Knowing a "hot" marina

How can we tell if a marina has an excessive amount of voltage running thru the water? Not having much experience with electricity, I thought there should be a way to use a volt meter or amp meter to see if a marina is considered hot. I'm thinking a marina shouldn't show any voltage in the water but maybe there always is some level.

Anyone knowledgeable in this?

The idea of a 'hot marina' is a myth, like the Greeks believing Zeus threw the lightening bolts down at earth when he was mad because they just didn't understand the cause of lightning.

In rare cases a boat can be affected by a neighbor boat with a stray current corrosion problem if they don't have a galvanic isolator, but almost always when a boat has a stray current corrosion issue it's their own problem.

Galvanic corrosion affects everyone everywhere.

AC leakage current from a boat can make the water dangerous to swim in, but is not a corrosion problem.

It's a complicated subject with few experts and lots of laymen with only partial understanding. If you're having an issue consult one of the experts. If you just want to learn the ABYC Corrosion course is excellent.

I had an issue with current in the water, it was discovered that previous work on my power pedestal left the ground wire unattached. I was burning through zincs at a higher rate than previous. Apparently there is a disc that measures the current in the water around your boat, the marina electrician said it is available at West Marine.

^^^^^ Exactly what I mean. An AC grounding conductor disconnected from a dock pedestal won't make galvanic corrosion accelerate and use an anode faster. It's a safety issue, but AC current in the water won't make you go through anodes faster. Without the AC grounding conductor your boat is now isolated from the surrounding boats even if you don't have a galvanic isolator (you should have one though).

Anyone giving expert advice should be able to draw the electrical circuit out of what is happening and explain the electron/ion flow path.

Post 3 said he was burning through zincs with pedestal ground unconnected. Explain why that was occurring @Fleming

SteveK said:

Post 3 said he was burning through zincs with pedestal ground unconnected. Explain why that was occurring @Fleming[/USER]

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I can't. It makes no sense. Lots of things affect the speed at which anodes are wasted. Salinity, current, frequency that the boat is used, bonding system, size and composition of the anode, other anodes on the vessel and their state, etc. But disconnecting the AC grounding wire will only reduce the risk of galvanic corrosion, not increase it.

For galvanic corrosion you need two different metals, an electrical connection between them, and both immersed in an electrolytic solution. If you can't draw out the electrical path, then it didn't happen that way.

OK, I will conjecture. The poster @Jorgeinseal probably has a DC positive wire current entering the water through a thru hull creating a current thru the zincs

As Fleming said this is a complicated subject. I often need to refer back to my training notes to refresh my memory on everything.

A boat that has a lot of running gear and zinc can find itself protecting the entire marina which would lead to excessive zinc consumption. Usually, a galvanic isolator solves this issue but, unsuspecting connections around the galvanic isolator can occur through things like phone lines, internet connections and other possibilities I have not thought of.

SteveK said:

OK, I will conjecture. The poster @Jorgeinseal probably has a DC positive wire current entering the water through a thru hull creating a current thru the zincs

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This is the most common scenario.

A DC positive wire causing current entering the water through a thru hull (Stray current corrosion, often erroneously called electrolysis) is easily differentiated from galvanic corrosion by time. Stray current corrosion happens over a matter of days, galvanic corrosion over months.

For those wanting to learn more, 'Metal corrosion in boats' by Nigel Warren is a great reference.

tiltrider1 said:

This is the most common scenario.

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From a bad negative wire that results in current "grounding" and going down a bonding wire

I didn't go into detail as to my situation, the OP asked if there was a way to measure current in the water and I replied "apparently" based on what the marina electrician told me. I've had 2 marine electricians out on separate occasions who tested my bonding system and everything was fine. This started when the marina upgraded the power pedestal due to a defective breaker and subsequently my boat started going through zincs monthly. Upon redispatch, they encountered the unconnected ground wire within the power pedestal. I can't explain as I'm no expert but my zinc burn rate is back to prior schedule. Maybe they lied to cover up some prior mistake.

I can make up scenario's that could explain what you were told and what you experienced but then it would mean your boat was leaking AC current. What is more likely is that you weren't told everything or weren't told correctly what was found and what was changed.

Here is what I found on my boat while rewiring and adding the Lithium, and inverter/charger system and ELCI. In prep for the ELCI I wanted to check for leakage prior so I wouldn't lock my self out. Prior to this I had to change zincs about every 4 months. So much that I gave my divers free reign to change them when needed. Its been months now since identifying the issue, troubleshooting and correcting it and the zincs look new. Very glad to have this fixed.

Barking Sands said:

Here is what I found on my boat while rewiring and adding the Lithium, and inverter/charger system and ELCI. In prep for the ELCI I wanted to check for leakage prior so I wouldn't lock my self out. Prior to this I had to change zincs about every 4 months. So much that I gave my divers free reign to change them when needed. Its been months now since identifying the issue, troubleshooting and correcting it and the zincs look new. Very glad to have this fixed.

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To be clear, you are saying that your zincs were wearing out because of an AC leak to the bonding system. A 4A~ AC leak to ground found and corrected stopped this wear.
This sounds like stray AC current causes zinc to wear because your boat is grounding that AC into the water and it travels to the neighbor boat and then to shore. While all bonded metal is 'hot' the zinc is the one that shows wear first.
I have never liked the mandate that AC ground be bonded to DC negative with this in mind.

SteveK said:

To be clear, you are saying that your zincs were wearing out because of an AC leak to the bonding system. A 4A~ AC leak to ground found and corrected stopped this wear.
This sounds like stray AC current causes zinc to wear because your boat is grounding that AC into the water and it travels to the neighbor boat and then to shore. While all bonded metal is 'hot' the zinc is the one that shows wear first.
I have never liked the mandate that AC ground be bonded to DC negative with this in mind.

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Yes..there was 4 amps of AC leakage when the neutral and ground were reversed at the plug that supplied power to the lead acid battery bank charger at the time. It was measured that about 3.7xx of that AC leakage was measured returning through the green ground system with shore power cord. These measurements were with about 15 amps coming into the boat for systems like air conditioning. But that left a small amount going somewhere else. Into the water through the zincs I presume. In addition, now thinking about it, when I had a bad battery last year, which caused the batt charger to continuously output more amps to the bank, the zinc wear was much worse. At the time I attributed the higher zinc wear to the bad battery and some unknown issue in the DC system. But now I suspect I just had a higher continuous AC leakage at that time due to higher amp load of the charger trying the charge a bad battery in that very same miswired AC circuit.

So in this case 4 amps of AC leakage with 3.7xx traveling back through the green ground wire and some small amount presumably going out the zincs.

I can give you a real life example, my boat when I bought it in 2012.

A guy down the finger about half a dozen berths from me complained to the marina that his zincs were disappearing much faster than in his previous marina. So they tested the shorepower lead at each boat on the finger. The test was to use a custom section of lead that exposed a few feet of all 3 wires. They had a short section with appropriate male & female connectors on either end to enable it to be temporarily placed between the pedestal and your shorepower lead. And then use a clamp meter on each of the 3 wires in turn. A difference in current between live & neutral indicated return via the water. They very quickly ascertained my boat was the problem one. To clarify the situation they asked me to load up the 30A shorepower to max by using AC appliances. That test revealed that 50%, 15 amps, was being returned via the water. A measured number, not infered or calculated. Just as well the boat was in saltwater and not fresh water! Not good at all to say the least, but neither the PO or myself had noticed anything unusual on my boat itself.

It took a very experienced marine electrician quite a long time to find the problem. It was an incorrect neutral to earth jumper on one part of the "shore-Gen-Inverter-off" Krauss&Naimer 3 pole rotary selector switch. The reason it took so long to find was that the switch was in a tight spot, and the errant jumper was only visible when using a small mirror on a telescopic arm, together with a flashlight. Very easy to fix once discovered. But few marina's would routinely test everyone's shorepower connections. It takes someone to recognise the marina is "hot" and ask the marina to systematically test each boats connection to find the cause.

That is why they revised the NEC to include GFIs on the docks. Electrical things can work but still be deadly.

We are getting conflicting information or I am not understanding what I am reading.
Several posters claim you do not lose zinc to AC current AND several posters have shown that you do indeed lose zinc to AC leaks into the water.
Come on, why is there an argument then that claims only DC current loses zinc. Can't have it both ways.

SteveK said:

We are getting conflicting information or I am not understanding what I am reading.
Several posters claim you do not lose zinc to AC current AND several posters have shown that you do indeed lose zinc to AC leaks into the water.
Come on, why is there an argument then that claims only DC current loses zinc. Can't have it both ways.

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Because the ones claiming AC leakage current caused the problem are using correlation to justify causation.

The 1st, "Here is what I found on my boat while rewiring and adding the Lithium, and inverter/charger system and ELCI." Assuming that one electrical problem was the cause when extensive other work was done. Correlation not causation.

The 2nd, causing a problem 6 boats away? Where's the causation? What happened to the 6 boats in between? What happened to the boat 6 slips away after your stray AC current leakage was fixed? Documented change in the wasting of his anodes, immediately?

Yes, AC current can cause corrosion, but it takes a LOT of current over a very small surface area and it's generally only aluminum that is affected.

A properly bonded boat will be spreading that AC leakage current over all the bonded underwater metals.

I've never conducted experiments myself, but every reputable source of marine corrosion information will tell you that boat corrosion issues are due to DC current.

Everyone says that aliens don't exist, but I saw some funny looking lights in the sky the other day so that's proof that they must exist and are here visiting us.

I agree with Fleming.

In fact the marina was hot if you were a swimmer and it would have been deadly hot if it was a fresh water marina.

The marina only supplies AC current so they tested for AC, found an issue and had it corrected. They then told the complainer that the marina is no longer hot and any issues with zincs is on him.

Now, what is often not said. The complainer very likely had a situation in his previous marina were the boat next to him had a lot of running gear and a lot of zink. The complainer’s boat was probably receiving protection from that boat. Now he changes marinas and is no longer receiving the benefit he was getting. Odds are his old neighbor is now finding his zincs last longer and the complainer is now experiencing normal zinc life.

Install an isolation transformer and all this becomes moot anyway. Plus, you'll never have to worry about ELCI dock power being snooty about your inverter phase sync again.

I moor in a freshwater marina which has older (non-ELCI/non-GFI) AC power. That can be a very dangerous situation, particularly where old boats with old, jury-rigged wiring are involved. The marina requires bi-annual current leak testing of every vessel using a system just like Insequent describes above. Any vessel which fails the test is disconnected from AC and cannot reconnect until it passes the test. That's the only way the marina can keep their insurance.

Because I have an isolation transformer, this is a non-issue for me. There is no measurable current leakage on my boat, so the testing is a pro-forma exercise in my case. But last year a boat near me failed with more than a full amp of measured leakage. No bueno. Were my anodes dissolving away because of that? Absolutely not. But if anybody had jumped in the water around there, it would have been a very bad situation.

Why not stop leakage of AC into the water by not bonding AC ground to DC bonding system? Or isolate battery DC negative from the zinc bonding?

Ertyqway said:

Install an isolation transformer and all this becomes moot anyway. Plus, you'll never have to worry about ELCI dock power being snooty about your inverter phase sync again.

I moor in a freshwater marina which has older (non-ELCI/non-GFI) AC power. That can be a very dangerous situation, particularly where old boats with old, jury-rigged wiring are involved. The marina requires bi-annual current leak testing of every vessel using a system just like Insequent describes above. Any vessel which fails the test is disconnected from AC and cannot reconnect until it passes the test. That's the only way the marina can keep their insurance.

Because I have an isolation transformer, this is a non-issue for me. There is no measurable current leakage on my boat, so the testing is a pro-forma exercise in my case. But last year a boat near me failed with more than a full amp of measured leakage. No bueno. Were my anodes dissolving away because of that? Absolutely not. But if anybody had jumped in the water around there, it would have been a very bad situation.

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In practice you are correct. Technically, this is not correct. While an isolation transformer masks the issue and allows you to function in the new ELCI environment you still have something that is wrong.

In the case where a neutral and a ground are swapped you have AC flowing through the whole boat. Under the right circumstances something bad could occur.

In the case of a slow switching inverter you only momentarily have an issue so the IT is a proper fix.

SteveK said:

We are getting conflicting information or I am not understanding what I am reading.
Several posters claim you do not lose zinc to AC current AND several posters have shown that you do indeed lose zinc to AC leaks into the water.
Come on, why is there an argument then that claims only DC current loses zinc. Can't have it both ways.

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I think some of the discrepancy comes in classifying zinc wasting rate or even rapid galvanic corrosion VS just having a slightly elevated loss of zincs. In my case I was changing zincs only slightly faster than my dock neighbors. If I let them erode more I could get 6 months from them before I was comfortable. But generally 4 months. Neighbors would get 1 to 1.5 years. If you have zincs that are lasting 1 month or have massive metal loss or pinking of props that would seem to point towards a DC problem.

From my limited understanding DC is much better at galvanic action because it is a "continuous stream" of electrons in one direction providing a continuous and one way anode/cathode reaction. And of course AC alternates directions which greatly reduces the this reaction. But there is no reason to believe that AC current completely nullifies any galvanic action to 0 potential when local chemical reactions are involved. I would be willing to bet there are losses in an AC leak that are one way due to chemistry differences at the anode. I see no reason why what goes out and off an anode chemically, has to return completely simply because the current reverses. I suspect that the vast majority of alarming, rapid, and destructive cases of stray current corrosion are all DC issues, but that AC issues like mine that will connect considerable current right to the anodes can likely cause accelerated losses that are noticeable.

tiltrider1 said:

In practice you are correct. Technically, this is not correct. While an isolation transformer masks the issue and allows you to function in the new ELCI environment you still have something that is wrong.

In the case where a neutral and a ground are swapped you have AC flowing through the whole boat. Under the right circumstances something bad could occur.

In the case of a slow switching inverter you only momentarily have an issue so the IT is a proper fix.

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It's true that if you have a current leak, the IT will make it so that it's not readable from the shore-side connection. That was not an issue in my case. We installed it because ELCI pedestals don't like slow inverter phase sync at all and treat it like a current leak even when there isn't one. ITs also have numerous other benefits as well, both for safety and maintenance, so I recommend them generally. But you are right that they won't fix a circuit leaking directly into the water.

SteveK said:

Why not stop leakage of AC into the water by not bonding AC ground to DC bonding system? Or isolate battery DC negative from the zinc bonding?

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The AC ground to DC ground connection is made for safety purposes. It's generally considered that the safety risk of not having it is greater than the safety risk and galvanic corrosion risk from having it. Plus the galvanic corrosion risk can be eliminated with a $100 galvanic isolator, so the trade off is usually considered a good one from a safety stand point. AC current can and does occasionally get onto a DC system. It can be an accident, broken wire, chafed wire, or it could be someone taking a black wire and assuming it's DC. By connecting the two there is now a path back to shore through the water instead of through a crew member. Combined with an ELCI & Galvanic isolator there is a definite safety advantage with little downside.

As for isolating the DC negative from the anode, it's pretty hard to do with an engine and straight shaft. Shafts don't always have a great electrical connection to the engine, but they usually have some. You can test your own boat by using an ohm meter and checking between shaft and engine when out of the water. And there are plenty of boats built without bonding systems at all, the only anode being on the shaft to protect the prop. The main purpose of the bonded boat is to reduce the risk of stray current corrosion.

Barking Sands said:

From my limited understanding DC is much better at galvanic action because it is a "continuous stream" of electrons in one direction providing a continuous and one way anode/cathode reaction. And of course AC alternates directions which greatly reduces the this reaction. But there is no reason to believe that AC current completely nullifies any galvanic action to 0 potential when local chemical reactions are involved. I would be willing to bet there are losses in an AC leak that are one way due to chemistry differences at the anode. I see no reason why what goes out and off an anode chemically, has to return completely simply because the current reverses. I suspect that the vast majority of alarming, rapid, and destructive cases of stray current corrosion are all DC issues, but that AC issues like mine that will connect considerable current right to the anodes can likely cause accelerated losses that are noticeable.

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You're just guessing.

Galvanic corrosion and stray current corrosion have clear, identifiable pathways of electron and ion flow. The direction of that flow is what determines which is the anode and which is the cathode. It can be confusing, which is why people are often surprised that with stray current corrosion the metal fitting that has the +voltage applied to it actually becomes the anode, even though with galvanic corrosion it's the more negative metal that becomes the anode. It's all about electron flow, and with AC they're just moving back and forth and not in a steady stream like DC, which is why AC requires very high (not 4 amps) current density to cause corrosion.

Adding to what I noted above, the marina asked to Bob (or Bill or Jim, cant remember his name), their local guy, to look at it. He did, and he had worked on the boat for the PO and was familiar with it. There was a galvanic isolator installed at the time. After 30 minutes or so he said "I dont know where the problem is. But you have a complicated boat with two gennies as well as an inverter and shore power connection." I was leaving Edmonds marina in a couple of weeks to haulout at Port Townsend for other work, so when I arrived I got the guru there on the case.

I never checked back with Edmonds to see whether the complainer continued to have high zinc loss or not. Or whether other boats around me were having issues while I was there. They may have been but had just not become aware of them. The points in posts above about cause and effect are noted. From my perspective the guys at Edmonds established I had a hot boat and my priority was to get it fixed ASAP.

After the errant jumper was removed I got a whole bunch of stuff done. That included an IT as well as a stepup/step down transformer. Also a new AC 230V/50Hz panel and inverter for Australian appliances. The old galvanic isolator was deemed to be not adding any value to my new system. and was removed. New bonding throughout and subsequent silver chloride testing testing etc. A few years ago as part of an insurance survey all the electreical systems were tested and signed off. I like having everything up to snuff on board.....