In the last two months, my boat's zincs have been replaced twice and they are at 50% on the recent hull cleaning. The cleaning service said that Beneteaus are known for fast zinc corrosion, but this is the first I've heard of it. Anyone else having this problem? Anyone have suggestions on what to do to fix the problem? It seems to me that the zincs should last 6-12 months.
Zincs corroding too fast.
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That does not seem logical. Is there a possibility of stray electrical current either from your shore power or a neighboring boat?
I have never replaced an anode in years. In fresh water, adjacent to a steel seawall, and attached to shore power. (magnesium anode since zinc wouldn't do any good anyway)
I have never replaced an anode in years. In fresh water, adjacent to a steel seawall, and attached to shore power. (magnesium anode since zinc wouldn't do any good anyway)
One assumes you are in a moorage slip - not anchored or on a bouy.
The best way to diagnose the cause of the wasting is to measure your hull potential then followup measuring at each of the members of the underwater metals collection on your boat. If you do you this will find the problem pronto. Have you measured the hull potential of your boat? If so what are the values?
Otherwise:
Do you know when this apparently accelerated zinc wasting started?
Are your neighbors also having accelerated zinc wasting?
Did new neighbors arrive coincident with the onset of accelerated zinc wasting?
If you have had 12 months between zinc changes before - and now the rate is half that - can you tell us what work has been done on your boat?
Charles
The best way to diagnose the cause of the wasting is to measure your hull potential then followup measuring at each of the members of the underwater metals collection on your boat. If you do you this will find the problem pronto. Have you measured the hull potential of your boat? If so what are the values?
Otherwise:
Do you know when this apparently accelerated zinc wasting started?
Are your neighbors also having accelerated zinc wasting?
Did new neighbors arrive coincident with the onset of accelerated zinc wasting?
If you have had 12 months between zinc changes before - and now the rate is half that - can you tell us what work has been done on your boat?
Charles
I am docked in a marina at Shelter Island in San Diego Bay, so it is salt water. I have not had the chance to ask my marina neighbors if they are having a similar problem yet, but definitely will. I am connected to shore power and to the best of my knowledge, there is no galvanic isolation in that circuit. I'm not exactly sure how I would measure the hull potential. I assume by potential, you mean voltage, but I don't know what contacts would be used. I took possession of the boat in August and moved it to the current marina. At the time of the survey, the zincs were replaced, and then they were replaced again after about 5-6 weeks since they were 60% gone. There very well may be some stray current in the marina, and there are a few boats that have not been properly maintained which may be the problem. I'd appreciate your advice on how to measure the hull potential. Thanks.
See attached diagram.
ps Be certain the "zincs" are zinc - no magnesium in salt water.
ce
ps Be certain the "zincs" are zinc - no magnesium in salt water.
ce
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Charles:: Havn't looked anything up yet but if memory is correct, doesn't he need to cross strap to the dissimilar metals to attain proper common grounding and inhibit the current draw? Chief, FCC lic#1890
Well your question is not completely clear to me but it is the underwater collection that matters in this case no matter the relative dis-similarity of each item in the group. So one measures at each item that is exposed to seawater. That way you isolate the one that is the culprit.
The obvious diagnosis in a case of very high rate of zinc loss is stray current coming from DC onboard the boat itself. At the reported rate of loss it is unlikely the culprit is from an external source.
Hence, going item to item will disclose the usual onboard suspects. The usual suspects are bilge pump wiring (or any other wires for that matter) exposed to bilge water, starter or alternator + connection corrosion exposed to motor block/shaft.
If the underwater metals are fully bonded then an onboard fault together with a fail in the bonding circuit will not trap the fault. Also I would verify there is an independent zinc at the terminus of the bonding circuit - if bonding is installed. If the amount of zinc is too little (insufficient surface area) there will be great apparent wasting.
In all cases - fully bonded or partial - check and verify that it is impossible that any DC ground return (black) could route through any bonding wire circuit (green).
The thing is - there is no way to zero in on the problem unless one first knows the present hull potential overall then the potential of each of the items in the underwater group.
Charles
The obvious diagnosis in a case of very high rate of zinc loss is stray current coming from DC onboard the boat itself. At the reported rate of loss it is unlikely the culprit is from an external source.
Hence, going item to item will disclose the usual onboard suspects. The usual suspects are bilge pump wiring (or any other wires for that matter) exposed to bilge water, starter or alternator + connection corrosion exposed to motor block/shaft.
If the underwater metals are fully bonded then an onboard fault together with a fail in the bonding circuit will not trap the fault. Also I would verify there is an independent zinc at the terminus of the bonding circuit - if bonding is installed. If the amount of zinc is too little (insufficient surface area) there will be great apparent wasting.
In all cases - fully bonded or partial - check and verify that it is impossible that any DC ground return (black) could route through any bonding wire circuit (green).
The thing is - there is no way to zero in on the problem unless one first knows the present hull potential overall then the potential of each of the items in the underwater group.
Charles
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Your answer would probably be quite sufficient if I knew what you are talking about. The whole measuring thing is what I don't get. What are you measuring and from what contacts? Where do I apply my leads from the voltmeter? Thanks.
How you measure - where you place the contacts to obtain the readings - is shown in the attached PDF diagram. If you have trouble seeing the diagram I attached please alert me and I will get it to you via e mail.
By the way - I wrote/edited my answer to Chief's question since you answered. I think our posts may have crossed.
Charles
By the way - I wrote/edited my answer to Chief's question since you answered. I think our posts may have crossed.
Charles
Great diagram. I didn't see the attachment at first. I will do this as soon as I can. Thank you very much.
For some reason Beneteau does not install a ground isolator on our boats, you could turn this into a research project, but the first thing I would do is have an isolator installed. They are not expensive. Monitor your zincs and you should see them last a lot longer.
Galvanic isolaters stop voltages from neighbor boats metals and the marina metals from passing along the AC safety green wire through your boat and back through sea water to the source. Zinc loss from galvanic activity can be fairly rapid - but not as fast as reported here.
A galvanic isolater will not stop DC stray current from ruining zinc if the source is on your boat. Also - if the source of stray dc current is from elsewhere in the marina - possibly a neighbor - a galvanic isolater will not trap DC voltage if the voltage is greater than 1.5 dcv.
Galvanic isolation is obviously worthwhile but there is nothing to gain installing an isolater - which are pretty expensive now that fail safe isolaters are required - without first measuring your hull potential shorepower plugged in/shorepower unplugged - thus confirming the level of voltage involved and also whether the source is your boat or elsewhere. Anyway the very high rate of wasting in this case probably means the source of zinc damage is dc stray current - not galvanic activity.
Charles
A galvanic isolater will not stop DC stray current from ruining zinc if the source is on your boat. Also - if the source of stray dc current is from elsewhere in the marina - possibly a neighbor - a galvanic isolater will not trap DC voltage if the voltage is greater than 1.5 dcv.
Galvanic isolation is obviously worthwhile but there is nothing to gain installing an isolater - which are pretty expensive now that fail safe isolaters are required - without first measuring your hull potential shorepower plugged in/shorepower unplugged - thus confirming the level of voltage involved and also whether the source is your boat or elsewhere. Anyway the very high rate of wasting in this case probably means the source of zinc damage is dc stray current - not galvanic activity.
Charles
The only reason Beneteaus tend have zincs replaced frequently is that the tiny little Beneteau prop zincs are inadequate for the task, IMHO.
Do you have a shaft zinc, or zincs? If not, add them.
I have both, a shaft zinc and a cone zinc behind the prop. They are both going to quickly.
We should keep in mind that when you don't have a galvanic isolator or isolation transformer then you may be protecting many other underwater metals, via the green wire, other than just your own. Your zincs are likely not sized to handle the entire marina but they are often ask to do just that. By simply adding GI's on boats where they are wasting, and have no other issues, have have taken zinc erosion from 2 months to a full season...
Course you must know what the source of the problem is first before just adding a piece of gear. I much prefer an isolation transformer to a GI but they are more expensive, heavy, large and can be noisy. There are only two good ways to really isolate your boat:
#1 un-plug
#2 Install an isolation transformer.
As you mentioned a GI only blocks voltages below 1.5V which is galvanic. They do not protect against DC leaks...
I suspect he could have an on-board DC leak, very often the case, or he may be protecting the metals of multiple other boats with his zincs via the AC green....
I did some measuring yesterday, and the results are confusing to me. Using the zinc pencil suspended in the water, I measured the potentials at the through-hulls for the head intake, the head discharge, the macerator discharge, the head sink drain and the bonding wire where it connects to the keel bolts. The results were the same whether the power cord was connected and hot, and with the batteries disconnected, both positive and common negative.
Head intake = .776
Head dischg = .634
Macerator dischg = .74
Head sink = .72
Bonding wire = .21
Anyone have a clue as to what is going on here?
Head intake = .776
Head dischg = .634
Macerator dischg = .74
Head sink = .72
Bonding wire = .21
Anyone have a clue as to what is going on here?
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