View Full Version : what anodes to use?

03-23-2012, 07:51 AM
mostly fresh to an occassional brackish run. it might sit in the fresh water for a day or two 3 tops and the brackish water for an overnighter.

zinc?? or Magnesium???


Morgan's Cloud
03-23-2012, 08:54 AM
I would say magnesium.

03-23-2012, 09:14 AM
Thanks is there any issue with mixing both? There are 2 on a Volvo 280
One is a bar at the bottom of the transom plate. And the other is by the prop shaft. I can find the bar in mag. But not the one by prop shaft

I don't want to create a battery should I go with both in zinc until I find them in mag. ?

Morgan's Cloud
03-23-2012, 09:26 AM
Not that it should make much difference , I didn't know you were talking about a Volvo .. It's been a l o n g time since I did zincs on a 270/280 .. I didn't know that there was options other than zinc available now.

Personally , I wouldn't mix them. Those units are so good that the only example I've ever seen of an electrolysis issue on one was where the owner had used coppaslip on the splined drive shaft and the throwoff went on the inside of the housing and got wet with salt water.

The zinc might be a bit slow to react in the water you describe though if it is called on to neutralise any galvanic activity.

03-23-2012, 09:39 AM
Price is a big difference too. I can get a set both anodes and new hardware in zinc for $25. The mag bar alone with no hardware is $40. I think I'll Zinc

Morgan's Cloud
03-23-2012, 09:46 AM
And to think the things are supposed to fall apart too ! haha

Personally , I think you'll be ok .. just maybe monitor things to make sure the boat doesn't actually have any self inflicted issues or you should end up in a 'highly active area' unknowingly .
Just remember Phil's advice .. always make sure the grounding surfaces are clean and bright .

03-23-2012, 11:23 AM
I've never mixed annodes, but I would think if you did you would at best use up the mag annode quickily as it would not only be protecting the drive, but the aluminum annode as well. I suppose once the mag was used up the aluminum would then start doing it's job.

Worst case, the aluminum and mag would themselves react and create their own current flow. Not sure on that though; seems like the former is the more probable scenario.

Here's a handy link about annodes, but no mention of mixing aluminum and mag.


03-23-2012, 01:13 PM
I would think you would want aluminum anodes which are designed for brackish water. Magnesium is only for freash, and zink is only for salt. Aluminum will hold up well in both.

Morgan's Cloud
03-23-2012, 01:54 PM
Judging by his post , it doesn't sound like Matty has an aluminum option .
Plenty of the two zinc styles he needs and only one (expensive) magnesium one on hand with the option to shell out mucho $ for another mag one ... or more .

03-23-2012, 02:04 PM
"Is anyone here a materials scientist?!" (or something close to that. ;) ) -Seinfeld

Some fun reading, that doesn't fully answer the question in my view but might get part way there: http://www.corrosionist.com/Galvanic_Corrosion.htm

03-23-2012, 02:29 PM
stop the presses I did find these in alum.


the first pic is where the prop anode goes around the prop shaft housing, in the second pic the dog bone about 6 inches long attaches with two bolts to the bottom of the trim ears you can see the bolt holes below where the rod for the reverse latch should go.

03-23-2012, 03:27 PM
marine parts source in TN had the mag. ones for less than $15 each

03-23-2012, 04:14 PM
Check out www.boatzincs.com/volvo_penta-aluminum.html (http://www.boatzincs.com/volvo_penta-aluminum.html)
That's where I got the aluminum ones for my 280T

Morgan's Cloud
03-24-2012, 08:32 AM
Sounds like shopping around pays off again !

03-24-2012, 08:49 AM
they were always there It was just the way I typed the search on ebay one way had like 6 items the other had like 100 items