Zincs are going fast

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Zincs are going fast

Postby Ereiss » Sun Nov 11, 2012 9:43 pm

Went to the boat today, first view after hauling, and found that the max-propos zinc is entirely gone and the two zincs on the shaft are well worn. These were put on fresh in August.

I'm wondering if the installation of the wind generator could lead to increased zinc consumption. Don't recall them going this fast prior to the installation but perhaps there have been other changes in the waters in Marion.

Any ideas how to test (next summer) for electrical leakage? Does anyone else find this amount of zinc consumption going on?

as always, appreciate your thoughts and suggestions.
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Re: Zincs are going fast

Postby GeoffSchultz » Mon Nov 12, 2012 7:34 am

Do you have a galvanic isolator on your 120V feed? The problem with zincs could easily be due to another nearby boat or the marina's electrical feed and not be related to you. There are meters which read the amount of protection that you have, but these meters are expensive and are typically only owned by boat yards.

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Re: Zincs are going fast

Postby Ereiss » Mon Nov 12, 2012 8:49 am

Actually never at a dock. All the zinc activity occurred at a mooring that is not near the docks. Guess next spring will try measuring stray voltage by connecting one end of gauge to prop shaft and other end in water (will that work?).
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Re: Zincs are going fast

Postby Salacia » Mon Nov 12, 2012 11:02 am

Hi Ed,
We were discussing this very thing at a recent club meeting. A lot of people experienced that this summer. General consensus is t hat warmer water speeded up the electrolysis. No scientific evidence. Just that you aren't the only one to experience this problem. Did you get aggressive barnacle growth also?

Stephen Lee
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Autopilot ST4000 problem

Postby Jack Woods » Mon Nov 12, 2012 4:46 pm

This is interesting.
I've had my boats in the same slip and marina for twenty odd years and my zincs
allways look close to new at haulout. This year was my first with the Freedom
(it doesn't have shore power) and at haulout the poor condition of the zincs was very
noticeable....

Jack
Last edited by GeoffSchultz on Mon Nov 12, 2012 6:12 pm, edited 1 time in total.
Reason: This appears to have been posted to the wrong topic & I spilt/merged it into this one.
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Re: Zincs are going fast

Postby Ereiss » Mon Nov 12, 2012 5:31 pm

didn't see abnormal barnacle growth but it could reflect my super premium bottom paint or the bottom scrubbing that I got in August. But the zinc on the max-prop was GONE and it was only put on in August, I was surprised.
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Re: Zincs are going fast

Postby peaceandfreedom » Mon Nov 12, 2012 6:27 pm

Something is going on with these zincs this year. For the first time in seven years my zinc was completely gone , and two zincs on a friends boat were gone as well.
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Re: Zincs are going fast

Postby rvivian » Mon Nov 12, 2012 11:36 pm

I have two "egg" zincs on my prop shaft and one is generally chaged out every three months.

A few years ago I had prop zincs at the same site that never showed any erosion.

I think the zincs that didn't erode were a different brand and a different metallurgy. Perhaps some EPA (or other ) regulation has changed what the zincs are composed of.

I think the newer zincs are just doing their job (better).
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Re: Zincs are going fast

Postby philipl » Tue Nov 13, 2012 3:28 pm

Mine too. Completely disappeared. I thought it might have vibrated loose as I felt a slight prop shaft vibration at the beginning of the season.
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Re: Zincs are going fast

Postby dwight » Wed Nov 14, 2012 12:54 pm

Zinc anodes are installed to protect expensive underwater metal from galvanic corrosion. A galvanic cell is formed by two or more, "dissimilar" metals (your zinc anode is one-half a galvanic cell); electrically connected together, (the bonding system or direct contact provide this electrical connection); immersed in a common electrolyte (the ocean). The difference in electrical potential of the two metals causes an electrical current to flow. The electrons in this flow come from the destruction (corrosion) of molecules from the "least noble" (more negative) metal (the anode). These electrons flow through the electrical connection between the two metals to the "cathode," then combine with ions in the electrolyte to flow back to the anode to complete the circuit. By selecting the metal used for the anode, we can control which metal corrodes and which metal is protected (Cathodic Protection). Any other metals in the electrolyte not electrically connected to this cell are in "free corrosion" and will not affect your zincs (anode).

Stray current is similar to galvanic corrosion in that the corrosion is driven by a difference in electrical potential. With stray current, the difference is caused by an external power supply. The size of this difference can cause severe corrosion to occur in weeks, days, or in extreme cases, even hours.

A galvanic isolator can protect your boat from galvanic corrosion caused by other boats connected to the same shore power system. These devices are highly recommended for boats living in marinas connected to shore power. Unfortunately, they can be overcome by stray current rendering them useless.

Marinas are difficult places to evaluate galvanic and stray current corrosion because they are dynamic. The level of corrosion can vary with the number of boats present and/or connected to the system. If you find you have a problem one day but not the next, it helps to try to determine what boats are present when the problem is evident.

There are electrical tests that can evaluate the level of corrosion and determine if it is galvanic or stray current. These tests can also be used to help identify the source of the stray current. It is also possible that stray current from nearby boats in a marina to cause corrosion on your boat, even if your boat is not connected to the shore power system. In answer to Ed's question, sticking the test lead of your meter in the water will some cases, expose stray current. The trick is to know where to connect the other test lead and to understand what it is telling you.

The Boatowner's Guide to Corrosion, by Everett Collier is used as the textbook for the ABYC Corrosion Certification Class. While it does a thorough job to documenting the subject, it can be difficult to understand in some areas and does not detail the electrical tests used to identify problems.

I am an ABYC Certified Corrosion Technician and currently teach their corrosion certification classes. I worked as an engineer at Freedom Yachts and owned Freedom 36 #71 for many years. In addition to services as an independent marine surveyor, I am available to evaluate complex electrical and corrosion problems on all boats not just Freedoms.
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