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Old 15-08-2019, 17:13   #1
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Fiberglass corrosion around anode bolts from electrolysis maybe

Hi Guys

I recently purchased a 30 ft Halvorsen monohull here in Brisbane Australia. Built around 1973 and named Kotori.

Here is a picture of fiberglass erosion around two metal rods inside my monohull, possibly bolts to an exterior anode or grounding plate. The depth of the erosion at the right bolt is about 1 cm which is very concerning to me.
Not sure how thick it is there. Its just past the turn up from the keel.

This picture is taken from the forward starboard quarter berth, looking towards the engine area. I think that copper bonding strip goes to the engine block from here.

What do you think this is? I didnt think electrolysis can cause corrosion in fiberglass.

Do you think I should attempt to repair the glass before correcting the corrosion problem? I have an electrician scheduled to come in and re bond all of the sea cocks.

The fiberglass stays moist there, so not sure if its possible to even glass over moist fiberglass.

I dont think I can do anything with the left bolt until the copper band is removed as it is very stiff and not moveable. Hard to get anything under it.

Any advice would be appreciated !
Noel
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Old 15-08-2019, 17:21   #2
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

Haul the boat, unbolt the plates, totally dry and replace everything, grind out and repair and reglass the area which is deteriorated, and take a close look at the electrical system to see if you can determine how electric current is getting to the plate.

Make sure that you are not providing a path for electricity to get to ground through this plate, (if for example, it is connected to the AC ground wire).
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Old 15-08-2019, 18:00   #3
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

Looks very much a dynaplate - which is often used for the grounding of a HF radio antenna.

The copper strap would have gone the HF antenna tuning box.

Does the boat still have a HF radio fitted? If not, remove it all.
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Old 15-08-2019, 18:09   #4
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

I would be removing it and glassing it all. I would also be getting rid of that old gate valve in the background. Judging by the photo did you buy a project boat?
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Old 15-08-2019, 18:29   #5
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

Neither stray current nor galvanic current can cause damage to fiberglass.
What you described sounds like hydrolysis ie. the resin is dissolving.

Did your surveyor not say anything about this ?
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Old 16-08-2019, 01:06   #6
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

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Originally Posted by boatpoker View Post
Neither stray current nor galvanic current can cause damage to fiberglass.
What you described sounds like hydrolysis ie. the resin is dissolving.
Did your surveyor not say anything about this ?
The OP did say:
“... I didnt think electrolysis can cause corrosion in fiberglass ...
... The fiberglass stays moist there...”
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Old 16-08-2019, 15:24   #7
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

You have been given some excellent advice by others. Myself I would be cancelling the electrician & booking a haul out. That gate valve looks like a disaster waiting to happen. How many others are there? If you replace all your metal thru hulls with True design fittings then bonding won't be necessary. My view is that bonding underwater fittings is a real contentious issue. You will find with a little research that there is as many for it as against.
Good luck & I definitely think that hauling out is the best way to fix your problem.
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Old 16-08-2019, 17:05   #8
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

Hi,
It is imperative to remove the CAUSE before the repair as it will happen again.
The wide copper strap is connected to a DC source and probably a HF SSB (external to hull) grounding plate. And, as you say, the engine. That DC dissolves metal. That creates a reaction with your fiberglass. So you are seeing the effect of DC current (stray current) generating marine electrolysis corrosion. Use Google to search for marine electrolysis and click on Conquer marine corrosion CAUSE.
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Old 16-08-2019, 17:16   #9
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

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Originally Posted by Corrosion-Eng View Post
Hi,
It is imperative to remove the CAUSE before the repair as it will happen again.
The wide copper strap is connected to a DC source and probably a HF SSB (external to hull) grounding plate. And, as you say, the engine. That DC dissolves metal. That creates a reaction with your fiberglass. So you are seeing the effect of DC current (stray current) generating marine electrolysis corrosion. Use Google to search for marine electrolysis and click on Conquer marine corrosion CAUSE.
Here we go again .... ELECTROLYSIS has nothing to do with boats. It is entirely different using induced current to produce hydrogen. Unfortunately it is a catchy word commonly used by the untrained or misinformed dock talkers.

As I said previously there are only two corrosion issues involving electricity on boats. 1. Galvanic current 2. Stray DC current and neither will affect the glass.

https://www.energy.gov/eere/fuelcell...n-electrolysis
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Old 17-08-2019, 17:33   #10
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

I have no idea if there is a similar phenomenon in fibreglass but I have occasionally seen a condition in wooden boats known as alkaline rot.It is caused by current between dissimilar metals in damp wood and I have seen it in the timber surrounding a bolt which went through the hull to an anode. It shows as tiny blisters on the inside and on closer examination the timber looks as though it has been dipped in acid. Similar conditions..........?
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Old 17-08-2019, 17:53   #11
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

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Originally Posted by Fore and Aft View Post
Judging by the photo did you buy a project boat?
Cheers
You win the prize for today's least necessary question...
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Old 17-08-2019, 18:36   #12
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

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Originally Posted by qwert View Post
I have no idea if there is a similar phenomenon in fibreglass but I have occasionally seen a condition in wooden boats known as alkaline rot.It is caused by current between dissimilar metals in damp wood and I have seen it in the timber surrounding a bolt which went through the hull to an anode. It shows as tiny blisters on the inside and on closer examination the timber looks as though it has been dipped in acid. Similar conditions..........?
You are correct about wood but no, it does not occur in polyester reinforced glass fiber.
(Retired Certified Marine Corrosion Analyst)
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Old 17-08-2019, 22:30   #13
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

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Originally Posted by Tillsbury View Post
You win the prize for today's least necessary question...
Judging by the photo I would say that it was a totally necessary question. The small area that was shown showed up other issues that need attention.
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Old 17-08-2019, 22:48   #14
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Re: Fiberglass corrosion around anode bolts from electrolysis maybe

Quote:
Originally Posted by Corrosion-Eng View Post
Hi,
It is imperative to remove the CAUSE before the repair as it will happen again.
The wide copper strap is connected to a DC source and probably a HF SSB (external to hull) grounding plate. And, as you say, the engine. That DC dissolves metal. That creates a reaction with your fiberglass. So you are seeing the effect of DC current (stray current) generating marine electrolysis corrosion. Use Google to search for marine electrolysis and click on Conquer marine corrosion CAUSE.
Oh goody, now you're an expert in fibreglass "corrosion"as well.
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