Have you considered installing 2 or 3 anodes and see if they all disappear? If you have an electrical issue maybe it would take longer for multiple anodes to wear away.
Disappearing zinc anode - Beneteau 323
- Thread starter chrisbeneteau
- Start date
Put two zincs on the shaft in--line.
You could try aluminium, vs. zinc.
Assuming you have the right diameter zincs -- it is possible you might not -- then, until proven otherwise, those sacrificial metals are protecting you from a worse fate.
Where do you sail? Are you in a marina? Do you have shorepower hooked-up? Do you have an isolator on the shorepower?
What are the other boats around you? Do others experience this? etc., etc., etc.
You could try aluminium, vs. zinc.
Assuming you have the right diameter zincs -- it is possible you might not -- then, until proven otherwise, those sacrificial metals are protecting you from a worse fate.
Where do you sail? Are you in a marina? Do you have shorepower hooked-up? Do you have an isolator on the shorepower?
What are the other boats around you? Do others experience this? etc., etc., etc.
I’m told not.
Zinc and Aluminum Sacrificial Anodes | Cruising World
Zinc Again: So you think you know the difference between zinc and aluminum sacrificial anodes?
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The top picture is Ron20324's boat with a Gori prop replacing the OEM.. The bottom picture is not mine, as i don't recall using both zincs at the same time. You can see the longer zinc bolts that can be bent to prevent unscrewing. The bottom pic might be the wider/not to be used zinc. The wider one will block water outflow from the cutlass bearing.
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I think there is a point that needs repeating, this boat is on a mooring, no shore power hooked up. The galvanic isolator would not help in this situation and near by boats would not play into this either. I think this is a mechanical issue, not electrical, but I really cannot figure out how this anode would separate itself. If it is being eaten away, then as soon as it 'disappears' something else would start to deteriorate.
I'm flummoxed...
dj
I'm flummoxed...
dj
It's not a simple answer. However, based upon the galvanic series as published in ASTM G82, zinc will likely go before aluminum. Here's a snapshot (for more details, pick up a copy of ASTM G82):
The further left you go on this chart, the more "active" a metal is. the further right, the more "passive" the metal is. Active metals protect passive metals. so as you can see, zinc tends to be further left than aluminum alloys. things get more complicated than this however, as oxides, the corrosion product of the metals participating, enters into the equation often changing this more idealized chart - that is very much the case for the aluminum alloys...
Sacrificial anodes are produced with complex formulas that are not necessarily made from just one of the alloys listed above. Anodes that work best in fresh water are not the same alloy as anodes that work best in sea water.
Stainless steels are notable in that they have both passive and active states.
It's complicated...
dj
A DC current leak on the boat will eat away the anode. A prime place to look for one would be in the bilge pump wiring.
If the leak is intermittent, say only occurs when the DC main is on, then look for a connection between 2 metals. Could be the bonding system, Could be within the AC wiring and bonding, Could be with an inverter. Could be a section of chafed wire that occasionally comes in contact with underwater metals.
Is there any pinking in the bronze prop? That would indicate galvanic action as the zinc leaches out of the prop.
Find a corrosion reference anode, like the one I mentioned earlier and test all the underwater metals. The boat will need to be in the water to do this. That test will tell if the problem is electrical or not. If not then it is a mechanical issue, however, it should be obvious if the anode was not installed correctly and this is the first time I've heard of one falling off.
If the leak is intermittent, say only occurs when the DC main is on, then look for a connection between 2 metals. Could be the bonding system, Could be within the AC wiring and bonding, Could be with an inverter. Could be a section of chafed wire that occasionally comes in contact with underwater metals.
Is there any pinking in the bronze prop? That would indicate galvanic action as the zinc leaches out of the prop.
Find a corrosion reference anode, like the one I mentioned earlier and test all the underwater metals. The boat will need to be in the water to do this. That test will tell if the problem is electrical or not. If not then it is a mechanical issue, however, it should be obvious if the anode was not installed correctly and this is the first time I've heard of one falling off.
I think a simple test would be to hang a "zinc guppy" over the side next season and monitor it's condition. This will tell you whether it's a mechanical or electrical problem. These "zincs" are available in different alloys, so I would chose one that is more "active" than whatever you use on the shaft.
Even with an electrical "leak" - I've not seen an anode completely gone in three months. Additionally, there usually is a directionality to the degradation, one of the indicators that the problem is electrical. If the "leak" is such that it completely consumed the anode, it's a significant leak. The prop should be also showing signs of degradation.
If there is an electrical issue, the test mentioned by @dlochner should quite easily identify it as such. I am really interested in learning the cause of this one...
dj (there are too many dj's on this forum...
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You don’t say where you sail and whether you are in fresh or salt water. That might help us.
Imam in fresh water on Lake Michigan. I have 2 anodes on my 1” shaft. But they are not zinc. They are magnesium. They are still on the shaft at the end of the season, but pretty disintegrated....
Greg
Where do you sail, fresh or salt water, you have to match the sacrificial metal to the salinity of the water. Also consider, where you are keeping the boat docked, stray electricity may be coming from a neighboring boat or faulty shore power wiring. Check and see if any of your neighbors are experiencing a similar problem.
We've seen DC leaks eat away anodes in days then go to work on thru-hulls etc.. This boat had the battery bank and much of the bank wiring fully submerged, due to a failed solder joint in the bilge pump wiring, and the anodes were completely gone. The brand new thru-hulls, installed that previous winter, were also toast. This happened in less than 30 hours. Obviously a battery is a huge DC leak but even small ones can destroy your anodic protection pretty quickly.Even with an electrical "leak" - I've not seen an anode completely gone in three months. Additionally, there usually is a directionality to the degradation, one of the indicators that the problem is electrical. If the "leak" is such that it completely consumed the anode, it's a significant leak. The prop should be also showing signs of degradation.
If there is an electrical issue, the test mentioned by @dlochner should quite easily identify it as such. I am really interested in learning the cause of this one...
dj (there are too many dj's on this forum...
We see just as many cases of DC leakage current on mooring sailed boats as we do on marina based boats. On moring sailed boats 98% of the time we find the issue originating on-board the customers boat yet 100% of the time the customer claims it is not an on-board issue.
Galvanic issues are obviously a problem in marinas but this is easily corrected with a Galvanic Isolator or better yet and Isolation Transformer.
Suggestions:
#1 If you have a metric shaft be sure you are using a metric anode.
#2 If you are using the correct anode for the shaft, bring in an ABYC corrosion specialist or you will likely have much worse, and much more expensive issues to deal with.
Yes, but you have ancillary damage in your example. The OP is claiming no other damage other than the missing anode.
i should have been more clear in my original post, saying with no other damages present, it's unusual to have an entire anode gone in only 3 months. I'm referring to small leaks, not huge ones like you are talking about.
If the OPs boat has all plastic thru-hulls, then they won't be affected. This is unknown. But this anode is on the prop shaft. If it's electrical, and happening as fast as stated, there would have to be damage to the prop. Even in your example above, there remains part of that thru hull. In this case, there is nothing left of the anode and no other damage stated.
This has been going on for years. It is not an isolated event. Given what has been stated by the OP, I find it difficult to see how it is electrical in nature.
dj
But does he actually know what he is looking for or at? In most cases, where there is a DC leak, we can find a dezincified prop, prop-shaft pitting, strut damage etc., provided the anode has been gone long enough. Without knowing when the last remaining bits of the anode actually dropped off the shaft, impossible to say.
Actually it is not all that uncommon for boats with electrical issues or boats that are under protected, anode weight wise..
Again, depends upon when the last bits of anode eroded away. As stated above does he actually know what dezincification looks like? Most don't, and are not trained for this. This is why corrosion specialists exist...
Every through hull in the boat was destroyed and unsafe to continue using. The outboard brackets and prop ends of the outboards were also destroyed as they were also in the water. Even the live-well pumps were destroyed.
As a corrosion specialist, and if the anode is the right size for the shaft, I would say there is a very high chance this is a small DC leak. Even a possibility that someone used the grounding/bonding circuit for a return DC negative path, we see this mistake all the time.. The real danger is in ignoring it and assuming it just "fell off"..
We were just working out this issue three weeks ago after the owner got tingled by the prop.
Because this 48VAC, on the AC grounding wire, was AC, not DC, you can see that the MaxProp anode, at 5 months old, is still ok. AC is very, very, very slow to cause corrosion issues but also very dangerous to swimmers. On a lake this would have been quite deadly. Anyone in the water around this boat ran chance of electric shock drowning, not good.. Two yards had tried to solve this issue before we were called in. There were numerous AC issues identified including a failed 15A rated inverter/charger transfer switch, that never should have been installed in the first place.