Galvanic Corrosion/zinc depletion question.

[BAD ORCA]

So, my diver billed me for a new shaft zinc at the end of march. I was previously billed for a shaft and strut zinc at the end of december. Previously before that, my zincs were lasting 6 months between changes, or longer. Now apparently only three.

Assuming he is being honest, the only changes i have made to the boats electrical system in the past three months, was the addition of a new Marco fresh water pump and a Shurflo shower pump. The Marco is on all the time only while i'm at the boat. The Shurflo has barely been used and is generally off all the time. When I leave the boat, I leave the AC plugged in and turned on. It only powers a single batetry charger for the bilge pumps, everything else is turned off.

I have a ProMariner30 galvanic isolator which is only a couple of years old. I assume its working perfectly as my zincs previously were lasting 6 months minimum. Maybe it died so i wil test it.

What could have possibly changed to create such an increase in zinc depletion? Why only the shaft zinc and not the strut zinc? I did not physically see the zinc that was supposedly changed in december, i'm only confirming it because i was billed for its replacement. The one replaced a couple of weeks ago i physically saw as the diver showed up while i was there and was 50% depleted.

How could adding a water pump or two have an effect on galvanic current on my own boat? I struggle to completely wrap my head around galvanic corrosion. Sometimes I think I get it, but when there is an issue, I cant seem to work it out. Its possible i guess i was mis-billed and the december replacement and it never really happened, but i want to assume it did for now and try and troubleshoot this on my own.

I do have a silver/silver chloride cell (which i have played around with a little) so i can do some basic testing tomorrow. Any advice on avenues to explore specifically or pearls of wisdom you can impart? I have read many, many articles on the web, but they all seem to parrot each other and only provide a very generalized theory and simple examples. I cant find any deep dives on the subject that give real practical "in laymens term" advice and examples, so most of the articles are pretty much useless. I do own Nigel Calders boat electrical book. I will dust it off this weekend and see if its of any help.

I guess a question comes to mind first is, is this more likely an issue from a neighbors boat or another boat on the dock? I had assumed a galvanic isolator would do the job completely, but i know they can only block so much current. Can they become overwhelmed from another boat plugged in somewhere else on the dock with more serious wiring issues? How could i even tell?

 

[colemj]

Did you see the anode he took off? Was that anode the exact same brand/type as the one you used previously? Has the boat been moved to a different spot?

Anodes should be changed when they are 50% depleted. However, determining % depletion by eye isn't very accurate. It is possible that the 6 month anode was 60% depleted and the 3 month anode 40% depleted. Between them might lie your missing 3 months.

Anode chemistry and quality are different among manufacturers, and this could account for different depletion rates. Also, zinc vs aluminum materials, if you made a change there.

Different water conditions can affect anode depletion rates if the boat was in different places between anodes.

I think you are safe ignoring the water pump and shower sump as causes.

Galvanic isolators only block 1A of DC current, some double that, so they theoretically can be overwhelmed. But this is unlikely unless the issue is coming from inside your boat. Adjacent boats get a lot of blame for corrosion, but this is really a low probability. Almost all corrosion causes come from within the boat experiencing it.

Mark

 

[dlochner]

If you have the silver chloride cell from BoatZincs.com there is a new manual available. The new manual is spiral bound and has photos in color. The new manual is only available to those who bought a silver chloride cell from them. The manual does a better job of expelling the corrosion process.

 

[dLj]

Check your bilge pump wiring - it may have deteriorated.

dj

 

[BAD ORCA]

Did you see the anode he took off? Was that anode the exact same brand/type as the one you used previously? Has the boat been moved to a different spot?

Anodes should be changed when they are 50% depleted. However, determining % depletion by eye isn't very accurate. It is possible that the 6 month anode was 60% depleted and the 3 month anode 40% depleted. Between them might lie your missing 3 months.

Anode chemistry and quality are different among manufacturers, and this could account for different depletion rates. Also, zinc vs aluminum materials, if you made a change there.

Different water conditions can affect anode depletion rates if the boat was in different places between anodes.

I think you are safe ignoring the water pump and shower sump as causes.

Galvanic isolators only block 1A of DC current, some double that, so they theoretically can be overwhelmed. But this is unlikely unless the issue is coming from inside your boat. Adjacent boats get a lot of blame for corrosion, but this is really a low probability. Almost all corrosion causes come from within the boat experiencing it.

Mark

Thanks Mark. The strut and shaft zincs they replaced in December i did not see, no idea. My diver/dive service has been exclusively cleaning and replacing zincs as needed. I have asked them to leave the old ones on the dock but they never do. My boat is in a marina, same slip, hasnt moved locations. Thats a good point. I did see the one they just changed. I mean it looked about 50% depleted. Your right its hard to tell.

Good question on what zincs they use. No idea. I guess they could have switched to cheapo zincs. I have read they can deteriorate more quickly. I dont think they ever used aluminum zincs but i could be wrong. Maybe I should ask. I'll do some testing tomorrow with the silver/silver cell and if nothing looks out of the ordinary, maybe this is what happened.

 

[BAD ORCA]

If you have the silver chloride cell from BoatZincs.com there is a new manual available. The new manual is spiral bound and has photos in color. The new manual is only available to those who bought a silver chloride cell from them. The manual does a better job of expelling the corrosion process.

Good to know. Thats the one I have. I will look into getting the newer manual.

 

[BAD ORCA]

Check your bilge pump wiring - it may have deteriorated.

dj

Thanks. No its all brand new (all new couple years ago) new pumps, new wires, switch etc...All with long leads that are far up outside the bilge. same for the switch. I have a Water Witch and the leads are all lead out of the bilge. Also, my bilge is bone dry 98% of the year. Only gets some water when it rains or im draining a tank or testing the pumps. Also, nothing on my boat is bonded.

 

[BigEasy]

If you have the silver chloride cell from BoatZincs.com there is a new manual available. The new manual is spiral bound and has photos in color. The new manual is only available to those who bought a silver chloride cell from them. The manual does a better job of expelling the corrosion process.

Purchased a test cell from BoatZincs a few years ago and purchase donut shaft zincs annually from them as well as drop (fish) zincs occasionally. VP of sales told me that the new spiral bound manual costs too much to provide free of charge unless you are a regular customer. I don’t know what the definition of “regular” is; I have been purchasing from them for over 10 years….even sent him a copy of my invoice for the silver chloride test cell. I was told that the cost would be $25 + approximately $10 shipping. Have no problem with paying shipping; however, I feel that $25 for the manual is a bit much. Very disappointed with their customer service.

 

[colemj]

Who wants a big spiral bound manual on a boat? Provide it as a pdf file. Free of manufacturing cost, and probably already in that format for printing anyway.

Mark

 

[dlochner]

Who wants a big spiral bound manual on a boat?

It's 8.5"x5.5 " and 40 pages. Not all that big.

They could have cut shipping costs by using USPS Book Rate instead of regular ground shipping.

 

[BigEasy]

It's 8.5"x5.5 " and 40 pages. Not all that big.

They could have cut shipping costs by using USPS Book Rate instead of regular ground shipping.

i didn’t have a problem with paying shipping (what ever reasonable amount it is). as Mark mentioned, they could have emailed a pdf file to me. Really, put the thing in an envelope, stamp it, & place it in the outgoing mail. Just disappointed in BoatZincs lack of customer service. Am I being unreasonable?

 

[jssailem]

There is the possibility that your boat is not the problem. A neighbor may be the cause.

My diver places the used zinc’s on my boat when he makes a change. I had a neighbor boat that was causing me to change zincs 3 times a year. He moved away. Now my zincs last 6-8 months.

One idea to gain some consistency is to buy the zinc and have them available for the diver when he shows up. Boat zincs is the source I use.

My diver likes them says they are easy to install.

 

[dlochner]

i didn’t have a problem with paying shipping (what ever reasonable amount it is). as Mark mentioned, they could have emailed a pdf file to me. Really, put the thing in an envelope, stamp it, & place it in the outgoing mail. Just disappointed in BoatZincs lack of customer service. Am I being unreasonable?

This is the explanation I received from Boatzincs.com:

Hey Dave, good morning and thanks for reaching out,

Very happy to help. For customers with a CRE in their history (I see yours, all set!) we can offer a replacement Guide. The price would be $25 plus the cost of shipping. As a copyrighted piece of IP, we’re unable to offer a digital copy. I can send you a PayPal invoice if you’d like, or you’re welcome to call in with your card info if that’s easier.

The new manual contains the core testing procedure from your original manual, but with significantly more context. We hope it serves you well.

Very Best,

Tyler Tchamitchian
Vice President

 

[BigEasy]

This is the explanation I received from Boatzincs.com:

Thanks Dave. Your response from the vice president was basically the same that I received. I am not going to pursue the issue any farther; if that’s their policy, so be it. Thankfully, I am not having any corrosion issues at this time. Would like to have a copy of Boatzincs‘s updated manual for general knowledge, but I don’t have to have it. Have several sources from net, US Power squadron‘s marine electrical course book, Calder, etc.

 

[sailme88]

I was going thru shaft zincs at a steady pace. Wasn't sure if I or a neighboring boat was the source of stay electricity.
Bought a battery isolator. I've had the same shaft zincs now for the 3 rd year...

 

[BigEasy]

Bought a battery isolator. I've had the same shaft zincs now for the 3 rd year...

Same here. Silver chloride test cell didn’t reveal any onboard problem; however, diver informed me that my prop blades were showing signs of severe corrosion. Was told that nearby boat was having problems; evidently his “electrician” had common & ground wires connected that really wreaked havoc on his boat & to a lesser degree on surrounding boats. Between neighbor correcting problems on his boat & me installing a galvanic isolator, I am now replacing one shaft zinc annually. In my case it was more of a stray current corrosion vs galvanic problem. Thankfully, I was able to purchase replacement prop blades on EBay at a great price.

 

[jssailem]

@sailme88, I’m unclear how the battery isolator is connected to giving you longer zinc time. Perhaps in the process of installing it you corrected the short that was electrifying the water around your boat.

Here is a quote from battle born about battery isolators.

What Is a Battery Isolator?
A battery isolator is a device that typically runs between a starter battery and a secondary battery. It can disconnect a battery from a power system either for charging or discharging purposes.

Most often, however, these devices protect a secondary or backup battery from any unnecessary drain.

If you’re considering a deep dive into battery isolators this might help. What Is a Battery Isolator?

 

[BAD ORCA]

There is the possibility that your boat is not the problem. A neighbor may be the cause.

My diver places the used zinc’s on my boat when he makes a change. I had a neighbor boat that was causing me to change zincs 3 times a year. He moved away. Now my zincs last 6-8 months.

One idea to gain some consistency is to buy the zinc and have them available for the diver when he shows up. Boat zincs is the source I use.

My diver likes them says they are easy to install.

I agree now. I think its a neighbor or maybe what Mark mentions above. I did the silver/silver chloride test this past weekend and everything checked out perfect, so my boats electrical is not the issue. I could have just been mistakenly billed also. I will have to monitor the situation. I might consider telling the dive company that I will start replacing them instead if this keeps happening. Maybe they switched to cheapo zincs. Now that I know my boats potential with fresh zinc, I can monitor it and test once a month to see how much it changes. With fresh zincs its 870. I think the low end of the range is 550. When it gets to 750 and then 650 ranges, maybe i will take a dive on the boat and see what that looks like.

 

[BAD ORCA]

Same here. Silver chloride test cell didn’t reveal any onboard problem; however, diver informed me that my prop blades were showing signs of severe corrosion. Was told that nearby boat was having problems; evidently his “electrician” had common & ground wires connected that really wreaked havoc on his boat & to a lesser degree on surrounding boats. Between neighbor correcting problems on his boat & me installing a galvanic isolator, I am now replacing one shaft zinc annually. In my case it was more of a stray current corrosion vs galvanic problem. Thankfully, I was able to purchase replacement prop blades on EBay at a great price.

OOF! damn that sucks. My neighbors on either side of me a fairly well off financially and seem to take good care of their boats. They use them all the time as well. I would assume their electrical and zincs are always in proper working condition.

 

[jssailem]

It really helps to know if you’re causing your own zinc corrosion. I bought the tester as well, and once I was pleased that my boat wasn’t generating the erosion of my zinc’s. I started checking near other boats, and though I could not discover the source, it really became obvious when the Boat nearby moved away.