Zinc Fish

[tkeithlu]

Welcome to the forum, Nightsky. Yes, I do use aluminum anodes on my steel boat. They give me about -1.3 volts on the test electrode.

[Jill on Maya]

Originally Posted by tkeithlu

Wow! 99% of what you would find lying around a yard is the same alloy of zinc. .

I'm very much in favour of recycling but what of the story Ive heard that some "zinc" anodes are made of alloys with only a portion of zinc?

The story comes from an experienced shipwright/ yard operator. He says the zinc sacrifices leaving holes in the anode where the zinc was and what is left may look like a partially eaten anode but in fact has very little zinc left. His source is someone who had a business of collecting discarded anodes from boatyards who said when melted down the zinc portion recovered was about 10%. Based on this "fact" the shipwright recommends replacing zinc anodes even if only partially eaten.

Contrast this with an Australian foundry who assured me this week that their anodes are 99.9% zinc.

We have become used to faux stainless steel. Could there be faux zinc anodes?

[Bruce K]

I have seen "Fish" anodes, hung from lifelines on fishing line, when asked the owner told me that they "last heaps longer' than when on wire, I agreed with him and did not argue. As I said before the Dunning Kruger effect explains many things.

[fstbttms]

Originally Posted by Jill on Maya

Contrast this with an Australian foundry who assured me this week that their anodes are 99.9% zinc.

Nothing special about this. This conforms to U.S. Mil Spec for zinc anodes. Most high quality anodes meet this specification and honestly, if you use anything that does not meet U.S. Mil Spec, you'll get what you deserve.

[Whitebread117]

For the op, we have a center cockpit with the main cockpit locker over the engine room. We ran a 10awg wire from the main bonding bus up through a hole drilled in the locker with a strain relief clamp inside the locker. Our fish resides in a little basket in the locker with 20 ft of extra wire- when in an unknown marina there's no setup just open locker, toss fish over the side, close locker.

Our home marina is brackish, has never proven to be "hot", and we have an isolator on the shore power. Our regular zincs last long enough we don't bother with the fish. But it's always ready to go in case we go somewhere questionable.

[tkeithlu]

The bits of zinc theory is theoretically possible, but quite unlikely. Casting an alloy so that blobs are one metal and large areas are another would be quite a trick. Moreover, there is another explanation for the observed pits. Any imperfection in the surface, such as a scratch, would supply more surface area and perhaps less surface oxide, both leading to a pit that in turn supplies more surface area, and we're off and running, with the current concentrating on the pits. When my flat aluminum anodes come off, they are covered with a matrix of pits, each about 6mm in diameter, not a smooth reduction in the surface. Would someone foist fake anodes on the market? They could, but the profit margin would be small, there not being a bunch of other metals that are cheaper and look the same. The only metals cheaper than zinc at present are lead and aluminum, so an aluminum/zinc alloy would be a possibility. But then, a lot of what you pay for an anode is production, shipping, and profit, not the metal itself. And, if anyone determined that you were doing it, and boats were damaged thereby, the law suits would be horrific. If I were an amoral foundry owner or anode importer, I don't think I'd take that risk.

[Lojanica]

Follow up.

Bonded a 2 copper wire to engine shaft and ran wire to cockpit. Slung fish over board clamped to wire. Fish was purchased from "zinc anodes" and is quite the nice set-up with the heavy wire screwed into the cast fish.

In any event it is working.

Found the source my neighbor's dock but the politics will be interesting in fixing that so I'll just use the fish. It might take a few mojitos with the dock owner to pry that problem loose from the hull

[tkeithlu]

I would hate to pull my boat out of the water and find that my anode system had somehow failed. Setting it up and then trusting that it is working for a year or more seems to me very risky, given the damage that could be done. The answer is a USD 125 silver chloride reference electrode, sometimes called a corrosion reference electrode, available from anode suppliers. Then you can log the voltage difference, with reference to a table of relative position in the "noble" metals, see that you are protected independent of whether you used new or old anodes, and occasional checks lets you know if the system is starting to fail. I started with 14 aluminum anodes. They get taken off, wire brushed, connections cleaned, and bolted back on with each haul-out, and I'm maintaining -1.3 volts, so I know I'm OK. Most of my anodes are starting their fifth year. You can no longer read the maker's logo on them, but if anything their surface area has increased given the pitting.

[Jill on Maya]

I like your reasoning Tkeithlu.

We will continue to clean and refit our zincs despite a pitted appearance - so long as the fastening holes have another run in them.

[tkeithlu]

Thank you, Jill. Best of luck with it.

[grjfield]

I've read several posts where zincs on saildrives are changed from as frequently as monthly to yearly. I have not changed mine in 2 years and they appear to have not deteriorated at all. I dive and inspect on a regular basis.

Is there a standard time for replacing zincs, or is it dependent on the amount of decay on the zincs?

My sailboat is 'stripped out' and I have the 'minimum' when it comes to electrical on board (led lights, depth sounder, running lights, circuits for gps, radio). As well, my electric saildrive is isolated from all other electrics and the saildrive itself is isolated electrically from the motor (by the belt).

I'll be pulling the boat out this summer and will bottom paint..but if the zincs are intact..is it ok to leave them alone and continue inspections until decay is apparent.

Thanks
G

[fstbttms]

Saildrive leg anodes that appear undepleted after two years are likely not doing their job. My recommendation would be to replace them, cleaning the contact areas very well before doing so.

[grjfield]

Thanks fstbttms.
I agree...I expect its better to be safe than sorry.
When I installed the new saildrive 2 years ago, the anode was screwed directly onto the saildrive, and a new 2 blade folding Flexofold (with small anodes) installed after that.
I also have a zinc fish connected to a saildrive bolt, then up and over the side. I figure it wouldnt hurt..and might help.

Out of curiousity, and this is 'way out there'....has anyone ever 'isolated' a saildrive by encapsulating with a large cup like device and then purging the saltwater with fresh water to reduce electrolysis? While too cumbersome for summer months when sailing frequently, it might be a worthwhile project to install over the winter months.

Any thoughts?

G