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Old 26-10-2014, 11:05   #1
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Zinc anode quality and positioning inside bilge

Hi all,

Haven't found anything on the forum on this, but likely there is a thread on this already?

I was wondering if there are zinc anode quality differences, or will the cheap ones from the local tool shop (in this case Biltema Norway) do? I'm thinking different purities etc.

I was also wondering if it makes sense to have anodes inside the bilge (steel boat), and also in spots where they are not in contact with water?

Thanks for your advice!

Cheers,
Phil
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Old 26-10-2014, 15:11   #2
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Re: Zinc anode quality and positioning inside bilge

Have a look here for some good information on the various types of anodes BoatZincs.com (978-841-9978) – The Online Superstore for Zinc Anodes

Never seen one on the inside but perhaps one might work if you had a very wet bilge (i.e constantly flooded )

The anode does need to be in contact with the water as the water is part of the electrical circuit that allows the anode to protect the steel.
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Old 26-10-2014, 16:43   #3
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Re: Zinc anode quality and positioning inside bilge

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Originally Posted by phipseml View Post
Hi all,
I was wondering if there are zinc anode quality differences, or will the cheap ones from the local tool shop (in this case Biltema Norway) do? I'm thinking different purities etc.
Zinc = zinc. Whether you are in Norway or in the IC1101 galaxy.
Quote:
I was also wondering if it makes sense to have anodes inside the bilge (steel boat),
Interesting question. The anode would have to stay submersed though. Otherwise any exposed steel would start to rust. Never seen it though. A few layers of http://www.marineware.com/epifanes-m...es-bilge-paint work fine also.
Quote:
and also in spots where they are not in contact with water?
Those would be called "spares".
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Old 27-10-2014, 02:07   #4
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Re: Zinc anode quality and positioning inside bilge

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Originally Posted by Draikhyan View Post
Zinc = zinc. Whether you are in Norway or in the IC1101 galaxy.
That's what I would have thought, it's just something someone here said about purities that made me wonder.

I guess I have to read up about the physics of anode action to properly understand the submersing issue. My logic was that the steel is conducting currents, too, and hence connects everything in contact with it - obviously false, and if it was correct, I suppose people would start having only one gigantic, centralized anode somewhere above the water line for easy inspection.

Following this, zincs on shrouds and stays don't make sense, either, I guess. So does anyone have a tip on how to prevent the plates the shrouds are attached to from rusting? Also, who knows what they are called?

Cheers,
Phil
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Old 27-10-2014, 04:12   #5
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Re: Zinc anode quality and positioning inside bilge

Don't think I'd trust Chinese zinc to be pure. There are lots of horror stories about their bronze (Groco recall) and steel (bending Rocna anchors) and milk (melamine) etc.
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Old 27-10-2014, 04:58   #6
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Re: Zinc anode quality and positioning inside bilge

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Originally Posted by phipseml View Post

Following this, zincs on shrouds and stays don't make sense, either, I guess. So does anyone have a tip on how to prevent the plates the shrouds are attached to from rusting? Also, who knows what they are called?

Cheers,
Phil
They are called chain plates. Keep them well painted and the rust stains from them are minimal. If it bothers you to have a few rust streaks, there are two options. Drill out the hole in the chain plate and insert a stainless spacer that projects out slightly from the chain plates surface preventing wearing of the paint by the turnbuckle. This is best done by cutting off the chain plate and drilling it on a drill press as a good fit is essential. Or you can replace them completely with stainless and weld them to the steel with a 309L electrode.

If you need zincs inside the bilge of a steel boat you have serious problems!!
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Old 27-10-2014, 05:25   #7
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Re: Zinc anode quality and positioning inside bilge

Quote:
Originally Posted by Draikhyan View Post
Zinc = zinc. Whether you are in Norway or in the IC1101 galaxy...
Zinc Anodes are cast from a high purity zinc alloy to ensure an even corrosion pattern, reliable electrical efficiency and long working life.
For instance, a zinc alloy in accordance with the US MIL A-1800H specifications:

Composition
Aluminium : 0.10 - 0.50 %
Cadmium / Amp.Yr : 0.025 - 0.15 %
Lead / kg : 0.006 % max
Iron : 0.005 % max
Copper : 0.005 % max
Silicon : 0.125 % max
Zinc : Remainder

Performance Standards
Open Circuit Potential w.r.t. Ag/AgCl: -0.95V
Consumption Rate : 11.25 Kg
Anode Capacity : 780 Amp.Hr

So, NO, zinc is not = zinc.
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Old 28-10-2014, 01:51   #8
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Re: Zinc anode quality and positioning inside bilge

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Originally Posted by Sailormantx View Post
They are called chain plates. Keep them well painted and the rust stains from them are minimal. If it bothers you to have a few rust streaks, there are two options. Drill out the hole in the chain plate and insert a stainless spacer that projects out slightly from the chain plates surface preventing wearing of the paint by the turnbuckle. This is best done by cutting off the chain plate and drilling it on a drill press as a good fit is essential. Or you can replace them completely with stainless and weld them to the steel with a 309L electrode.

If you need zincs inside the bilge of a steel boat you have serious problems!!
Thanks for that. I'm not really concerned about rust streaks per se, but more about developing rust bubbles under the turnbuckle and a long term weakening of the chain plates. In fact, our chain plates to have a short spacer as you described installed. Still rust bubbles, which we removed and painted now, anyway.

The zincs in bilge thing was more a preventative idea rather than a necessity. Our bilge is dusty and well painted so far.
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Old 28-10-2014, 01:53   #9
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Re: Zinc anode quality and positioning inside bilge

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So, NO, zinc is not = zinc.
OK, thanks for these specs! So the guy here was right, and it makes sense. Do you have an idea on how to see the alloy quality, or is just about trusting the producer? That would be very helpful, since there are not many shops here with zincs except the cheap home improvement style shop. Thanks...
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Old 28-10-2014, 03:29   #10
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Re: Zinc anode quality and positioning inside bilge

I have a wet bilge and was advised a few years back to keep a few old anodes in there. I got these from a discard bin at the local boatyard at the end of the season. The explanation was that the keel bolts are ss but the wires to the bilge pump are copper and that creates though weak but current nevertheless. I don't see any deterioration of the anodes and so far they lasted a few seasons but I do plan on replacing the shaft gland soon as I get closer to my liveaboard/cruising schedule.
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Old 28-10-2014, 03:45   #11
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Re: Zinc anode quality and positioning inside bilge

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Do you have an idea on how to see the alloy quality, or is just about trusting the producer? That would be very helpful, since there are not many shops here with zincs except the cheap home improvement style shop. Thanks...
See Skarpenord Corrosion offers high quality anode alloys under the trademarks CORAL and NORANODE

Skarpenord Corrosion A/S makes aluminium anodes to NORSOK specifications and zinc anodes to US military specifications. Hard to get better quality anodes.

I'd suggest you try the aluminium anodes. The world is slowly shifting towards aluminium anodes instead of zinc anodes.

Al
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