question about zinc selection

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
M

maggiecat1003

Veteran Member
Joined
Feb 15, 2021
Messages
26
Our boat docks in the Housatonic River and we boat in the LI Sound. Last year I put traditional Zinc based "zincs" on our boat. I know there are different metals in different types of zincs plates. I put the ones on that were recommended at the nearby West Marine but I am not sure they are correct.

Should we be using the aluminum based for anti corrosion based on the salinity of the river?

We are also replacing the galvanic isolator this season while out on the hard as we blew through the new zincs I put on last year and I am concerned about this a problem to be updated.

Any advice is appreciated.
 
maggiecat1003 said:
Our boat docks in the Housatonic River and we boat in the LI Sound. Last year I put traditional Zinc based "zincs" on our boat. I know there are different metals in different types of zincs plates. I put the ones on that were recommended at the nearby West Marine but I am not sure they are correct.

Should we be using the aluminum based for anti corrosion based on the salinity of the river?

We are also replacing the galvanic isolator this season while out on the hard as we blew through the new zincs I put on last year and I am concerned about this a problem to be updated.

Any advice is appreciated.
Click to expand...

Hi Maggie,

I am also in the river, where do you keep your boat? I'm at PYC next door to Safe Harbor in Stratford. My zincs are also pretty shot by the end of the season (End of April till end of October). I've thought about aluminum since the water is somewhat brackish. I have't tried them yet because my understanding is that you shouldn't mix Al and Zinc and I'm not sure I can get everything in Aluminum including the ones in the diesel, thrusters, etc. I'm guessing I can, just haven't spent the time or effort looking. I'm content going through a set of zincs in 6 mos and replacing them all in the spring for now. I haven't seen them completely erode or fail in a season. A friend also in the river experiences the same. At first I suspected an electrical problem but everything checks out ok on my boat. Have you asked other boaters near you what they are using?
 
Last edited:
Sorry for not being able to cut in the chart, but I'm doing this on my phone.

https://www.boatzincs.com/faqs.html

Go down to question T7 and there is a chart to help you select the right anode based on your situation. West Marine probably recommends zinc anodes because that's what they carry, not because its best for people in your area.

Regarding mixing Al and zinc, you should have all of the same type outside your boat, but the engine is in a different body of water (the water in the heat exchanger) so that anode can be different than the hull anodes. I have aluminum anodes on my hull and zinc in the engine, but I'm going to go to aluminum in the engine as well. I cant remember the supplier off the top of my head, but I'll check my notes and let you know who has aluminum engine anodes.
 
Last edited:
Maggie,
First off, corrosion issues (including anode depletion) can be a very variable and complex issue where even the "experts" can have vastly differing opinions (for example bond or isolate the various metals).

Also, I am not an expert on this subject, but have owned boats for almost 20 years and have done a reasonable amount of research on the subject. It is my understanding that (in theory) when a zinc anode is immersed in freshwater (often brackish as well), that a coating develops on the zinc material greatly reducing (or even eliminating) it's effectiveness. The only way to "get back to a functioning status" is to scrape off the coating. Just operating the boat does not do it. Therefore, in your case (mooring in a river) aluminum anodes would probably be the best choice as they work in all water types and are not subject to the same "coating" issues. You are correct, all anodes in the same body of water (ocean, river, etc.) should be of the same material, especially when a bonding system is in place (all items that are part of the bonding system). I freshwater flushed my engine and generator, so I started using aluminum anodes from Performance Metals for that reason, but left zinc on the boat exterior as we were in the ocean.

I strongly advise you to discuss with your neighbouring boats their anode experience, as if yours differs greatly from theirs you may be best served hiring a professional in this area of expertise. Stray current from your boat or others nearby can cause anodes to erode quickly, so this should not be ruled out without some method of determining if that is a concern for you. Good luck with this problem, the answers may be harder to determine than you hope (I hope not).
 
I would go with aluminum anodes. And as said above the engine is a separate body of water so you can use different anodes in the engine but I would try to get aluminum for the engine also.
 
I agree with both answers above. All anodes that are bonded together need to be of the same material. Therefore, engine anodes and thruster anodes (from what I have researched) can be zinc if they are not available in AL. I asked (by email) the opinion of the manager of the maintenance team at the marina where I store for the winter and pay for some services. He is very good and I fully trust and respect him. When I get his answer I will post it here.

There is a school of thought that says not to bond metal thru-hulls. It reduces the chance of stray current problems and also lighning strike problems. West Marine has an article recommending not bonding the thru-hulls and my understanding is that bonding them is common in the US but not in other countries.

As Tom points out, it's a complicated issue with differing opinions, so speak to an expert or 2 if you can. I personally wouldn't simply replace a galvanic isolator just because you think it could be a problem.
 
Bkay said:
Ah, found it. Performance Metals has aluminum engine anodes if you go that route.

https://performancemetals.com/collections/pencil-anodes
Click to expand...

I agree - PM has been a great source for me for ALUM engine anodes. Theirs have a steel wire core that reduces breakage and they have a very wide selection. You just need Plug pipe thread, rod dia and rod length to search through their availability. If you can't find an exact length easy to go ned longer and cut down if not enough room for the longer one.

Side Power Thrusters have gone to alum exclusively and not a problem as the thrusters are not tied to other anodes.
 
Thank you all I have learned a huge amount from the expertise here from helpful input. More points on current, corrosion etc. than I realized. Complex subject, boats, metal, salt water, current, anodes; so many input variables

Based on above inputs I am coming to the following conclusions for next season and my pending work.

Aluminum all around including the engine pencils (learning for me).
I will hold off on the galvanic isolator but for sure identify where it is located on the boat. I have already various suggestions of where to look.

So am I also understanding correctly that if someone is leaking DC charge into the water around us it corrodes us as well?

Blue Moon I have seen your boat at PYC. We are on the south side of the doc closest to you. Based on your comments my zincs did not do much different from yours if you replace every season. That is easy enough as well. This is a job I can handle myself!

Comodave - I have not seen your boat but I believe you run the marina by the bridge and restaurant upriver from where we are at Brewer SH.

Thanks for all the advice. The best thing about learning is all it takes is asking questions and the willingness to read.

Appreciate the help.
The weblink for the zinc orders makes it easy.
 
Hi Maggie,

Welcome to TF, lots to learn from lots of great people here. If you are ever intersted in moving a couple hundered feet North, I can sponsor you for the club and you'll save about 50%. Not certain but I think slips are available, if not you can wait till one is.

My understanding about other boats leaking current is yes, it can affect your zincs. Current in the water wants to reach electrical ground and will travel through the path of least resistance. So that path could be through your thru-hulls and bonding system (e.g. in your bow, though your wires and out your stern to reach the dock). I've also heard that problems are rarely another boat, not that it doesn't happen, I think it's more wishful thinking than a common occurence. Good to know we are experiencing similar corrosion. A friend on the other side of the river does as well. I think it's just the nature of where we are. Let me know how you make out with the AL.

Also, FYI I reached out to SHM to diagnose my boat and they do apprently have the equipment and expertise. In the end I did some measurements myself and convinced myself I was ok. But if you suspect a problem, reach out to them before you launch. Some measurements need to be done in the water and some out.
 
When I brought an aluminum boat back to my dock, I found an ABYC certified corrosion dude (I think that's the technical term) to do an electrical survey while I watched. He charged by the hour plus an upcharge to come to my dock (he works at a boatbuilder a few miles away) and I told him I wanted to watch so I never needed to hire him again.

He was great and took time to explain what he was looking at and why. It actually went pretty quickly since I could take care of throwing switches and connecting/disconnecting power while he took readings. I was out for the price of an hour and a half of his time, plus I went out and bought a silver/silver chloride half cell and now incorporate that into my quarterly maintenance program.

I acknowledge, that's a bit of overkill for someone who owns a fiberglass boat (it's a mandatory skill if you own aluminum), but it's still quite interesting to watch and pretty easy to do once you know how. If you decide to have someone take a look at your setup and amount of anodes, by all means arrange to be there to assist and watch.
 
No, I don’t run a marina. I am retired, thankfully, and that allows me to work on my boat pretty much every day.
 
Comodave,
Sorry for the mixup on your specifics. I guess I should have looked closely at your city!!
Anyway thank you for the good advice.
Congrats on being retired.
I would be happy to work on my boat every day if I could!!!
Still have 2 college boys and one to go for college to sort out. Until them the boat is still a part time hobby. Right now hanging on to get through this phase of life with a smile on my face!
 
Keep it simple.
Aluminium for fresh water, lead for salt.
If you want to get really technical then make a 'ring main' of all your seacocks and link them to your anode.
 
Irish Rambler said:
Keep it simple.
Aluminium for fresh water, lead for salt.
If you want to get really technical then make a 'ring main' of all your seacocks and link them to your anode.
Click to expand...
Just curious... what are you protecting with lead?
Never heard of that for general salt water use but maybe something unique?
 
Bacchus said:
Just curious... what are you protecting with lead?
Never heard of that for general salt water use but maybe something unique?
Click to expand...

Protecting the environment from wildlife, maybe?
 
Maybe he meant to say zinc instead of lead. Never heard of using lead as an anode. Don’t really know why people still use zinc at all. Aluminum works everywhere and is better for the environment. I can see a day when zinc will not be legal like copper in bottom paint but I am not an expert in environmental issues…
 
Comodave said:
Maybe he meant to say zinc instead of lead. Never heard of using lead as an anode. Don’t really know why people still use zinc at all. Aluminum works everywhere and is better for the environment. I can see a day when zinc will not be legal like copper in bottom paint but I am not an expert in environmental issues…
Click to expand...

From what I see around here, I don't think most long-time boaters even know about AL anodes or even if they did they don't care. They have been replacing zincs all their lives so they see no reason to change. But I agree with you and will be migrating to AL going forward (I think).
 
Yes, some will never try anything new. Just because it has been done that way forever doesn’t mean that there isn’t a better way to do it now.
 
Apologies If my humour offended anyone and my reference to lead should of course be read as zinc.
The bottom line is that whatever metal you use has to be a less 'Royal' metal than the pieces you are trying to protect i.e propeller/shaft/ seacocks etc.
The logic is that any electrical field will attack the less 'Royal' softer disposable/easily replaceable metal attached to your boat and will disintegrate/rot away first, leaving your propeller/shaft/ seacocks intact.
As Comodave refers to there are other methods available which perform a similar job by creating an electrical field to 'ring fence' your boat.
As others have mentioned its hard to break tradition as the cheap anodes are usually easily exchanged by the owner when he/she lifts their boat for a hull clean.
Incidentally I see some folk say they lift out annually because of fouling.
In my experience I use the anti fouling the local fishermen use as the locals will use what they find most effective for local conditions, as such I only lift out once every five years.
 
Last edited:
Comodave said:
Yes, some will never try anything new. Just because it has been done that way forever doesn’t mean that there isn’t a better way to do it now.
Click to expand...

I don't disagree. I'm just saying that is probably the reason. A friend nearby who has had boats his entire life and is docked in the same area as me and when I asked him if he had tried AL anodes, he looked at me like I had 2 heads.
 
Irish Rambler said:
Apologies If my humour offended anyone and my reference to lead should of course be read as zinc.
The bottom line is that whatever metal you use has to be a less 'Royal' metal than the pieces you are trying to protect i.e propeller/shaft/ seacocks etc.
The logic is that any electrical field will attack the less 'Royal' softer disposable/easily replaceable metal attached to your boat and will disintegrate/rot away first, leaving your propeller/shaft/ seacocks intact.
As Comodave refers to there are other methods available which perform a similar job by creating an electrical field to 'ring fence' your boat.
As others have mentioned its hard to break tradition as the cheap anodes are usually easily exchanged by the owner when he/she lifts their boat for a hull clean.
Incidentally I see some folk say they lift out annually because of fouling.
In my experience I use the anti fouling the local fishermen use as the locals will use what they find most effective for local conditions, as such I only lift out once every five years.
Click to expand...


I have to lift out annualy for winter storage and after 6 mos in the water my zincs are mostly used up and my hull could use a cleaning, especially from barnacles on the underwater metals. I could never go multiple years.
 
I like to get mine out at least once every two years. I want to inspect the bottom myself. My own sanity check.
 
Redhook98 said:
I like to get mine out at least once every two years. I want to inspect the bottom myself. My own sanity check.
Click to expand...

You own a big slow expensive boat. Your sanity does not need checking. lol
 
Anode selection

Zinc, aluminum or Magnesium are all anodes often called 'zincs' in a generic manor.

I'd recommend that you might have a 'leak' that could be causing the fast depletion of your anodes. The galvanic isolator may need to be replaced but if you have a ground that is not working a new GI won't stop the fast depletion.

There are ways to check but I'd suggest an electrician (ABYC certified) come to your boat to check it out. That would be the safest approach.

Good luck.
 
I try to get people to refer to anodes as anodes not zincs unless they actually are made out of zinc. Too many people, including the PO of our current boat, think that they need zinc anodes. And they use zinc anodes in freshwater. The PO told me the zincs on our current boat were great because they never needed replacing. Duh!!! I checked what was on the boat when we bought it and they were indeed zinc anodes in the Great Lakes. They are now aluminum anodes.
 
Good point Dave. And to further that thought, my boat was a freshwater boat before I bought it. It came with a stern zinc plate from the manufacturer, and pencil zincs in the Yanmar and zincs on the thrusters. I'm sure this is standard practice but I wonder why the initial commisioning didn't consider that this boat was going to be in freshwater only. There was nothing on the tabs, rudder, or shaft till I had zincs put on when I bought it and moved it to salt. (and yes, I mean "zinc" anodes). Corrosion in freshwater is not as big a problem as salt, but still it should have been properly outfitted. I don't think the previous owner paid any attention to this and maybe that's somewhat normal on lakes for casual boaters. The zincs on the thrusters were actually pretty worn, otherwise the others looked fine.
 
I don’t understand why boat builders don’t go with aluminum anodes instead of zinc anodes. Guess they have a steep learning curve too.
 
You must log in or register to reply here.

Similar threads

S
Propeller Shaft Zinc Reality Check
Replies
8
Views
463
Snapdragon III
Snapdragon III
J
Swim platform bonding
Replies
22
Views
2K
boatnbump
boatnbump
Mambo42
Used zinc annodes
Replies
22
Views
2K
Hobbit
Hobbit
Brisyboy
Prop speed and the need for zincs
Replies
6
Views
1K
Each finger a marlinspike
E
Shrew
Service/Maintenance
Replies
8
Views
737
O C Diver
O C Diver

Latest posts

Back
Top Bottom