Anode advice needed

[Sunsetrider]

Here are pics of my shaft anode, both sides. Clearly it has seen some action. Surprisingly, it seems to me it is aluminum, but otoh I don’t know what zinc would look like. I want aluminum for my seafaring adventure, but having difficulty sourcing an aluminum donut for my 30mm shaft. My questions:

Should I put this back on? Still a fair amount of material left on it. But no easy job putting on a fresh one later. Costly to pull ashore.

Where to source a new one?

I have posted a more intriguing question as well about stuffing following this one.

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[Sunsetrider]

Some say aluminum is inappropriate for fresh water because of oxidation, but it is best suited to handle both fresh and salt, which is what I will need. I wonder how one would clean off the oxidation?

[jetter]

Magnesium is the way to go in fresh water. Boatzincs will ship free anywhere in US with $100 order. I do not recommend you try shipping to Canada. Between shipping fee and customs the price will make you think they are gold.

http://www.boatzincs.com/engine-magnesium-sizes.html

[Sunsetrider]

I am going to travel into salt water so magnesium won't work for me. I am in Canada but I do have a usa shipping address if need be. obviously would prefer to source here if possible. don't want to upset the trade deficit!

[dkirsop]

Your anode needs replacing. Good practice is to replace them when the have lost 50% or more of their weight. Yours is about there judging from the pictures. Zinc is usually the standard replacement for salt water. You should be able to find what you need at a good chandlery.

[Sunsetrider]

all my research indicates that zinc is not recommended in fresh water, and I will be several months at least once n fresh before entering salt water. Aluminum can operate in both and is longer lasting than zinc in salt.

[Sunsetrider]

I found a 30mm aluminum collar at marine2go online. Nothing in

[dkirsop]

Because you are located in a freshwater port it makes sense that aluminum would be the dominant product. Here, everything is salt so zinc is the go to product. I know both Martyr and Canada Metals produce zinc anodes in your required size but your supplier may have to order them in, or you may just have to plan on replacing your anodes once you reach salt water.

[dkirsop]

This thread offers some advice on cathodic protection
viewtopic.php?f=28&t=10640

[Sunsetrider]

As mentioned earlier, all the sources I have read rate aluminum superior to zinc for salt water, so I wouldn’t pay to haul the boat to switch. No trailer in any case.

[dkirsop]

If you put a zinc anode next to an aluminum anode the zinc will disappear first before the aluminum anode starts to corrode. This is because zinc has a corrosion potential of -1.0V and aluminum has a corrosion potential of -0.76V. By comparison magnesium has a corrosion potential of -1.6V. All of these alloys work but will sacrifice at different rates. Magnesium is used in fresh water because it has the highest corrosion potential of all 3 alloys and can work in a low conductivity environment (ie. fresh water).

For what it is worth Zinc will offer better protection than aluminum in salt water but either will provide a reasonable level of protection. Regardless what marketing companies publish the chemistry doesn't change. I'll keep using zinc thanks.

[Sunsetrider]

I guess the factor I found convincing is that aluminum is said to last longer than zinc, and that counts a lot for me if my plan to stay in the tropics actually works out. I have ordered two.

[Sunsetrider]

Here is my new aluminum anode n place. Don Casey seems to recommend it over zinc for salt and brackish water, and it works in fresh as well.

[WillieC]

Make sure you have enough room for the shaft to move forward, if it needs it. The RB transmission that came with the 3B needed room to move when it went into reverse. Depending on the wear of the inner clutches. The newer 17C with the MS transmission does not have that issue.

Either way, operate the shift lever while somebody is watching the shaft back there, or watch it at the tranny output coupler. Before it goes back in the water, preferably.

[Sunsetrider]

Will do. The new collar is the same width as the former, so I expect things will operate as before.