Non active zinc suddenly VERY active. - SailNet Community
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post #1 of 45 Old 07-27-2015 Thread Starter
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Non active zinc suddenly VERY active.

The zinc on my rudder skeg has never been active though many years and several marinas. I've been at this marina about a year and the skeg zinc is suddenly very active (see picture). The prop zinc was always active, though now, the pock marks in it are much larger, deeper, like moon craters. Before, it would deteriorate more evenly and slower.
The new marina is a little farther South, and may have a little less tidal flow.
Are these zincs showing definite signs of a "hot" marina (or neighbor)?
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post #2 of 45 Old 07-27-2015
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Re: Non active zinc suddenly VERY active.

first do you have a galvanic isolator connected to your shore ground. you may be protecting everyone else's boat near you

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post #3 of 45 Old 07-28-2015 Thread Starter
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Re: Non active zinc suddenly VERY active.

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Originally Posted by overbored View Post
first do you have a galvanic isolator connected to your shore ground. you may be protecting everyone else's boat near you
No, but never have. Why would things suddenly change?
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post #4 of 45 Old 07-28-2015
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Re: Non active zinc suddenly VERY active.

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Originally Posted by L124C View Post
No, but never have. Why would things suddenly change?
Because, if I understand you right, you have moved your boat to another environment. In the new area / marina the electric potentials may differ from the old one (most likely do, in fact).

When one experience the zinc goes away fast, first thing to look for is the electric installations on ones own boat.
Often connected to shore power? Then, a galvanic isolator is often good to have.
There are other potential areas that can be investigated, but the shore power connection is the first to look at.

It may be the surrounding boats / water that actually is causing your problems. This is unusual, but do happen.

/J
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post #5 of 45 Old 07-28-2015
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Re: Non active zinc suddenly VERY active.

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Originally Posted by L124C View Post
The zinc on my rudder skeg has never been active though many years and several marinas. I've been at this marina about a year and the skeg zinc is suddenly very active...
The anode pictured does not appear to be depleting particularly rapidly. It looks as it should after a year. If (in the past) that anode lasted for many years, it was likely not doing it's job. I would submit that you are trying to solve a problem that does not exist.
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post #6 of 45 Old 07-30-2015 Thread Starter
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Re: Non active zinc suddenly VERY active.

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Originally Posted by Fstbttms View Post
The anode pictured does not appear to be depleting particularly rapidly. It looks as it should after a year. If (in the past) that anode lasted for many years, it was likely not doing it's job. I would submit that you are trying to solve a problem that does not exist.
So my question was....Why did it suddenly go to work.

I don't know that it is a "problem", but when a zinc stays in pristine condition for 8 years (AKA "is not doing it's job") then looks like that one in a year, something has obviously changed. The most obvious change was the marina.

I don't have any problem changing the zinc, but if I'm in a hot marina/berth, I want to know about it. I'll run some tests.
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Re: Non active zinc suddenly VERY active.

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Originally Posted by L124C View Post
I don't have any problem changing the zinc, but if I'm in a hot marina/berth, I want to know about it. I'll run some tests.
1.- That anode does not need to be replaced.

2.- If that is all the depletion the anode shows after a year in your current marina, the marina is not "hot".

While I do not know why the zinc is now showing normal depletion, it is certain that you absolutely had a problem previosly, with an anode that did nothing for 8 years. You do not have a problem now, IMHO.
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post #8 of 45 Old 08-03-2015 Thread Starter
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Re: Non active zinc suddenly VERY active.

1.- That anode does not need to be replaced.
Never said it did. The question in the OP was, why is the zinc suddenly active. If you don't know the answer, no need to post.
2.- If that is all the depletion the anode shows after a year in your current marina, the marina is not "hot".
[COLOR="blue"]Then...were the other marinas the boat was in (with no activity on that zinc) "cold"?
While I do not know why the zinc is now showing normal depletion, it is certain that you absolutely had a problem previosly, with an anode that did nothing for 8 years. You do not have a problem now, IMHO.
Other than not needing to replace the skeg zinc, what could that "problem" possibly have been? Prop was protected by the shaft zinc, and eroded at half the rate it is eroding at now. What was the problem?
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Last edited by L124C; 08-03-2015 at 02:57 AM.
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post #9 of 45 Old 08-03-2015
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Re: Non active zinc suddenly VERY active.

As Jaramaz indicated something has changed either in your vessel or due to moving to a new marina to increase the galvanic action causing your sacrificial anodes (zincs) to corrode faster.

As he said start with your boats electrical system, are all equipment bonding good and clean and in proper working order, are the grounds AC and DC properly connected and in good corrosion free condition. Is the shore power connections in good condition free of chaffing and do the pins properly engage within the plug or is one out of alignment, this is sometimes hard to see by itself, but if you had a know good plug compare them to each other the only difference should be only minor(very) wear. Inspect the female end of the connectors also they should all look the same and be at the same depth, is one pushed further back than another, again comparing to a known good also helps in this.

Lastly, galvanically isolate your boat from the marinas AC power with at least a galvanic isolator, or an isolation transformer, though this is expensive.

To answer why would you suddenly need a galvanic isolator, hmmm keeping it simple without getting into a whole lot of electrical power generation theory. Simply put, while most think of ground as zero volts this is actually not always the case, what we call ground is simply a common reference point to take a measurement from, and this point can differ from point to point depending on a multitude of conditions. Simply put, at your previous marina the AC voltage may have varied around a different voltage reference than at your current marina, resulting in increased zinc depletion you are seeing now. An example is shown in the picture I have included, on top is an AC signal, middle is a DC voltage level, bottom is the two signals combined, or summed together note the AC signal/voltage is riding the DC voltage level, if this is happening on your vessel then this could be the cause of increased corrosion.
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Last edited by CVAT; 08-03-2015 at 04:23 AM.
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post #10 of 45 Old 08-03-2015
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Re: Non active zinc suddenly VERY active.

Quote:
Originally Posted by L124C View Post
Other than not needing to replace the skeg zinc, what could that "problem" possibly have been? Prop was protected by the shaft zinc, and eroded at half the rate it is eroding at now. What was the problem?
The problem was that you had an anode that was not providing protection. That is why it lasted for 8 years.

BTW- You might want to consider learning to use the "Quote" function so conveniently provided with each post on this forum.
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