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Old 19-03-2016, 14:04   #1
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Steel boat bonding engine & neg battery to hull

My question is, would bonding the engine and negative battery terminal to the hull remove any stray currents that may be affecting the hull paint? I know that electrolysis is a complex matter so what do others with steel boats do to reduce/stop this corrosion? What success have you had?
I look forward to reading the insights of others.
Each time I haul small bubbles of paint are lifting from the metal of the hull. The metal is shiny steel but it needs grinding back and reapplying primer and antifoul. I presume the cause of this is electrolysis that may be due to stray currents.
The hull anodes attached to the keel and skeg anodes lose paint around the stainless studs welded to the mild steel. All the through hull fittings are mild steel with Force Five marelon stop cocks attached.
There is a bronze keel cooler onthe outside of the hull for the refrigerator and the paint around it is attached in good condition with no bubbling.
The stainless steel shaft and bronze propellor are isolated from the hull and
engine by a poly flexible coupling and the p-bracket bearing. There are no corrosion issues with shaft or prop.
The vessel sits mostly on an open swing mooring away from marinas.
Michael
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Old 20-03-2016, 09:04   #2
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Re: Steel boat bonding engine & neg battery to hull

Quote:
Originally Posted by micknor51 View Post
My question is, would bonding the engine and negative battery terminal to the hull remove any stray currents that may be affecting the hull paint? I know that electrolysis is a complex matter so what do others with steel boats do to reduce/stop this corrosion? Michael
Steel boat owner for 23 years

The best way to achieve this on a steel boat is to have NO current flowing through the hull, this means the engine, is not grounded through the block /hull and all the electrical devices on the engine have a positive and negative feeds going to the battery, check Radio earths/grounds as well as ICOM 802 SSB’s leak current through the ground even when turned off unless an isolation bridge is installed


Quote:
Originally Posted by micknor51 View Post
Each time I haul small bubbles of paint are lifting from the metal of the hull. The metal is shiny steel but it needs grinding back and reapplying primer and antifoul. I presume the cause of this is electrolysis that may be due to stray currents.
Michael
We have this as well and I have seen it on other steel boats, I have heard it described as “Paint Osmosis”

I have been told you can “over Zinc” a steel boat so I am trying less zincs this time but will only know if this is the solution when I next haul. The steel under the blisters is like new!!! Maybe well worth doing some reading on the subject?

Quote:
Originally Posted by micknor51 View Post
The hull anodes attached to the keel and skeg anodes lose paint around the stainless studs welded to the mild steel.
Michael
Are you sure the studs are stainless?

When we replaced ours with MGDUFF parts, the studs were mild steel welded onto the hull and we have no paint lose at the bases of the studs


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Originally Posted by micknor51 View Post
All the through hull fittings are mild steel with Force Five marelon stop cocks attached.

There is a bronze keel cooler on the outside of the hull for the refrigerator and the paint around it is attached in good condition with no bubbling.

The stainless steel shaft and bronze propellor are isolated from the hull and
engine by a poly flexible coupling and the p-bracket bearing. There are no corrosion issues with shaft or prop.
Michael
All the above sound OK

Good luck and let us know what you do
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Old 20-03-2016, 12:29   #3
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Re: Steel boat bonding engine & neg battery to hull

Thanks for your reply Triumphant.
I will check for any spurious earth connections to the hull.
We only have VHF radio so no issues with SSB stuff.
The studs attaching the anodes are definately stainless.
So what are MGDUFF parts? Not something from 'The Simpsons'??
Cheers
Michael
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Old 20-03-2016, 12:46   #4
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Re: Steel boat bonding engine & neg battery to hull

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Thanks for your reply Triumphant.

So what are MGDUFF parts? Not something from 'The Simpsons'??
Cheers
Michael

See Cathodic Protection Systems ǀ Marine Anodes ǀ MGDUFF a UK firm specializing in Anodes etc.
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Old 20-03-2016, 13:06   #5
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Re: Steel boat bonding engine & neg battery to hull

I'm not going to be a lot of help but can share in your misery.

We have 2 steel boats and I have had some similar problems and gone down this path as well.

My "research" tells me there are 2 camps A) isolate so there are no currents and B) tie the engine to the hull at one intentional ground point.

I ended up choosing B for the simple reason that if you have an intentional ground and then get an unintentional ground there will be less problem. It is less maintenance and one less thing to check every so often. I believe B is the more common solution.

I think either solution will work.

We have been struggling with some blistering issues on our small boat, which was supposed to have an isolated engine, but didn't due to a goofy engine mount issue. When I replaced the mounts, and feed the unintentional engine ground, the VHF antenna ground caused problems. So I've now installed a solid connection from the hull to the engine ground.

I too have heard of "over zinc" on a boat. You need a silver half cell to check it out.

The paint may also be an issue, or if you are moored in fresh water it make cause electrolysis.

Frankly I've read so much contradictory stuff, and talked to so many contradictory factory reps, I don't know who to believe.
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Old 20-03-2016, 13:08   #6
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Steel boat bonding engine & neg battery to hull

If you have a galvanic isolator, tie the ac and dc grounds together; if not, keep the ac and dc grounds separate.


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Old 20-03-2016, 13:50   #7
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Re: Steel boat bonding engine & neg battery to hull

Almost everything in every post here is ...... wrong. It would take a 10 chapter post to explain all so I'm not even going to try. Bite the bullet and hire a qualified corrosion analyst to determine cause and correction.
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Old 20-03-2016, 14:02   #8
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Re: Steel boat bonding engine & neg battery to hull

Better yet hire three, four, or five and see if they all say the same thing.

I see you are a surveyor, hopefully a good one. They are rare. Most I've run into, well it would take 10 chapters. But you do have a dog in the fight, professional curtesy and all that.

Here's a bit of advice for the OP, google Scott Fratcher Metal Boat repair or some such thing. PDF download. Some love him, some hate him. I think he's all right. Dirt under his knuckles kinda guy. A lot of what he says fits with my experience.

Another thing you may try is to subscribe to "the metal boat society" and check out their forum. My take is they are centered around new build projects, not a lot on maintenance. But give it a go, lots of good professional folks there.
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Old 20-03-2016, 14:22   #9
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Re: Steel boat bonding engine & neg battery to hull

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The paint may also be an issue, or if you are moored in fresh water it make cause electrolysis.
The only dog I have in this fight is warning the OP about statements like this.

Don't know if they have community colleges in Australia but if they do, take a night course on corrosion analysis because you are certainly not going to learn anything on this thread.
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Old 20-03-2016, 16:20   #10
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Re: Steel boat bonding engine & neg battery to hull

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Originally Posted by Triumphant View Post
See Cathodic Protection Systems ǀ Marine Anodes ǀ MGDUFF a UK firm specializing in Anodes etc.
Ah now I see. i am coming to UK in May I will check them out.
Ta muchley.
Michael

hpeer
Thanks for the comments and commiserations.
I am with you on the multiplicity of possibilities/cotradictions from 'experts'.
Saaremaa is moored on Lake Macquarie a salt lake with a channel to the ocean so no fresh water issues. (Any Great Lakes in Australia are either saline or dry).
I do subscribe to the Metal boat Society but as you say it mostly about new builds.
Scott Fratcher I have come across him before, good idea I'll check him out.

snotter
Thanks for your suggestion but Saaremaa is not wired for AC, hence no galvanic isolator, as we rarely use marinas.

boatpoker
Thanks for such wonderful insights but not actually helpful really.
If you have nothing useful to offer then why bother.
Yes we do have 'Community Colleges' in Australia known as TAFE Colleges but I do not think they offer courses in corrosion analysis/electrolysis etc.
If you read the original post I was interested in what other metal boat owners do stop/reduce corrosion.
The Benford 38 Cruiser is steel or plastic?
Ta anyway
Michael
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Old 30-03-2016, 22:09   #11
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Re: Steel boat bonding engine & neg battery to hull

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Frankly I've read so much contradictory stuff, and talked to so many contradictory factory reps, I don't know who to believe.
Man - Aint THAT the truth!
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Old 31-03-2016, 00:27   #12
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Re: Steel boat bonding engine & neg battery to hull

Your problem may not be electrolysis at all.
Other possibilities could be poor preparation (poor blasting, no washing down to get rid of chlorides etc) or poor paint application (not allowing solvent to dry out between coats.)
Little osmotic cells form, bubble the paint, and the metal is absolutely clean.
We have been fighting this for years on our boat. Will abrasive blast this year and am going to be absolutely anal about prep and paint application.
Regards,
Richard (moored at Pretty Beach)
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Old 31-03-2016, 10:27   #13
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Re: Steel boat bonding engine & neg battery to hull

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Your problem may not be electrolysis at all.
Other possibilities could be poor preparation (poor blasting, no washing down to get rid of chlorides etc) or poor paint application (not allowing solvent to dry out between coats.)
Little osmotic cells form, bubble the paint, and the metal is absolutely clean.
We have been fighting this for years on our boat. Will abrasive blast this year and am going to be absolutely anal about prep and paint application.
Regards,
Richard (moored at Pretty Beach)
Thanks Richard,
I don't think it is poor prep/paint application etc. The last time I ground back to bare metal (Nov 2014) I used Altra-Lock 576, then 3 coats of Altex Epoxy No 1 Primer before the antifoul Altex No 5, allowing the correct drying times.
In March this year the paint had come off so I have tried Altex Primashield (its a single pack paint but I thought why not try something new) 3 coats before the antifoul, Altex No 5 again. I will have to see what happens next year.
I'll try not to bore you but here is a little history.
We had the hull dry blasted back to bare metal in 2009 and coated it with an epoxy that needed a sealer over the top (which we were not told). Result, water penetrated the paint to the hull and we had many places where paint came off during the jet wash. Fun times!!
Hull was then wet blasted back to shiny steel in May 2010, then it rained for a week creating a lovely red/orange hull. Altra-Lock 576 was applied and 3 epoxy coats on top before the antifoul. Paint was good until Nov 2014.
Meanwhile I am getting a copy of Scott Fratcher's 'Metal Boat Maintenance' to see what he recommends.
Ah the joys of a steel boat.
Michael
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Old 30-08-2016, 06:18   #14
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Re: Steel boat bonding engine & neg battery to hull, FIXED

A few months down the track and it looks like the electrolysis stray current problem has been solved.
I got hold Scott Fratchers book 'Metal Boat Maintenance' and after doing a bit of research came across a product called SeaBis System. The SeaBis unit is a small computer that links to the + and - of the battery with a third wire attached to the hull metal. If all is good with no stray current a green Normal lights up. If there is stray current occurring red Critical or Severe lights up. If minimal stray current a Caution lights up.
In my case the VHF aerial was causing a Critical signal. Solution change VHF aerial to one that is fully insulated. I used a GME AE31, A$90 from Whitworth Marine.
The auto pilot caused a Caution light and is disconnected until problem solved.
The engine battery negative caused a Critical. Problem solved with a switch that isolates the connection when the engine is not in use.
Engine battery positive connection to the starter motor caused a Caution. Problem solved with separate isolator switch.
The SeaBis System is A$550 so not cheap but it comes with training and support from the supplier, Glen Bishop, a retired Royal Navy submarine engineer. Web: www.seabis.com. He is based in South Australia.
I have found him very helpful.
I am looking forward to less or no blistering hull paint next antifoul.
Michael
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Old 30-08-2016, 20:37   #15
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Re: Steel boat bonding engine & neg battery to hull

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I have been told you can “over Zinc” a steel boat so I am trying less zincs this time but will only know if this is the solution when I next haul.

your zinc level is easily measured with a silver silver chloride cell and a volt meter. it's not something you guess at.
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