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Old 31-10-2010, 09:58   #1
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Zincs Gone this Year

Boat got hauled out today. Beside some bottom growth the thing that jumped out at me was all the zincs are gone, where last year they were only half gone (6 month season).

Before we run wild let me say that the boat is on a mooring and didn't spend a single day in a marina slip or plugged into shore power all year.

When I think of things that I did different this year from last I come up with this:
- due to a corroded thur fitting last year I unbonded all my thur fitings last year
- I did run the inverter more this year, but would estimate that it would average out to 10-15 minutes/WEEK!
- I did hook up two automatic bildge pump switches that are powered directly off the battery (via a fuse). These I wired into parallel with the pump breaker so it will run off either float switch or via the breaker and the ground for all are the same. The switches consist of 1 Rule float type and 1 Water Witch capacitance switch that always flows some current.

Do you think the Water Witch could be causing enough current flow to eat those zincs?

Any other ideas?

Thanks
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Old 31-10-2010, 10:06   #2
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The current in that switch would be microamps, would it not? I'm having a hard time seeing how that would cause all that much galvanic corrosion. I'm leaning toward the fact that you un-bonded the thru-hulls. Is it possible that the same current that previously caused your thru-hull to corrode is now playing havoc with your zincs?

Sad to hear that people are pulling their boats out of the water so early. Here in San Francisco, we're still enjoying baseball season. What gives?
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Old 31-10-2010, 10:08   #3
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I am guessing un-bonding followed closely by the inverter, what zincs were gone? where where they placed? If you are having corrosion issues IE corroded thru hull followed by wasted zincs it sounds like you are leaking currant somewhere, DC leak will do by far more damage than AC leaks. I would suggest a professional, You can throw darts at this all day long but if you do not FULLY understand it you will be wasting your time. This is one of those things where myth is by far more prevalent than fact. Ask 10 different people your will get 10 different answers, one might be right!
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Old 31-10-2010, 10:50   #4
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Any submerged telephone or power cables near your mooring area?
We have one shallow bay where, prior to fiber optic and sat-uplink, mooring
chains would lose their zinc, along with the boats, in 3 months.
This is where all the Cable & Wireless trans-ocean cables come ashore.
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Old 31-10-2010, 11:48   #5
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2 shaft zincs and 1 on the prop.
Same mooring field as last year.
I acturally think the bonding wire to the corroded thur hull fitting from last year was not well connected to the engine block. And prior to this the boat had been in a marina connected to shorepower so it's hard to say whether there is any relationship on that.
Yes that Water Witch is probably milli-amps normal current.
I don't see how unbonding the thur hulls would make the zincs waste faster.
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Old 31-10-2010, 12:01   #6
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Electrolysis is a funny thing. Sometimes it just changes for no apparent reason and the best you can do is to add more anodes at the next haulout to make sure you do not run out before the boat gets hauled again.
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Old 31-10-2010, 14:17   #7
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Quote:
Originally Posted by Don Lucas View Post
- due to a corroded thur fitting last year I unbonded all my thur fitings last year
Your thru-hulls were corroding before you removed the bonding wires and now the zincs are corroding - this could be a clue - if underwater components are not galvanically identical, bonding them completes a circuit and causes corrosion where otherwise there would be none - removing the bonding wires could be allowing your zincs to corrode now where before the thru-hulls were corroding instead. But for the zincs to corrode because they are protecting your boat they still need to be tied into the bonding system somehow.

Bonding also causes corrosion by completing circuits for stray current originating outside the boat. Things to consider: higher water currents increase cathodic protection requirements - did you use the boat more?, water temperature, pH and salinity - new factory/waste treatment plant upstream?, anode quality and how well they were installed ... new underwater cables in the area.

Nigel Calder does an excellent job covering stray current corrosion, bonding and cathodic protection in his book "Boatowner's Mechanical and Electrical Manual". You can do some tests on the hard, but you need to be in the water for other tests. Read up on it and do what you can over the winter, and you can finish up when you float the boat next spring.

Anodes work by generating a small galvanic current - DO NOT just add more/larger anodes as over protection is also harmful. Nigel Calder covers how to determine whether a zinc's weight or surface area needs to be increased. Testing for the correct anode size requires that the boat be in the water so you might want to schedule your splash time at the end of the day to have time to check, and if your anodes are incorrectly sized they should be able to leave the boat in the slings overnight giving you time to buy and install the correct size. (Remember to tip the guys extra if you ask for this. )
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Old 31-10-2010, 15:03   #8
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Quote:
Originally Posted by David M View Post
Electrolysis is a funny thing. Sometimes it just changes for no apparent reason and the best you can do is to add more anodes at the next haulout to make sure you do not run out before the boat gets hauled again.
In this particular case I would say the OP has plenty of zinc on the running gear and adding more is simply a band-aide and does nothing to solve the problem, which will be ongoing, without correction. It is likely that there is an electrical issue aboard and I would say that having a marine electrician go through the boat's electrical system to locate it would be money well spent.
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Old 31-10-2010, 15:12   #9
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Quote:
Originally Posted by ShipShape View Post
Testing for the correct anode size requires that the boat be in the water so you might want to schedule your splash time at the end of the day to have time to check, and if your anodes are incorrectly sized they should be able to leave the boat in the slings overnight giving you time to buy and install the correct size.
The OP's Cal 39 has a an 1.25" shaft and typically would carry one or two anodes on it. Since he stated he also lost his prop zinc, we can assume he has a feathering prop that needs a zinc as well. The only other likely place that this boat would have a zinc is the strut, but since the OP makes no mention of it, I assume his boat does not carry one. It seems clear that "the correct size" zincs have been in use on this boat and the only option the OP has would be to change the number, and as I mentioned above, this is not going to solve his problem.
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Old 31-10-2010, 15:14   #10
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Multimeter in the bilge?

Have you tried putting one probe of a multimeter in the bilge water and one on ground or positive? Then try the same test with one or both of the pump switches disconnected...

I am not familiar with the bilge pump switches that you mention but the one in my boat can carry enough current to run the bilge pump at full capacity.

As leakage into my bilge is small I have relocated the switch to above the residual water level.
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Old 31-10-2010, 15:17   #11
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Quote:
...if underwater components are not galvanically identical, bonding them completes a circuit and causes corrosion where otherwise there would be none...
Any discussion about galvanic or stray current corrosion requires some genuine adherence to correct terminology or we will get lost in the woods.

There are three legs on the galvanic corrosion milk stool:
1. Dissimilar metal components,
2. Submerged in the same electrolyte,
3. Electrically connected.

Quote:
Electrolysis is a funny thing.
By the way, and for the record, electrolysis is defined by the Merriam-Webster Dictionary as: "a. The producing of chemical changes by passage of an electric current through an electrolyte." Electrolysis - Definition and More from the Free Merriam-Webster Dictionary Electrolysis is a misnomer when applied to galvanic corrosion as electrolysis is not taking part in the galvanic corrosion process.

For the sake of this discussion, I am going to use a portion of the ABYC's E-2 description of a cathodic protection bonding system: A green insulated, tinned, stranded conductor of at least AWG 8 connected to each underwater metal component and with a resistance to the sacrificial anode of <= 1 ohm. (There are other conditions and caveats, but this is the simplest working definition.)

Now that we have that out of the way...From a galvanic corrosion standpoint, unbonded underwater fittings manufactured of high quality bronze will literally out last most owners. If these same fittings are bonded, as defined above, then they will be electrically at the same potential, and galvanically, less negative (more noble) than the anode that is the third component of this system.

Quote:
..removing the bonding wires could be allowing your zincs to corrode now where before the thru-hulls were corroding instead.
As stated, this is fundamentally impossible. The galvanic series precludes the "...thru-hulls were corroding instead." from happening. And by removing the bonding wire, the OP has removed one of the three conditions for galvanic corrosion to occur.

Two more factoids:
Galvanic corrosion is a slow process.
Stray current (DC) is a very, very rapid process.

The OP now has a cathodic protection system comprised of three zinc anodes, a bronze composition propeller, a stainless steel shaft, and an electrolyte. His anodes have wasted twice as fast this season than last. Same mooring, etc. The existing problem is within that system or a "sneaker" that is attached to the system that wasn't before.

When the OP found a less than optimum connection of his wasting hull fitting to the cathodic protection system, he could have stopped the wastage by providing the <= 1 ohm connection of that thru hull to the CP system.

I will not venture to try and troubleshoot what the root cause of this problem is. Corrosion issues can only be solved by understanding the processes involved and crawling around the vessel with a very good voltmeter and a Ag-Ag Cl half cell. So, once again, I agree with Wayne: hire a professional.

Hope this helps.
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Old 31-10-2010, 15:24   #12
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Quote:
Originally Posted by CharlieJ View Post
By the way, and for the record, electrolysis is defined by the Merriam-Webster Dictionary as: "a. The producing of chemical changes by passage of an electric current through an electrolyte." Electrolysis - Definition and More from the Free Merriam-Webster Dictionary Electrolysis is a misnomer when applied to galvanic corrosion as electrolysis is not taking part in the galvanic corrosion process.
+1

Thank you

Electrolytic corrosion and electrolysis are not the same thing, despite the common error of using the terms interchangably.
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Old 01-11-2010, 11:37   #13
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Well I think I'll start by redoing all the bilge pump wiring and the grounding negative wiring in general.

In thinking about it more the thur fitting that had the problem last year was bonded to the fuel tank (alum), but the grounding wire from that thur hull fitting back to the engine block basically fell apart when to was replacing the fitting (so it wasn't really connected last year). When I redid the fitting and unbonded the fittings I ran a fresh ground wire to the block which was connected to the fuel tank (so this year it was connected and the zincs got eaten). Due to location there's a lot of wires running past that fuel tank and maybe 1 has become flayed. So maybe hooking up a multimeter between the fuel tank ground wire and the engine block will show something (would still think the current would prefer to go back to the battery instread of to the sea though the engine/shaft).

One thing I know I'll not planning to do is bond the thur hull fittings back together. In doing some research I see nothing good to come from connecting these together into something that is going to past a possible current. I would perfer to replace zincs than have a fitting corrode away like last year where I found a 1-1/4" fitting that was only being held in by some caulking.

But if a real strong case can be proven/shown to me I am always willing to consider.
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Old 01-11-2010, 12:41   #14
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Just to complicate matters, Professional Boatbuilder, IIRC, did an article some years back about un-bonded under water fittings, with the variety of casting alloys available, setting up there own little potential problems between any two.
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Old 01-11-2010, 12:44   #15
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Just to complicate matters, Professional Boatbuilder, IIRC, did an article some years back about un-bonded under water fittings, with the variety of casting alloys available, setting up there own little potential problems between any two.
That is sort of the point in bonding in the first place
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