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Old 03-08-2007, 10:47 PM
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Default Zinc vs Aluminum anodes

Does anyone know what the best and suggested anode type to use for the Merc 350 MPI Horizon is? I learned that my marina has switched to using aluminum from Zinc? I can't find the information on the merc site, so I'm looking to the true knowledge pit to help me out. Any help would be appreciated....
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Old 03-09-2007, 12:10 AM
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Default Re: Zinc vs Aluminum anodes

Why would you use aluminum anodes to protect aluminum parts? The anode needs to be less noble in order to protect the valuable metals. Zinc and Magnesium are the standards for anodes. Magnesium is less noble than zinc, but this is usually not a good thing because having too much of a difference in nobility increases the galvanic activity. Magnesium is for fresh water use only. Stop trying to be different and stick with the zinc.
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Old 03-09-2007, 01:46 AM
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Default Re: Zinc vs Aluminum anodes

aberke,

I suggest you buy the OEM anodes from your favorite Merc dealer. Mercury Marine has been using aluminum anodes for many years. They are said to be more active and thus offer more protection. The Mercury anodes are made of an aluminum-indium alloy and are manufactured by Canada Metals.

It should be noted that Canada Metals offers many anodes for the aftermarket as well, but I am told by my Mercury mechanic that the OE and the aftermarket anodes are not the exact same alloy.

Whatever you do, NEVER mix types of anodes. If a boat has multiple anodes they must all be the same or only the least noble among them will be doing all the "work" of protecting your equipment.
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Old 03-09-2007, 01:50 AM
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Default Re: Zinc vs Aluminum anodes

This was just posted on another site in response to the same general question: http://www.outdrives.com/bulletin/se...91/sb91_19.pdf Perhaps the aluminum of the drive case is of nobler alloy than the sacreficial anode?
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Old 03-09-2007, 06:50 AM
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Default Re: Zinc vs Aluminum anodes

Welcome to THT aberke

Quote:
76GMC1500 - 3/8/2007 11:10 PM Why would you use aluminum anodes to protect aluminum parts? The anode needs to be less noble in order to protect the valuable metals. Zinc and Magnesium are the standards for anodes. Magnesium is less noble than zinc, but this is usually not a good thing because having too much of a difference in nobility increases the galvanic activity. Magnesium is for fresh water use only. Stop trying to be different and stick with the zinc.
Good standardresponse but not always true e.g. I have been told that Merc now has aluminum anodes for some of their outdrives

But why did you have to tack on the final sentance. The new poster is asking a good question and is not seeking to be put down . . . give the guy a break . . . geeeez
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Old 03-09-2007, 10:38 AM
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Default Re: Zinc vs Aluminum anodes

Zinc - for Saltwater use
Aluminum = for freshwater use
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Old 03-09-2007, 10:40 AM
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Default Re: Zinc vs Aluminum anodes

Quote:
KevinM - 3/9/2007 7:38 AM

Zinc - for Saltwater use
Aluminum = for freshwater use
No, aluminum is for both fresh and saltwater use. Zinc is obsolete for both.
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Old 03-09-2007, 03:58 PM
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Default Re: Zinc vs Aluminum anodes

Well the actual spec was pre 2001 Merc called for Zinc in saltwater and post 2001 was aluminum in both fresh and saltwater.
The aluminum alloy used in anodes is very different from normal aluminum. It includes about 5% zinc and a trace of Indium, which prevents the build up of an oxide layer. Aluminum Anodes last 50% longer and will provide better protection than that of Zinc, aminly bcause of longevity. Aluminum anodes can be used in salt and brackish water environments. Aluminum alloy is also environmentally friendly, unlike zinc, which is considered a pollutant.
Zinc can become very active and actually cause hydrogen bubbles that strips the paint. All in all zinc is still a good sacrificial metal, but due to maintenance concerns where as the sacrificial anodes get overlooked and hence cause major corrosion issues, along with environmental concerns aluminum is the recommended anode by Merc.
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Old 03-09-2007, 06:31 PM
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Default Re: Zinc vs Aluminum anodes

Quote:
auguste - 3/9/2007 5:50 AM

. The new poster is asking a good question and is not seeking to be put down . . . give the guy a break . . . geeeez
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Old 03-09-2007, 06:44 PM
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Default Re: Zinc vs Aluminum anodes

Had an Alpha outdrive a few years back zinc, when I pulled for season new prop was bad from corrosion. I called to order a new one and stated the problem and was told to switch to aluminum. Stayed in the same slip over the next couple of years and never had a problem again. Salt and brackish river.
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Old 03-09-2007, 07:21 PM
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Default Re: Zinc vs Aluminum anodes

Am I right in saying that the alu propeller also acts as anode? That is what I think I read on a Yamaha catalog. What about the little adjusting anode skeg under the ventilation plate? Also seems alu and standard
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Old 03-09-2007, 08:12 PM
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Default Re: Zinc vs Aluminum anodes

Quote:
XV2PS - 3/9/2007 4:21 PM

Am I right in saying that the alu propeller also acts as anode? That is what I think I read on a Yamaha catalog. What about the little adjusting anode skeg under the ventilation plate? Also seems alu and standard
No, that would be incorrect. There are lots of different aluminum alloys. The aluminum that a propeller is made of is very different than the aluminum-indium alloy used in the Mercury anodes.

The trim tab anode (found only on Mercury outboards and MerCruiser sterndirves) is made of the same aluminum-indium alloy.
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Old 03-09-2007, 08:21 PM
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Default Re: Zinc vs Aluminum anodes

You must put aluminum anodes on a Merc drive. The zinc does not work anymore. Ask me how I know this. MERC WILL NOT WARRANTY ANY CORROSION DAMAGE.
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Old 03-09-2007, 09:23 PM
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Default Re: Zinc vs Aluminum anodes

Quote:
Tom W Clark - 3/10/2007 7:12 AM

Quote:
XV2PS - 3/9/2007 4:21 PM

Am I right in saying that the alu propeller also acts as anode? That is what I think I read on a Yamaha catalog. What about the little adjusting anode skeg under the ventilation plate? Also seems alu and standard
No, that would be incorrect. There are lots of different aluminum alloys. The aluminum that a propeller is made of is very different than the aluminum-indium alloy used in the Mercury anodes.

The trim tab anode (found only on Mercury outboards and MerCruiser sterndirves) is made of the same aluminum-indium alloy.
Well, yes, for the trim tab, I think I am correct. Yes, they are different alloys, but what it means as regard as to the first reply is that even you use zinc everywhere, the trim tab also acts as anode an is made of aluminum alloy. So it does not seem to be an offense to the engine to use another alloy. Now I say "seems", I am no expert, but if manufacturers do....

I should find back later the reference of the aluminum propeller partly acting as an anode (but actually it is painted which would not be coherent). Anybody else have seen this reference of alu propeller also acting partly as anode? Actually, using my propeller as anode would also be annoying
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Old 03-09-2007, 09:43 PM
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Default Re: Zinc vs Aluminum anodes

XV2PS,

I don't think you understand. The trim tab on a Mercury outboard is DESIGNED TO BE a sacrificial anode. I have always thought is was rather bizarre that Mercury would make a component that is critical to the performance of the boat an anode that deteriorates over time, but none the less that is what they have (nearly) always done.

Whatever the rim tab anode is made of, aluminum-indium, zinc or magnesium, it had better be the exact same material as the other anodes on the motor.

Do not worry, your propeller is not made of any of these materials.
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Old 03-09-2007, 09:47 PM
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Default Re: Zinc vs Aluminum anodes

Quote:
Tom W Clark - 3/10/2007 8:43 AM

XV2PS,

I don't think you understand. The trim tab on a Mercury outboard is DESIGNED TO BE a sacrificial anode. materials.
Do not worry, I understand that very well for some years already. Not only on Mercury.

edit:
I wrote above
Quote:
the trim tab also acts as anode an is made of aluminum alloy
So I understood it was an anode, but might be wrong about inner anodes being in zinc and that one being in alu alloy.

But most likely I was wrong for the prop being an anode.
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THT topic with explanations here:
http://www.thehulltruth.com/forums/t...ighlightmode=1
more pics here (all is mixed up):
http://s136.photobucket.com/albums/q...2PS/?start=all

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Old 03-09-2007, 09:49 PM
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Default Re: Zinc vs Aluminum anodes

Do you think that zinc, aluminum, or magnesium would have helped this guy?
What a waste...


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Old 03-09-2007, 10:29 PM
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Default Re: Zinc vs Aluminum anodes

dang
if he painted the drive he would have been ok LOL
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Old 03-09-2007, 11:47 PM
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Default RE: Zinc vs Aluminum anodes

Due to historically high zinc prices, some are now switching to aluminum anodes- equally effective in saltwater.
Magnesium is for freshwater only.
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Old 03-10-2007, 12:30 AM
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Default Re: Zinc vs Aluminum anodes

Q: So, which anodes should I use? Zinc, Aluminum or Magnesium?
A: Zinc and aluminum anodes have similar corrosion protection characteristics and
provide very good protection for boats operating in either salt or brackish water.
Magnesium anodes are specifically intended to provide superior protection for boats
that operate in freshwater only. Caution: Magnesium anodes are much more active
than zinc or aluminum, and disappear relatively quickly in salt water. Magnesium is
much too strong for – and can damage – outboards, sterndrives and aluminum-hull
boats that operate in salt or brackish water
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