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PostPosted: Mon Aug 30, 2010 4:33 am 
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Location: Saint Johns, Florida
Chekika wrote:
You are absolutely right, Jerry. When I attached zn electrodes to my AI (& my wife's AI), the assumption was that most of the corrosion is coming from use in salt water. One person suggested to me to run a wire from the electrode down into the water--probably a good idea, but I have not done it. I have 4 electrodes, 2 on each side--attached near the SS pin at the aka/x-bar hinge. When out sailing, I hope that there is a salt water link between the aluminum aka, the pin, and the anode.


Keith,

I have heard of attaching the zincs to wires hung over the side and attaching the wire to whatever you want the zinc to protect but it sounds like you're planning to keep the zincs out of the water and run a wire from them into the water. I don't think it will work.

Another thing is that it is my understanding that the zincs were used to prevent the corrosion due to the different electrical potentials created by connectig a boat to shore power. In some marinas the water was so "hot" that you could loose your zincs very quickly and in others they would seem to last forever.

I have owned 4 diferent boats, both sail and power, all of which had zincs installed in all the recommended places. All of the boats would get corrosion around a stainless screw used in aluminium unless something was used to coat the screw to prevent the local electrolysis. I think you can install zincs all over an AI and still have corrosion problems.

I asked before and got no replies but I'll ask again. Has anybody that is using zincs had them start to dissolve? If they are doing any good they will dissolve.

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PostPosted: Mon Aug 30, 2010 9:03 am 
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Location: South Florida
Jerry,

You are not going to get significant dissolving zn anodes unless you have them in the water continuously--that is not going to be the case with AI/TIs. The zn is a sacrificial metal which corrodes when there is an electrical contact made between the aluminum-steel-zinc. Salt water contact between the metals greatly facilitates the process. If the zn is not part of the equation, the aluminum is the sacrificial metal. I understand there are electrical currents on boats in marinas which may add another factor, but it does not change the basic equation.

I'm not sure why you think running a wire from the zinc to the salt water would not work. It would assure a contact between the zn-salt water and the Zn-Aluminum-steel. This should facilitate the corrosion of the Zn rather than the aluminum

I'm currently in a motel in West Yellowstone typing this. It is about 40 deg and raining--so my wife, Nancy, and I are taking a break. We will be heading out to camp along the Lamar Valley in an hour. I will be looking forward to seeing this thread when back in touch.

The sun just peaked out.

Keith

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I sail: Key Biscayne, Everglades to Cape Romano, Ft Desoto, Cedar Key

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PostPosted: Mon Aug 30, 2010 12:07 pm 
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According to a guy named Jim, a technical support person at Galvotec Alloys, Inc., a company that manufactures and sells zinc and aluminum sacrificial anodes, a zink will not do any good unless the zink is submerged in an electrolyte (water).

I described our boats and he said zinc anodes will do nothing to protect them from corrosion.

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PostPosted: Tue Aug 31, 2010 7:17 am 
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dosjers wrote:
zinc anodes will do nothing to protect them from corrosion... unless the zinc is submerged in an electrolyte (water)

Disagree.

First, note that Aluminium will corrode aerobically (ie, in air), but quickly forms an aluminium oxide layer that actually protects it to a good degree from further corrosion. Doesn't stop it entirely, but slows it a big heap. "Unlike steel, when aluminium corrodes the resulting layer of oxidation is air-tight and rock hard, keeping the material underneath very highly protected. Even scrapes and scratches will form their own protective coat over time."

Galvanic corrosion, which is a way bigger problem however, does not require "continual immersion". In our yaks, we have periodic immersion... well, they periodically get wetted by salt water anyway... but then we store them. That salt water "dries"... or does it? Actually salt is strongly hygroscopic, so it absorbs water from the atmosphere.

This absorption of water by the 'dried' salt provides a concentrated electrolyte, which enhances the galvanic reaction... kinda like adding an overly-strong acid to your car battery. Decades ago, I lived in a flat close to the ocean for a while, and saw mega corrosion of aluminium framed windows, which had been installed with steel screws. Over the last decade, I've done a lot of camping, mostly ocean-front. Any aluminium in contact with steel (such as screws etc) was rapidly destroyed.

Ideally, we should all thoroughly wash down our yaks with fresh water - and every piece of gear we use - after every salt water outing. But even if we actually did do that, we still wouldn't get rid of all the salt in every nook and cranny.

To protect our investment, it would be cool if Hobie would offer a custom zinc sacrificial anode - maybe something that could simply slip inside the aka cross braces.

In the meantime, I'll be looking for a suitable zinc anode to fit inside a x-bar myself!

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PostPosted: Tue Aug 31, 2010 1:36 pm 
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Max,

I'm not going to argue with you. All I am going to say is the information I got was from a technical support person in a company that manufactures and sells zinc and aluminum sacrificial anodes.

Personally I'm not going to waste my money on them but if they make you feel better then knock yourself out.

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St. Johns, Florida
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