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post #1 of 31 Old 03-05-2014 Thread Starter
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Zincs

Hi, I have an Oday 30 that has lived all of it's life on the Great Lakes and has not needed any sacrificial metal protection to date. I would sure appreciate any help from you salt water sailors. I am pretty much at a loss on this issue.
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Phil
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post #2 of 31 Old 03-05-2014
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Re: Zincs

So.. what's the issue exactly??

..and welcome to Sailnet, Phil

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post #3 of 31 Old 03-05-2014 Thread Starter
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Re: Zincs

I thought that a boat in salt water had to have a sacrifiial metal to protect things like engine, mast, prop and shaft. Am I just borrowing trouble or is this an issue

Hey, I see why you ask about an issue, part of my post didn't make it through. I am thinking of taking my boat to salt water this summer. I should have proof read.

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post #4 of 31 Old 03-06-2014
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Re: Zincs

All boats with dissimilar metals in an electrolyte need protection, even in fresh water. I assume you haven't seen any external electrolysis, but it can occur where you can't see it as well. However, salt water is a much better conductor and more important to have a zinc attached to your shaft and/or prop, assuming you have an inboard.


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post #5 of 31 Old 03-06-2014
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Re: Zincs

salt water - zinc
fresh water - magnesium
brackish water - aluminum indium

For an anode to work, both mating surfaces must be clean and there must be good contact, something less than 1ohm resistance. Two out of 40 boats I recently checked in a yard had good continuity between anode and the metal to which it was mounted. This can be checked with any cheap multimeter.

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Re: Zincs

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Originally Posted by blewinn View Post
I thought that a boat in salt water had to have a sacrifiial metal to protect things like engine, mast, prop and shaft. Am I just borrowing trouble or is this an issue

Hey, I see why you ask about an issue, part of my post didn't make it through. I am thinking of taking my boat to salt water this summer. I should have proof read.
All good.. To answer your question, yes, you'll need a zinc and it doesn't need to be an expensive one. There's usually a spot on the prop and/or shaft to fit it to. Talk to the people at your friendly boat-yard.

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For an anode to work, both mating surfaces must be clean and there must be good contact, something less than 1ohm resistance. Two out of 40 boats I recently checked in a yard had good continuity between anode and the metal to which it was mounted. This can be checked with any cheap multimeter.
A zinc installed anywhere in contact with the electrolyte (salt water in this case) is capable of 'protecting' metals for a reasonable distance around it - not just the ones it's in electrical contact with - this is why it's possible to be 'overprotected' in certain marina situations. ..but being in electrical contact is certainly preferable.

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Re: Zincs

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A zinc installed anywhere in contact with the electrolyte (salt water in this case) is capable of 'protecting' metals for a reasonable distance around it - not just the ones it's in electrical contact with - this is why it's possible to be 'overprotected' in certain marina situations. ..but being in electrical contact is certainly preferable.
That is incorrect. An anode without a connection is just a piece of metal in the water. You have to think back to high school chemistry where a galvanic cell is created by immersing two different metals in an electrolyte and connecting them with a conductive wire. One of the metals become a cathode (more noble) and the less noble metal becomes an anode..... you have just built a battery ! The anode gives up electrons to the cathode. That is why they are called "sacrificial anodes". Without good contact there can be no galvanic current flow and therefore no cathodic protection.

Do not buy off brand anodes. Anodes from China can do more harm than good. Take a look at the Martyr website for more info. They make high quality products

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Last edited by boatpoker; 03-06-2014 at 05:30 PM.
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Re: Zincs

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That is incorrect. An anode without a connection is just a piece of metal in the water. You have to think back to high school chemistry where a galvanic cell is created by immersing two different metals in an electrolyte and connecting them with a conductive wire. One of the metals become a cathode (more noble) and the less noble metal becomes an anode..... you have just built a battery ! The anode gives up electrons to the cathode. That is why they are called "sacrificial anodes". Without good contact there can be no galvanic current flow and therefore no cathodic protection.
BoatP, you can build a perfectly good battery without connecting the anode and cathode together "with a conductive wire". An anode (zinc) and a cathode (most other metals) in an electrolyte (salt water) = a battery, and galvanic current will happily flow in the electrolyte. If this wasn't true, lead-acid batteries would never discharge on the shelf.

..at least, that's what we were taught in high-school chemistry.

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Re: Zincs

Do you understand what continuity is or what bond integrity is ? I suggest you visit the previously linked Martyr site and refresh your memory. Glavanic current needs a path it does not just jump around in the water at the millivolt levels involved in galvanism.

Or this report can explain it for you

When reading the report or looking at the Martyr site look for the terms "bond integrity", "electrical contact" and "coupled". All of these terms refer to continuity.

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Last edited by boatpoker; 03-06-2014 at 07:20 PM.
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Re: Zincs

Thanks for the replies. So pretty much if I have a zinc on the prop shaft and insure that everything metal on the boat is connected to the prop shaft as in grounded, I will be good to go.
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