launch, by whom and how was it put on,how is the electricity escaping?
These are questions I would be asking myself.
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Old 09-07-2012, 07:17   #4
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Re: Stray current and antifoul failure/ delamination

Andina* has considerable expertise in Marine Electrolysis < Electrolysis >, and should have an informed opinion on this subject.
* Cruisers & Sailing Forums - View Profile: Andina


In my experience, general detachment (peeling in sheets) of bottom paint (on FRG hulls) suggests that the prep work was faulty, the paint was applied too thickly, or multiple coats were applied too quickly.

Electrolytic Corrosion is caused when an external (Stray) current finds a path between two metals in the presence of an electrolyte. The two metals may be of exactly the same type or different types.
Electrolytic currents can generate chlorine gas, which may cause blistering of the surrounding antifouling paint. However, Iíve never seen it cause extensive (generalised) peeling, though it may so do.

Galvanic Corrosion occurs when two dissimilar metals are in contact with each other, in the presence of an electrolyte, such as seawater.
Any time you have two different metals that are physically or electrically connected and immersed in seawater, they become a battery. Some amount of current flows between the two metals. The electrons that make up that current are supplied by one of the metals giving up bits of itself-in the form of metal ions-to the seawater.
The most common casualty of galvanic corrosion is a bronze or aluminum propeller on a stainless steel shaft; but metal struts, rudders, rudder fittings, and aluminum saildrive, outboard, & stern drives are also at risk. Under no circumstances should antifouling containing cuprous oxide biocide be applied to aluminum hulls nor drives.
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Old 09-07-2012, 17:47   #5
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Re: Stray current and antifoul failure/ delamination

I suspect a faulty paint system (material, age, etc.) or faulty application of the paint system (insufficient substrate preparation, insufficient substrate cleaning; etc). If you were experiencing stray current corrosion, you would see evidence on the affected underwater metal components. And it would not be pretty.
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Old 09-07-2012, 18:23   #6
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Re: Stray current and antifoul failure/ delamination

Quote:
Originally Posted by CharlieJ View Post
I suspect a faulty paint system (material, age, etc.) or faulty application of the paint system (insufficient substrate preparation, insufficient substrate cleaning; etc). If you were experiencing stray current corrosion, you would see evidence on the affected underwater metal components. And it would not be pretty.
And it would not be generalized on the boat. I would be localized where there are metal components.

I've experienced bad paint batches before. Seems most likely, just after terrible surface prep.
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Old 10-07-2012, 05:26   #7
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Re: Stray current and antifoul failure/ delamination

Your antifouling problem is very unlikely. To be a stray current problem on a fibreglass boat.
To explain in very simple terms for a stray current problem you need a circuit. The electricity has to enter and leave (I said it would be in simple terms). The copper mixed in the antifouling does make make a continuous circuit it is bits of copper not a continuous strip of copper.

You can get symptoms like you describe around metal fitting (seacocks, saildrive etc) but not the hull on a fiberglass boat.

Antifouling incompatibility, poor adhesion of the lower layers of antifouling, poor application of current antifouling, or just too many layers of old and new antifouling are much more likely to the cause.

The anode depletion is a separate problem and needs to be investigated. A hanging anode may help in the mean time, but they are difficult to get right and often do nothing.
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Old 13-07-2012, 16:45   #8
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Re: Stray current and antifoul failure/ delamination

I have to agree that delaminating is a sign of poor preparation or application. I had antifouling come off in large sheets one year. The cause was the coal tar epoxy undercoat was left to harden too long which gives it a glossy hard surface that the antifouling won't stick to. The yard admitted their mistake and redid the whole bottom again free (71 ft).

If the delamination was concentric around the anodes you might make a case for too much protection but I doubt it.

On a metal boat, theoretically AC leakage will not cause electrolysis but I found out the hard way that it will cause bubbles under your bottom paint. This is caused by pin holes in the paint allowing the AC current to pass through the salt water under the paint and create bubbles of chlorine. You can see the bleached trails in the bottom paint where the bubbles rise over it to the surface.

If you don't have a Galvanic Isolator it is a $100 investment that can more than pay for itself over the years.
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