Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 07-04-2021, 21:45   #1
Registered User

Join Date: Jun 2020
Location: La Conner, WA, USA
Boat: Atlas Pompano 21
Posts: 22
Aluminum anodes not preventing corrosion

Hello everyone, I'm looking for opinions on aluminum anodes. Everything I read on the internet says they're great (in salt water), but my experience has been different.

Ever since installing aluminum anodes on my prop shaft and rudder last summer I've noticed a build up of white powder (presumably galvanic corrosion) on the rudder and through hulls. I asked the yard manager at the shop where I keep my boat about this, and he says that he won't install the aluminum zincs, even if people ask for them.

I keep my boat on the hard most of the time, but it can spend a week or two in the water at times, even in winter. It's in salt water, and never connected to shore power. I have not had this problem with zinc anodes.

Have others had good experience with aluminum anodes? I'd like to use them if I can.
ScottRhodes13 is offline   Reply With Quote
Old 07-04-2021, 21:53   #2
Registered User
 
AKA-None's Avatar

Join Date: Oct 2013
Location: Lake City MN
Boat: C&C 27 Mk III
Posts: 1,345
Re: Aluminum anodes not preventing corrosion

Hmmm I’d always thought al anodes e we re for fresh water not salt? But I could be wrong
__________________
Special knowledge can be a terrible disadvantage if it leads you too far along a path that you cannot explain anymore.
Frank Herbert 'Dune'
AKA-None is offline   Reply With Quote
Old 07-04-2021, 23:03   #3
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 4,511
Images: 7
Re: Aluminum anodes not preventing corrosion

The galvanic potential of zinc is -0.98 to -1.03 volts and that for aluminium alloys -0.76 to -1.00 volts. The consequence of this is that you need a greater surface area of aluminium anode to generate the same amount of protective current. You might just need more aluminium anodes.
__________________
Satiriker ist verboten, la conformité est obligatoire
RaymondR is offline   Reply With Quote
Old 07-04-2021, 23:18   #4
Registered User
 
Simi 60's Avatar

Join Date: Jun 2016
Location: Australia
Boat: Milkraft 60 ex trawler
Posts: 3,214
Re: Aluminum anodes not preventing corrosion

Maddox anodes?

https://www.marineprotectionsystems..../maddox-anodes
Simi 60 is offline   Reply With Quote
Old 08-04-2021, 04:06   #5
Registered User
 
Sailmonkey's Avatar

Join Date: Sep 2009
Location: Houston
Boat: '76 Allied Seawind II, 32'
Posts: 8,585
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by AKA-None View Post
Hmmm I’d always thought al anodes e we re for fresh water not salt? But I could be wrong


Aluminum are good for salt as well as brackish water.

Magnesium is for fresh water.
Sailmonkey is online now   Reply With Quote
Old 08-04-2021, 04:26   #6
Registered User
 
LittleWing77's Avatar

Join Date: Oct 2018
Location: Toronto, Ontario
Posts: 1,666
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by ScottRhodes13 View Post
Ever since installing aluminum anodes on my prop shaft and rudder last summer I've noticed a build up of white powder (presumably galvanic corrosion) on the rudder and through hulls. I asked the yard manager at the shop where I keep my boat about this, and he says that he won't install the aluminum zincs, even if people ask for them.
When one considers the ultimate replacement costs of your rudder's metal components (and rebuild) and replacement of all of your thru-hulls and/or potential thru-hull fail in the meanwhile, I would immediately return to zinc anodes without delay.

Respectfully, Scott, this is one of those times I do not understand why a boat owner would insist upon using an ineffective option which is causing/going to cause exponentially worse long-term damage to key components of his boat, just to economize.

Pay attention to your Yard Manager !

Kindly meant,
LittleWing77
LittleWing77 is offline   Reply With Quote
Old 08-04-2021, 07:07   #7
Registered User

Join Date: Apr 2019
Posts: 62
Re: Aluminum anodes not preventing corrosion

OK, that is very odd. Like you, I understand aluminum anodes are superior to zinc in many applications. I agree that white powder does seem to indicate galvanic corrosion.

I currently have zinc, but was planning on shifting to aluminum on my aluminum vessel per recommendation of BoatZinc and my yard. Aluminum anodes are definitely not ineffective as mentioned above. I wonder if the comment about having the correct mass of anode is right. Do you have access to a corrosion reference electrode (a silver/silver-chloride half cell)?
Pelican_38 is offline   Reply With Quote
Old 08-04-2021, 07:25   #8
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 4,413
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by AKA-None View Post
Hmmm I’d always thought al anodes e we re for fresh water not salt? But I could be wrong
You're wrong.
Attached Thumbnails
Click image for larger version

Name:	zinc type chart.jpg
Views:	211
Size:	73.3 KB
ID:	236144  
fstbttms is online now   Reply With Quote
Old 08-04-2021, 07:33   #9
Registered User

Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft Catalina 381
Posts: 1,930
Re: Aluminum anodes not preventing corrosion

Keep in mind, aluminum anodes aren't just aluminum. They're typically Navalloy, which is an alloy of aluminum, zinc, and indium IIRC.
rslifkin is offline   Reply With Quote
Old 08-04-2021, 07:41   #10
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 4,413
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by ScottRhodes13 View Post
Ever since installing aluminum anodes on my prop shaft and rudder last summer I've noticed a build up of white powder (presumably galvanic corrosion) on the rudder and through hulls.
Are your thru-hulls bonded to the anodes in any way?
fstbttms is online now   Reply With Quote
Old 08-04-2021, 07:53   #11
Registered User

Join Date: Oct 2018
Location: Dallas, TX
Posts: 334
Re: Aluminum anodes not preventing corrosion

If your boat is spending a majority of the time on the hard then the white powder is possibly normal atmospheric oxidation of zinc. Zinc oxide is a white powder. Galvanic corrosion requires an electrolyte solution to complete the circuit between the dissimilar metals.
NPCampbell is offline   Reply With Quote
Old 08-04-2021, 08:00   #12
Marine Service Provider
 
fstbttms's Avatar

Cruisers Forum Supporter

Join Date: Oct 2006
Location: Under a boat, in a marina, in the San Francisco Bay
Posts: 4,413
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by NPCampbell View Post
If your boat is spending a majority of the time on the hard then the white powder is possibly normal atmospheric oxidation of zinc. Zinc oxide is a white powder. Galvanic corrosion requires an electrolyte solution to complete the circuit between the dissimilar metals.
What zinc? He's using aluminum anodes. Also, this doesn't explain why he's seeing the white powder on his rudder and thru-hulls.
fstbttms is online now   Reply With Quote
Old 08-04-2021, 08:04   #13
Registered User
 
Dsanduril's Avatar

Join Date: Aug 2011
Location: Petersburg, AK
Boat: Outremer 50S
Posts: 3,777
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by RaymondR View Post
The galvanic potential of zinc is -0.98 to -1.03 volts and that for aluminium alloys -0.76 to -1.00 volts. The consequence of this is that you need a greater surface area of aluminium anode to generate the same amount of protective current. You might just need more aluminium anodes.
"Aluminum" anode is really a misnomer, a proper "aluminum" anode is an aluminum-indium alloy with a galvanic potential of -1.1V, greater than the -1.05V generally reported for zinc alloy anodes. Maybe the OP has aluminum rather than aluminum-indium anodes? We've been using "aluminum" anodes for about 3 years and show no signs of any problems and slightly improved life (that latter is hard to measure because we replace once every year or so, and that is almost always as a preventive maintenance task when doing other work rather than a completely wasted anode that needs replacing).

Click image for larger version

Name:	Al anode 1.PNG
Views:	89
Size:	84.8 KB
ID:	236145
Click image for larger version

Name:	Al anode 2.PNG
Views:	65
Size:	43.6 KB
ID:	236146

source
Dsanduril is offline   Reply With Quote
Old 08-04-2021, 08:11   #14
Registered User

Join Date: Oct 2018
Location: Dallas, TX
Posts: 334
Re: Aluminum anodes not preventing corrosion

Quote:
Originally Posted by fstbttms View Post
What zinc? He's using aluminum anodes. Also, this doesn't explain why he's seeing the white powder on his rudder and thru-hulls.
My experience is with cars in which I see white oxidation all the time due to nuts and bolts being made of zinc. However, that is a good point, zinc wouldn't be used below the water line for anything but brass and that oxidizes blue/green.
NPCampbell is offline   Reply With Quote
Old 08-04-2021, 08:49   #15
Registered User

Join Date: Jun 2020
Location: La Conner, WA, USA
Boat: Atlas Pompano 21
Posts: 22
Re: Aluminum anodes not preventing corrosion

Wow! Thanks for all the replies so soon.

I don't remember what brand of anode these were, but I bought them from a reputable dealer, so I'm sure they're the right composition.

The through hulls and rudder are bonded together. I will need to investigate, but I think they're bonded to the engine ground, too. I'm not happy with the bonding, it's just a wire connected to the fitting with hose clamp. I know that's not recommended, but don't see a better way. I keep the battery switch off when docked, so don't think there's a stray current problem.

The suggestions to consider the size of the anodes make sense. I will look into a corrosion reference electrode -- I haven't heard of those. As one responder mentioned, corrosion can cause expensive problems, so I hate to experiment just to see what works.

The guy at the boat yard said that when the aluminum anodes are out of water much of the time, they oxidize and form a coating that prevents them from working as efficiently as they should, so that could be my problem.
ScottRhodes13 is offline   Reply With Quote
Reply

Tags
aluminum, corrosion, galvanic

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anodes? We Don' Need No Stinkin' Anodes! fstbttms Construction, Maintenance & Refit 11 10-01-2021 09:21
Ideas for preventing galvanic corrosion on rudder quadrant JPE Construction, Maintenance & Refit 9 09-11-2020 00:14
Any DIY portable anodes to prevent galvanic corrosion? Joe from ny Electrical: Batteries, Generators & Solar 21 25-07-2016 11:11
Preventing Corrosion on Galvanised Anchors (April 1) noelex 77 Anchoring & Mooring 15 01-04-2014 21:23

Advertise Here


All times are GMT -7. The time now is 08:14.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.