Anodes crusty - still working?

[Comodave]

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!

They are right.

 

[Mac G]

We currently cruise in salt and use zinc but plan to visit Great Lakes so sounds like we should switch to aluminum prior. Do you all concur?

 

[Comodave]

We currently cruise in salt and use zinc but plan to visit Great Lakes so sounds like we should switch to aluminum prior. Do you all concur?

Absolutely. Then I would stick with aluminum after you go back to saltwater if you do.

 

[Mac G]

Good idea. Thank you

 

[fstbttms]

If anodes are lasting a year, that's usually an indication they are not working.

A blanket statement like this is inaccurate. For example, a 6X12 transom plate like this should last at least quite a long time, certainly more than a year.

 

[klee wyck]

A blanket statement like this is inaccurate. For example, a 6X12 transom plate like this should last at least quite a long time, certainly more than a year.

This question haunts me a bit I must admit. I have due respect for both the post above and the post he quoted.

During the last haul for my steel vessel which was more than two years from the previous haul, I did not replace a single anode of likely 20 or more that are deployed on the vessel. The well-respected yard I was in that works on mostly commercial and military craft, many of which are metal, did not seem the least bit concerned when we had the discussion about this.

I wish there was more unanimity on the subject. That is the normal pattern for that steel boat. On the cat in warm water, which is FRP, the intervals are much shorter, and both are based on the 50% rule.

 

[Steve DAntonio]

Indeed, I should have qualified that statement, if the anode lasts a year, with no signs of consumption, it almost certainly is not working.

Anodes should be replaced when no more than 50% depleted.

I'm not sure I've seen a properly functioning anode experience less than 50% depletion over the course of a year, if so it's an exception, and/or the vessel is over-zinced.

Klee, your vessel's protection level can be easily assessed with a reference cell test, detailed here https://stevedmarineconsulting.com/...rosion-protection-level-editorial-old-vs-new/ It is possible, if your hull is well encapsulated in epoxy primer, that your anodes aren't being called on to protect very much at all, and you may be over-zinced as well. Again, a reference cell test will confirm your protection level, if it's correct, too low or too high.

Corrosion, its analysis, causes and prevention, is by far the most misunderstood and misdiagnosed phenomena in this industry.

 

[HeadedToTexas]

Corrosion, its analysis, causes and prevention, is by far the most misunderstood and misdiagnosed phenomena in this industry.

I am in the water treatment industry and that is no exception here. Corrosion is mysterious and its control is fraught with both good and bad science.

 

[klee wyck]

Indeed, I should have qualified that statement, if the anode lasts a year, with no signs of consumption, it almost certainly is not working.

Anodes should be replaced when no more than 50% depleted.

I'm not sure I've seen a properly functioning anode experience less than 50% depletion over the course of a year, if so it's an exception, and/or the vessel is over-zinced.

Klee, your vessel's protection level can be easily assessed with a reference cell test, detailed here https://stevedmarineconsulting.com/...rosion-protection-level-editorial-old-vs-new/ It is possible, if your hull is well encapsulated in epoxy primer, that your anodes aren't being called on to protect very much at all, and you may be over-zinced as well. Again, a reference cell test will confirm your protection level, if it's correct, too low or too high.

Corrosion, its analysis, causes and prevention, is by far the most misunderstood and misdiagnosed phenomena in this industry.

Well, the good news is that there are signs of consumption on the surfaces of the anodes, just very little and very slowly at the rate of around 3+ years to 50%. Probably over zinced. There must be 30# of anodes on the hull from tip to tail, maybe more.
But, if they were not working, would there not be evidence of that inside or outside this metal vessel at some point? I have been on watch on this vessel for 8 years. The inside and outside of the hull and its appendages are quiet outside of a bleed now and then around the port lights.
I could believe she is well encapsulated. I oversaw the blast and recoated early in my ownership, but even at that time I remember thinking that I had jumped the gun on the coating work since both audio gauge and inspection were clean.

 

[fstbttms]

I'm not sure I've seen a properly functioning anode experience less than 50% depletion over the course of a year...

I see it every day- large transom anodes, anodes on struts, gudgeons, weed shoes etc. Either the anode is a substantial piece of metal or it is not being asked to protect much or it is attached to a part that is electrically isolated. In any case, less than 50% depletion within a year's time is very common in certain applications and absolutely not necessarily indicative of an anode not doing its job. I make this statement with confidence because I dive the same boats month after month, year after year and often decade after decade, so I see what is going on with the anodes and the metals they are meant to protect over the long term, not just when a particular boat is experiencing some sort of corrosion or rapid anode depletion issue.

 

[Steve DAntonio]

I see it every day- large transom anodes, anodes on struts, gudgeons, weed shoes etc. Either the anode is a substantial piece of metal or it is not being asked to protect much or it is attached to a part that is electrically isolated. In any case, less than 50% depletion within a year's time is very common in certain applications and absolutely not necessarily indicative of an anode not doing its job. I make this statement with confidence because I dive the same boats month after month, year after year and often decade after decade, so I see what is going on with the anodes and the metals they are meant to protect over the long term, not just when a particular boat is experiencing some sort of corrosion or rapid anode depletion issue.

I don't doubt the veracity of your anecdotal observations. However, bronze, for instance, is naturally corrosion resistant, and technically needs no cathodic protection (sacrificial anodes) to remain corrosion resistant. Some boat builders install bonding systems and hull anodes, and connect bronze underwater metals to them, others don't. Do the latter's metals corrode? Generally no. So, without a control, saying you believe anodes are working because you don't see corrosion is using the absence of evidence approach; it's not scientific.

A manganese bronze propeller, on the other hand, requires cathodic protection because its alloy contains zinc, and it will dezincify (causing it to turn pink) unless cathodically protected.

Ultimately, the in water reference cell test (and hauled continuity test), is the ultimate arbiter of whether or not anodes are properly connected, working (or of they are working too well) and of adequate mass. The maximum allowable resistance between any anode and any protected metal is just 1 ohm (that includes anodes that are connected to underwater metals by bonding wires). That standard can't be confirmed through any amount of observation, and if an anode is lasting over a year, it's a candidate for testing at the very least.

One ohm is a lofty goal, and one that's easily not achieved by even the slightest irregularity in contact between an anode and the surface it's installed over, or a corroded bonding connection located in the bilge, which of course is very rare, not.

Every steel or aluminum vessel would benefit from a permanently installed reference cell, which enables real-time monitoring of the protection level. https://www.suremarineservice.com/Electrical/Monitoring-Stations/

On the subject of over-protection or over-zincing, doing so creates an alkaline solution around protected metals (and often a telltale halo effect). Since aluminum is amphoteric, it will experience pitting from over-protection. It is also harmful to timber vessels, they suffer delignification around protected metals. It can be an issue with steel, but it's indirect, as the alkaline will lift coatings, which then exposes the steel to rust. On FRP vessels it's purely a paint failure issue, this article explains the phenomenon in greater detail.

https://stevedmarineconsulting.com/...al-do-you-need-wi-fi-or-texting-smoke-alarms/

 

[klee wyck]

I don't doubt the veracity of your anecdotal observations. However, bronze, for instance, is naturally corrosion resistant, and technically needs no cathodic protection (sacrificial anodes) to remain corrosion resistant. Some boat builders install bonding systems and hull anodes, and connect bronze underwater metals to them, others don't. Do the latter's metals corrode? Generally no. So, without a control, saying you believe anodes are working because you don't see corrosion is using the absence of evidence approach; it's not scientific.

A manganese bronze propeller, on the other hand, requires cathodic protection because its alloy contains zinc, and it will dezincify (causing it to turn pink) unless cathodically protected.

Ultimately, the in water reference cell test (and hauled continuity test), is the ultimate arbiter of whether or not anodes are properly connected, working (or of they are working too well) and of adequate mass. The maximum allowable resistance between any anode and any protected metal is just 1 ohm (that includes anodes that are connected to underwater metals by bonding wires). That standard can't be confirmed through any amount of observation, and if an anode is lasting over a year, it's a candidate for testing at the very least.

One ohm is a lofty goal, and one that's easily not achieved by even the slightest irregularity in contact between an anode and the surface it's installed over, or a corroded bonding connection located in the bilge, which of course is very rare, not.

Every steel or aluminum vessel would benefit from a permanently installed reference cell, which enables real-time monitoring of the protection level. https://www.suremarineservice.com/Electrical/Monitoring-Stations/

On the subject of over-protection or over-zincing, doing so creates an alkaline solution around protected metals (and often a telltale halo effect). Since aluminum is amphoteric, it will experience pitting from over-protection. It is also harmful to timber vessels, they suffer delignification around protected metals. It can be an issue with steel, but it's indirect, as the alkaline will lift coatings, which then exposes the steel to rust. On FRP vessels it's purely a paint failure issue, this article explains the phenomenon in greater detail.

https://stevedmarineconsulting.com/...al-do-you-need-wi-fi-or-texting-smoke-alarms/

All good stuff. I will definitely do the reference cell again now. I think the last time I checked with a reference cell was 2018 so overdue and will consider the installation of the monitoring station.
I am thinking about your encapsulated metals comment. While I do not understand the subject nearly well enough, I believe the trouble we are trying to avoid is the result of susceptible metals either in a brine or effectively with a completed circuit to a brine.
I can imagine that a steel hull with excellent coatings is not in or connected to a brine. With Libra having closed circuit keel cooling, no mixing in the exhaust, and no heat exchangers, there is also no brine connected to her machinery. Only one thru hull below the waterline. It is common on Dutch steel boats, and this includes Libra, that even the stern tube is not effectively containing a brine. In some cases, it is an oil bath and in the case of Libra it is packed in grease which is under constant pressure by an autolube mechanism coupled to the main shaft.
So, likely reduced pathways overall for the flow of electrons.
I will attach two photos of the last haul a year ago after a two-year interval from fresh anodes. First is a view from a distance which gives an indication of anode mass and placement. The second is a close up of one near the stabilizers we were installing at the time. I see evidence of activity on the anode, but much more than 50% of the mass remaining.
Comments welcome.

 

[fstbttms]

So, without a control, saying you believe anodes are working because you don't see corrosion is using the absence of evidence approach; it's not scientific.

I didn't say that I beleived that a particular anode was working because I didn't see corrosion. Never said that, never inferred that. I said that depending upon the anode and its application, anodes frequently do not reach 50% depletion within a 12-month period and that THAT is not necessarily indicative of their not working.

But saying that every anode on every boat needs to be replaced within a year of being installed is patently ridiculous. I wish however that you were correct (unfortunately you are not), as I earn my living selling and installing sacrificial anodes. :lol:

 

[Steve DAntonio]

All good stuff. I will definitely do the reference cell again now. I think the last time I checked with a reference cell was 2018 so overdue and will consider the installation of the monitoring station.
I am thinking about your encapsulated metals comment. While I do not understand the subject nearly well enough, I believe the trouble we are trying to avoid is the result of susceptible metals either in a brine or effectively with a completed circuit to a brine.
I can imagine that a steel hull with excellent coatings is not in or connected to a brine. With Libra having closed circuit keel cooling, no mixing in the exhaust, and no heat exchangers, there is also no brine connected to her machinery. Only one thru hull below the waterline. It is common on Dutch steel boats, and this includes Libra, that even the stern tube is not effectively containing a brine. In some cases, it is an oil bath and in the case of Libra it is packed in grease which is under constant pressure by an autolube mechanism coupled to the main shaft.
So, likely reduced pathways overall for the flow of electrons.
I will attach two photos of the last haul a year ago after a two-year interval from fresh anodes. First is a view from a distance which gives an indication of anode mass and placement. The second is a close up of one near the stabilizers we were installing at the time. I see evidence of activity on the anode, but much more than 50% of the mass remaining.
Comments welcome.

Sounds good, you can't go wrong with ref cell testing. Based on your design it does sound as if you are well-encapsulated. Did you say you have an oil-filled shaft log? Is it an off the shelf product or custom made by the builder?

Contrary to popular belief, there is typically no interaction between raw water systems inside the vessel, i.e., heat exchanger anodes, and metallic plumbing, and the water in which the vessel floats, and hull anodes, the run is typically too long and too narrow for ions to flow through water. Thus, pencil anodes in heat exchangers don't try to protect the hull, even if electrically connected, and hull anodes don't try to protect heat exchangers and internal metallic plumbing.

 

[klee wyck]

Sounds good, you can't go wrong with ref cell testing. Based on your design it does sound as if you are well-encapsulated. Did you say you have an oil-filled shaft log? Is it an off the shelf product or custom made by the builder?

Contrary to popular belief, there is typically no interaction between raw water systems inside the vessel, i.e., heat exchanger anodes, and metallic plumbing, and the water in which the vessel floats, and hull anodes, the run is typically too long and too narrow for ions to flow through water. Thus, pencil anodes in heat exchangers don't try to protect the hull, even if electrically connected, and hull anodes don't try to protect heat exchangers and internal metallic plumbing.

Thanks Steve,
In the case of Libra, the shaft log is packed in grease (not oil). There is a grease reservoir, and it has a pump driven by a belt coupled to the main shaft keeping the log full and under positive pressure. We find this auto lube arrangement common in agricultural equipment. It is original equipment. Grease fills the void around that shaft from the gland in the engine bilge to the aft bearer where the shaft exits the vessel. That aft bearer is original and has been in place for 37 years. Still no play in the shaft as measured by a dial indicator. The main shaft is coupled to the gear by a CV joint (also common in agriculture). Smooth as silk.
The log on Klee Wyck, which was also a steel Dutch vessel, was filled from a header tank full of oil mounted above the log that was kept full so that one, also OEM, was an oil bath under gravity pressure.
I think these are well conceived and well proven designs.

 

[Steve DAntonio]

Thanks Steve,
In the case of Libra, the shaft log is packed in grease (not oil). There is a grease reservoir, and it has a pump driven by a belt coupled to the main shaft keeping the log full and under positive pressure. We find this auto lube arrangement common in agricultural equipment. It is original equipment. Grease fills the void around that shaft from the gland in the engine bilge to the aft bearer where the shaft exits the vessel. That aft bearer is original and has been in place for 37 years. Still no play in the shaft as measured by a dial indicator. The main shaft is coupled to the gear by a CV joint (also common in agriculture). Smooth as silk.
The log on Klee Wyck, which was also a steel Dutch vessel, was filled from a header tank full of oil mounted above the log that was kept full so that one, also OEM, was an oil bath under gravity pressure.
I think these are well conceived and well proven designs.

A belt-driven grease pump?! That sounds interesting, what regulates it? What keeps the log from becoming mass of emulsified water and grease.

Keeping the inside of the shaft log from rusting on a steel vessel is a challenge, filling with oil or grease is one solution, as is Seatorque, see below.

There was a stuffing box system, the name escapes me now, that used a reservoir of ATF, long gone now. Regarding the vessel with the oil-filled shaft log, is there a lip seal at the aft end of the shaft?

Seatorque offers such a system today, as a self-contained unit, I have specified it on several new build projects, up to 100 feet, it works very well. Home - Seatorque Control Systems

 

[klee wyck]

By way of an update on my long-lived anodes for Steve and any others still tuned in.
With mounting paranoia and armed with my trusty reference cell, I spent an hour or two today looking at hull potential in various areas on Libra.
Reading ran the range of -950 to -1280 mv on various metal components of the boat, but mainly the hull.

I am satisfied with that. Probably leans toward over protected a bit, but with a steel hull and no indication of poor performance in bottom paint over a long period, I'm calling it good. I will worry less for awhile about anodes lasting multiple years before they are 50% consumed.