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Zinc recommendations?

10K views 53 replies 15 participants last post by  eherlihy 
#1 ·
I need to buy a bunch of zincs, because I'm out. At the start of each season I have always put 2 on the propshaft, and have at least 2 in reserve.

I've tried a bunch of different sacrificial zinc anodes on my prop shaft over the years. Some have been better than others. In particular, I liked the one that had a copper (or maybe it was brass?) core, which provided the electrical contact with the shaft, and provided reinforcement to the mounting screws. The problem is I cannot remember what brand that particular zinc was...

So I went shopping, and find that prices for Zincs (NOT including Aluminum or Magnesium) are all over the place.
Prices from Amazon for a 1" (common to many sailboats) zinc anode are as follows:
  • Martyr - $14.59 FREE shipping = $14.59
  • B&S - $13.97 + $4.94 shipping = $18.91
  • Technoseal X3 - $10.68 FREE shipping = $10.68
  • Sea Shield - $7.63 + $5.49 shipping = $13.12
  • X-3 Zimar - $8.19 + 8.88 shipping = $17.06

and JD offers the Camp X3, which "Offers copper contact for permanent ground..." for $8.28 - I am thinking that this may be the one that I liked.

I also ordered a Bossler & Sweezy zinc a couple years ago. At the time it was $17.00 plus shipping.

Which brands of sacrificial ZINC anodes am I missing? Is there one brand of sacrificial zinc that you prefer?

Thanks in advance!
 
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#3 ·
... and your preferred zinc is; which?
 
#5 ·
I have installed many, many thousands of anodes over the course of my 22 years as a hull cleaner. I only use Reliance anodes. Made in Canada to U.S. mil spec, they are the best you can buy, IMHO.

I haven't had the opportunity to use all of the other brands mentioned, but here are my opinions on those I have:

1.- Martyr. Made in China. That alone is enough to make me avoid them. This brand also has the BB insert for a supposed better electrical connection. I believe that not only does the BB actually hinder the proper seating of the anode on the shaft, but I like to think that a part this simple can be manufactured to tolerances that allow for good contact.

2.- Camp. Utter garbage. I wouldn't use these anodes on my worst enemy's boat.

3.- Sea Shield. Good stuff, made in California. The only reason I don't buy them is that the fasteners tend to be hard to drive and when you're underwater, that's an issue.
 
#6 ·
I only use Reliance anodes. Made in Canada to U.S. mil spec, they are the best you can buy, IMHO.
Interesting. Reading MIL-A-18001K there are three paragraphs of particular note (composition, dimensions, and testing).

Military specifications are in the public domain (except for some very few classified ones) and anyone can cite them. Martyr, which you don't think much of, are also built to the same spec. Of course that doesn't mean they actually MEET the spec since there is no testing unless being sold to someone like the U.S. government who either contracts for the testing or does it themselves.
 
#7 ·
Thanks to both of you for feedback, and opinions. This is the kind of feedback I was hoping to receive. I can't like your posts from my phone, but will when I return to my pc.
 
#8 ·
Some have been better than others. In particular, I liked the one that had a copper (or maybe it was brass?) core, which provided the electrical contact with the shaft, and provided reinforcement to the mounting screws. The problem is I cannot remember what brand that particular zinc was...
Godfrey..
 
#9 ·
#12 ·
Assuming you have a fiberglass boat in salt water and desire to protect underwater bronze [typical through-hull], manganese bronze [most props], and stainless steel [prop shaft], you might also consider using aluminum alloy anodes.

They last longer than zinc and are lighter to keep in inventory. Or, for the same weight as zinc you get a lot more anode and consequently useful life.

I gave up using zinc anodes several years ago and haven't had any issues [on our boat matching the above assumptions...]

This Cruising World article will get you started...

Cheers! Bill
 
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#13 ·
I use the Aluminum ones on my Saildrive in Saltwater They are recommended by Yanmar. we test and get the correct voltage readings for max protection. they are also cheaper then zinc an added plus. made by Reliance. they last about 9 months.
 
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#15 ·
That is a general statement and does not always hold true. you do not want to have different alloy anodes connected to the same galvanic cell on the same boat. there are cases where it is OK. Such as a very large water makers where they use aluminum alloys on the salt side and magnesium on the fresh water side of the system.
We use a zinc anode for the salt water cooling which is on the inside of the saildrive as it is a separate anode cell than the one on the outside of the saildrive. I was concerned that the only anode available was zinc and so consulted the experts. it was explained that you could do this as they are separate anode cells. and if they were not then there would be no reason to have any anode on the inside of an engine. the prop on a saildrive is isolated from the saildrive by rubber bushing so the prop being all bronze does not require an anode.
 
#16 ·
Yeah, it is a general statement because except in special circumstances where you've got high impedance between the anodes it's true for the vast majority of boats and boaters.

If you've got a zinc pencil in your engine and you shut your raw water seacock when not running it, it won't fight your shaft zinc most of the time. If you've got fresh water separating one system from another like your water maker or a water heater, you can get away with it. Even a bow thruster with aluminum anodes at one end of the boat may be able to coexist with zincs at the prop end, but maybe not depending on the length of the boat and the salinity of the water. Throw a bonding system into the mix and you've just added further combinatorial uncertainty.

The bottom line is that if you've done your homework and determined both theoretically and practically that mixing anode species isn't a problem on your boat, go for it. If you haven't, won't, or can't do the legwork then as a general rule mixing anodes is not advised.
 
#18 ·
I'm curious how one visually determines that one brand zinc is better than another.

A zinc is supposed to give up electrons and decay, if it is working. Therefore, one might assume a zinc that decays faster is working better. I suspect people value zincs that last longer, but that could also mean they aren't working well.

How do the experts determine the difference?
 
#19 · (Edited)
The issue that I have with sacrificial zinc anodes is that the area of a prop shaft anode which decays fastest, is also the most critical to the anode staying attached to the prop shaft; the area around the machine screws. With an anode made of zinc, this area can be completely consumed, and the anode will fall off, while there is substantial zinc remaining on the anode.

I typicaly launch in May, and plug my boat into shore power only while I am staying aboard while in the marina. Typically this is when I am teaching a class at the marina. When I am not planning to be aboard for more than a day, I unplug at the dock box. I also have a galvanic isolator installed on the AC grounding line. The bronze through hulls on my boat are not connected to the bonding circuit (yes, I know the tradeoff that I am making). Come late August, if I am using 100% zinc anodes, at least one of my anodes will have fallen off.

I have learned that one trick to prevent this is to paint a stripe of nailpolish around the exterior surface of the zinc, from the hole for the screw, to the other hole for that same screw. This slows the erosion of the zinc in that area, and allows the screw to hold the remainder of the zinc to stay in place. Now I have to find some nailpolish...

If the zinc has a copper core, this helps with the electrical connection to the propshaft, and, depending upon how the core is constructed, it can help mitigate the zinc falling off.

FWIW - I just bought 6 Camp X-3 sacrificial zinc anodes for ~$50 total. These should hold me for a season and a half.
 
#26 · (Edited)
The issue that I have with sacrificial zinc anodes is that the area of a prop shaft anode which decays fastest, is also the most critical to the anode staying attached to the prop shaft; the area around the machine screws. With an anode made of zinc, this area can be completely consumed, and the anode will fall off, while there is substantial zinc remaining on the anode.

I typicaly launch in May, and plug my boat into shore power only while I am staying aboard while in the marina. Typically this is when I am teaching a class at the marina. When I am not planning to be aboard for more than a day, I unplug at the dock box. I also have a galvanic isolator installed on the AC grounding line. The bronze through hulls on my boat are not connected to the bonding circuit (yes, I know the tradeoff that I am making). Come late August, if I am using 100% zinc anodes, at least one of my anodes will have fallen off.
To be clear, I install 2 prop shaft zincs.

I am loosing a zinc after 4 months, but not necessarilly completely consuming the zinc. I believe that the area of the zinc around the screws is consumed, and that once this happens, the zinc simply falls off.

I replaced a missing zinc on my propshaft in August. That zinc did not have the copper core that the Camp zinc's have. The other zinc, which is a Camp, survived the entire 5 month season, and the remainder is still on the shaft. (I'll have to take some pictures of the ramainders of my zincs and post them later this week.)

I believe that part of the problem may actually be my boat. I have a stainless steel shaft, a bronze prop and strut, and a PSS Shaft seal. The engine is tied to the bonding circuit, as is the lead keel. Many of you know that the PSS Shaft seal has (I believe this is key) a graphite flange, which seals against a stainless steel rotor, which is mechanically, and electrically, attached to the propshaft via stainless steel set screws.

Looking at the galvanic series table;


you can see that there is a large electrical potential between graphite and zinc. I believe that this electrical potential is, at least partially, the cause of the increased zinc consumption.
 
#21 ·
It is 4 months, but ya I agree that's a lot of zincs. I suspect that it is one of my neighbors (or the dock), as the guy next to me was complaining of the same problem.
 
#23 ·
I did a 1-year side-by-side test of zincs and have a few observations.

Nail polish. I would be interested in pictures. In my tests it didn't do much. Mostly the corrosion worked under it.

Milspec. If they are all milspec, guess what; corrosion rate just depends on mass. Heavier last longer.

I seriously doubt a brass ball makes any difference.

Grease. If you are worried about contact, why not do what you do for electrical contacts; waterproof grease? I used it on several dozen and it seemed to help. Certainly wastage was very uniform.
 
#24 ·
I get a season (7 months in the water) on one set of anodes, but only barely. They are 90% decayed by then. I prefer to replace once mid-season, but don't always get to it. Didn't this year. Fingers crossed.

I don't fully comprehend why the Max Prop zinc goes fastest. He whole thing is bronze (except the screws), so it should be protecting against the conenction to the shaft. But then, why wouldn't the shaft zinc protect it.
 
#28 ·
... and I dug this up in another (related) thread;
IF your marina is a HOT marina, depending upon the time you want to have your boat dived and zinc replaced, will depend upon HOW many zincs to put on. With 2 zincs, I go about 4 months, 3 zincs I can get a bit more ie 7 months and one will be dang near gone! ie literally! My max prop does not have a tip zinc from what i can tell, so the extra zinc is liked by a lot of folks in my marina, recommended by the local repair place at the marina to stave off excess damage.

The how much frankly will depend upon the marina etc!
....

marty
 
#31 ·
I was finally able to figure out what brand of zinc lasted so long.

In my pic above, the remains of the zinc on the left, which lasted 5+ months is a B&S ~ $19. The zinc on the right, a Camp was only in the water for 2 months. The predecessor to the zinc on the right, also a Camp, fell off at less than 4 months. IMHO it is worth paying 2x for a zinc that will last twice as long because it will save me from having to change the zinc in the water. While I have a lot of respect for Maine Sail's recommendadtions, I am NOT going to spend $43 each (5X the price of a Camp) for sacrificial zinc anodes.

I wish that I could have figured this out before I bought a supply of six Camp zincs... Going forward, I will spend the extra $ for a B&S.

Hopefully, some of you will learn from my mistake.
 
#34 ·
That's pretty obvious, which is why it's the first thing I had tried. I got hundreds of hits, but upon going to dozens of pages they all said, "Material: zinc". I've also talked on the phone to actual people at West Marine, Defender, and BoatZincs.com and got pretty much the same answer that "it's not that important, just use zinc for the pencil, even though you will have aluminum on the shaft." I'm unwilling to accept that answer at this point.

Maybe I missed something, or Google's smart searching algorithm buries it on page 98 for me but puts it at the top for you. But if someone could post a link to the source that you used to purchase your aluminum pencil anodes, I'll follow up.
 
#36 · (Edited)
When I look, they all list aluminum for shaft and hull, but when you go to pencil anodes, they only show zinc.

So I'd appreciate it if you show me a link that lists aluminum pencils on their inventory. I'll take it from there.

Your statement about no problem mixing zinc and aluminum is a little surprising. I'd welcome some debate on that topic. (Data taken with a reference cell automatically wins the debate. lol) My heat exchanger has continuity with engine block and transmission, so I believe the pencil is just there to protect from voltage drop due to the long path and marginal conductivity through the transmission to the prop shaft. But even with marginal continuity, mixing anodes may be dangerous IMO.
 
#38 ·
Been doing aluminum and zinc pencil for several years on two different boats. one is shaft and the other is saildrive. do not see any problems. inside the engine is a different Galvanic cell. just like two batteries separate electrolyte.
 
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#40 ·
Thanks for the info. That link wasn't first on my list - it was buried down a few pages. That's the only one I've found with aluminum.

But Drew's observations may lead me to stick with zinc for my heat exchanger. I'm going to have to renew my lapsed Practical Sailor subscription and check it out for myself. The PS tests in Rockhold Creek would be very relevant, even though I've moved up the bay a ways.

I'll do some continuity checks when I get to the boat, but I now realize that even if I have full continuity of the "ground"/cathodic surfaces, the respective electrolye baths may be separated far enough apart that different anodic materials may not feed off each other. I'm just starting to understand this stuff. I didn't worry about it on my prior boat because I just pulled the outboard out of the (fresh) water to avoid corrosion.

I'm also going to look over my shaft zinc anodes more closely. I think there were some pretty strong signs of white zinc oxide passivation layers forming in the pitted areas, so aluminum would almost certainly be better.

FWIW, I do not have an anode in my hot water heater. Mfr's recommendation is not to use one unless there is known high corrosive content in the fresh water used to fill it.
 
#42 ·
I think I've decided to stick with zinc for both shaft and HX pencil. I picked up a new shaft anode at WestMarine/PortSupply today. But my zinc from last year had only moderate erosion - it has about 80% of the zinc remaining. It was a short season, with launch not occurring until June 19, so I am not sure I can get another full-length season out of the old zinc.

Is there any reason not to put the new zinc on the shaft, and also leave the old one there?

Also, it looks like the yard painted my strut with the same Barnacle Barrier paint that they used on the prop. Is their any reason not to paint the strut with normal ablative antifouling paint that I'll be using on the bottom?
 
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