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

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

djmarchand said:

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

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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

I just purchased a new set for our Great Lakes/fresh water boat. Switched from zinc to magnesium. Expecting to see increased "erosion".

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.

Lou_tribal said:

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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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

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

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.

C lectric said:

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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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?
____________________
Ken Hatt Trick

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.

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.

By definition, they are sacrificial. I get by with annual inspections, and as-needed, replacements.

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.

Ken

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.

foggysail said:

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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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.

Ok after few weeks (months) here are the pictures of my anodes after 1 season. They were put in new in may 2017 and pictures were taken end of October 2017. What do you think about it? (On the blury shaft pic the first anode is the new one, the second is an old zinc one I left there)
Note: they are all zinc.

Very disappointing Lou. They need polishing, what must the fish think.

Lou,

Is your boat in salt water? In one of the preceding you said the anodes were magnesium and now you said they are zinc. In freash water they should be magnesium or aluminum. Why did you leave the old anode on your shaft in addition to the new one?

BruceK said:

Very disappointing Lou. They need polishing, what must the fish think.

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Yeah I know I am leasy, I should sand and varnish them

L

Comodave said:

Lou,

Is your boat in salt water? In one of the preceding you said the anodes were magnesium and now you said they are zinc. In freash water they should be magnesium or aluminum. Why did you leave the old anode on your shaft in addition to the new one?

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My boat is in fresh water. The anode I installed are magnesium. The one that is zinc is an old one on the shaft (the background most on the pic). I kept it there as the bolts were stuck and was thinking it would not make any damage to keep it. The old one was installed by the PO who was not caring much about anodes.

L

You should get rid of the zinc anode. All anodes in the body of water should be the same material.

Comodave said:

You should get rid of the zinc anode. All anodes in the body of water should be the same material.

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Regarding the anode wear, is it a normal wear?
Wondering the "normal" rate of wear and when to change them as it is the first time I change them.
I read that they should be changed when half dissolved is this correct?

L

Lou_tribal said:

Regarding the anode wear, is it a normal wear?
Wondering the "normal" rate of wear and when to change them as it is the first time I change them.
I read that they should be changed when half dissolved is this correct?

L

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Are those little critters on your anodes? Sure look like they are suffering more from lack of use than from wear. At that rate you will be replacing them in 2035, when they are totally hidden by the critters and you have forgotten they are even there.

You must be in clean fresh water, where no stray current can pass.

koliver said:

Are those little critters on your anodes? Sure look like they are suffering more from lack of use than from wear. At that rate you will be replacing them in 2035, when they are totally hidden by the critters and you have forgotten they are even there.

You must be in clean fresh water, where no stray current can pass.

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Not sure I understand correctly. What you call critters are pits in the anode material.
Yes I am cruising in a fresh water river. I just try to find out what is a normal wear rate for anodes as I don't have much background for this.

L

Lou_tribal said:

Yeah I know I am leasy, I should sand and varnish them

L

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If you varnish them they last a long time.

I added a new anode to the prop nut last year, previously there were only two anodes on the hull and none on the prop or shaft. I was getting about 3 years on the hull anodes before I felt they needed replacement, being only wet 4-5 months of the year and not spending much time at the docks.

The new prop nut anode was 60-70% gone in a single summer of operation... The hull anodes showed virtually no loss of material (aluminum anodes). I am assuming all the motion of the prop is responsible, and that by moving the anode closer to the source replacing the other anodes will be more infrequent.

I was surprised that all of the aluminum lost was off the single anode, but it makes perfect sense.

From all the comments I guess I can deduct that wear is normal, nothing to worry about and the anodes will be fine for another year.
I will check the continuity before splashing just in case.

L

Lou_tribal said:

From all the comments I guess I can deduct that wear is normal, nothing to worry about and the anodes will be fine for another year.
I will check the continuity before splashing just in case.

L

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Lou.
Your anodes are in wonderful condition. If that's all the depletion you get they'll last for many, many years. (Many years.)

Take the miss matched one off. It is likely causing the pitting on the other one. I've not yet had one that the bolts were seized and couldn't be undone. Use a longer handle on the Allen wrench.

Greg S said:

Lou.
Your anodes are in wonderful condition. If that's all the depletion you get they'll last for many, many years. (Many years.)

Take the miss matched one off. It is likely causing the pitting on the other one. I've not yet had one that the bolts were seized and couldn't be undone. Use a longer handle on the Allen wrench.

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Thank you Greg. I will remove the old one next spring.

L

The retailer of my outboard said I should smear the anode with petroleum jelly when stored out of water for an extended period.
We`ve no need to haulout here in winter but would that apply to anodes on boats stored out of water? Or is it BS. My outboard anode, never smeared with jelly, looks fine.