Jump to content
Dozer

Aluminum anodes in salt water - can this be an issue

Recommended Posts

After purchasing the boat about 3 months ago, I replaced all the anodes on the outdrives.

I have noticed what looks like scaling on the stainless props and the trim piston rods. Also the new “C” rings on the trim piston caps are rusty and only been on the boat for less than a month when I replaced everything with brand new kits.

I purchased the anode kits from Amazon, so I decided to go back and look at exactly what I had purchased. They are aluminum and not zinc. My boat is in Salt water only, would the aluminum anodes not work as well as zinc anodes, and be the cause of the scaling (whitish looking coating) on my stainless props and trim piston rods?

The anode kit said its for salt and brackish water  Link to Amazon -- kits I purchased

 Thanks

Share this post


Link to post
Share on other sites

The scaling is likely due to aluminum molecules moving from the anodes to your stainless steel parts.  I get similar deposits in fresh water with my magnesium anodes.  This is likely because aluminum (especially the variants used in anodes) is a more active metal than zinc, so you're seeing more activity than you did with the zinc anodes.

On the C-rings,  is it possible that the replacements are of a different metal/lower quality than the originals?

Share this post


Link to post
Share on other sites

If your boat sits strictly in salt water, not brackish, the zinc anodes would offer a better protection than aluminum. The aluminum anodes work well in wide range of waters but the extreme ends of spectrum that is strictly fresh water (not much left), and strictly salt water. Check BoatZincs site for more info, they also offer a wide range of reasonably priced quality anodes including those made by Martyr.

For more detailed info check the answer to question T7 in the FAQ section on BoatZincs site ... BoatZincs FAQ

Share this post


Link to post
Share on other sites

Thank you all for your responses

I just ordered two new sets of zinc anodes -- now I have some serious fishing weights I can use.... :)

Share this post


Link to post
Share on other sites

I must say, that 99% of the time I agree with Richard. But............

I would call Merc and see what they recommend. BoatZinc.com is a great saltwater provider of anodes. They are based here in Mass and saltwater is really there thing. Not all anodes are made equally.

I have twin Volvos with AL and do not have that problem. OR maybe what you are seeing is the start of growth forming. I paint both my drives and props because the growth is quick and heavy.  In FL, it must be worse!    

Share this post


Link to post
Share on other sites

Well at this point I don't have much to loose - the new Zinc Anodes are on the way.

Also I noticed that the current Aluminum  anodes are starting to get a whitish chalky coating on them -- not sure if that is normal or not. On my other boats all I remember is the anodes would start feeling rough and overtime you could see all the pitting. Which is when I would change them. I wish there was a way to tell the difference between Zinc and Aluminum anodes...I'm not sure what the previous anodes were that I replaced. But they were fairly pitted when I removed them, specially the cone ones at the end of the props.

So once I install the new ones, I'll keep you all posted, hopefully that will take care of the problem

Share this post


Link to post
Share on other sites

You can feel the weight difference between Mg, Al, and Zn anodes ... Mg is very light, Al feels twice as heavy as Mg, and Zn feels twice as heavy as Al.

The whitish coating might indicate that Al is too active for your water. If enough scale forms it will insulate the anode from the waters the boat is in, and render it inactive.

The local water salinity and other mineral inputs/impurities, water temperature, etc make the difference. Also something to keep in mind, a stray current from the dock, marina, other boats or your own boat. If anything has changed, electrically speaking, where the boat moors, the life of anodes and other metals on the boat will be affected until the situation is rectified.

Keep us posted ...

Share this post


Link to post
Share on other sites

There is no easy answer!

Why?  The exact water chemistry, the metallurgy of your boat, the stray currents around you and the length of time the boat is in the water....all matter.  Then, there is the ACTUAL metallurgy of the anode.  They are all allows and not pure metal.

This is a good read 

https://www.boatingmag.com/how-to/choosing-right-sacrificial-anode

BTW, when aluminum corrodes, you get Aluminum Oxide.  It’s white.  If the anode is covered in it, it is no longer working.

Share this post


Link to post
Share on other sites

To support Rich W.

My 2002 original anodes went over 10 years with no attacking of Aluminum drive parts. It looked like a sponge.  BUT

We have NO electric power on the docks.

Share this post


Link to post
Share on other sites
7 hours ago, Dozer said:

Well at this point I don't have much to loose - the new Zinc Anodes are on the way.

Also I noticed that the current Aluminum  anodes are starting to get a whitish chalky coating on them -- not sure if that is normal or not. On my other boats all I remember is the anodes would start feeling rough and overtime you could see all the pitting. Which is when I would change them. I wish there was a way to tell the difference between Zinc and Aluminum anodes...I'm not sure what the previous anodes were that I replaced. But they were fairly pitted when I removed them, specially the cone ones at the end of the props.

So once I install the new ones, I'll keep you all posted, hopefully that will take care of the problem

anodes are starting to get a whitish chalky coating on them. That is normal, its like a powder. The questions is, how fast is this happening? You might a voltage leak, that is eating your anodes.  

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×