Zinc or aluminum anodes for my sailing area?

[josrulz]

I was reading up on zincs on sailnet here, searching old posts, etc., and discovered the concept of aluminum anodes versus zinc. New to me, since we just bought our first boat. The boat is up north and in salt water, so I'm pretty sure the shaft zinc is, well, zinc. When we splash the boat in Spring, we'll be sailing her home to Maryland, where she'll be kept on the Chesapeake, just south of Annapolis, probably on the South River, Rhode River, or West River (still not sure). We'll be sailing both north and south of here, but for no more than 2 - 3 weeks at a time. She'll spend most of her time just south of Annapolis.

Should we be installing an aluminum anode instead of zinc? Also, are they are other anodes that should be aluminum instead of zinc? Anyone from my area care to chime in?
Thanks,
J

[eryka]

I'm no expert, but from a chemistry point of view, zinc is even further from brass or bronze than aluminum is. More dissimilar = more likely to degrade easily? More sacrificial and hence more protective? Many of the sites offering aluminum anodes say they last longer than zinc - is that a good thing? Don't you *want* them able to degrade easily?

Maybe this article will shed some light?

One advice that has been consistent - all your sacrificials should be made of the same material (otherwise they sacrifice for each other, rather than your prop/shaft!!!)

Hope this helps at least a bit.

[josrulz]

Originally Posted by eryka

I'm no expert, but from a chemistry point of view, zinc is even further from brass or bronze than aluminum is. More dissimilar = more likely to degrade easily? More sacrificial and hence more protective? Many of the sites offering aluminum anodes say they last longer than zinc - is that a good thing? Don't you *want* them able to degrade easily?

Maybe this article will shed some light?

One advice that has been consistent - all your sacrificials should be made of the same material (otherwise they sacrifice for each other, rather than your prop/shaft!!!)

Hope this helps at least a bit.

Thanks eryka! OK, after reading the article in your link, and also re-reading some Nigel Calder as well as some West Marine catalog, here's what I figured out.

You are correct that aluminum is more "noble" than zinc. The order would be aluminum, zinc, then magnesium. So this confused me--why would they recommended zinc anodes for salt water, aluminum for brackish water, and magnesium for fresh? That seems out of order.

OK, so according to the West Marine catalog, in brackish water, zinc can become less active, and become covered in zinc oxide film which totally shuts it down, leaving other metals at risk. Aluminum apparently doesn't do that.

This is all new to me, so if I'm wrong, please set me straight. Anyone? Anyone? Bueller?

Of course, even if this is all accurate, if teh vast majority of boat-owners in my area are successfully using zinc, then I have no reason to do anything different. Less complicated is a good thing.

Eryka, do you use zincs on your boat? Our boat won't be very far away.
-J

[JohnRPollard]

Originally Posted by josrulz

....

Of course, even if this is all accurate, if teh vast majority of boat-owners in my area are successfully using zinc, then I have no reason to do anything different. ...

We have been successfully using zinc for many years, in the exact location where you plan to keep your boat, and using it in much the same way as you plan to.

[Fstbttms]

Originally Posted by josrulz

So this confused me--why would they recommended zinc anodes for salt water, aluminum for brackish water, and magnesium for fresh? That seems out of order.

My understanding is that zinc anodes do not have the electrical potential to overcome the greater resistance offered by freshwater. Do what the catalog recommends, don't necessarily take what your dock neighbors suggest as gospel. There is a lot of ignorance and bad info out there. The local experts would be marine electricians or hull cleaners.

[josrulz]

Thanks everyone. I agree with Fstbttms that owners don't always know. However, I'm guessing that it's salty enough here for zincs to work OK. So far, those I've talked to (on and off Sailnet) have said they use zincs in this area.

We'll probably stick with zincs this year, and keep an eye on them this year.

Thanks!
-J