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Old 30-11-2022, 16:50   #1
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Advice needed : Survey found electrolytic corrosion

Hi all,

So I think I've found the right boat for me, she's a corten steel 1987 Feltz Skorpion built in Germany (I'm here in New Zealand).

I just had her surveyed on Monday. The surveyor, (a captain and engineer with many decades of experience) found some blisters and bubbling up around the zinc anodes. He's asked me to get an electrical engineer in to take a look as he thinks it may be electrolytic. My issue is, the original electrician the previous owner used is booked out to the end of the year, meanwhile the broker's sales agreement says I only have until monday to make my decision! Regardless of if I want a follow up survey.

So, this is a small excerpt from my survey report -- how serious is this, and at what difficulty to fix? This is a steel boat so any and all corrosion concerns me greatly. (I'd insert an image but seems this forum doesn't support it)

"The hull exhibited many blisters in the antifouling. When opened, shiny steel was found to be underneath.

"This has been an issue in the past, as around all the skin fittings, it was obvious that repairs had been undertaken at some stage.
The cause for this would appear to be electrolytic. It is advised that a marine electrician should check this to ensure that there are no issues attributed to the vessels systems.
The anodes all showed little wear apart from two hull anodes which had slight erosion. Noticed on the starboard hull were studs for extra anodes.
Too many anodes can be an issue as too little. This may be the reason for two missing.


Regardless, I am wondering, A. how to repair the blisters (re-haul out and anti-foul again?) but more importantly, B. how to stop them or get to the root cause? And how serious is it? He does go on to say the hull itself is in good shape. "Plating on the hull showed very little wastage."

Related : when looking at the boat I did see a "Victron Galvanic Isolator" installed.
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Old 30-11-2022, 18:00   #2
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Re: Advice needed : Survey found electrolytic corrosion

Iíve only had one Corten hulled yacht but it had a similar problem. I hauled it out and abrasive blasted the hull up to the sheer then repainted it. Sailed it for 10 years , sold it ( bottom still good) and I saw the boat hauled out 20 years after the paint job, still good. She was wired above ground and had an indicator panel to alert me to any connection or leakage of DC to hull.
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Old 30-11-2022, 18:12   #3
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Re: Advice needed : Survey found electrolytic corrosion

You can buy a metal thickness gauge online from Amazon. There are many models to chose from. Any DIY-er can operate it.
Around $200 will get you a good one.
Just press the little sensor finger against the hull, and voila, it will read the thickness.
If you know how thick the plating was originally, you can quickly deduce if corrosion is an issue.
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Old 30-11-2022, 18:17   #4
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Re: Advice needed : Survey found electrolytic corrosion

Interestingly, I built my own steel boat many years ago. It was my home for around 15 years. When the new owners had the boat hauled for the survey, the surveyor had one of those gadgets. Could'nt find anything out of spec. That boat is still around, 40 years and counting.
Steel is so strong, that a minor thickness loss is nothing.
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Old 30-11-2022, 20:25   #5
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Re: Advice needed : Survey found electrolytic corrosion

I think all you will get in response are a few guesses and some anecdotal stories which might be interesting but not relevant.

I would call the currently un - available electrician who you reference and ask him to recommend another - there can’t be only one and he probably knows other competent inspectors.
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Old 01-12-2022, 00:27   #6
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Re: Advice needed : Survey found electrolytic corrosion

Quote:
Originally Posted by jorxster View Post
..................
So, this is a small excerpt from my survey report -- how serious is this, and at what difficulty to fix? This is a steel boat so any and all corrosion concerns me greatly. (I'd insert an image but seems this forum doesn't support it)
.............
You should be able to attach pictures to your posts by clicking on the 'Manage Attachments' button in the 'Attach Files" box and follow the prompts. Just like I have done here with this reply.

This is on the 'Additional Options' section below the main text box on the 'Reply to Thread' page.

See red marked up section on screenshot.
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Old 01-12-2022, 08:30   #7
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Re: Advice needed : Survey found electrolytic corrosion

Quote:
Originally Posted by jorxster View Post
The surveyor, (a captain and engineer with many decades of experience) found some blisters and bubbling up around the zinc anodes.

[B][I]"The hull exhibited many blisters in the antifouling. When opened, shiny steel was found to be underneath.

"This has been an issue in the past, as around all the skin fittings, it was obvious that repairs had been undertaken at some stage.

The anodes all showed little wear apart from two hull anodes which had slight erosion. He does go on to say the hull itself is in good shape. "Plating on the hull showed very little wastage."
At face value it doesn't seem that the hull is wasting away, getting and using a thickness gauge may put some concern aside but that doesn't seem to be an issue.
I would be first checking to see if there is an impressed currant cathodic system on board.
They operate quite well at protecting the steel but need to stay within a fairly narrow range.
Are the thru hull fittings galvanically compatible with the hull?
Are there any unaccounted-for wires connected to the hull/fittings/anodes?
On older steel boats it's not uncommon to find some electrical device that a previous owner has installed and used the hull structure as a ground return path, (a huge no-no).
It might also be something as simple as a non-compatible application of primer/paint.
Agree some further investigation needed.
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Old 01-12-2022, 09:03   #8
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Re: Advice needed : Survey found electrolytic corrosion

I kinda agree on the paint thing.

I built a steel boat, and my first paint application had horrific end results.
I did the usual zinc primer from one company, as the first coat, immediately after I sand blasted it, but found it difficult to apply, so I later switched to another paint company for the remainder build up layers before applying the antifouling paint.

After launch, it didn't take long, and the bottom of the hull was blistered from one end to the other.
I was stunned at the result.

I had no choice, but to sandblast the below water line hull down to bare metal again, and re-apply paint, but this time, all layers from the same company brand.
This did the trick, and I never had a problem with the paint after that. All paint was a two part epoxy.

I am by no means a paint expert, I didn't have a problem with the above water line paint, only that portion in the water.

Over the years, I re-painted the hull several times, from cobalt blue, to light blue to white, but used a two part polyurethane. Ironically, the original epoxy paint was considered a good primer for the two part polyester paint after a good sanding. Never had a problem.

But a non-compatible paint system could certainly be a problem.
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Old 01-12-2022, 09:54   #9
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Re: Advice needed : Survey found electrolytic corrosion

Quote:
Originally Posted by jorxster View Post
I just had her surveyed on Monday. The surveyor, (a captain and engineer with many decades of experience) found some blisters and bubbling up around the zinc anodes. He's asked me to get an electrical engineer in to take a look as he thinks it may be electrolytic. My issue is, the original electrician the previous owner used is booked out to the end of the year, meanwhile the broker's sales agreement says I only have until monday to make my decision! Regardless of if I want a follow up survey.

For a 1980s boat unless it's in great shape and you're paying top dollar I think you'll have a tough time getting the seller to do much of anything. It would help to know how much you're paying.


Generally, it is unwise to pay an electrician to diagnose electrical problems on a boat you do not own, so you should focus on choices where either you proceed with the sale anyway or have the seller pay to have the work done.



Is the survey complete at this time? Can you get insurance?


If the survey is complete and you can get insurance then: You can walk away from the deal, ask for price concessions based on the survey findings, or proceed with the deal as it is. Use your best judgment to adjust your offer based on the findings of the survey. If the repair work costs more than you expected, well, welcome to boat ownership.



If the survey isn't complete then my advice would be to ask the surveyor to complete it with the findings he has made, and proceed from there. You paid the surveyor, right? It's their job to come up with a survey, not come up with a list of reasons why they can't perform a survey.



If the survey is complete and the boat isn't seaworthy and insurable, then your best move is to insist that the seller make repairs before proceeding with the sale. They may be unwilling to do that, in which case you can either walk away or try to find temporary insurance to cover the hull while you make repairs on the hard. Or, if you're willing to take the risk and the yard will allow it, buy the boat without getting insurance.
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Old 01-12-2022, 10:36   #10
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Re: Advice needed : Survey found electrolytic corrosion

I might add, (in reference to a previous post about paint failure,) that for best success the blasting and re-painting needs to be done in an environment of low humidity, and with a warm surface.
Primer is applied immediately upon blasting to white metal, even a few hours wait will allow moisture to collect in the tiny pores of the blasted steel.
Moisture will compromise the bond.
High humidity/cold steel = paint failure.
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Old 01-12-2022, 16:22   #11
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Re: Advice needed : Survey found electrolytic corrosion

I can remember with absolute clarity the living hell I had to endure while blasting and painting my boat, in the middle of a Florida summer no less.
While blasting and painting the outside was a living hell, it paled in comparison to the misery I had to endure during the blast and paint procedure on the inside of the hull.

I was, off course, bedecked in leather protective gear plus blasting helmet, etc...my best guess is that it was 1,345 f inside that suit.
It took around 10 days to do it all. Were I to do it again, I'd hire somebody !!

Switching gears, rust problems on a steel hull invariable begin on the inside of the hull. Water, condensation, etc, can collect along beams, frames, and so on, so this is the place to check. It's a difficult job as bulkheads, all the interior bunks, etc, make this a laborious job.

Finally, the inside of the hull should insulated, so getting at the hull requires moving insulation. There is no way in hell, I'd have a non-insulated steel boat.

Having said all this, I wonder how the surveyor approached this job ??

As a point of reference, my boat was launched in 1980 and it's still around, now on it's 3rd owner.

It's tough to beat a steel boat. It is massively strong, but like any boat, requires regular maintenance.

I relate some my experiences so as to see things from a steel boat owner.

Good luck to ya...
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Old 04-12-2022, 12:34   #12
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Re: Advice needed : Survey found electrolytic corrosion

**DECIDED TO PURCHASE**

My surveyor got in touch with the marine electrician who installed the victron galvanic isolator:

"The present osmosis won't kill the boat, but it does alert us to a possible fault.
A galvanic isolator protects you from the dock only.
Not on board low currents.

So my advice is to live with it until the new year and then get a check done.
Next haulout remove the blisters and prepare the metal correctly.
Then you should be fine mate"

I'm not sure if he means to strip down the entire hull or probably just the areas around the anodes that show blistering.

Image attached, thanks for the screenshot showing how.


But I've decided to purchase her! she will be my first yacht, a true bluewater cruiser. Feltz Skorpion 1987

Thank you all for your advice!
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Old 04-12-2022, 14:17   #13
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Re: Advice needed : Survey found electrolytic corrosion

Congratulations on the new boat Jorxster.
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Old 04-12-2022, 14:38   #14
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Re: Advice needed : Survey found electrolytic corrosion



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Old 04-12-2022, 16:20   #15
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Re: Advice needed : Survey found electrolytic corrosion

Congratulations on your new boat.

As to cause, is the boat perhaps over-zinc-ed? We've a steel keel, lead filled partway, and were at one time with too many zincs, and the bottom paint made bubbles and the tops blew off eventually.

Follow the electrician's advice, both as to cause and to repairs.

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