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Old 19-04-2011, 21:22   #16
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Re: What do you Zinc?

Button zincs. I take the two halfs and open them up. Take the screw off, put the new button on, all done. Funny enough I go through button zincs on my rudder straps faster than my shaft zinc.

Replace your own zincs if you can. A lot of commercial divers (not all, but a lot) are rip offs and replacing zincs that are fine. Mine last me roughly six months and the previous diver (before I dove myself) was changing them every 1-2 months.
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Old 19-04-2011, 22:06   #17
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Re: What do you Zinc?

Totally agree with Rebel heart. Something else you can do to reduce the zinc errosion is to hang a sacrificial big zinc over the stern when at anchor or in a marina. These look like a zinc fish with a stainless line attached. The connecting cable is attached to your common bond point.
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Old 19-04-2011, 22:17   #18
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Re: What do you Zinc?

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Originally Posted by Lancerbye View Post
Totally agree with Rebel heart. Something else you can do to reduce the zinc errosion is to hang a sacrificial big zinc over the stern when at anchor or in a marina. These look like a zinc fish with a stainless line attached. The connecting cable is attached to your common bond point.
You know I always wondered what the hell people were doing with that.
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Old 20-04-2011, 05:11   #19
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Re: What do you Zinc?

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Originally Posted by At sea View Post
... Personally, I have never believed it and have acted accordingly and with no adverse consequences to date. I wait till an anode is 90% gone and then replace it. I judge that the last 10% would do as good a job as the first 10% but am mindful that being left with no protection is not worth the risk in extracting that last little bit.

To my mind, if there is some zinc left then the anode has the capacity to do the job that it is designed to do. My experience says this theory holds true...
You don’t appear to understand how sacrificial anodes work, and you're absolutely wrong.

The amount of protection a zinc anode provides depends on its surface area. It takes a zinc with about 1% the surface area of the metal it’s protecting.
The longevity of a sacrificial zinc anode is a function of its weight and composition.

As an anode is “consumed”, it loses both mass and surface area, reducing it’s electrical effectiveness.

Sacrificial Anodes: Aluminium Sacrificial Anodes,Zinc Sacrificial Anodes,Magnesium Sacrificial Anodes,Bracelet anodes,Cathodic Protection Systems

Anode - Calculation

http://www.performancemetals.com/ima...m%20Anodes.pdf
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Old 20-04-2011, 05:18   #20
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Re: What do you Zinc?

As the zinc corrodes is it preventing OTHER bronze parts from "suffering" or is the zinc taking most of the hit and the more zinc the more it takes.

Can someone explain exactly what happens down there?

Let's set this up.

Six New bronze prop, new bronze thru hulls. Boats are side by side in slips in a 400 boat marina in salt water. All have shore power connected... boats are identical. Zincs are on prop shaft.

Boat A - no zinc
Boat B - zinc with 6 square inches of surface area
Boat C - zinc with 12 square inches of surface area
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Old 20-04-2011, 05:47   #21
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Re: What do you Zinc?

A surveyor once told me that you could over zinc a boat. I had trouble following that claim thinking that the more zinc you used the better the protection, but he explained it by saying that the larger quantity of material would cover a larger area of water and thus more ions flowing. The protection would still be there, but why put more than you need. No explaination as to how you determine the optimum amount of zinc to use.
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Old 20-04-2011, 06:24   #22
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Re: What do you Zinc?

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Originally Posted by At sea View Post
Those whose minds are closed - like Illusion - need not apply. Allow those of us who like testing rather than swallowing to go about our merry ways.
Waiting for the smoke to clear...
So I take it you can not
enlighten the rest of us idiots on the chemical composition of a typical zinc anode and how you can determine it's true composition by sight once partially eroded?


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Old 20-04-2011, 06:41   #23
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Re: What do you Zinc?

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Originally Posted by At sea View Post
Personally, I have never believed it and have acted accordingly and with no adverse consequences to date.
How do you know that you have not suffered adverse consequences? Have you had the chemical composition of your bronze prop tested? When bronze starts to show obvious signs of electrolysis, the damage is done and cannot be reversed.

What is the current percentage of cooper in your underwater bronze fittings? Is it the same as it was when it was new? How do you know?

The recommendations to change zincs based on wear is based on chemistry and scientific facts, not anecdotal beliefs.

With your system of zinc maintenance, you will be correct right up until the time when you discover that you were wrong. It will be an expensive lesson.
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Old 21-04-2011, 05:43   #24
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Re: What do you Zinc?

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Originally Posted by S/V Illusion View Post
Spend the money and replace it/them or risk sacrificing much more expensive parts - your choice.
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Originally Posted by GordMay View Post
You donít appear to understand how sacrificial anodes work, and you're absolutely wrong.
Quote:
Originally Posted by doug86 View Post
The recommendations to change zincs based on wear is based on chemistry and scientific facts, not anecdotal beliefs.
At the risk of further upsetting members quoted above, I will now divulge that I have never had a shaft anode on my steel vessel for the past 30 years. And contrary to the views of herd members, neither my shaft nor prop has exploded mid ocean and both are still in perfect working order.

But to Doug86 and doubtless the others this is 'just mere and unreliable anecdotal evidence' and, as such, it is to be discounted because you won't find it in the text books or the sales blurbs.

My reasoning (a foreign concept, it seems, to some) for taking such an approach is that while acknowledging that some galvanic interaction will occur between the bronze propeller and the stainless shaft, they are so close to each other on the electrolytic scale that there is seldom accelerated corrosion, and especially so if the propeller is painted.

And the proof of the veracity of this reasoning is in the pudding.

So for those whose minds are still open on such issues, I suggest trying it and reporting your experiences to our board.
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Old 21-04-2011, 06:10   #25
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Re: What do you Zinc?

Quote:
Originally Posted by At sea View Post
... I wait till an anode is 90% gone and then replace it. I judge that the last 10% would do as good a job as the first 10% ...
... To my mind, if there is some zinc left then the anode has the capacity to do the job that it is designed to do. My experience says this theory holds true ...
Quote:
Originally Posted by At sea View Post
...I will now divulge that I have never had a shaft anode on my steel vessel for the past 30 years ...
... neither my shaft nor prop has exploded mid ocean and both are still in perfect working order ...
Two, differing, propositions.
As I said (post 19), your first proposition is absolutely wrong!
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Old 21-04-2011, 06:58   #26
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Re: What do you Zinc?

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Originally Posted by At sea View Post
This is a claim that everybody seems to make but I'd suspect that 99% of the claimants are just repeating what they've heard rather than having independently determined its veracity.

Personally, I have never believed it and have acted accordingly and with no adverse consequences to date. I wait till an anode is 90% gone and then replace it. I judge that the last 10% would do as good a job as the first 10% but am mindful that being left with no protection is not worth the risk in extracting that last little bit.

To my mind, if there is some zinc left then the anode has the capacity to do the job that it is designed to do. My experience says this theory holds true.

Keep in mind that the anode depletes at the same rate (under the same conditions) no matter what its original size, and 50% remaining of a 5kg anode is 100% of a 2.5kg anode. That is, half the big one is exacly the same as a whole (brand new) smaller one.

I also figure I've saved a bucketload of cash over the years by using the anodes for their near full useful life.

Convince me otherwise

Re the underwater changeover query, I'd never do it. Scrubbing the anodes to see just how much zinc is left is easy underwater and should be done but that's all I'd do. Best to careen against a pole or wall or do a quick slipping and make sure the job's done properly imo.
I have in fact done thousands of hours of "research", during my "boat building" 21 years... It helped keep me going! However, I mostly base my opinions regarding Zincs on 40 years of experience & thousands of dives.. First, I hammer tap the Zinc home when screwing it down snugly...

I wipe down my hull with a kevlar gloved hand every time I take the boat out, (unless moving every day or so), and inspect the zinc each time. One needs to scrape the scale off of the surface to expose new Zinc, or just wipe the slime off if that is all that's on there. (It won't work as well if sealed away from the water by scale.)

Also.... they need to be replaced when half way corroded away because to varying degrees, the electrical contact with the shaft becomes more tenuous over time, due to scale, growth, and slight removal of the inner Zinc surface. Also, the material becomes more porous, weaker, the threads on the screw closer to failure, and the Zinc is close to sliding down the shaft or flying off, due to this loosening & weakening characteristic. At "half way gone", the wall thickness on the outer part of the screw hole is almost down to "0"! It otherwise has nothing to do with what volume of Zinc is necessary to continue protection.

My prop was $1,000, and the glassed in strut is bonded to the shaft internally, so it is protected by the shaft Zinc too. I have a lot to loose if a Zinc comes off. Even with this level of care, I have had them both slide down & fly off. Luckily I caught it in time.

I take my half used Zincs to West Marine. They send them off to be melted down into new usable Zincs. If you save enough of them over time, you can sell the metal to a recycler.

Best of luck, Mark

You can see from this photo... When I was left high & dry on a side creek of the Georgia ICW, due to inaccurate soundings and an unusually high tide, I noticed that my properly installed and recently inspected Zinc (10 days back), had loosened and slid down the shaft. New Zincs seldom do this!
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Old 21-04-2011, 06:59   #27
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Re: What do you Zinc?

Quote:
I will now divulge that I have never had a shaft anode on my steel vessel for the past 30 years. And contrary to the views of herd members, neither my shaft nor prop has exploded mid ocean and both are still in perfect working order.
First you said that you always waited until it was 90% gone, now you admit you never had one to begin with. How can your 30 years of not using a shaft anode possibly have any bearing whatever on the issue of shaft anode erosion?

Quote:
But to Doug86 and doubtless the others this is 'just mere and unreliable anecdotal evidence'
.

If you are going to use quotes, at least be accurate. I never used the words mere and unreliable.

Quote:
while acknowledging that some galvanic interaction will occur between the bronze propeller and the stainless shaft, they are so close to each other on the electrolytic scale that there is seldom accelerated corrosion, and especially so if the propeller is painted.

Some galvanic interaction
might be fine with you, but perhaps those who choose to limit that to the smallest degree possible through the use of sacrificial anodes are not just victims of a hoax perpetrated by the unthinking masses, but are actually accomplishing something.
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Old 21-04-2011, 10:04   #28
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Re: What do you Zinc?

Quote:
Originally Posted by Mark Johnson View Post
... Also.... they need to be replaced when half way corroded away because to varying degrees, the electrical contact with the shaft becomes more tenuous over time, due to scale, growth, and slight removal of the inner Zinc surface. Also, the material becomes more porous, weaker, the threads on the screw closer to failure, and the Zinc is close to sliding down the shaft or flying off, due to this loosening & weakening characteristic. At "half way gone", the wall thickness on the outer part of the screw hole is almost down to "0"! It otherwise has nothing to do with what volume of Zinc is necessary to continue protection ...
Wrong.
It has everything to do with the electro-chemical issues related to surface area & mass (both related to volume), as well as the peripheral mechanical issues you mention.
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Old 21-04-2011, 12:56   #29
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Re: What do you Zinc?

I swapped out an old "Atomic4" with a Perkins 4108 in my boat and installed a shaft isolator between the gearbox and propshaft. The shaft and prop are both bronze and the only zincs I've used in 24 years are pencil zincs in the engine cooling system. For 13 years prior to the engine swap I used a shaft zinc that was changed anually as the only zinc on the boat. The boat is fibreglass and in salt water and is hauled every third year for bottom paint and inspection/maintainance. I cant find any damage or galvanic erosion or even discoloration (pink) on thru-hulls, transducers, prop or shaft and I've promised myself to re-install the shaft zinc if any shows up. The boat has never been bonded and has never seemed to need it. I suspect this is somewhat unusual but it's been working too long for me question it
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Old 21-04-2011, 13:08   #30
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Re: What do you Zinc?

Jesse, glad to hear your confirmation that all the years of chemistry that predicts that there would be no galvanic corrosion between two surfaces of the exact same metal is true.
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