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Old 09-08-2011, 08:21 AM
Laker Laker is offline
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Zinc in fresh water ?

I have been reading the Prop gone! thread , and decided to pose a question here as opposed to tagging on to that thread ...

I am in fresh water here in Lake Michigan. My float periods are relatively short , 4 months or so. My prop , shaft , and cutlass bearing casting are original (1966) and in good condition. I have no zincs. I see zincs on a lot of other boats hereabouts , but I have grown complacent regarding galvanic action.

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Old 09-08-2011, 12:58 PM
JOHN COOKSON JOHN COOKSON is offline
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R\E Zincs In Fresh Water

Are you on a mooring or in a marina?

If you are located in a marina during the summer zincs are a good idea.
If the marina is connected to shore power stray currents can devlope that will pull metal from the prop, shaft, or strut.

Metal junk on the bottom can under certain conditions act as a battery with the prop - not good

These marinas are described as "hot marinas".

It would be intersting to put a zinc on for the summer and see how much is consumed.

TRUE GRIT
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Old 09-08-2011, 01:09 PM
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Quote:
Originally Posted by Laker View Post
My prop , shaft , and cutlass bearing casting are original (1966) and in good condition. I have no zincs.

I submit that you have your answer.
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Old 09-08-2011, 01:34 PM
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It's called Electrolysis. Other boats going by give off Electrolysis. This can attack the metal parts of your boat. The Zincs take up most of the Electrolysis. Zincs are sacrificing plates. In a marina you can hang zincs over the side. They don't have to be attached to your metal parts.
Your boat when under power gives off the same Electrolysis. On slow moving boats under power...it's a magnet for sharks.
Eels draw Electrolysis from salt water. It is a power man has not yet learned how to tap into.
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Old 09-08-2011, 02:07 PM
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Quote:
Originally Posted by domenic View Post
It's called Electrolysis. Other boats going by give off Electrolysis. This can attack the metal parts of your boat. The Zincs take up most of the Electrolysis. Zincs are sacrificing plates. In a marina you can hang zincs over the side. They don't have to be attached to your metal parts.
Your boat when under power gives off the same Electrolysis. On slow moving boats under power...it's a magnet for sharks.
Eels draw Electrolysis from salt water. It is a power man has not yet learned how to tap into.
Uhm...

I'm not a chemist, but let's see if we can't clear one or two things up here.

Electrolysis is not radiation or something that is "given off" by a boat. In our application, the more technically correct term than "electrolysis" is galvanic corrosion. It is a chemical reaction that occurs between two dissimilar metals when in proximity to each other in an electrolyte. An electrolyte is a solution that conducts electricity. Salt water is an electrolyte.

Different metals have different tendencies to be more or less electrochemically active in an electrolyte. The more "noble" a metal is, the less likely it will be galvanically corroded. The more "base" a metal is, the more likely it will be galvanically corroded.

When you have dissimilar metals (e.g., steel and bronze) in proximity in a conductive solution, the difference in potential between the two metals causes a gradual flow of electrons from one to the other - they essentially are functioning as the anode and cathode in a battery, and cause a weak electrical current to flow. The more base metal between the two will be galvanically corroded. As between stainless steel and bronze, bronze is more base, which is why a bronze propellor on a stainless steel shaft in salt water eventually will look like it has dissolved in acid - the bronze will be subject to galvanic corrosion because it is more base than the stainless steel shaft.

If there is a source of an impressed current nearby - like a bad ground on wiring in a marina - it can greatly accellerate the process.

The rate of the reaction is affected by the difference in "nobility" of the two metals, the distance between them, and the electrolyte.

The reason a zinc works is because zinc is way down at the bottom of the "base" metals, while stainless is much higher up near the "noble" metals. Bronze is a little lower than stainless, but is higher than zinc. Zinc is more galvanically reactive than bronze or stainless steel. So rather than the reaction occurring between the steel and the bronze, with the bronze becoming galvanically corroded, the reaction will occur bewteen the steel and the zinc - and the bronze and the zinc - with the zinc being galvanically corrorded.

I'm completely confounded by the statement that it is a power man has yet to learn how to tap into. Man has been using elecrolysis and various types of electrochemical reactions for at least 200 years. There is evidence that the ancient Egpytians constructed electrolytic batteries - although they might not have fully understood the physics and chemistry behind how they worked.

The principles and mechanics of electrolysis and galvanic corrosion are very well understood today and it is used on an industrial scale to extract very high-purity metals.

Electric eels do not "draw electrolysis" from salt water. Again, electrolysis is not a substance or matter, or even a mysterious energy field. It is a reaction. Electric eels generate a current using highly specialized organs that actually resemble a multi-plate battery. The organs take advantage of these same principles and use sodium, which is a charged ion, to generate sudden short burst of electricity.
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Old 09-08-2011, 02:30 PM
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My understanding of electolysis is that in a marina while hooked up to shore power you can do the most damage. For example and this is not scientific, but here it is. My boat was hooked up to shore power all winter and my friends boat was not. We both have martec folders and similar shafts etc. Once the water became warm enough to get into it probably around June or so I jumped in and found my prop was fouled with some hard stuff which I think is electrolysis. I checked my friends boat and his had none of this. We both have zincs on our shafts and they were partially eaten up.

I have discussed this with other people who appear to be in the know and they indicate that stray current is pulled into you prop and shaft when hooked up to shore power and that you won't get it when not hooked to shore power. In other words the stray current goes into your prop and shaft trying to find a ground. Also, I am in fresh water.

I guess the long and short of it is zincs are cheap shafts and props are not.

DVD
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Old 09-08-2011, 02:30 PM
hanleyclifford hanleyclifford is offline
 
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I wonder if Laker has a bronze driveshaft. Having a bronze prop and shaft would greatly reduce the strength of the electrochemical reaction.

Last edited by hanleyclifford; 09-08-2011 at 02:41 PM.
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Old 09-08-2011, 02:34 PM
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I LIKERUST....

I read that some years ago. It is not correct. Testing on the matter started in 1945 from data taken from the Germans.
It seems if I post it is day time, you would say it is night. If you have some sort of problem with me, stop talking around your elbow to get to your thumb, and spit it out.

Last edited by domenic; 09-08-2011 at 02:36 PM.
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Old 09-08-2011, 02:43 PM
hanleyclifford hanleyclifford is offline
 
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Not to stir the pot unduly but...strictly speaking electrolysis is the decomposition of water into it's component parts, hydrogen and oxygen.
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Old 09-08-2011, 02:48 PM
JOHN COOKSON JOHN COOKSON is offline
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Rust observed in post #3 no problems so far.

DVD, in post #6, said zincs are good insurance.

Both are right.

TRUE GRIT
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Old 09-08-2011, 03:05 PM
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I used to design, and build ABS approved T vessels. I know a little about boats. I have been a part of groups that have done research on the subject of electolysis. And yes, America is not the only country doing research on powering vessels using electolysis.
I have always felt looking for the Fountain of Youth a more worthwhile venture.

Here is a little project kids have been doing for years.

Science Projects - Splitting Water
We use chemically- made electricity to power many ... out of the water similar to the process called electrolysis. ... Energy Story | Science Projects | ...
www.energyquest.ca.gov/projects/split_​h2o.html - Cached

Last edited by domenic; 09-08-2011 at 03:24 PM.
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Old 09-08-2011, 03:38 PM
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Quote:
Originally Posted by domenic View Post
I LIKERUST....

I read that some years ago. It is not correct. Testing on the matter started in 1945 from data taken from the Germans.
It seems if I post it is day time, you would say it is night. If you have some sort of problem with me, stop talking around your elbow to get to your thumb, and spit it out.
Wow, don't know where this came from.

I have no problem with you. I also don't beat around the bush and have no hidden agenda or ulterior motive. I am merely stating the facts regarding galvanic corrosion. If I see someone post something that I believe to be incorrect, I see nothing wrong with submitting information I believe to be more correct. It has nothing to do with who posted it. It seemed to me from your previous post there was some misunderstanding on your part as to what galvanic corrosion actually is and what causes it, particularly when you stated that certain things "give off" electrolysis and that eels draw it from salt water. These statements are incorrect.

I don't know what your'e referring to with any of your most recent statements above - in particular, what is it that you're saying "is not correct"?

As I mentioned above, even though everyone uses the term "electrolysis," the more correct term for what we're talking about is "galvanic corrosion." And as Hanley correctly points out, electrolysis actually is more correctly a term used to describe the splitting of water molecules into oxygen and hydrogen though the use of a cathode and an anode in solution with an applied electric current. This process was used as least as early as 1800. This is historical fact. The use of electricity applied to electrodes in an electrolytic solution to extract very pure metals from the solution has been in practice for over 100 years. That too is historical fact.

The fundamental principles of electrochemistry are the same, so in general the process of electrolysis is related to the process of galvanic corrosion, so everyone simply uses the term "electrolysis" to describe the process.

Your last post seems to be referring to the use of electrolysis to separate hydrogen from water, which can then be used as a fuel, such as in a hydrogen fuel cell. That is quite a different thing from what we're talking about here.

I have no desire to engage in a pi**ing match on an internet forum. Been there; done that; I've been on internet forums and mailing lists for over 15 years; it's completely fruitless and I'm over it. I think what's happened is a simple, old-fashioned misunderstanding. I see no need to take it as a personal attack, because I assure you it's not.
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Old 09-08-2011, 03:50 PM
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RUST SAID:
"I think what's happened is a simple, old-fashioned misunderstanding. I see no need to take it as a personal attack, because I assure you it's not."

I will take it as that.
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Old 09-08-2011, 09:03 PM
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Laker - If I had a boat in Lake Michigan I would have a zinc on that prop. "Fresh water" still has electrolytes other than sea salt and zincs are cheap but props are not. The zinc would probably last a long time especially if your shaft is bronze.
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Old 09-08-2011, 09:10 PM
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This may help the discussion:
http://corrosion-doctors.org/Forms-g...-corrosion.htm
Note that galvanic corrosion and stray current corrosion are two different beasts, the latter being supercharged.

The stray current variety is the bane of marinas regardless of what type of water.
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Old 09-08-2011, 09:11 PM
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Smile

What Hanley said, especially if you are on a marina that has power. You never know what you are docked next to. We have an area of our marina that extends toward the Navy Jetty...the boats closer to that have their zincs eaten more the closer they are docked in relation to that Jetty. It has power rigged out there everywhere for any conceivable requirement.
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Old 09-08-2011, 10:19 PM
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In salt water you use "zincs", fresh and brackish you use aluminum, and magnesium.
Right????
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Old 09-08-2011, 10:29 PM
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Question

Quote:
Originally Posted by Ball Racing View Post
In salt water you use "zincs", fresh and brackish you use aluminum, and magnesium.
Right????
Interesting notion and I have read that somewhere else, too. What intrigues me is that zinc lies between magnesium and aluminum near the bottom (anodic) end of the series chart; so how come they are both better than zinc in fresh water?
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Old 09-08-2011, 10:35 PM
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I read that zinc in fresh water forms a "skin" over it as a first reaction,
therefore it can no longer erode away. Making it no longer the sacrificing metal.
The others types seem to not form a protective skin over themselves.
But I have no hands on data to show this as proof positive.

Daniel
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Old 09-08-2011, 10:45 PM
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Smile hmmm

Interesting. Can anyone explain to me why the zincs near (what I think is electricity) don't last as long...I just heard it happens but not sure why.
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Old 09-08-2011, 11:26 PM
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I'm in fresh water.
My zinc is 6 years old and looks almost new.
I'm also on Shore Power.

Just lucky?
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Old 09-08-2011, 11:45 PM
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Quote:
Originally Posted by Maurice View Post
Interesting. Can anyone explain to me why the zincs near (what I think is electricity) don't last as long...I just heard it happens but not sure why.

Mo,

One cause of stray currents is from other boats nearby that are not properly protected. This is an excerpt from my Galvanic Isolator project on my website (http://www.chessie.com/boat/projects.shtml) that explains it and what to do about it:

============

...Soner or later, every boat owner gets introduced to the galvanic corrosion that happens when you put two dissimiliar metals that are electrically connected into saltwater. You quickly learn to install and maintain an appropriate number of zincs to protect your valuable underwater hardware, such as through-hulls and prop shafts.

What some don't know, however, is that it's possible to do everything right and still have galvanic corrosion! The problem happens when you're connected to shore power. Even if all your A/C devices, like your battery charger, are transformer isolated, there's still the safety ground. This is connected directly to your boat's system ground, to which all your underwater hardware is bonded. As a result your boat's ground, through the marina's wiring, is now connected to every other boats grounds and hardware! And if any of them aren't properly protected, they'll cause a galvanic current that'll start eating your zincs! This uses them up too quickly, and then least noble of your hardware starts going.

The obvious solution is to disconnect the safety ground. But this is a serious safety hazard unless you are absolutly sure that everything is transformer isolated, and remains that way. So, what we really want, is something in series with the safety ground that doesn't conduct most of the time, but will conduct the full service current in case of a short.

It turns out that there is such a device. It depends on the fact that virtually all galvanic circuits are driven by only a few tenths of a volt. A silicon diode drops about 0.6 volt. Below this, it doesnt conduct at all. Above this, it conducts heavily. Since 0.6 volt isn't really enough, we put two in series for 1.2 volt. And since diodes only conduct in one direction, we put another pair in parallel in the opposite direction.

This is basis of a galvanic isolator. Real-world devices are more complicated, including things like fail-safe, A/C leakage bypass, and monitoring. But at their heart, there are four diodes. ...
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Old 09-09-2011, 01:26 AM
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Smile Excellent explanation

Thanks Edward,

I got it...very well presented. I looked at your site....nice job!!
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Old 09-09-2011, 08:32 AM
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Thanks , gang. My shaft is SS . I have very little exposed shaft. (Raised Catholic , very modest.) I am in a marina. I generally do not keep the shore power rigged unless there is a specific need ; power boats either side of me are on all the time. Prior to my 7-8 year renovation layup which ended last year I know I had wiring/grounding problems for a variety of reasons , including the unpleasant experience of nearly being put on my ass when brushing my arm against the centerboard pennant! That has not happened since re-wiring. As previously stated , my old prop is in good shape , as is the bronze intake strainer which I removed , sand blasted (walnut shells , not glass beads) and re-installed recently.

Soon the yard will fill with laid up boats up here at 43 dg north , and will take a tour to see which sailboats have zincs and where they are located.

Parting question : with no space available on the prop shaft , what is a good location for zincs on a sailing hull.

All in the interest of preventing electrogalvonics...
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Old 09-09-2011, 09:41 AM
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This is the best zinc solution I have found.

Last edited by hanleyclifford; 07-13-2016 at 09:33 PM.
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