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Zinc eroding / bond inquiry

Apr 4, 2016
3
Hunter 336 Key Largo
Hey everyone,
I have a 1997 336. It has a 1" shaft and I put one zinc on it. Should I put more than one? I'm replacing it every two months because it is eroding so quickly in the marina.

I have briefly spoke to a few people that suggest a galvanic isolator should be installed. I currently do not have one.

I was also told to check my bonding wires to engine, thru hulls, strut bolts,keel bolts, and air conditioning unit.

On this sailboat, there is no bonding wire on the true hulls, no bonding wire on the strut bolts, no bonding wire that I can tell on the air condition unit. Should there be?
I do have bonding wire going to the three keel bolts, but it just terminated onto a bolt on the compression post.

The shore power cord is not laying in the water, and from what I can tell, the AC and DC is just going to a ground bus bar.

Are there any other 33-35' Hunters the same or similar to the lack of bonding items?
How can bond the shaft better or at all or reduce the eroding time of the zinc? The strut has a zinc and in the past 7 months, still looks in great shape.
 
Feb 26, 2011
1,159
Achilles SD-130 Alameda, CA
Two anodes will (in theory) provide protection for twice as long as one. So yes, add another anode. And a galvanic isolator is never a bad idea. Bonding all the underwater metals is a controversial subject. Personally, I recommend against it.

What I would recommend is having a marine electrician go through your boat's systems to determine the cause of your rapid anode depletion.
 
Oct 22, 2014
11,693
CAL 35 Cruiser Portland OR, moored EVERETT WA
Personally, I recommend against it.
So Fastbttms. Do you encourage your clients to remove bonding provided by the boat manufacture, or just not to add it if it is not there?
 
Sep 8, 2014
2,551
Catalina 22 Swing Keel San Diego
I defer to @fstbttms advice as he is far more knowledgeable than myself on this issue, but I would only add that you may want to ask your neighbors around the marina if they are experiencing similar issues. Some marina can have a stray current issue that coming from another vessel or something else underwater. We have a relatively new marina in the south bay of San Diego and several residents have the same problem, stray current has been identified as the culprit however I have not heard of a source being identified yet.
 
Feb 26, 2011
1,159
Achilles SD-130 Alameda, CA
So Fastbttms. Do you encourage your clients to remove bonding provided by the boat manufacture, or just not to add it if it is not there?
I do not encourage anybody to make wholesale changes to their onboard electrical system without the advice of a qualified marine electrician. If it ain't broke, don't fix it.
 
Sep 25, 2008
5,558
Alden 50 Sarasota, Florida
Two anodes will (in theory) provide protection for twice as long as one. So yes, add another anode.
CAUTION
This is a patently wrong statement.

Anytime you use an anode, you are effectively creating a battery. By adding anode material in the form of a second one,all you accomplish is to increase the battery effectively by a factor of two while spreading the erosion over a wider surface area of anode material.

While you might think there is no harm in doing this, remember the other side of the 'battery' is your boat metal which can suffer exponentially.

It is far better to find out why you have a problem rather than using a bandaid which will only exacerbate the problem.
 
Jan 30, 2012
1,047
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
The chemistry does not support this conclusion. Additional zinc will extend total zinc life because additional anode quantity will not result in additional potential. Zinc is - 1.3v max - no matter how much you bolt on.

But Don is right - there is no question you need to measure hull potential. Hire it done or follow the diagram attached and give us your results.

Charles
 

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Feb 26, 2011
1,159
Achilles SD-130 Alameda, CA
CAUTION
This is a patently wrong statement.
Try again, chief. :thumbup:

Protection provided by anodes is a function of anode surface area. More surface area = more protection. Is it possible to "over-zinc"? Yes. But two shaft anodes is not going to do that. And as Charles Erwin (who actually knows what he's talking about) said above, "Additional zinc will extend total zinc life because additional anode quantity will not result in additional potential."
 
Apr 2, 2011
185
Catalina 27 Niceville, FL
Adding more zincs would just be a band aid to the problem. With AC and DC grounds connected, you will get rapid zinc depletion, unless you have a GI or isolation transformer. You could just separate the grounds, but many people would say that's a bad idea, but nobody seems to know just why.
 
Jan 30, 2012
1,047
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
Separating DC negative and AC grounding (green) is dangerous.

The reason is this: If an AC short occurs between the AC and DC system the DC system is now energized by AC. Separation of the two means there is no path to AC ground. All you have to do is touch a DC appliance and AC passes through you on its way to AC ground and you are toast. Very risky.

But if the two are connected then when an AC/DC short occurs there is a path to ground, the breaker trips, and you are not toast. Much safer. (And that is why this connection is ABYC mandatory.)

As to anode depletion - AC grounding (green) connected to DC negative (and so necessarily the propeller/shaft) will not accelerate anode loss rate unless your neighbor/the dock/whatever is not protected - in which case your zincs deplete because they are protecting the neighbor/dock/etc. If this is the reason for accelerated zinc loss then unplug the shore power cable or install a galvanic isolater (or other AC isolation device.)

Problem in this case is we have no potential readings, which means no data, which means no diagnosis is yet possible.

Charles
 
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Oct 30, 2011
542
klidescope 30t norfolk
Can you leave your boat unplugged for month and see if that reduces annode depletion and have you actually seen the depleted anodes or is it a divers recommendations to change so often .
 
Jun 8, 2004
7,819
-na -NA Anywhere USA
When talking with my customers, I generally use to speak in layman's terms. The anode is depleting and you can always as some suggest add things to prevent but first you have to figure out what is causing the problem as it appears from your statement this is now occurring in the marina where you are at. The first question how long have you owned the boat, is this just now occurring, did you move to the marina where you are now berthed, any new slip tenants, any old shore power chords in the water and if so checked for integrity, any other complaints from adjoining slip holders and so on.
The next approach is to disconnect from the dock shore power and throwing over a sacrificial anode to see what happens to that as well. As you can see I am always taking an investigative approach to determine what is causing this in order what to do. Has anyone or you contacted the marina about this as well? Then based on what you know, then go the next step.
 
Apr 2, 2011
185
Catalina 27 Niceville, FL
But if the two are connected then when an AC/DC short occurs there is a path to ground, the breaker trips, and you are not toast. Much safer. (And that is why this connection is ABYC mandatory.)
Doesn't ABYC recommend a GI or IT to go along with the connection of the AC/DC grounds?
 
Feb 6, 1998
11,160
Canadian Sailcraft 36T Casco Bay, ME
Hey everyone,
I have a 1997 336. It has a 1" shaft and I put one zinc on it. Should I put more than one? I'm replacing it every two months because it is eroding so quickly in the marina.
Sounds like you're protecting all the boats around you with your anode...

I have briefly spoke to a few people that suggest a galvanic isolator should be installed. I currently do not have one.
Yep you;'re protecting the other boats with your anode.. At a bare minimum you need a GI...

I was also told to check my bonding wires to engine, thru hulls, strut bolts,keel bolts, and air conditioning unit.
This person really does not know what they are talking about...

On this sailboat, there is no bonding wire on the true hulls, no bonding wire on the strut bolts, no bonding wire that I can tell on the air condition unit. Should there be?
No real need for it. Bonding only serves to slow corrosion or erosion by spreading the load over a larger mass. It can actually be worse than not being bonded in certain situations.

I do have bonding wire going to the three keel bolts, but it just terminated onto a bolt on the compression post.
This is part of your lightning bonding system not a corrosion bonding system.

The shore power cord is not laying in the water, and from what I can tell, the AC and DC is just going to a ground bus bar.
You're most likely suffering from "galvanic corrosion" (created by immersing dissimilar metals in an electrolyte) not AC stray current or even DC stray current, which is very fast.

First things first. At a bare minimum, if plugging into a marina, you will need a Galvanic Isolator. The GI should be a "fail safe" model. Many Hunters came from the factory with a Charles isolation transformer so check for that first..

If you don't have an isolation transformer install a GI and see how your anode life is after installation. If anode life is still not sufficient then it's time to call in an ABYC corrosion specialist.

The only truly safe way to plug in at a marina is with a properly wired isolation transformer. A GI prevents "galvanic currents" but it does not protect against "stray current". There is a difference. A properly wired isolation transformer 100% isolates you from shore power and other boats in the marina. I say "properly wired" because I see far too many of them incorrectly wired thus defeating the entire point of the installation.

DO NOT disconnect/unbond your AC Green/Protective Earth and DC ground. This is a human safety issue for both those on-board your vessel and those not on-board your vessel.

AC White/NEUTRAL and AC Green/PROTECTIVE EARTH should NOT be bonded on-board the vessel unless an inverter is actively inverting (actively creating AC) or a generator is actively generating AC. The only other time AC Neutral and AC Ground/Earth can be connected on the boat side of the vessel is when you have an isolation transformer.

There is ZERO debate on the issue of the AC Green being bonded to DC ground, except among those who don't grasp the issue.

The AC/DC grounding bond is actually mandatory federal law under Europe's ISO RCD standards (unless an RCBO/RCD is fitted), it is required under the ABYC standards (even with an ELCI), Transport Canada standards, NMMA standards and everyone in the industry from Charlie Wing, Nigel Calder, Don Casey, Steve D'Antonio, Ed Sherman, Kevin Ritz, Blue Sea Systems etc. etc. etc. etc.. are in 100% agreement on this human safety issue issue.

Please, if you do not understand your boats AC & DC wiring don't mess with it.
 
Jan 22, 2008
878
Fed up w/ personal attacks I'm done with SBO
There is ZERO debate on the issue of the AC Green being bonded to DC ground, except among those who don't grasp the issue.
There are some of us who have more of a grasp than we'll ever be credited and have the credentials to back it up. My observation here: interesting that here has been zero mention of ABYC required ELCI/GFCI technology and it's contribution to the human safety issue independent of the bond.
 
Feb 6, 1998
11,160
Canadian Sailcraft 36T Casco Bay, ME
There are some of us who have more of a grasp than we'll ever be credited and have the credentials to back it up. My observation here: interesting that here has been zero mention of ABYC required ELCI/GFCI technology and it's contribution to the human safety issue independent of the bond.

Neil,

Like I have suggested before, if you feel so strongly about "unbonding", please get on the ABYC electrical committee and do your part.

The safety standards are for human safety. Corrosion can be dealt with in many ways and the ABYC also covers this. Even with an ELCI the ABYC still requires an AC/DC grounding bond.