Zincs, Aluminum or Magnesium?

Half Off

Half Off

Member
Jan 25, 2007
433
Dubuque, IA
Boat Info
2004 280 Sundancer
Engines
4.3 Apha 1 Gen II's
Trying to decide which would be correct choice for Alpha 1 outdrives in fresh water. Is Aluminum good enough or should I go with Magnesium?
 
Half Off said:
Trying to decide which would be correct choice for Alpha 1 outdrives in fresh water. Is Aluminum good enough or should I go with Magnesium?
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I use magnesium after I found that aluminum didn't provide enough protection.
 
Our 87 has Magnesium but it's only in the water for weekends or for a week at a time. No problems what so ever. I don't know what the 300 DA has on it and will have to take a look. We boat in freshwater, but we're planning a two week trip to the San Juans and it will be in salt water. Do we need to change our zincs or will the magnesium provide sufficient protection for the two week exposure? I'm assuming the magnesium will suffice?
 
Magnesium will cause too much galvanic action in salt water and dissolve very quickly. You may want to change them before just because it's cheaper to put aluminum on for two weeks than to replace the magnesium when you return.
 
NoWakey said:
Absolutely magnesium.
We made the change last year and I could not believe how much it cut down on the corrosion of our Bravo III's.
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Did you add the new prop anode for the pre-2004 BIII drives?

I have them on order. I will install before we splash.

propeller-nut-mag-complete.jpg
 
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Thanks for the replies. I have been to BoatZincs.com and that is why I posed the question to begin with because I am not quite sure which one to go with. I don't want to spend the extra money on Magnesium if they won't perform any better than Aluminum in my situation.

OK, so according to BoatZincs.com

On chart "A", "For vessels with AC shore connections and NO galvanic isolation" in fresh water and with a SS prop they recommend aluminum anodes.

On chart "B", "For vessels with AC shore connections WITH galvanic isolation" in fresh water and with a SS prop they recommend either Magnesium or Aluminum anodes.

So I guess the my next question would be - how would one tell if they have shore power with or without "galvanic isolation"?
 
Presentation said:
Did you add the new prop anode for the pre-2004 BIII drives?

I have them on order. I will install before we splash.
Click to expand...

Doug,

Yes I did. The prop nut anode made a big difference. I was amazed by the end of our season last year how much of a hit the prop nut anode had taken.
I think I can state that by going to magnesium, and adding the prop anode has brought all corrosion issues with our lower unit to a halt.

Jim
 
Half Off said:
So I guess the my next question would be - how would one tell if they have shore power with or without "galvanic isolation"?
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Galvonic Isolator is typically on the boat, usually near the plug-in for shore power. As far as I know, Sea Ray has had them as a standard item when their boats have shore power connections. (Aside, If anyone knows how to actually test their isolator to make sure it is functioning, please let me know.)
 
Half Off said:
So I guess the my next question would be - how would one tell if they have shore power with or without "galvanic isolation"?
Click to expand...

Half Off - Take a look at the 120V AC wiring diagram in your owners manual. Follow the shore power inlet (plug) past the main breaker and you will see how it is wired into the AC grounding connection to the DC bonding system. The manual states "a galvanic current isolator is standard on all Sea Ray boats".

In addition to the magnesium annodes, make certain your Mercathode system(s) are working during the season. When at a sandbar or shallow anchorage, I use a nylon brush during the season and lightly rake it over the Mercathode's reference annodes to keep the zebras off. I do the same to the sacrificials.

Mother nature kicking your butt in Dubuque today? She's kicking ours good here!
 
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gerryb said:
(Aside, If anyone knows how to actually test their isolator to make sure it is functioning, please let me know.)
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My 280 has this model 802074 GALVANIC ISOLATOR, ZINC SAVER II 30AMP. From the ZINC saver web site.
Testing Your Zinc Saver.

Disconnect the shore power. With your digital multi meter on DIODE CHECK- read across the input and output of your zinc
saver. Readings will be about 900/1000 (depending on the meter ) (This takes a few minuets as the new internal capacitor must charge and discharge) Swap the probes over to the opposite way , readings should be the same ( plus or minus 10% ). If you get full continuity ( 000 ) Disconnect one wire from the zinc saver and read again. If it reads full continuity ( on the wire ) then your green wire ground is incorrectly wired by-passing your zinc saver. You must find this problem and fix it.
 
Thanks again for all the replies. I sent an email to boatzincs.com and they answered today (on a Sunday morning no less!!). Here is their reply to my question of Aluminum or Magnesium anodes for a Alpha 1 outdrives in fresh water with SS props.

"Since you have stainless steel props I suggest going with magnesium anodes to get experience with them in your operating environment. They will definitely provide better protection than aluminum anodes. The downside is their shorter life due to their lower overall energy compared to aluminum, and the possible galvanic coupling of the magnesium to other underwater metals around your dock. You’ll need to keep an eye on them during the season to see how they hold up."

Jeff, I am actually 2 1/2 hours West of Dubuque (the boat lives at Dubuque Marina) but Mother Nature is kicking our a$$ here also. Blizzard warning for the rest of today.
 
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