Will Non-Bonded Anode Sacrifice?

[rardiH36]

Question for the long-time boat owners and (if reading) the electrochemical engineers or scientifically inclined among the membership:

At a typical marina say that a zinc or Al alloy anode is suspended/immersed in saltwater by a synthetic piece of line. Therefore has no electromechanical connection to anything else metal. Six months later it is brought to the surface. The marine growth then is scraped away.

Other than surface tarnishing, will the anode look pretty much like when it was new? ... That is no deep pitting?

Asking the question to help me feel better given that my hanging over the side backup "fish" anode has depleted big time over the past eight months = evidence that hanging an anode will protect my bronze prop for a while even though the shaft anode fell off last week. My hanging anode is electrically bonded to the shaft inside the boat with a shaft brush. And for redundancy, also I have run a parallel pigtail from the anode direct to the engine block.

Picture of the removed anode attached. (I did replace with a new one.) The small shiny section in the anode is from a hack-saw cut I made after it's retrieval from the water to see how much good metal might still remain below the surface pitting. Looks the same to me as the surface of new anode I hung in its place. The anode is a military spec Al alloy type. I put the anode pictured in my bench vice and bent it almost 90 degrees. Then straightened it out again. The Al alloy remained pliable. To me an indication that inside, the anode still hadn't sacrificed all its electrons.

Impressions and experiences please!

 

[Don S/V ILLusion]

Don't know what a "typical marina" is but you are correct that a sacrificial anode must be electrically bonded to the metal to be protected.

Who told you otherwise?

 

[jibes138]

Question for the long-time boat owners and (if reading) the electrochemical engineers or scientifically inclined among the membership: At a typical marina say that a zinc or Al alloy anode is suspended/immersed in saltwater by a synthetic piece of line. Therefore has no electromechanical connection to anything else metal. Six months later it is brought to the surface. The marine growth then is scraped away. Other than surface tarnishing, will the anode look pretty much like when it was new? ... That is no deep pitting? Asking the question to help me feel better given that my hanging over the side backup "fish" anode has depleted big time over the past eight months = evidence that hanging an anode will protect my bronze prop for a while even though the shaft anode fell off last week. My hanging anode is electrically bonded to the shaft inside the boat with a shaft brush. And for redundancy, also I have run a parallel pigtail from the anode direct to the engine block. Picture of the removed anode attached. (I did replace with a new one.) The small shiny section in the anode is from a hack-saw cut I made after it's retrieval from the water to see how much good metal might still remain below the surface pitting. Looks the same to me as the surface of new anode I hung in its place. The anode is a military spec Al alloy type. I put the anode pictured in my bench vice and bent it almost 90 degrees. Then straightened it out again. The Al alloy remained pliable. To me an indication that inside, the anode still hadn't sacrificed all its electrons. Impressions and experiences please!

it depends. If the water is acidic you might see some degradation. Then because of grain boundaries you might see some preferential attack along them. Anodes aren't sacrificing electrons. Whole atoms are sacrificed. It is an electroplating process.

 

[rardiH36]

Don't know what a "typical marina" is but you are correct that a sacrificial anode must be electrically bonded to the metal to be protected.

Who told you otherwise?

Hello Don:

- By "typical marina", I am thinking where other boats are within feet/yards of my boat and connected to AC. And those infamous "stray hot currents" are invigorating the sub-surface environment.

- Yes, I know that an anode must be bonded to protect. But I have never read anywhere that non-bonded sacrificial anode (which is zinc or Al-alloy that readily gives ups their electrons before SS or Bronze) won't still sacrifice over time in a hot marina. I wouldn't think so but I really don't know. I guess an analogy would be say a diver put on a shaft anode right over a lot of marine growth on the shaft without first scraping the marine growth off the shaft back down to shiny SS metal. As such the new shaft anode has no or compromised electrical bonding. The owner might notice that the zinc isn't depleting at the normal rate but otherwise he just assumes that all is OK. Until the next haul out when the prop is going pink and/or is pitted.

 

[Ralph Johnstone]

Given that we don't have an excess of data here, I would recommend that you run, not walk to your nearest marine supplier and purchase a large surface area zinc plate anode and immediately add this to your original hanging anode. Something electrically major is going on by the look of that hanging anode. Even for an aluminum hanging anode, that corrosion looks looks to be excessive. Better safe than sorry. Also, any reason for using an aluminum hanging anode rather than the garden variety zinc ?

Asking the question to help me feel better given that my hanging over the side backup "fish" anode has depleted big time over the past eight months =evidence that hanging an anode will protect my bronze prop for a while even though the shaft anode fell off last week.

To have your shaft anode FALL OFF after eight months is excessive given all the self sacrifice the hanging anode was willing to donate. Next time you may want to consider installing more than one shaft zinc as a backup Any chance your marina is beside a sulphuric acid plant .

At a typical marina say that a zinc or Al alloy anode is suspended/immersed in saltwater by a synthetic piece of line. Therefore has no electromechanical connection to anything else metal. Six months later it is brought to the surface. The marine growth then is scraped away.

Other than surface tarnishing, will the anode look pretty much like when it was new? ... That is no deep pitting?

There will only be moderate corrosion as there is no galvanic couple (dissimilar metals) involved. However, if there are outside currents introduced, you will get more severe corrosion.

The above is the easy part. Now to find out what's causing the problem.

 

[rardiH36]

Ralph:

Thanks.

Aluminum alloy anode because I have read that this is the future direction. Longer life and more eco-friendly.

My post/situation is after 8 months at a new (to me) marina. Very possible someone nearby is introducing stray current.

My previous regime at the previous marina was zinc on the shaft and Al-indium alloy for the hanging. This was because of my investigation that Al sacrifices at a slight faster rate than zinc. Easier/cheaper to replace the Al-indium hanging when depleted than the zinc on the shaft. Seemed to work. I replaced the hanging Al twice before it was time to do the shaft Zn. After my last haul-out, and after discussion with the yard manager, I decided this time to put Al-Indium also on the shaft. The hanging had more mass. So if the hanging did have good bonding, I would have expected that yes the shaft Al-Indium anode would have depleted first.

As to more data, the only thing I can think of is that I never 110v AC my boat to the dock. I generally just go day-sailing. Between sails, my 30w solar panel recharges the minimal depletion I do to the batteries. And keeps them topped up. So other than the very occasional over-night and the need for the coffe-maker the next morning, I don't do AC.

 

[Don S/V ILLusion]

I'm not sure if you are asking an academic question or if there is a problem you are trying to correct.

For any anode to 'work' effectively, it must be part of a circuit. In effect, you create a battery thru whic a small current flows. Absent an elec circuit, no 'battery' is formed. Sea water, in itself, is obviously a good conductor but simply having stray current in its ambient environment doesn't complete a circuit.

If you are actually seeing depletion of your shaft anode, adding more doesn't fix anything. There is an argument that adding more anode exacerbates the problem.

Although improper grounding in a marina's elec system could cause a problem, it's more likely a result of a boat owner not thoroughly eliminating bad or multiple grounds on his own boat.

 

[Maine Sail]

As to more data, the only thing I can think of is that I never 110v AC my boat to the dock. I generally just go day-sailing. Between sails, my 30w solar panel recharges the minimal depletion I do to the batteries. And keeps them topped up. So other than the very occasional over-night and the need for the coffe-maker the next morning, I don't do AC.

If you are not plugged in to shore power then the only anode wasting is being caused by your own vessel. Most likely a small DC leak, multiple ground paths or using a bonding circuit wire to carry DC current.... Do you have graphite packing? What alloy is your shaft? Prop?

 

[Charles Erwin]

I am always surprised to look at aluminum alloy anodes after they have been in service
awhile because they do not look at all like worn zinc. You would swear by the the appearance of aluminum that there something is big time wrong.

Then you measure the hull potential and you find out that that weird looking aluminum anode is in fact still quite active and things are actually just fine.

An actual hull potential measurement is probably better than guessing by anode appearance - at least it is in my shop. And - doing so is both cheap and simple.

Charles

 

[rardiH36]

I am always surprised to look at aluminum alloy anodes after they have been in service
awhile because they do not look at all like worn zinc. You would swear by the the appearance of aluminum that there something is big time wrong.

Then you measure the hull potential and you find out that that weird looking aluminum anode is in fact still quite active and things are actually just fine.

An actual hull potential measurement is probably better than guessing by anode appearance - at least it is in my shop. And - doing so is both cheap and simple.

Charles

Charles:

Appreciate your response. And for the pdf you attached with info about how to use a multimeter to check for a zinc's protection status. I'll do it!

Regarding your observation about the appearance of Al/Indium alloy anodes, I included in my opening post the condition of my Al alloy fish anode metal to call attention to the shiny metal revealed by the hack-saw cut, and that I had bent the anode almost 90 degrees and then straightened again without the anode breaking. I think that a zinc anode that had the same appearance would be brittle. These observations lead me to believe that irrespective of the ugly appearance of the surface, my Al alloy anode was still sacrificing/protecting. The fish anode that I pictured only was brushed clean -- after 8 months in salt water. Every time that I pull up the fish anode, I shake it in the water. Marine growth sluffs off. And if the anode is generally free of growth, I can see the surface layer sluffing off as well.

Not that it really adds anything to the discussion, but attached is another picture of the 8-month anode and a brand-new one. Weight of the new is 9.5 oz. Weight of the eight month is 5.5 oz.

 

[rardiH36]

Hello Maine Sail:

Thank you. I will have to dig into investigating possible "DC leaks" that you mention. My shaft is SS and at last haul-out showed no evidence of pitting even within the cutlass bearing when I replaced it. The prop is a Campbell Sailer prop - bronze alloy. I don't have graphite packing. All my +12V DC goes to one of those red A/B/Off switches, with the exception of "always on" leads to my bilge pumps and a trickle voltage to the stereo in order to maintain the memory. The A/B/Off switch is always in the off position when I am not at the boat.

How do I determine if I might have multiple ground paths?

Again thanks.

rardi

 

[Charles Erwin]

Rardi

Maine Sail will provide his usual wise and always accurate thoughts - but what I would do is measure per the diagram first with batteries physically connected, then batteries physically disconnected. Make your disconnects at the DC neg battery posts and be sure to disconnect your shore power cord as well. If there is a difference in those measurements - we talk further. If not, then all is skookum

Charles

 

[Chris Patterson]

Shookum? Charles, that's some pretty rough language to be using on a family forum

 

[rardiH36]

I will be visiting my boat today. Will report back with findings! Actually hoping to eventually discover that all is not skookum ... need to know what is going on...

... Particularly with Maine Sail's observation that without me being plugged in to AC, anode wastage likely to be a fault in my own system. Makes sense I guess because my bronze not-bonded-to-anything through-hulls always have checked out bright yellow when scraped at each haul out. The only different metal electrical potential that is in the water is the prop on the ss shaft.

 

[Charles Erwin]

Do you have strut and rudder post? Are they bonded together? Do they have there own aluminums? (No having both zinc and aluminum - but aluminum 'fish' OK.)

 

[rardiH36]

Charles:

Once again, thanks your keen interest:

Inboard Yanmar I have. So yes a strut. The 34 year old 1980 OEM strut was an issue at the last haul-out when I and the yard attempted to press out the in-need-of-replacement cutlass bearing. (pics attached of what is looked like after the attempt.) Hunter originally bonded the strut with a wire to the engine block. Many years before I bought the boat the wire had galvanically corroded away from the strut mounting bolt. I didn't reattach because 1) the bolt was unreachable and 2) I figured that since the strut was electrically isolated by the rubber bearing it was probably best to leave as is. Anyway, the the replacement strut now is wire bonded to the engine block as per the original OEM configuration. It was painted with several coats of non-conductive underwater primer. Then painted with copper-based hard anti-fouling paint.

As to the rudder post: Not really bonded by any wire. But of course the post is connected to the quadrant which is in hard contact with the SS steering wire that ultimately makes electrical contact at the pedestal. Past checks with an audible continuity checker indicate that all is connected. But I also wonder if a lot of metal surface area in salt water within a few feet of each other might also create enough of "connection" that all would appear to be bonded even if not.

 

[Charles Erwin]

Strut bonding to the motor block (if no drive saver) simply means that the shaft anode is protecting the strut too. And that is good in case the coating is damaged.

Do your field work - no boat changes yet.

Charles