Aluminum Anodes

Does anyone have experience with aluminum anodes versus zinc anodes in saltwater? All I have read says they are at least equal or better. West Marine will no longer be carrying zinc anodes so aluminum looks like the future.

Tom

Tom,

I'm not an expert. We have a member that cleans boat bottoms and changes anodes for a living. Perhaps he'll chime in here.

I believe that aluminum is for fresh water and zinc is more suited for salt water (???).


Edit: look what Craig (AKA Some Clueless Idiot (don't believe everything you read)) attached to another thread!

Have been researching this subject for my own boat.
I'm informed that either aluminium or zinc is fine in fine in salt water but all anodes must be the same (all aluminium or all zinc). G

From the experts chiming in before.....

Aluminum is fine in salt water, it may just need to bring replaced more often.

Yes, all the anodes should be the same, except that you can use zinc externally and pencil aluminum zincs in machinery if isolated from the block and bonding system (or maybe that is given enough that the water in a heat exchanger is just considered a different body of water as I have heard it described).

We switched about 3 years ago to aluminum anodes. Hobo spends 4-6 months in salt and the balance in brackish waters. We had a corrosion survey done by electrical tech who used a silver/silver-chloride electrode. We wanted to see if our bonding system was properly protecting Hobo and that we didn't have any stray current in AC or DC systems. We checked every breaker (AC/DC), bonding point plus all the neutrals, grounds and shore power.

The results showed that the bonding system and AC/DC systems were fine and we were within the recommended range of -550 to -1100 millivolts. We tested -635 millivolts. Since at the time we were in brackish water, the tech suggested we get a little more negative so we switch to aluminum anodes. After the change we retested and the reading was -1028.

When we changed to Al, the cost was within $20 for the 3 anodes and we have found they last longer and the zincs they replaced.


If Hobo was in salt 100% of the time, we would stay with Al.

Not nearly as scientific as Larry, but I switched to Al this season. Just hauled out, and the anodes are about as wasted as the Zn were, maybe a little less. Our setup is two bonded diver's dreams on the stern and one collar on the propshaft. Zinc pencils in the heat exchangers. Diver's dreams last for four. seasons, shaft anode one. Boating is in a combination brackish and salt. I'll stay with Al now, seems more environmentally friendly.

Switched two seasons ago, minimal difference noted in how fast they wear away. I will probably replace them when I re-coat the bottom paint in the spring just because I want a really good look at them 360 degrees around.

Giggitoni said:

Tom,

I'm not an expert. We have a member that cleans boat bottoms and changes anodes for a living. Perhaps he'll chime in here.

I believe that aluminum is for fresh water and zinc is more suited for salt water (???).


Edit: look what Craig (AKA Some Clueless Idiot (don't believe everything you read)) attached to another thread!

Click to expand...

I have noticed the attachment in the above post before - be aware that there are other sites / mfg that do recommend Alum for fresh water and claim it is very close to Magnesium in effectiveness.
Note Sidepower has gone exclusively to Alum anodes for their thrusters - no more zinc. I talked to them and they say it's OK because their thrusters are isolated and won't interact w/ other boat metals.

Alum is becoming more and more available and Ive been able to find everything I need including pencil anodes in multiple sizes although I have found that I can't get everything I need from one mfg but guess that will change as Alum becomes more common.

I switched to all aluminum this year because I spend a lot of time in brackish water. I get hauled tomorrow so I'll see how they (and my other under water metals) fared.

Ken

Except in heavy downpours (rare in the last few years), I suspect our Napa River lower waters are largely salty. Noticed that barnacles form on my treated propeller, but that's three feet under water and fresh water "floats." Actually don't know what my "zincs" are, but since they're replaced in Richmond with saltier SF Bay waters, I'd bet they (all ten of them) are zinc. Inspected and replaced as needed annually.

Bacchus said:

I have noticed the attachment in the above post before - be aware that there are other sites / mfg that do recommend Alum for fresh water and claim it is very close to Magnesium in effectiveness.
Note Sidepower has gone exclusively to Alum anodes for their thrusters - no more zinc. I talked to them and they say it's OK because their thrusters are isolated and won't interact w/ other boat metals.

Alum is becoming more and more available and Ive been able to find everything I need including pencil anodes in multiple sizes although I have found that I can't get everything I need from one mfg but guess that will change as Alum becomes more common.

Click to expand...

On the boat we're on for the loop, we have Side Power (Sleipner) bow and stern thrusters and stabilizers. Also have gone from salt to fresh. Aluminum have been perfect for this application.

I have 18 anodes on my aluminum boat and all the worn zincs were replaced with aluminum. Mine are all welded on. The zincs that had not worn since last time we're getting worse but they were not wearing any faster than the auminum which was lasting very well. I still can't buy 2 1/2" shaft aluminum anodes so they are still zinc and they have lasted very well.

The zinc anodes and the aluminum anodes are (if I remember correctly) adjacent to each other on the galvanic scale so I don't think you have to sweat mixing them.

Aluminum (Al) anodes are approved for use in FW, SW and brackish, this according to not only anode manufacturers but ABYC's chapter E2 'Cathodic Protection'. Among other things, they are resistant to a phenomenon to which zinc (Zn) anodes are susceptible, when it, zinc, enters fresh or brackish water, it develops a coating and essentially goes dormant until cleaned or replaced. This will not occur with aluminum.

The one problem I've faced with aluminum anodes in some applications is the froth they develop, it can make removal of pencil anodes in engines and other heat exchangers difficult. Because the water in engines and onboard heat exchangers is considered a different "body of water", using zinc here and aluminum on the hull is not problematic. In fact, for this reason, there is no interaction between anodes in this gear, engines, heat exchangers etc, and those on the hull, and it is why your engine's pencil zincs don't (try to) protect your propeller, and vice versa.

While I don't recommend it, I have seen Al and Zn anodes mixed on hulls and if in close proximity to each other the Al tends to protect the Zn, after the Al is depleted, the Zn begins to corrode. Not ideal, but not harmful. If possible it's best to use all Al

If you enter fresh or brackish water for any length of time (hard to say exactly how long, a day or more; you can see the coating, it's usually off white or brown), zinc anodes are put to sleep, so after leaving they would need to be cleaned or replaced. Only use non-metallic brushes or ScotchBrite pads to clean anodes, never a wire brush.

Larry M said:

We tested -635 millivolts. Since at the time we were in brackish water, the tech suggested we get a little more negative so we switch to aluminum anodes. After the change we retested and the reading was -1028.
.

Click to expand...

My guess is that your zincs were just about wasted. There is only 50 millivolts difference between aluminum and zinc, -1.1 vs -1.05 volts. That aside, you made the right choice switching to aluminum.

I have used aluminum now for at least 10 years or so. And only one anode at that, a diver's plate mounted on the stern below the water line. I also built shaft brushes to eliminate the need for shaft anodes.

I test my system a couple of times a season with my silver-silver chloride half cell. The thing I have noticed over the years is that as the season comes to an end, my test voltage falls to range between -0.65 to -0.64 or so. And when the boat is hauled, the anode is just about shot.

Just purchased a new anode for next season. The prior anodes were 1/2"X6"X12". The new HARD TO FIND diver's plate is 1"X6"X12" which should double its life capacity. Zinc with its 350 (there about) amp hours/pound capacity just would not cut it compared to aluminum with about 1100 amp hours/pound capacity.

markpierce said:

Noticed that barnacles form on my treated propeller, but that's three feet under water and fresh water "floats."

Click to expand...

Markpierce--

I had soooo much growth on my shafts and props for years that just removing the stuff after haul was a serious task. The shafts used to have at least 1" of solid growth. I tried copper plating the props, bottom painting the shafts and later added bottom paint to the props. All to no avail!

Now what I did find that WORKS at least to my satisfaction is to first paint the shafts and props with Rust-Oleum's zinc chromate which sticks to the metals and then paint over the metals with a HARD bottom paint.

For the last two years (will see again this year in a couple of weeks when hauled) my shafts and props have been for the most part growth free. Bottom paint by itself didn't work because it didn't stay on the bare metal.

For any and all helpful information, contact boatzincs.com.
They are there to serve. They can also help you determine if your boat is over or under "Zinced"

Pgitug said:

For any and all helpful information, contact boatzincs.com.
They are there to serve. They can also help you determine if your boat is over or under "Zinced"

Click to expand...

With the current trend, maybe they should change their name

foggysail said:

With the current trend, maybe they should change their name

Click to expand...

Guess what happens when you go to boatanodes.com?

fstbttms said:

Guess what happens when you go to boatanodes.com?

Click to expand...

Someone needs to tell them they need to reverse that and change the page title.

Xsbank said:

I still can't buy 2 1/2" shaft aluminum anodes .

Click to expand...

Take a look at BoatZincs.com. # X-11AL