Anodes: Zinc or Aluminum?

[Luis P]

I just bought a 45ft Regal powerboat and I am not sure that I understand the information that I received about anode material.

I was told by the previous owner that the stern zinc anodes needed to be replaced with similar ones (sold by Volvo, the maker of the engines on the boat).
From my mechanic and from some other boat owners I got the information that I could replaced them with aluminum anodes.

So I wonder what can happen if I move from zinc to aluminum; what would the differences be? If I make this change on the stern anodes can I still use zinc for the engine and generator anodes?

My boat is used in salt water, mostly at the ICW ion Florida.

Your expertise and help will be greatly appreciated.

[sailhog]

You can go with aluminum. The advantage is that they last significantly longer as an anode. My understanding is that zinc is less "noble" metal and therefore, somehow, will waste away more quickly, sacrificing itself instead of the tin in your bronze running gear. I've always wondered if aluminum offers less protection, but I'll standby while someone else weighs in on this. I've used aluminum for a little over a year now.

[rlynch03]

My understanding is the Aluminum anodes are for brackish waters and the zincs are for salt water.

[fstbttms]

Originally Posted by rlynch03

My understanding is the Aluminum anodes are for brackish waters and the zincs are for salt water.

Not quite.

[a64pilot]

If you mix anodes, it seems that the aluminum ones will waste away first, sort of protecting the zinc ones as well as of course the metals you want to protect.
I take this to mean that the zinc anodes are then inactive, but assume the metal they are protecting, is still protected by the aluminum anode.
I hang a large guppy type of aluminum anode on my boat, that is connected directly to the engine block, it seems to work well as it wastes away, but at a rate that it’s going to last well longer than a year, and the prop anode wastes away at a much slower rate when the big anode is in the water.
The generator pencil zinc anode seems to not be wasting away at all, but it’s only in water when the generator is running too as sea water drains from the heat exchanger when the pump is off.

I much prefer aluminum ones, partially as I’m sometimes in brackish water, up the St. John’s where you can see fresh water turtles and alligators, so it’s definitely pretty fresh

[Group9]

Originally Posted by rlynch03

My understanding is the Aluminum anodes are for brackish waters and the zincs are for salt water.

Simplified, but basically correct. And, lots of people who think they are in salt water, are actually in brackish.