Aluminum shaft anodes

[Mischief Managed]

I tried aluminum shaft anodes last Spring on some advice from a trusted friend. They seem to work really well and wore faster and more evenly than zinc shaft anodes typically do for me. The other anodes on the boat are zinc and they all had less wear than normal, I assume due to the aluminum being more reactive and doing the heavy lifting, so to speak. None of the underwater metal parts on the boat showed any signs of corrosion so I will clean up the zinc anodes and leave them in place for another year and I'll just put new aluminum shaft anodes on. Anything wrong with this plan?

 

[Fleming]

Probably ok. How much is bonded to your hull anodes? Metal rudders, all seacocks? Do you have separate anodes on your trim tabs and/or rudders? Is your shaft connected to your bonding system (<1 ohm between DC negative and the shaft when measured out of the water)?
In general it's better to use all of one type, but if you're shaft doesn't have a good ground connection to the rest of your DC negative and bonding system it won't matter.

 

[JackConnick]

Are you in fresh or salt water? Aluminum is better for fresh water, generally.

 

[BB-marine]

I use all Aluminum alloy anodes on my boat. We cruise in fresh , brackish and salt water waters. I installed aluminum when we left on the loop. I had a diver replace them when we were at Thunderbolt Georgia about 9 months after installing and launching the boat. I could have gone much longer the anodes where about 75% there. I do recommend using all the same anode material especially when the boat has all under water metals bonded. The shafts in many cases are not bonded unless a bonding brushes are used. There is a 50/50 chance without brushes. I would still use only one type of anode and would recommend going all aluminum. It worked well for me. I found that zinc anodes do not work well in fresh water and if used in fresh water or brackish form a coating over a short period of time that makes them useless. The aluminum work well in fresh, brackish and salt.
Brian

 

[rslifkin]

Are you in fresh or salt water? Aluminum is better for fresh water, generally.

Aluminum anodes are fine in fresh or salt. Depending on what metals you need to protect they may or may not be adequate in really clean fresh water, magnesium may be needed there. But you definitely can't run magnesium anodes in salt, so aluminum is as universal as it gets.

 

[Taras]

I'd go with all the same type of anode. If one is aluminum and another zinc, then you are introducing more dissimilar metals.

 

[Mac2]

There was another thread here talking about excessive wear on a aluminum shaft anode for a de-icer. No one answered if a shaft anode wears faster due to spinning. I have no space for a shaft anode. I added the propeller nut/anode. This would give you additional/backup protection.

 

[Bacchus]

As Taras suggested all the same composition for anodes is the recommendation. This is especially true where parts are bonded so essentially the same cell. My understanding is that it is not required where protected parts are a different cell... as is the case with engine & tranny cooler pencil anodes as well as many / most thrusters.