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Old 12-25-2018, 05:42 PM   #1
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Mixing aluminum and zinc anodes

Is there any harm in mixing the two? From what I am reading, it's OK to do. My boat is in salt water year-round (San Juan Islands, WA) and I have anodes on the transom, skeg, prop shaft, swim step struts, and bow thruster.
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Old 12-26-2018, 03:29 AM   #2
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Well, the zinc ones will disappear first based on the galvanic potential. Then, if there is a distance between whatever you are trying to protect and the aluminum anodes you will get some corrosion. In short, IMO, it makes no sense at all to mix different anode types.
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Old 12-26-2018, 03:35 AM   #3
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No you should not mix them unless one type is in the engine and the other type is on the hull or shafts. With two types of anodes in the same body of water, one will erode faster and the other will not be protecting the boat. Stick with one type.
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Old 12-26-2018, 07:26 AM   #4
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Agree mixing not recommended if in the same electrical cell. Wondering where you have read its OK?
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Old 12-26-2018, 07:59 AM   #5
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It is a good question. Did some quick reading and from what I found the aluminum anodes are more active. If placed on the same circuit as zinc they will protect all the metals including the zinc. It makes sense that if the aluminum goes first zincs will kick in later. If the metals are not connected (bonded) to one another no harm is done they will protect whatever they are attached to.

When I do bonding checks propeller shafts usually have the highest resistance connection to bonding systems. Keeping an anode(s) on the prop would seem to be good insurance. If you put an aluminum there and zinc everywhere else it would be depleted more rapidly negating your efforts.

Aluminum has not caught on in the area I am located (brackish) possibly due to lack of local inventory. I find a lot of sleepy zinc on hulls. Most are caked with a layer of general corrosion.

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Originally Posted by jhance View Post
Is there any harm in mixing the two? From what I am reading, it's OK to do. My boat is in salt water year-round (San Juan Islands, WA) and I have anodes on the transom, skeg, prop shaft, swim step struts, and bow thruster.
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Old 12-26-2018, 10:21 AM   #6
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Corrosion: Buying, Owning and Maintaining Boats and Yachts
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Old 12-26-2018, 10:27 AM   #7
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Good information on this site, I have purchased from them happy customer
https://www.boatzincs.com/faqs.html
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