Discolored hull paint, bonded thru hulls with no anode

[LifesBetterWhenYoureBeating]

I've recently noticed some discolored bottom paint on the hull, around some thru hulls. Upon further investigation I noticed that those were the only thru hulls properly connected to the bonding bar, but the sacrificial anode connected to the bonding bar was no longer there. As I understand, this discoloration (I don't have an underwater camera, but it looks similar to the last photo) is usually a sign of stray AC current, is that right? That would be a possibility as I've spent two months in marinas recently.

I'm also wondering if having the thru hulls connected together without a sacrificial anode could've caused some galvanic corrosion as well? The thru hull fittings don't look worse than when I bought the boat a year ago, but I'm including photos of them in case anyone can see signs of that.

Until I get a new anode I'm going to isolate all thru hulls, but I've also read some claims that there's no benefit in connecting bronze thru hulls to an anode. Is that really the case? Only for bronze or brass too? How can I identify what those old thru hulls are made of?

Thanks in advance! Attachment 267000Attachment 267001Attachment 267003Attachment 267002Attachment 267004Attachment 267005Attachment 267006

[ItDepends]

Let's start with what the thruhulls are made of. Bronze. If they were brass they would have dissolved years ago.

It is not "stray AC current" that is the problem it is stray DC current. This is a bit complex, because in marinas the best source for this troublesome stuff can actually be your AC power cord.

An anode does nothing to protect against stray currents, in fact the stray currents can make the anode dissolve very quickly. Is that what has happened?

Bonding or not bonding, is not a simple answer. Anybody who says "Always bond" or "Never bond" is going to be wrong--sometimes. Just as an example, your thruhull vlaves have stainless steel valve stems and chrome plated balls, so they are not all bronze either...

If you are having marina current issues, it MIGHT help the thruhull fittings, but that current is going SOMEWHERE. Probably out your prop shaft. Your prop might be suffering as badly as your paint.

There are literally whole books written on this subject, and the amount of detail needed to be able to give an accurate answer is really tough to transmit. Like a complete (and accurate!) wiring diagram...

Get this book, and follow the troubleshooting recommendations for faults. He also has a really good explanation on how and why to bond or not.

[LifesBetterWhenYoureBeating]

For some reason the attachments were messed up, so here they are



Attachment 267026Attachment 267027

[LifesBetterWhenYoureBeating]

Originally Posted by ItDepends

Let's start with what the thruhulls are made of. Bronze. If they were brass they would have dissolved years ago.

It is not "stray AC current" that is the problem it is stray DC current. This is a bit complex, because in marinas the best source for this troublesome stuff can actually be your AC power cord.

An anode does nothing to protect against stray currents, in fact the stray currents can make the anode dissolve very quickly. Is that what has happened?

Bonding or not bonding, is not a simple answer. Anybody who says "Always bond" or "Never bond" is going to be wrong--sometimes. Just as an example, your thruhull vlaves have stainless steel valve stems and chrome plated balls, so they are not all bronze either...

If you are having marina current issues, it MIGHT help the thruhull fittings, but that current is going SOMEWHERE. Probably out your prop shaft. Your prop might be suffering as badly as your paint.

There are literally whole books written on this subject, and the amount of detail needed to be able to give an accurate answer is really tough to transmit. Like a complete (and accurate!) wiring diagram...

Get this book, and follow the troubleshooting recommendations for faults. He also has a really good explanation on how and why to bond or not.

The link to the book didn't work. It took me to a page with a bunch of product suggestions

I guess you meant that if I'm having marina current issues it might help to not bond the thru hulls? Seems like that sentence was missing a word.

I'm not sure if I had marina current issues, but
https://www.passagemaker.com/technic...-in-coal-mines suggests the paint discoloration is usually caused by stray AC current whereas stray DC would cause pitting and corrosion. That's why I thought it happened when I was at a marina.

[Rumrace]

No metal bits hanging off a boat should have bottom paint with zinc or copper in it. The metal bits become anodes. That said you appear to have zinc paint on a bronze fitting which will eat it as fast as brass maybe faster. Zinc and tin war.
It’s impossible to guess you paint condition from pictures. It needs some love is all.
I’m using red and white plastic throughhull on a Donzi so I don’t have to paint them. But it’s a trailer boat.

[fstbttms]

Originally Posted by ItDepends

An anode does nothing to protect against stray currents, in fact the stray currents can make the anode dissolve very quickly.

Well, that is simply not true.

[Searles]

Does the vsl have a RCD and galvanic isolator on the shore power induct to the vsl ,this is a safety issue ,is the DC negative connected to the earth or the AC Earth to the so called earth wire to the anode ,personal preference is to not bond bronze fittings ,even those with s/s balls and stems ,plus do you have a shore powered battery charger ,is that earthed to the vsl earth ,⚓️⛵️

[Bowdrie]

Originally Posted by fstbttms

Well, that is simply not true.

Not so fast, it's not cut-and-dried, nor etched in stone for either side.
Anodes generally work reasonably well for "Galvanic" applications, such as a bronze prop on a stainless shaft.
When electricity is introduced, all bets are off.
Electron flow can, (and will,) shift the positions on the nobility chart/scale.
Isolated bronze parts underwater do just fine with no electrical connections to them nor any zincs on or connected to them.
Rumrace, there are tens, (hundreds,) of thousands of boats in which the bronze thru hulls are painted over with paint containing copper.
AC stray currant can do huge damage, the initial pits formed in the metal become galvanic cells which take on some of the properties of a diode.
This causes the two halves of the sine wave to be unequal, both in height of wave and area under the curve.
The difference is similar to pulsating DC.
There are some basics related to grounding/bonding schemes, but the individuality of each case precludes "one size fits all" answers when electrons are allowed to flow.

[goboatingnow]

The best is fit RCBO and don’t bond imho !

[LifesBetterWhenYoureBeating]

Originally Posted by Searles

Does the vsl have a RCD and galvanic isolator on the shore power induct to the vsl ,this is a safety issue ,is the DC negative connected to the earth or the AC Earth to the so called earth wire to the anode ,personal preference is to not bond bronze fittings ,even those with s/s balls and stems ,plus do you have a shore powered battery charger ,is that earthed to the vsl earth ,[emoji572]️[emoji569]️

What is RCD? I thought I had no galvanic isolator but this vessel spent most of its life in marinas in the states so maybe it has one and I just haven't seen it yet (vessel is new to me). It'd be somewhere between the shore power plug and the panel, I guess?

My DC negative is not connected to the Earth.

Not sure about AC earth connected to earth wire, need to track that down

Not sure about battery charger connected to earth either

[goboatingnow]

RCD. Residual current disconnect. RCBO RCD WITH Overload breaker

[LifesBetterWhenYoureBeating]

I've done a bit more reading and investigation on the boat's connections and this is what I found

AC Grounding is not connected to DC negative, nor to bonding circuit (confirmed by checking for continuity) . As I understand it, that would come from connecting the case ground of my inverter charger to the DC negative. Is that correct?
(I understand the above can be dangerous and will address it, together with a thorough review of my AC system, before connecting to shore power)

Given that, it seems to me I can discard the original hypothesis that the paint damage around bonded thru hulls (but not isolated ones) was caused by establishing a shore side galvanic circuit between my boat and a neighbor. Does that make sense?

Now that leaves me with the question of what has caused said paint damage around some but not all thru hulls? Maybe just the fact that they were bonded without an anode?

[goboatingnow]

Originally Posted by LifesBetterWhenYoureBeating

I've done a bit more reading and investigation on the boat's connections and this is what I found

AC Grounding is not connected to DC negative, nor to bonding circuit (confirmed by checking for continuity) . As I understand it, that would come from connecting the case ground of my inverter charger to the DC negative. Is that correct?
(I understand the above can be dangerous and will address it, together with a thorough review of my AC system, before connecting to shore power)

Given that, it seems to me I can discard the original hypothesis that the paint damage around bonded thru hulls (but not isolated ones) was caused by establishing a shore side galvanic circuit between my boat and a neighbor. Does that make sense?

Now that leaves me with the question of what has caused said paint damage around some but not all thru hulls? Maybe just the fact that they were bonded without an anode?

Definitely try and keep ac and Dc ground separate , if worried with a whole boat RCD as additional AC protection

[goboatingnow]

Originally Posted by goboatingnow

Definitely try and keep ac and Dc ground separate , if worried with a whole boat RCD as additional AC protection

Sorry I meant add a rcd if worried

[boatpoker]

Suggest you buy one of these (lots of options on the market) and learn how to use it.
https://www.westmarine.com/promarine...-14121503.html There are other options .. if you have a decent multimeter you can buy the silver/silver/chloride half cell on it's own such as the one I use ... https://www.boatzincs.com/corrosion-...ode-specs.html
Both of these will come with instructions.

As a retired Certified Marine Corrosion tech I don't agree (completely) with a single post on this thread. I will not comment otherwise as is well known, this will result in a pissing match.