Sense or Nonsense Hanging Zinc Anode Overboard?

[Scot McPherson]

Stick the points of an ohm meter in seawater and get back to me. The only way an ohm meter can register anything is because an electric current is able from point to the other, if it can't. It registers infinity, meaning the point are isolated from one another.

[sailorchic34]

Originally Posted by goboatingnow

The key to establishing whether any CP is working , is to invest in a half cell reference and use a good DVM with a 10 MOhm input resistance. Then you can establish the potentials of all the supposedly protected metals and determine if in fact they are being protected at all.

dave

Alas, if I had the money to buy a silver half cell reference, I could afford to have a diver install a zinc. Pretty sure my prop zinc, well the remains of it fell off a few weeks ago, right before I did my fishy zincy thingy.

My fish BTW is home made. It connects a zinc with a #12 copper wire via an intermediate stud post through the deck to another conductor attached directly to the engine. Voltage was measured between the wire from the zinc and the deck stud. (I await various innuendos about deck studs and blondes)

My boat is not bonded otherwise. I'm in the camp that boat bonding can and does work when new. But poor upkeep and corrosion on the bonding terminals will effect it's efficiency and can do more harm then good over the long term

BTW, I actually check my fishy weekly. Interesting enough when I read the -0.64 volts I was in salt water in the central bay. Currently in brackish water and getting -0.306V, which I believe is still acceptable. I may need to get a magnesium anode for the fresh water delta.

[sy_gilana]

We do that all the time. We only haul out every six years, so the extra zincs make our welded on zincs last longer. Also sometimes we are in a marina next to another boat that has bad juju going on. I always put a multimeter between my hull and his and if I find DC there, I hang anodes between us. It works.

[GordMay]

Ag/AgCl silver/silver chloride reference Cell @ $38
➥ https://www.a-msystems.com/p-391-ref...rode-cell.aspx

[sailorchic34]

Originally Posted by GordMay

Ag/AgCl silver/silver chloride reference Cell @ $38
➥ https://www.a-msystems.com/p-391-ref...rode-cell.aspx

Yep, and a diver only costs $20 with a $12 zinc. Alas that tells you a bit about my current financial condition. I is Very frugal/broke at the moment, :-P

I used parts and wire on hand for my fishy zincy thingy. At some time, I'll need to actual buy more zinc's. That hopefully will be some years from now.

BTW what the Silver reference does is give you a known material with a certified galvanic voltage potential to measure the mV against in a given soil / water location. Knowing that my prop is in the range of about -0.38V to -0.45V, rather then a -0.15 silver reference cell, I think I'm close enough.

[a64pilot]

Originally Posted by fstbttms

Of course not. Again, a guppy is just a bandaid. If you have a severe corrosion issue, adding anodes is not solving the problem.

It occurs to me that if hanging an anode overboard with a wire were a truly effective form of protection (as some here would have you believe), nobody would bother mounting them on the shaft, prop, strut, rudder etc., etc.

I'm trying to understand what your problem with this is.

No one but you has said anything about an un-bonded electrode.
No one has made any claims about protection from severe corrosion, and
No one but you has said anything about them being a replacement for the normal zincs.

Sailor Chic has special circumstances, but no one has told her, her add on zinc is an acceptable replacement for her prop zinc and I assume she will replace it when she can.

The silly guppie zincs if properly used can be an additional insurance, and my help alert you if something bad is going on in time to do something about it, if improperly used they are worthless.

[goboatingnow]

Originally Posted by Goudurix

That's my boy!

If I remeber well about -0.5V below the metal's own potential is a good level of protection, no?

Jan

The voltage of the protected item, as compared to its "free potential " in seawater needs to be raised by 250mV to be protected, Raising it further does little and can causes problems in metal boats.

heres a straightforward guide to doing so, buy a acknowledge measurement leader

http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

Dave

[fstbttms]

Originally Posted by a64pilot

I'm trying to understand what your problem with this is.

No one but you has said anything about an un-bonded electrode.
No one has made any claims about protection from severe corrosion, and
No one but you has said anything about them being a replacement for the normal zincs.

Sailor Chic has special circumstances, but no one has told her, her add on zinc is an acceptable replacement for her prop zinc and I assume she will replace it when she can.

The silly guppie zincs if properly used can be an additional insurance, and my help alert you if something bad is going on in time to do something about it, if improperly used they are worthless.

My "problem" is that several here have inferred (if not outright claimed) that since they are hanging a guppy zinc, they are adequately protected, based on the fact that they have seen the guppy in various stages of depletion. My point is (and I have personally seen it many times) is that this may simply not be the case. If you want to hand a zinc over the side, knock yourself out. Assuming you now have nothing to worry about because you have done so is foolish.

[Scot McPherson]

I am not making that claim at all. I will however say, hanging a zinc guppy will NOT cause any harm, it only has a potential to help whether that potential is actualized or not.

[sailorchic34]

Originally Posted by goboatingnow

The voltage of the protected item, as compared to its "free potential " in seawater needs to be raised by 250mV to be protected, Raising it further does little and can causes problems in metal boats.

heres a straightforward guide to doing so, buy a acknowledge measurement leader

http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

Dave

Thanks Dave, a lovely description of testing with a reference cell. So what I have is a limited bonding buss with a zinc on a wire rather then attached to the hull, as the example used by fluke shows. I'm actually planning on attaching the rudder post to my tiny bond buss real soon now. There was a BIG zinc on the rudder shoe.

Maybe when I'm rich and famous and can afford the $38 reference cell, I'll let ya'll know how my fishy zincy thingy works with the reference cell.

[sailorchic34]

Originally Posted by fstbttms

My "problem" is that several here have inferred (if not outright claimed) that since they are hanging a guppy zinc, they are adequately protected, based on the fact that they have seen the guppy in various stages of depletion. My point is (and I have personally seen it many times) is that this may simply not be the case. If you want to hand a zinc over the side, knock yourself out. Assuming you now have nothing to worry about because you have done so is foolish.

Myself, I'm saying I'm protected as I've read a rather nice voltage differential potential between the zinc and the engine. The only way I would have had current was if there was a potential between the zinc, prop and prop shaft in the water. My DC is separated from the AC (despite what ABYC says) and I've no DC in the deep bilge, so no stray current potential. Got to love that electron flow.

BTW I did measure the OHM's between the engine and prop shaft, which was unity. OK meggering it would have been better, but I don't have a megger.

The advantage to my zinc on the wire is it allows me to do both a visual inspection and also take a voltage reading anytime. Visual will tell me how much is left and if it's getting calcified. The true test of it's working is of course the voltage potential. something you can't do with a prop zinc without a reference cell.

[stubones99]

Why not have either a VOM (volt / ohm meter) and put one lead to your ground and one to the anode in the water. If you have voltage or amperage flow, you have an open ground.

This isn't a bad idea when you are in brackish water going to fresh water, or salt water, since different anodes work best in each type of water. Whenever you have a current flow (either way), you have corrosion.

If you keep track of the readings at a dock, you can tell how far your anodes have been consumed, because the voltage differential will go up as they are eroded away.

The isolation transformer would isolate you from the shore power so nothing bad gets in on the power line. It won't protect or detect internal faults in your boat though.

If you're worried about a mis-wired dock power, invest in Marinco's GalvanAlert which hooks between your boat and the shore power connection and shows a hot or mis-wired dock box.

Here is a kit including a VOM and reference probe to do your own corrosion detection test.
RDI-CRE-KIT Corrosion Detection Kit

Cheaper than most people sell the reference probe for more than their $110 kit.

Use one to test regularly and you know the condition of your anodes ("zincs") without diving under the boat.

I think there is a vendor that makes a dash mounted (permanent mount) corrosion sensor but I don't recall who it is...

[Goudurix]

Originally Posted by goboatingnow

The voltage of the protected item, as compared to its "free potential " in seawater needs to be raised by 250mV to be protected, Raising it further does little and can causes problems in metal boats.

heres a straightforward guide to doing so, buy a acknowledge measurement leader

http://assets.fluke.com/appnotes/ele...r/B0269b_u.pdf

Dave

Hey I dived into some of the links provided (eg Fluke) and refreshed some of the sleeping knowledges from the past... and data on Ag/AgCl reference electrodes. If there is cathodic protection by an anode, the anode (the zinc in this case) pumps electrons into the cathode. The zinc loses zinc ions into the electrolyte (seawater). The anode actually becomes more negative, not more positive. It all depends how the VOM meter is switched.
One measures the voltage differential between the reference electrode (the Ag/AgCl half cel) and the metal (in this case your prop shaft or the bonded metals) and it should measure about 250 mV lower than without the zinc connected. Eg for bronze it should lower from -0,30V to -0,55V. If you coect + and - leads to the VOM meter the opposite way you will off course measure + values.

[Goudurix]

Originally Posted by sailorchic34

Myself, I'm saying I'm protected as I've read a rather nice voltage differential potential between the zinc and the engine. The only way I would have had current was if there was a potential between the zinc, prop and prop shaft in the water. My DC is separated from the AC (despite what ABYC says) and I've no DC in the deep bilge, so no stray current potential. Got to love that electron flow.

BTW I did measure the OHM's between the engine and prop shaft, which was unity. OK meggering it would have been better, but I don't have a megger.

The advantage to my zinc on the wire is it allows me to do both a visual inspection and also take a voltage reading anytime. Visual will tell me how much is left and if it's getting calcified. The true test of it's working is of course the voltage potential. something you can't do with a prop zinc without a reference cell.

Hi Sailorchic34,
I see you're in SF Bay I guess cold water even in summer however it just takes a 3mm wetsuit, a diving mask and fins to have a quick look underwater. The visual inspection is the best inspection and at a fraction of the cost of a haulout. Or find a gentleman on the dock willing to do it

Jan

[goboatingnow]

Originally Posted by Goudurix

Hey I dived into some of the links provided (eg Fluke) and refreshed some of the sleeping knowledges from the past... and data on Ag/AgCl reference electrodes. If there is cathodic protection by an anode, the anode (the zinc in this case) pumps electrons into the cathode. The zinc loses zinc ions into the electrolyte (seawater). The anode actually becomes more negative, not more positive. It all depends how the VOM meter is switched.
One measures the voltage differential between the reference electrode (the Ag/AgCl half cel) and the metal (in this case your prop shaft or the bonded metals) and it should measure about 250 mV lower than without the zinc connected. Eg for bronze it should lower from -0,30V to -0,55V. If you coect + and - leads to the VOM meter the opposite way you will off course measure + values.

well yes the anode becomes more negative, but convention is that you regard the anode as the negative side ( current follows by definition opposite to election flow) . Hence the net effect is that the potential between the anode ( as a ground reference and the cathode increases)

dave