Electrolysis on thru hulls

[SILENTKNIGHT]

These are the thru hull halo's, & the transom zinc i just pulled the boat. Its been in water since July 2021. No other boats around . No power issues on dock.

I have the Charles isolation transformers on board.
How do i find the problem?

 

[tiltrider1]

I suspect you are using a 70% copper bottom paint like Pettit Trinidad Pro. I also suspect your thru hulls are connected to a diver dream zin at the back of your boat.

 

[SteveK]

subscribed

 

[Comodave]

It looks like the plate is worn away excessively. It needs to be changed out at 50% wear. If the plate wears away enough so the through hull isn’t properly protected then the metal through hull will start to wear. The anode most likely will need to be replaced about every 6 months or less. Only way to know when is to keep checking the anode to see when it is 50%. Now you may have to replace the through hull.

 

[catalinajack]

I suspect you are using a 70% copper bottom paint like Pettit Trinidad Pro. I also suspect your thru hulls are connected to a diver dream zin at the back of your boat.

What is the import of these two observations?

 

[psneeld]

Halos are sometimes, maybe most of the time, caused by too much zinc.

BOTTOM PAINT HALOING.

""Haloing" of bottom paint is sometimes observed on boats with bonding systems that are in poor condition or are providing overprotection of the bronze components. It's most prevalent with vessels using black or other dark-colored bottom paint and is more common with certain brands containing higher amounts of copper.Jul 23, 2018"

 

[SILENTKNIGHT]

im not sure what type of paint was used prior?
I will clean all the connections and start with that. I was also told use zinc spray also? on the halo spots then have the yard bottom paint.

is there any specific reading the multimeter would show if i went to each connector?

 

[C lectric]

I agree with the suggestion of the halo, too much zinc for what needs protection.

Get yourself a silver, silver chloride electrode from:

https://www.boatzincs.com/corrosion-reference-electrode-specs.html

Get the book and read it so you have an understanding about what the meter shows you and you can use it.


Use your own DMM for testing. You will also need a long black lead with a probe/alligator clip for touching each item you wish to test.

Read their notes about testing and what to look for.

There may be other contributory problems. If you don't see something then you may need to get a MARINE electrician to help.

Then once sorted you can then check the voltages at each item to ensure they are protected properly and also not overdone.

I do this at least twice yearly.

 

[FWT]

Befuddled.

Can someone explain "too much protection."? Seems nonsensical in the plain english of it.

 

[tiltrider1]

What is the import of these two observations?

As others have mentioned, too much zinc used with a 70% copper paint often results in halos around thru hulls. There are two ways to combat this. Switch to 55% copper paint or use an electro guard on your zinc.

 

[tiltrider1]

Befuddled.

Can someone explain "too much protection."? Seems nonsensical in the plain english of it.

My understanding is that overprotection prevents the copper ions from leaving the paint which allows marine growth to attack the paint and cause rapid deterioration.

 

[C lectric]

Overprotection was a more common worry with wooden boats. A too high voltage could actually damage the wood around any metal protrusions into the seawater.

There is a range of acceptable voltages depending upon the metals involved and the voltages should be within those ranges even on fiberglass boats.

And yes the same is true of metal boats. These will require different treatments.

Strictly speaking there is a lot more to anode protection than most of us realize. Go to far you may actually cause damage.

I am no expert about this. I used to study these books for my info.

--Metal Corrosion in Boats. Nigel Warren. Likely out of print but still valid. May find copies in used book stores or on Ebay

--The Boatowners Guide to Corrosion. Everett Collier.

Also :

--Nigel Calders book covers some of this, Electrical and Mechanical Boatowners Guide now in its 3rd or fourth revision. An older edition will also still be valid , Used.

--Your Boats Electrical System. Conrad Miller & E.S. Maloney Also used book stores or Ebay

--Boat Owners Illustrated Handbook of Wiring Charlie Wing.




There will be others.

 

[SteveK]

I wanted to know what is overprotection and found this Zinc overprotection
Having a wood hull and experiencing this

Wood Rot – cellulose is a natural polymer which gives wood its remarkable strength. Cellulose is a
major component of wood where lignin holds the cellulose together. Over protection resulting from
the galvanic current flowing between the anode and cathode destroys the lignin and thus the effects of wood rot are often noted.

I had that issue when I bought the boat and immediately removed the bonding after thru hulls were replaced along with a ring of wood because of this. So far no problems. While advised not to install the transom zinc, I did anyway and it lasts two years now as it is only bonded to the shafts and struts.

Here is another source from Practical Sailor

 

[tiltrider1]

In the case of wood hulls. Over zincing creates way too many negative ions which combine with the salt water to create a mild acid. This acid won’t harm fiberglass but it attacks the softer wood in a wood plank. Eventually the wood plank ends up like Swiss cheese around the through hull fitting.

 

[Steve DAntonio]

Halos are sometimes, maybe most of the time, caused by too much zinc.

BOTTOM PAINT HALOING.

""Haloing" of bottom paint is sometimes observed on boats with bonding systems that are in poor condition or are providing overprotection of the bronze components. It's most prevalent with vessels using black or other dark-colored bottom paint and is more common with certain brands containing higher amounts of copper.Jul 23, 2018"

Fully agree on over-protection. Do a reference cell test if you want to be sure https://stevedmarineconsulting.com/...rosion-protection-level-editorial-old-vs-new/

 

[SILENTKNIGHT]

Hi Steve thank you for replying. I know you are quite well-versed on this as I have read your website quite impressive.
I have all the necessary anodes attached to my metals.
The bus bar in my boat is in perfect condition no corrosion.

All my connections inside the boat on the metals are also in good condition.

As a friend suggested he told me first to just disconnect all the bonding wires on my metal inside the boat.

And start with spraying cold galvanizing zinc spray on all my metal.. he said this will stop any further attack on the bronze..?

And my boat yard apply the same bottom paint to everyone's boat nothing fancy (Interlux), and I am the only one with this halo around my bottom through hulls , and also including my transom anode the is a halo.

My friend said he will go through each connection with a special fluke meter and measure for resistance ?

 

[sparky66]

You may want to verify that your isolation transformer is properly installed.

 

[SILENTKNIGHT]

not sure what that means? The Transformers were installed with the boat manufacturer . They are charles transformers, two square boxes.
How do you inspect the transformers?

 

[sparky66]

not sure what that means? The Transformers were installed with the boat manufacturer . They are charles transformers, two square boxes.


Well, hopefully the builder installed them correctly. It is not uncommon to find them wired incorrectly and they no longer isolate.

 

[Steve DAntonio]

SDA: Responses below.

Hi Steve thank you for replying. I know you are quite well-versed on this as I have read your website quite impressive.
I have all the necessary anodes attached to my metals.
The bus bar in my boat is in perfect condition no corrosion.

All my connections inside the boat on the metals are also in good condition.

SDA: All good.

As a friend suggested he told me first to just disconnect all the bonding wires on my metal inside the boat.

SDA: Eliminate the bonding system? I would not do that, bonding offers more benefits than liabilities. See https://stevedmarineconsulting.com/wp-content/uploads/2014/03/BondingSystems138_05.pdf

And start with spraying cold galvanizing zinc spray on all my metal.. he said this will stop any further attack on the bronze..?

SDA: Is the bronze being attacked? Bronze is naturally very corrosion resistant. If you wanted to isolate the metal, I would use a two part epoxy like Interprotect 2000e, rather than cold gal. One of the solutions to haloing, is exactly this approach, encapsulate in epoxy.

And my boat yard apply the same bottom paint to everyone's boat nothing fancy (Interlux), and I am the only one with this halo around my bottom through hulls , and also including my transom anode the is a halo.

SDA: A ref cell test will eliminate the mystery, it will tell you right away if you are over-protected. It's not so much the bottom paint as it is the ratio of the weight of anodes, compared to protected metals, so two boats with the same paint can have different results.

My friend said he will go through each connection with a special fluke meter and measure for resistance ?

SDA: Nothing special about the meter, just an ordinary multimeter with long leads, checking resistance, while hauled out, between anodes and protected metals, resistance must not exceed 1 ohm.

SDA: Someone did mention isolation from shore, via the transformers, that should be confirmed, if they are wired as polarization rather than isolation, and I see that often, there is no way to know this without testing it or looking closely at the terminals on the transformer. If not isolated, then your anodes are connected to, and protecting, nearby vessels.

 

[SteveK]

SDA: Someone did mention isolation from shore, via the transformers, that should be confirmed, if they are wired as polarization rather than isolation, and I see that often, there is no way to know this without testing it or looking closely at the terminals on the transformer. If not isolated, then your anodes are connected to, and protecting, nearby vessels.

Is that because the battery negative is bonded to the AC ground to protect you from an AC power leak? Other than that is there another way your anodes protect a neighbor boat.

 

[Steve DAntonio]

Is that because the battery negative is bonded to the AC ground to protect you from an AC power leak? Other than that is there another way your anodes protect a neighbor boat.

It is because the bonding system is, or should be, connected to the AC safety ground, which then connects your underwater bonded metals, and anodes, to neighboring vessels via that ground path, through the shore cord green safety ground wire, and thence to other vessels. If you don't have a transformer wired for isolation, or a galvanic isolator, your anodes may be protecting a neighboring vessel that is wired in the same fashion. Or, a neighboring vessel's anodes may be protecting your UW metals, if yours are depleted and his or hers are not...

 

[SILENTKNIGHT]

Steve tou info is very supportive and easy to understand. I wish I could find someone of your caliber here in Long Island

 

[psneeld]

My experience is there are experts scattered around, just few and far between.

Good ones travel and not all the top of the heap yards have experts in every field of boating....but they are a better start than most local yards.

 

[SteveK]

Is a marine charger or an inverter charger AC ground isolated from the DC negative similar to the isolator or transformer?

 

[Steve DAntonio]

Is a marine charger or an inverter charger AC ground isolated from the DC negative similar to the isolator or transformer?

Great question. Broadly speaking no, because the chassis of the charger or inverter must be grounded, and that ground is common with the bonding system and the shore power safety ground. You need a galvanic isolator, which is pretty inexpensive and easy to install, or a transformer wired for isolation.

 

[SteveK]

Great question. Broadly speaking no, because the chassis of the charger or inverter must be grounded, and that ground is common with the bonding system and the shore power safety ground. You need a galvanic isolator, which is pretty inexpensive and easy to install, or a transformer wired for isolation.

Thanks SDA. I have a galvanic isolator. I was looking for how stray AC current can get into the water through the bonding system. Grounding the chassis to the bonding network seems like a prime candidate even though the source may not be from the inverter but from another electric appliance on the circuit.
The inverter charger is the only prewired link I came up with, the rest would be an accidental connection.

 

[Steve DAntonio]

Thanks SDA. I have a galvanic isolator. I was looking for how stray AC current can get into the water through the bonding system. Grounding the chassis to the bonding network seems like a prime candidate even though the source may not be from the inverter but from another electric appliance on the circuit.
The inverter charger is the only prewired link I came up with, the rest would be an accidental connection.

Stray AC current is a horse of a different color. Galvanic isolators actually allow AC current to pass, by necessity, but block DC. Since most corrosion is a DC phenomenon, that deters corrosion, but allows AC faults to be safely "cleared" by a circuit breaker.

In fact, grounding the chassis to the AC safety ground system, which is, or should be, connected to the bonding and DC negative systems, is actually safer, as an AC short to the chassis will/should cause the inverter or charger supply breaker to trip. If the chassis is not grounded, it can remain energized until it is touched by a person, who is also making contact with a grounded surface like an engine or seacock, which could lead to an electrocution.

With some rare exceptions, all of the vessel's "grounding" and "grounded" (there is a distinction) systems should be common, these include bonding, DC negative, AC safety ground and lightning. If they are all common, a "hot" AC conductor making contact with any, or anything they are connected to, tanks, engine blocks, equipment enclosures and chassis, should clear the fault by allowing that current to return to its source, tripping a breaker.

AC current leaking into the water is primarily an in water electric shock drowning (ESD) risk, rather than a corrosion issue. Both are bad but obviously the ESD is far worse.

Some additional reading...

https://stevedmarineconsulting.com/electric-shock-drowning-and-elcis-explained/

https://www.cruisingworld.com/how/inspect-your-grounding-system/

https://www.cruisingworld.com/story/how-to/sailboat-grounding-systems/

https://stevedmarineconsulting.com/bonding-systems-and-corrosion-prevention/

 

[JDCAVE]

Steve: Thanks for input on this topic!

Jim

 

[SteveK]

Steve: Thanks for input on this topic!

Jim

+1.