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Old 10-15-2017, 06:54 PM   #1
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Sacrificial anode - what to expect

Hello fellow TFers.
Last week my boat was hauled out and yesterday I went to empty it for winter.
Before splashing in may I replaced all the anodes with new ones and added few where the previous owner was not looking.
My question is what wear to expect after 6 month?
I was a bit surprised by the level of wear as I found them well marked from dissolution.
I will take a picture next weekend to illustrate this.
I may worry for nothing but it is the first time I install new anodes.

L
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Old 10-15-2017, 07:04 PM   #2
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Hull anodes usually last a year or more before needing replacement. If yours are going before that, it may be due to an electrical problem in your boat or an adjacent boat at your marina.

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Old 10-15-2017, 07:10 PM   #3
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Hull anodes usually last a year or more before needing replacement. If yours are going before that, it may be due to an electrical problem in your boat or an adjacent boat at your marina.

David


Ok if they should last 1 year I guess mine are fine. I was not expecting such a wear!
I am in fresh water and my anode are magnesium.
For the two round ones on the rudder I can see that they decreased by something like 1/8th of an inch. Was not thinking it was so much.
A question from some green wood captain lol

L
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Old 10-15-2017, 07:12 PM   #4
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I just purchased a new set for our Great Lakes/fresh water boat. Switched from zinc to magnesium. Expecting to see increased "erosion".
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Old 10-15-2017, 08:18 PM   #5
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Your anode use sounds about right especially for magnesium. Better it is being used than not. If you are not happy with the time they last then either add bigger ones or another anode or two.

Just do not go overboard [??] on them. Even on fiberglass boats there can be some odd effects if the zincing is really overboard. .

Dave Gerr has published some ways to calculate, roughly, how much zinc is needed for some applications.
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Old 10-15-2017, 08:32 PM   #6
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Originally Posted by Lou_tribal View Post
Ok if they should last 1 year I guess mine are fine. I was not expecting such a wear!
I am in fresh water and my anode are magnesium.
For the two round ones on the rudder I can see that they decreased by something like 1/8th of an inch. Was not thinking it was so much.
A question from some green wood captain lol

L
Magnesium has a much shorter life than zinc or aluminum. Of course Zinc isn't appropriate for fresh water. We use aluminum.

Boat zincs has charts, Chart A and B, that you can reach from this page to help in your selection. Also a table showing a comparison by material.

BoatZincs.com (978-841-9978) - FAQs
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Old 10-15-2017, 08:46 PM   #7
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Thank you all, as it was the first time I was checking anode from new set I was not sure about what to expect. As mentioned I was thinking that if they look dissolved it was a good clue that there were working as expected but in the same time I was worrying that if they are too much dissolved something was wrong. I guess I am thinking and worrying too much

L
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Old 10-15-2017, 09:24 PM   #8
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Generally if they are half gone you should replace them. When we had a boat in southern California we would get about 6 months or so from actual zincs since it was salt water. We just hauled our boat in Michigan which I had installed aluminum anodes on this spring. Although they are not half gone, I will change them over the winter so I don't have to change them during the summer next year. With the erosion that has occurred this year I don't think they will last another season and not go below the halfway mark.
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Old 10-15-2017, 09:29 PM   #9
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Originally Posted by C lectric View Post
Your anode use sounds about right especially for magnesium. Better it is being used than not. If you are not happy with the time they last then either add bigger ones or another anode or two.

Just do not go overboard [??] on them. Even on fiberglass boats there can be some odd effects if the zincing is really overboard. .

Dave Gerr has published some ways to calculate, roughly, how much zinc is needed for some applications.
Clark, I don't think I'm getting enough zinc wear, meaning they may not be doing their job. I have two transom plates that are two years old and they're pitted, but they look like they could go easily for another year. I have an isolation transformer which may be part of the explanation.

The boat is presently on the hard. What I intend to do is put a meter between the zincs and underwater metal and look for .5 ohms. Is this in the ball park?

Also, how can I get at the Dave Gerr data? Is it at this site?
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Old 10-15-2017, 11:51 PM   #10
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Re: Dave Gerr. You might try googling for the info. about it. I haven't looked but I would guess other sources would be available. If need be I could try scanning the pages.

0.5 ohm between the zinc plates and the metals would be a good figure. Most meters have trouble getting reliable readings past that unless it's a highly specialized meter which is not needed for this. Generally I look for less than 1 ohm.
Check the meter probes themselves and clean them as any oxidation can affect readings at that level. Clean a spot on the zinc and on the metal you are checking. Then use the meter.

Yes, an isolation transformer will reduce the likely hood of zinc wastage from leaking A.C.

If the plates are large enough that may be why you don't see a faster zinc wastage. Large zincs compared to the metals protected, no leakage either from your boat or others, and the result may be what you are experiencing.

If the ohm reading is on the high side then check the zinc mounts themselves. Some times the zinc wastage can affect the actual mounting area. If so then a good cleaning may be in order to restore the mounting area, both on the zinc and the pad.

One of the best ways to check zinc action and the protection at each piece of equipment is the use of a silver/silver chloride half cell. They are available from Boatzincs.com and can be used with a dmm quite effectively.

I use one I bought a long time ago from Promariner as a kit, an analogue meter, and it has helped big time showing me a couple cases where the bonding had been lost.

All you should need is the cell from Boatzinc and a long ground lead with a large, heavy duty alligator clip along with your DMM. At the time I bought mine I was too ignorant of what was available and I don't think folk like Boatzinc was around.
I like my meter but now I would simply get the cell.
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Old 10-15-2017, 11:53 PM   #11
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If the boat is on the hard then perform a continuity check between your zinc plates and all your under water metal. Use a multi meter set to ohms and look for OL on the display.

If you have continuity you will have protection.
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Old 10-16-2017, 01:10 AM   #12
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By definition, they are sacrificial. I get by with annual inspections, and as-needed, replacements.
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Old 10-16-2017, 06:17 PM   #13
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I've gone to aluminum but with 4 shaft "zincs" one on each rudder and 2 on the transom, they are about 50% wasted after 6 months.

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Old 10-19-2017, 09:13 AM   #14
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The amount of surface area of exposed metals, types of metals to be protected along with the water conductivity are going to determine the anode life.
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Old 10-24-2017, 08:58 PM   #15
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The amount of surface area of exposed metals, types of metals to be protected along with the water conductivity are going to determine the anode life.


We put our boat to rest yesterday until spring. Prior to hauling, I tested my anode's performance. SOLID! My measured voltages on all metals including my shafts which are bonded via my custom made (by me) shaft brushes were in the -0.78 range. The readings matched those taken back in May when we launched.

My single anode is a stern mounted aluminum 6 X 12 X 1" diver's plate style. Last year's test of my anode performance prior to haul caused concern when I saw my galvanic protection starting to fail. Sure enough, after hauling I found my anode almost completely disintegrated. So this year I purchased one that is 1" thick instead of 1/2" thick.
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