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Random Quote: If you want a fish to grow,let it go. If you want a fish to cook and grow don't take a picture
Getting ready to replace my engine anodes and want to be sure to get the best protection available. I understand that Zincs and for salt water, and Aluminum for "salt and freshwater".
Although it is an offshore boat, I run through 4 miles of brackish Loxahatchee River to get to and fro the inlet. At homebase, she sits on a lift.
Should I be using Aluminum anodes rather than zinc?
You are going to want zincs. They are sacrificial, protecting your engines from corrosion. Aluminum essentially become part of the engine and provide no corrosion protection.
I'd go aluminum. If they don't last an entire season, then consider switching to zinc.
Just for clarification, sacrificial anodes come in three flavors - from most noble to least noble it's zinc, aluminum alloy, and magnesium.
The less noble the metal, the more likely it will become the anode instead of the cathode. Since the anode side of a battery is the one that gives up ions, you want the little replaceable chunks of metal to sacrifice themselves instead of your engine.
Aluminum anodes are still far less noble than the aluminum on an engine. They are more aggressive than zinc, but less aggressive than magnesium. People often use zinc for saltwater, aluminum for brackish, and magnesium for fresh. Fresh water doesn't conduct electricity as well as salt water, so you need a more aggressive anode to ensure that they do indeed become the anode. Salt water is a much better conductor, so magnesium would protect really well, but would dissolve too quickly.
Start with aluminum, and if they aren't dissolving at all by the end of the season, you can go more aggressive (ie magnesium). If they are dissolving too quickly, then move back to zinc. I'm guessing aluminum will be the best match.
4 miles of brackish to the inlet? I would run zinc without a doubt. How much corrosion is going to happen in 8 miles of brackish water. The Alluminum Burgers and Palmer Johnsons are delivered with with Zincs on the Great Lakes, not saying they're the end all but protecting their investments is something that they would take more than a passing interest in.
Another dumb question? is the boat dry slipped or wet slipped. I would consider what to use as this is more important as to the few miles of water you run the boat in.
This is from everybody's favorite marine retailer;
Quote:
Which anode is right for you?
Zinc or aluminum for salt water: If you are a saltwater boater, you should install zinc anodes to prevent galvanic corrosion on the engine and underwater parts of your boat. Look for aluminum anodes as a possible replacement because they last longer while providing the same level of protection as zinc.
Magnesium for fresh water: Since freshwater is much less conductive than saltwater, magnesium anodes are the best choice because they're more active (less noble) than zinc or aluminum so they will protect your engine parts much more effectively. Caution: do not use magnesium anodes in any application other than a freshwater because they corrode rapidly, exposing your boat and engine to possible damage.
Aluminum for salt & brackish water: More active than zinc, aluminum anodes are a good compromise for a mix of fresh and saltwater, e.g. in the brackish water of river deltas. In brackish water zinc is too passive and magnesium corrodes too rapidly (because of the water's salt content), leaving your boat without adequate protection.
Based on the feedback here, I'll likely go with zincs, but would be interested in putting a set of aluminums on to see firsthand the difference in how fast they deteriorate. I think the zincs being replaced are original - 7yrs!
Based on the feedback here, I'll likely go with zincs, but would be interested in putting a set of aluminums on to see firsthand the difference in how fast they deteriorate. I think the zincs being replaced are original - 7yrs!
If the original zincs lasted 7 years, why use anything else. Some folks have to replace anodes multiple times yearly!
Zinc vs. Aluminum Anodes 
