Anodes crusty - still working?

[Insequent]

I have just replaced engine and oil cooler anodes. They all look similar, with a crusty substance that I assume is a hydrated zinc oxide or similar substance. One of the cooler anodes, which are about 1cm in diameter, had material dislodged on removal. Scraping that with the end of a screwdriver removed more of this material, which is soft and crumbly, revealed a hard zinc metal core of about 4-5mm. My question is, are they still working as anodes are supposed to work?


These anodes had been in use for 16 months. The ones before that looked the same and had been in use for 14 months. My home berth is near the Brisbane CBD, about 12nm upstream from where the river enters Moreton Bay. At the river mouth salinity is 30 psu, regarded as an even mix of river (fresh) water and ocean water. So water is obviously "brackish" at my marina. But I do anchor out in the Bay, saltwater quite a lot. At least 75 nights per year. So using magnesium anodes isn't advisable, they'd be gone very quickly. Should I be using aluminium anodes instead of zinc anodes?

 

[Insequent]

I have just checked the website of my local supplier, who manufacture anodes. Their comment below would suggest that I stay with zinc.

The sea water efficiency and driving potential of modern aluminium anode alloys is slightly better than zinc anodes. This means that in sea water, for an anode of equivalent dimensions, an aluminium anode will offer slightly better performance and slightly longer life. The down side of aluminium anodes is that they are not as efficient as zinc anodes in brackish and fresh water.

https://www.cathodicanodes.com.au/cathodic-protection/

So i'll stay with zinc. But change annually as I would not want to deal with them breaking off while I'm trying to remove them. The crumbly material has no strength at all.

 

[O C Diver]

I have just replaced engine and oil cooler anodes. They all look similar, with a crusty substance that I assume is a hydrated zinc oxide or similar substance. One of the cooler anodes, which are about 1cm in diameter, had material dislodged on removal. Scraping that with the end of a screwdriver removed more of this material and revealed a hard zinc metal core of about 4-5mm. My question is, are they still working as anodes are supposed to work?


These anodes had been in use for 16 months. The ones before that looked the same and had been in use for 14 months. My home berth is near the Brisbane CBD, about 12nm upstream from where the river enters Moreton Bay. At the river mouth salinity is 30 psu, regarded as an even mix of river (fresh) water and ocean water. So water is obviously "brackish" at my marina. But I do anchor out in the Bay, saltwater quite a lot. At least 75 nights per year. So using magnesium anodes isn't advisable, they'd be gone very quickly. Should I be using aluminium anodes instead of zinc anodes?

Aluminum would be a better choice. It works in salt, brackish, and fresh. Zinc is less effective in brackish and near worthless in fresh.

Don't know what you're paying for Aluminum anodes (which have a stainless steel holder), but I usually assume I'm replacing them when I remove them. The general rule I've heard is " half or less, replace ".

I consider all anodes cheap insurance. You never know when a boat next to you is leaking AC current into the water and eating your half wasted anodes away.

Ted

 

[Insequent]

Ted
We posted about the same time. The manufacturer I linked to is saying zinc is more efficient than aluminium in brackish and fresh water, contrary to what you posted. Do you have any supporting info for your comment?

 

[O C Diver]

I have just checked the website of my local supplier, who manufacture anodes. Their comment below would suggest that I stay with zinc.

The sea water efficiency and driving potential of modern aluminium anode alloys is slightly better than zinc anodes. This means that in sea water, for an anode of equivalent dimensions, an aluminium anode will offer slightly better performance and slightly longer life. The down side of aluminium anodes is that they are not as efficient as zinc anodes in brackish and fresh water.

https://www.cathodicanodes.com.au/cathodic-protection/

So i'll stay with zinc. But change annually as I would not want to deal with them breaking off while I'm trying to remove them. The crumbly material has no strength at all.

I don't think that's true.
Sidepower, the bow thruster company, switched to Aluminum several years ago. Believe you will also find some outboard motor manufacturers using aluminum.

After doing some research while refitting my boat, I switched to aluminum as my boat spends the most time in fresh, then brackish, and finally salt water.

Ted

 

[scott_free]

Aluminum would be a better choice. It works in salt, brackish, and fresh. Zinc is less effective in brackish and near worthless in fresh.

Don't know what you're paying for Aluminum anodes (which have a stainless steel holder), but I usually assume I'm replacing them when I remove them. The general rule I've heard is " half or less, replace ".

I consider all anodes cheap insurance. You never know when a boat next to you is leaking AC current into the water and eating your half wasted anodes away.

Ted

I have always wondered why the aluminum anode holders are SS rather than brass/bronze. Any reason why?
Also agree with your comments on AL being a much better choice in fresh water. Not sure I agree with other poster who indicated zinc being a better choice for fresh.
Scott

 

[O C Diver]

Ted
We posted about the same time. The manufacturer I linked to is saying zinc is more efficient than aluminium in brackish and fresh water, contrary to what you posted. Do you have any supporting info for your comment?

I can find several anode manufacturers that agree with what I wrote. However, I don't consider them unbiased sources of information any more than your source.

I tend to think well of BoatUS regarding this type of information as I don't see a monetary incentive.

From their website: https://www.boatus.com/expert-advice/expert-advice-archive/2012/july/how-do-sacrificial-anodes-work

Not zinc

In recent years cadmium in zinc has become an environmental concern, leading to a movement in the direction of aluminum anodes. Such anodes are effective even for protecting aluminum components — lower end cases, for example — because the aluminum used in the anode is a more anodic alloy. Aluminum alloy anodes are almost certainly to become more common. It has not happened already only because the cost of aluminum anodes has been higher than zinc without any discernible benefit to the boat owner. Today aluminum is actually cheaper than zinc. In addition, aluminum anodes tend to last longer, they work better than zinc in brackish water (and maybe in salt water as well) and they appear to be better for the environment. When making the switch from zinc to aluminum, ALL of your anodes must be aluminum. This can be a problem in some locales as many local marine suppliers still do not stock a wide selection of aluminum anodes. That will eventually change.

In freshwater, magnesium anodes protect underwater metals better, particularly underwater aluminum. However, magnesium is a good choice for freshwater only. If any of your boating is also in brackish or salt water, fit aluminum anodes.


Ted

 

[O C Diver]

I have always wondered why the aluminum anode holders are SS rather than brass/bronze. Any reason why?

The aluminum would catastrophically react (deteriorate) with brass or bronze pencil anode holders.

Ted

 

[Insequent]

Scott, don't shoot me I'm only the messenger! The manufacturer I quoted above does say aluminium is slightly better and longer lasting in saltwater. Which would explain Ted's observation about Sidepower and some of the outboard manufacturers.

As for fresh water, I don't know and you guys are saying the opposite to the local manufacturer. Their factory is about 40 minutes drive from me and although I've been there a couple of times over the years last time I ordered online and had a bunch delivered. I guess I could visit them again and ask for more detail on the fresh water aspect. But I think zinc is working well enough for me not change.

What I'd like to know is whether the crusty ones I removed were still working.

 

[Insequent]

The obvious thing to do was put a meter on the crusty anodes. I did, and their was no conductivity from the crusty stuff to the bronze holder. Even worse, the anode I scraped back to zinc metal had no connectivity. Yikes! The anode threads must have corroded to the non-conductive ?oxide! So I need to re-visit my anode inspection & replacement approach.

My meter did say that a brand new zinc pencil had good conductivity to the anode holder. I've no idea how long it takes for the threads get an insulating coating develop on them.

I'm also thinking that I should put something on the zinc threads before screwing into the bronze holders. I could use CRC, but is there anything better?

 

[O C Diver]

Scott, don't shoot me I'm only the messenger! The manufacturer I quoted above does say aluminium is slightly better and longer lasting in saltwater. Which would explain Ted's observation about Sidepower and some of the outboard manufacturers.

As for fresh water, I don't know and you guys are saying the opposite to the local manufacturer. Their factory is about 40 minutes drive from me and although I've been there a couple of times over the years last time I ordered online and had a bunch delivered. I guess I could visit them again and ask for more detail on the fresh water aspect. But I think zinc is working well enough for me not change.

What I'd like to know is whether the crusty ones I removed were still working.

I don't think you would have an issue either with aluminum or zinc as it sounds like you don't go in freshwater and your brackish is sufficiently salty.

Both aluminum and zinc generate a crusty outer coating, but continue to work inspite of the coating. Regarding the remaining anode, think of the good surface area of the anode. As the surface area is reduced, the deterioration of the remaining good metal increases as a function of surface area size. Not saying you can't use them, but the second half will go away faster than the first half.

Ted

 

[O C Diver]

I'm also thinking that I should put something on the zinc threads before screwing into the bronze holders. I could use CRC, but is there anything better?

I put sealant on my pencil anode holders, but ALWAYS check the resistance between the pencil holder and what it's screwed into with an ohm meter on the sensitive scale.

Ted

 

[Insequent]

My anode holders have never leaked, so I've never used sealant on them. Do you use sealant on the pencil anodes when screwing into the anode holders also? What sealant do you use?

 

[O C Diver]

My anode holders have never leaked, so I've never used sealant on them. Do you use sealant on the pencil anodes when screwing into the anode holders also? What sealant do you use?

There's no reason to use sealant between the pencil and the holder as there's no possible point for it to leak. I suppose you could use contact enhancing jell, but I've never found the need. If you found a pencil anode that hadn't deteriorated as expected, that might be a conductivity problem between the pencil and the holder. If you think you're having a conductivity problem between the old holder and a new pencil, soak the holder in muriatic acid for 15 minutes to clean the holder good as new.

I use pipe dope (not tape) between the holder and the heat exchanger.

Ted

 

[O C Diver]

As a side note, aluminum pencil anodes don't generally screw into the holder. A stainless wire or rod is attached to the holder and the aluminum anode is cast around the wire or rod. It is my understanding that this is done to increase the contact area between the stainless and the aluminum.

Ted

 

[Comodave]

We are in all freshwater here. I see people using zinc anodes and they say they are great because they last forever. When I explain to them the reason they last forever is that they are not working due to the coating they develop in freshwater they get an ah ha moment. I use aluminum anodes on the hull and magnesium in the engines since they are a different body of water and I couldn’t find the engine pencil anodes in aluminum. Please don’t believe the source that says zinc works better in freshwater because it actually doesn’t work.

 

[Insequent]

Dave, I hear you. Practical tests/experiments are hard to dispute. For me, its brackish or salt so I should be fine with zinc even if aluminium is better.

I dont know whether the coating you can see in the pics in post#1is the same as what happens to zinc in fresh water or not. But clearly the crusty coating, and progressive conversion of zinc metal into some soft white crap is an indication that the anode is not doing what it should even it is still working a little bit.

 

[Insequent]

Thanks Ted. What I've found is that the pencil, when new, does have good contact with the holder. But for all of the crusty ones I've tested (a dozen) there is essentially zero contact between the pencil and the holder. So contact gel is definitely going to be applied now! The 8 zincs I installed a few days ago are all coming out to get treated! Oddly enough, for the crusty one that unscrew from the hold there does not seem to be much evidence of corrosion or coating.

I'll also need to clean the outside holder threads, and the threads in the block. For the anodes I just installed some of the holders had good electrical contact with the block. Some, however had poor connection to th block, but good connection to another anode holder, via the brackish water. Bloody hell! Need to fix that.

And yes, when the pencil thread have broken off inside the holder I've used a bench drill to get the majority of the zinc out and then muriatic to finish. Mostly I'll run a tap into the holder as well.

 

[psneeld]

On my Lehman, I went through several pencil zincs a year Part is normal and the other is just flow wear from silty water. The 6 months I sat in a slip they lasted, but I changed them before departing on a long trip.

Always being in brackish water except a few days here and there in pretty fresh river water the zincs worked good enough on that old engine. Newer engines using more exotic metal combinations may like the higher performing aluminum.

The rule of thumb I was taught is 50% wastage, but even that can leave you with zincs that aren't making good contact or not enough of it left to be effectively protecting. In salt water I would probably be checking/changing them at least 2X per year if sitting, and at least monthly checks and replacing the bad ones and checking continuity on all.

Of course a better way to know what anodes are best and protecting is to use a silver-silver chloride electrode.

 

[Bacchus]

Brian
I agree with Ted, Dave & others. I have sourced all my engine anodes from Precision Metals and they supply many retailers. Here is what they say and cite re metals & use.
https://performancemetals.com/pages/sacrificial-anodes-faqs

Their pencil anodes have the steel reinforcing wire/ rod cast in but they do have threads for attaching to the holders.

I have a boater friend that brought his boat from salt to fresh and we discussed anode matl. He could not find one of his hull anodes in alum but switched others out. He told me his zinc was better than alum as it lasted forever....???
I have tried to explain but he can make up his mind and dig in at times so I don't push it with him but I'm sure you get the point.

https://performancemetals.com/

 

[lwarden]

As a general practice, I put a small bead of sealant (RTV) at the very base of the anode where it touches the brass plug. I don't put any on the threads. The idea here is to prevent any water from getting inside the threads and wasting the external threads of the zinc. This stops them falling off when well worn and should improve conductivity between the two. So far this seems to work well.

 

[J.T kearney]

Hi All
Great thread on zincs and aluminum. I'm stuck in the middle here. In Puget Sound we use our boat about 100 hrs a year between May and September and fresh water rinse after using the boat for long week ends. During the off season it's pickled with RV anti freeze. I'm not going through much zinc, but was thinking it was because fresh water is not as corrosive. My engine is a Yanmar 315 hp 6lya-ute, any ideas?
Cheers J.T.

 

[O C Diver]

Hi All
Great thread on zincs and aluminum. I'm stuck in the middle here. In Puget Sound we use our boat about 100 hrs a year between May and September and fresh water rinse after using the boat for long week ends. During the off season it's pickled with RV anti freeze. I'm not going through much zinc, but was thinking it was because fresh water is not as corrosive. My engine is a Yanmar 315 hp 6lya-ute, any ideas?
Cheers J.T.

As mentioned earlier, I would consider switching to aluminum to cover all your bases. Don't know if RV antifreeze has any effect on anodes, but would probably check. I use to pickle my charter boat for the winter, but always replaced anodes before starting the season.

If you're rinsing the raw water system after each use, that could also explain reduced deterioration. If the boat floats in freshwater when not used, aluminum may be a better choice if a neighbor is leaking AC current into the water.

Ted

 

[Insequent]

Brian
I agree with Ted, Dave & others. I have sourced all my engine anodes from Precision Metals and they supply many retailers. Here is what they say and cite re metals & use.
https://performancemetals.com/pages/sacrificial-anodes-faqs

Their pencil anodes have the steel reinforcing wire/ rod cast in but they do have threads for attaching to the holders.

I have a boater friend that brought his boat from salt to fresh and we discussed anode matl. He could not find one of his hull anodes in alum but switched others out. He told me his zinc was better than alum as it lasted forever....???
I have tried to explain but he can make up his mind and dig in at times so I don't push it with him but I'm sure you get the point.

https://performancemetals.com/

Don, that looks to be a very good supplier. So far I have not been able to locate anyone in this part of the world who stocks aluminium pencil anodes.

There likely is little demand here, the vast majority of boats in fresh water are trailer boats. Houseboats are in some areas, but likely mostly powered by outboards, for which aluminium anodes are available.

 

[Steve DAntonio]

I have just checked the website of my local supplier, who manufacture anodes. Their comment below would suggest that I stay with zinc.

The sea water efficiency and driving potential of modern aluminium anode alloys is slightly better than zinc anodes. This means that in sea water, for an anode of equivalent dimensions, an aluminium anode will offer slightly better performance and slightly longer life. The down side of aluminium anodes is that they are not as efficient as zinc anodes in brackish and fresh water.

https://www.cathodicanodes.com.au/cathodic-protection/

So i'll stay with zinc. But change annually as I would not want to deal with them breaking off while I'm trying to remove them. The crumbly material has no strength at all.

That's very strange and essentially the opposite of what's true, aluminum is effective in fresh, salt and brackish water, zinc is ineffective in fresh an brackish water.

The accumulation on the anodes appears to be calcareous, a coating that occurs when zinc is exposed to fresh water. It can be brushed off, with a non-metallic brush or ScotchBrite pad.

If anodes are lasting a year, that's usually an indication they are not working. Anodes should be be replaced when no more than 50% depleted, after that point, the voltage driving potential usually drops too low to enable them to continue to provide protection.

More here https://stevedmarineconsulting.com/galvanic-isolators-and-zinc-anode-selection/

Attached from ABYC E-2

 

[Insequent]

Thanks Steve

Posts from others and some US-based sources convinced me of what you highlight a number of days ago. Just why the local manufacturer claims zinc is better than aluminium in fresh water is a puzzle. The only aluminium anodes they supply are long anodes for domestic hot water heaters etc. So far I cannot locate a local supplier of pencil aluminium anodes.

And yes, the calcareous? coating was concerning me as I indicated in my first post. It is fairly hard, acts as an insulator, but dissolves readily in muriatic acid. I have installed new pencil zincs, this time with conductive grease on both the pencil threads and the holder threads and used a meter to confirm good conductivity between the pencil and the holder as well as the holder and the engine & oil cooler housing.

I'll check monthly for the time being and clean them if need be. I am 12nm upriver in my home marina, and clearly the water is brackish, and indeed may have fairly low salinity.

 

[Serene]

[SNIP]

I'll check monthly for the time being and clean them if need be. I am 12nm upriver in my home marina, and clearly the water is brackish, and indeed may have fairly low salinity.

Especially with all the rain we have had lately, the salinity in the river is probably lower than normal.

 

[Steve DAntonio]

Performance Metals supplies aluminum anodes exclusively, including pencils. They led the charge on aluminum as a superior anode.

The only issue I have encountered is, with aluminum, they can develop a 'froth' which does not hinder performance, but it can make removal of a pencil anode difficult. Try it and check regularly to see if you have this issue.

https://performancemetals.com/

 

[HeadedToTexas]

And yes, the calcareous? coating was concerning me as I indicated in my first post. It is fairly hard, acts as an insulator, but dissolves readily in muriatic acid.

If it foams with muriatic acid, then it's calcium carbonate. If it doesn't foam, then it's an oxide of the metal from the anode. Calcium carbonate typically deposits at the cathode of hydrolysis reactions.

Either way, the coating may be crusty and hard on your knuckles, but it is porous and the electrons that make cathodic protection work whiz right through the crust. It takes a far more dense layer to create enough resistance to "insulate" the metals.

Performance Metals supplies aluminum anodes exclusively, including pencils.

https://performancemetals.com/

Thanks, Steve. Great resource!

 

[Bill Wells]

I am in the California Delta (fresh water) the boatyard have been telling me for the last 20 years to use aluminum anodes..... They seem to work great!