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Paint bubbling around anodes?


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Boat is out of the water after 7 years. My plan was to get the baseplate blasted and epoxy it as the boat is now 17 years old. Also key the existing 7 year old epoxy on the hull sides and give that another couple of coats.

 

The job I did 7 years ago seems to have protected the sides really well. There's no damage to the paint along the waterline. However, when I pressure washed one side I found that the epoxy has bubbled especially around the anodes which now need replacing. The anodes are the original 17 year old ones plus others that were welded on 10 years ago. They all need replacing. The paint around the anodes lifts when it's hit with the pressure washer. There's no pitting to the steel underneath the paint. The bubbles weren't full of water. 

 

So does anyone have any idea what's caused the bubbling around the anodes? The only thing I can think of is that for 5 years I had a TV ariel on a pole bankside wedged behind the steel piling. It didn't occur to me that I could be bypassing my GI. Could that be it? Galvanic action accelerating anode depletion and causing the paint around the anodes to bubble. The first 2 coats of epoxy have aluminum flake if that's relevant. 

 

Anyway the plan now is to blast the sides and forget about the baseplate as it seems to be in perfect condition.

 

 

IMG_20220729_142920.jpg

 

IMG_20220729_142801.jpg

 

IMG_20220729_142819.jpg

Edited by blackrose
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Perfectly normal. Even red lead blisters around anodes.  Poor surface prep makes it worse.

There is a view that once the hull is encapsulated in epoxy there is no need for anodes...................................

Its still worth treating the baseplate, it is the only bit of steel that is not epoxy coated, so where will the most corrosion be concentrated in future.................................?

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23 minutes ago, Tracy D'arth said:

Perfectly normal. Even red lead blisters around anodes.  Poor surface prep makes it worse.

There is a view that once the hull is encapsulated in epoxy there is no need for anodes...................................

Its still worth treating the baseplate, it is the only bit of steel that is not epoxy coated, so where will the most corrosion be concentrated in future.................................?

 

You say it's perfectly normal but I've never seen it before and neither has the owner of the yard. The anodes have definitely eroded over the last 7 years.

 

Yes the baseplate is the only part of the hull that's not been painted along with the BT tunnel and the rudder stock tube. I'm still intending to paint both of those.

 

The baseplate hasn't been painted for 17 years while the sides have always been. If corrosion was was going to be concentrated on the unpainted baseplate during that time why isn't it corroded? 

 

In an ideal world I'd definitely paint the baseplate, but my time and resources are limited and I've decided those resources are better spent on the sides. 

Edited by blackrose
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57 minutes ago, MartynG said:

That's what anodes are meant to do.

 

Yes I know,. I don't think you're following the thread. I was replying to Tracy who said that if a boat is painted in epoxy then arguably there's no need for anodes.

 

The baseplate isn't painted but since anodes only work on line of sight principal I would think that's irrelevant. 

 

1 hour ago, Tracy D'arth said:

It won't float without a bottom!  🩲

 

As I said, the baseplate is in perfect condition after 17 years with no paint. 

Edited by blackrose
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When I re-epoxied my boat hul the epoxy was mostly good (apart from impact damage) except around the anodes area where the epoxy was still mostly present but flaked off easily revealing a pristine metal surface with no pitting.  

 

 

IMGP6834.JPG

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7 minutes ago, system 4-50 said:

When I re-epoxied my boat hul the epoxy was mostly good (apart from impact damage) except around the anodes area where the epoxy was still mostly present but flaked off easily revealing a pristine metal surface with no pitting.  

 

 

IMGP6834.JPG

 

That's what I've got. But what's causing the paint to flake off around the anodes? Why would the bond between steel and epoxy have become weaker around the anodes than the rest of the boat? 

Edited by blackrose
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13 minutes ago, blackrose said:

Ok, it's a known phenomenon to some people but that's not quite the same as it being "perfectly normal". 

We found exactly the same on our boat. The 2 pack had blisters near the anodes, with the metal showing no significant corrosion.

 

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Ok. I don't think it's normal for paint to bubble anywhere on a boat and especially if nobody can explain why it's happening, but it's obviously something that happens with epoxy around anodes over time. I wonder if it happens with bitumen and other types of paint? I guess it's difficult to know as they don't last long enough to tell. 

Edited by blackrose
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I wonder if it is to do with the space behind the anode as anything fitted over a painted surface is likely to be among the first areas of a coating to deteriorate.

 

Edited by BWM
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My thoughts are that the boat was painted, then the area to be fitted with anodes was scraped to metal, the anodes welded on, then the area (except obv the anode itself) was repainted, not quite as well as the original paintwork. Thus, this would be the first to 'go' after a number of years. BUT, its a non-issue because its so close to the anode, its beneficial effect is strongest and it doesn't corrode (much, if at all).

 

But its just a hunch.

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1 hour ago, blackrose said:

Ok. I don't think it's normal for paint to bubble anywhere on a boat and especially if nobody can explain why it's happening, but it's obviously something that happens with epoxy around anodes over time. I wonder if it happens with bitumen and other types of paint? I guess it's difficult to know as they don't last long enough to tell. 

 

 

On outboard engines (Ali-Alloy legs) I have found that the paint close to the anode does indeed come away - I have done some research in the past and found that it is possible to 'over-protect ' (too much anodic protection) and you get "anode burn / blistering" so gave up and just lived with it.

 

However, it could be that in the waters you are in, the anode is 'working hard' and that huge lump of magnesium is fizzing away and affecting the paint.

On my cruiser the anodes are about 200g  - no huge 2.5 or 5kg anodes.

 

Apparently Magnesium anodes can result in paint damage (anode burn / blistering) and can only be used with certain types of paint.

 

Just a thought and something you may wish to investigate, a quick google for "over anodic protection on a boat" yielded this article :

 

(Subsitute magnesium for Zinc)

 

How Much Sacrificial Zinc Does Your Boat Need? | Yacht Management South Florida (myyachtmanagement.com)

 

Can You “Over Zinc” a Boat?

Over zincing happens when there is too much anodic protection. Having an excessive number of sacrificial anodes installed on your boat can lead to unintended consequences. Boats with fiberglass hulls are less likely to be affected by over zincing, but wooden and metal hull boats are particularly susceptible to the negative effects of over zincing which include:

  • Burnback and discoloration
  • Paint delamination and flaking
  • Caustic wood rot

So, how much sacrificial zinc does your boat need? Cathode protection systems vary depending on the type and size of your boat and where it will operate. Typically, sacrificial anodes should have 1 to 2 percent of the surface area of the metal surface it needs to protect.

For the more precise measurements, have professional complete yacht care specialists develop the cathode protection and anti-corrosion systems of your boat or yacht. At Yacht Management South Florida, our certified technicians provide premium yacht management and yacht maintenance services.

Zinc replacement can be done dockside, but zinc installation typically requires a haul-out. Fortunately, we can schedule both dockside assistance and yard periods for your vessel. Contact us to talk with one of our customer service representatives today.

 

 

and this :

 

Boat Corrosion Protection With Anodes | BoatUS

 

 

Which Type Of Anode Is Best?

As mentioned above, anodes can be made of zinc, aluminum, or magnesium, and each type has different uses. The majority of anodes are the familiar "zincs." While zinc anodes have worked well for years, aluminum anodes are even more effective because they can create a higher voltage (driving force) and have a much higher capacity (useful life) for the same weight. Aluminum anodes also do a better job of protecting in both freshwater and saltwater. The majority of boats should be fitted with aluminum anodes.

Magnesium anodes are even more powerful than aluminum (and more expensive) and are best used only with the advice of a specialist because in some situations, they can overprotect and cause paint blistering and other problems.

Edited by Alan de Enfield
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Zinc anodes are no good on fresh water. They are not sufficiently reactive.

Magnessium is the usual anode material on fresh water but it  will erode fast on salt or brackish water.

Aluminium anodes are suitable for both fresh and salt water but whether they are available in the sizes required for a narrowboat I wouldn't know.

I change anodes every two years on my GRP cruiser but they are relatively small anodes.

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On 30/07/2022 at 13:20, Tracy D'arth said:

There you go,      they can overprotect and cause paint blistering and other problems.

 

Yes, but I don't think most people would consider paint blistering and other problems "perfectly normal". The clue is in the word overprotect.

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46 minutes ago, blackrose said:

 

Yes, but I don't think most people would consider paint blistering and other problems "perfectly normal". The clue is in the word overprotect.

 

 

 

It is 'normal', in that it is a well known phenomina on boat metalwork - going back 30 or 40 years I had it on outboard legs - maybe the use of bitumin has been masking it on steel NBs, but now new paint types are being used the problems are starting to  'surface'.

 

Why not speak to the paint manufacturer and explain the problem and the anodes you have and the environment  (clean, polluted, mucky, agricultural run off, etc etc water) you are in, and say you have seen mention in a couple of articles that some paints can be affected if adjacent to magnesium anodes - is this paint one of them, or, do they have any other suggestions ?

Edited by Alan de Enfield
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I don't think there is a perfect answer to this except to say it doesn't really matter. A great lump of mag stuck on a boat will attack paint in a circle of maybe 12 - 15 ", a smaller lump will probably attack paint in a 6" circle but might not protect much more than 3` away. Anodes should be placedat regular spacings all along the hull but then you might not get in a lock. I have not given up with them but they are carefully placed near dissimilar metals (propeller etc) and some on the bottom but none along the middle of the sides. Anodes are a bit like God, I don't believe in God but I don't want to risk going to hell so I don't argue with the church, I don't believe in anodes nut I've got some on the boat.

Edited by Bee
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56 minutes ago, blackrose said:

I disagree. A phenomenon that may occur but isn't supposed to happen and seems to be poorly understood can hardly be described as normal. Anyway, this is just semantics. I'll talk to SML and Jotun tomorrow to see what they say. 

 

 

It is understood, it is known about but probably not as much in the narrowboat world as in other areas.

 

The paint flakes or peels when there is an 'overactive' anode(s) in the vicinity, it is not regularly seen on NBs (probably) because they use bitumin which may well be lost thru bumps, scrapes and water with diesel residue in it.

 

 

IMG_20220729_142801.jpg

 

 

 

Your anodes are way way way too much eroded away, they must be really 'fizzing', where ever you are you should try and identify 'why'.

Your anodes should be replaced at around 50% of their original size/weight or you will not have enough mag to protect the boat.

What happens if you 'pop' those blisters ? What's underneath them ?

 

It is obviously something to do with the paint / water / magnesium 'mix' for "System 4-50" to have the same issue.

 

 

IMGP6834.JPG

 

 

 

Some of the things that can cause excessive anode activity :

 

 

Why is it critical to check and maintain anodes?
Generally sacrificial anodes need to be replaced when 50% consumed. Correct corrosion protection to vital boat parts is not achieved if anodes are left to deplete below 50%. Generally the size and amount of anodes installed to each moored vessel are designed to last up to 12 months. However, many factors can contribute to anodes depleting at a faster rate including; water temperature, salinity, water current flow, stray electrical current and vessel or jetty wiring faults. Therefore, checks are often required monthly, quarterly or six monthly checks to determine the depletion
rates of sacrificial anodes.

Edited by Alan de Enfield
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5 minutes ago, Alan de Enfield said:

 

 

It is understood, it is known about but probably not as much in the narrowboat world as in other areas.

 

The paint flakes or peels when there is an 'overactive' anode(s) in the vicinity, iy is not regularly seen on BBs because they use bitumin which will probably be lost thry bumps, scrapes and water with diesel residue in it.

 

 

IMG_20220729_142801.jpg

 

 

 

Your anodes are way way way too much eroded away, they must be really 'fizzing', where ever you are you should try and identify 'why'.

Your anodes should be replaced at around 50% of their original size/weight or you will not have enough mag to protect the boat.

 

It is obviously something to do with the paint / water / magnesium 'mix' for "System 4-50" to have the same issue.

 

 

IMGP6834.JPG

 

 

 

Some of the things that can cause excessive anode activity :

 

 

Why is it critical to check and maintain anodes?
Generally sacrificial anodes need to be replaced when 50% consumed. Correct corrosion protection to vital boat parts is not achieved if anodes are left to deplete below 50%. Generally the size and amount of anodes installed to each moored vessel are designed to last up to 12 months. However, many factors can contribute to anodes depleting at a faster rate including; water temperature, salinity, water current flow, stray electrical current and vessel or jetty wiring faults. Therefore, checks are often required monthly, quarterly or six monthly checks to determine the depletion
rates of sacrificial anodes.

Are you talking magnesium in fresh water Alan or zinc in salt water?  I rarely replace anodes on any inland water boat in less than 3 to 4 years. A well epoxied boat, sides and base plate will usually go 6 to 8 years on magnesium in fresh. 

Edited by Tracy D'arth
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