Stern Drive Anode
 

I noticed the tiniest bit of oxidation on my boat's stern drive and my neighbor recommended I install an anode (and I've since learned that it ought to be a magnesium anode). I'm not certain what to do or where to install it/what style to get. The sterndrive is Volvo-Penta with an aluminum prop. Thoughts?

If it's a Volvo it should already have some type of anode on it. The problem is Volvo ships all of their drives, regardless of where they are going with salt water anodes. I, and most of us, I would assume, use our boats in fresh water only or at least most of the time. My Volvo DP drive (2000 Four Winns)pitted significantly before I could research the problem and you're right, you want magnesium not zinc for fresh water.

Blue Thunder

You are correct on magnesium. Zinc tends to corrode on the outside and scale over instead of dissolving in a uniform manner. Magnesium is a much better choice. I think with the more rapid rate of electrolysis in salt water the zinc does not have time to scale and works just fine.

Review the reply that starts, "This is from boatzincs.com"

http://www.boatered.com/forum/topic.asp?TOPIC_ID=112161

more than one anode
 

I have more experience with Mercruisers than VP, but I wanted to point out that you likely have several anodes (4-6) on the outdrive - the discussion here implies there is just one, which is likely not the case.

All of them need to be changed over to magnesium for fresh water use - they each protect different sections of the upper and lower drive assemblies...

Perhaps this will help !!

http://www.boatzincs.com/volvo_penta-magnesium.html


And for those of you with MerCruiser -- and wonder where the annodes are ........... This gives a great pictorial

http://www.boatzincs.com/bravo3-mag-kit.html for Bravo 3

http://www.boatzincs.com/alpha-one-gen2-mag-kit.html For Alpha 1

Do you need anodes on outboards, too? I have a Merc and a Yamaha. Never noticed if they have them.

I would fully expect anodes on your lower unit. Any time there's two or more types of metal in the water, the least noble of metals will dissolve through electrolosis. Anodes are less noble than the rest of the lower unit, so they dissolve first. If you tilt the the thing out of the water whenever it's at rest, the anodes will last years in our water.

Grady -- I would be SHOCKED :eek: if your outboards lower unit did not have them.

On the Merc, look at the under side of the Cavitation plate (above the prop).

What year & model of VP do you have? I have a 2000 DP-S which has two anodes. You should definitely go with mag anodes. Don't waste your time with Boatzincs.com, I tried to get mag anodes from them last year and got the run-around. Go see Charlie at Thurston's Marina Parts Dept. He got them for me in a week.

can u tell by looking?
 

what type they are? how do i tell if my alpha 1 has salt or fresh water anodes?

bravo 3 drives use an aluminum anode. The idea being, the bare anode will carode before the painted i/o.

I took the aluminum anodes off mine and put on magnesium.