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Old 06-10-2016, 11:57   #1
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Reference Cell Test Results, Help to Determin Resolution

I got my boatzinc reference probe and did some testing. Now I need some help with the data. For background, I've been loosing a pair of shaft zincs in 3mo and have had significant pitting in the lead keel the past 2 winters requiring epoxy, refairing, repaint. more background in previous thread here:
Stray Current Isolation Testing?
Testing was done at the mooring with the probe hung over the side near the prop. The bonding wire runs from the negative side of battery, to engine, engine to keel bolt (disconnected as stated below), keel to mast. Here’s the results….

Test conditions. “Fish” zinc on shroud (connected to keel) and 1 shaft zinc:
______________Bat sw OFF _____ lots ON _____ Keel Bond remove dc off
Shaft__________ -962mV________ -965mV________ -945
Engine_________ -810mV________ -885mV________ -815
Keel bolt_______ -827mV________ -858mV________ -780
Bnz Thru ______ -146mV________ -146mV_________ na

___________ keel bond removed lots On _____ Eng@1100rpm
Shaft______________ -938__________________-935mV
Engine_____________ -931 _________________-903mV
Keel bolt____________ -802 _________________ -850mV
Bnz Thru_____________ na _________________ -146mV

Partial Repeat with fish zinc out of circuit, only 1 shaft zinc:
_________________Bat sw OFF____________ lots ON
Shaft______________ -903mV_____________ -875mV
Engine_____________ -686mV_____________ -663mV
Keel bolt___________ -678mV_____________ -675mV
Bnz Thru ___________ -145mV____________ -144mV

_____ Keel Bond Removed batt off ___ keel bond removed lots On
Shaft_________ -891 ______________________ -874
Engine________ -703 ______________________ -862
Keel bolt______ -648 ______________________ -701

Voltage between Engine and Keel when bond is lifted:
Lots DC ON: 149mv and 135mV (fish zinc out and in respectively, keel +)
Batteries off: 68mV and 53mV (fish zinc out and in respectively, keel +)

Testing bilge water:
Bilge pump running/not running had no effect on voltage in bilge water
Bilge water voltage would start out high (more neg like -660) then reduce over a few min to -520mV… maybe because I’m using el cheepo DMM?

I would love people to weigh in on some conclusions. Here are some observations I have...
1) The shaft and engine are not well connected electrically showing 150mV-200mV+ difference. poor connection could explain loss of lead keel, but I would think it would slow the shaft zinc loss, right?
2) Turning on DC or the Engine On reduces the difference between shaft and engine, but not consistently. In general DC circuits ON results in a higher negative potential on the engine bonding system. Per the Boatzinc manual, this more negative value means better protection... hmm.. electrical leakage is good!?
3) When keel bond is lifted the difference between engine and shaft potential generally reduces to a few dozen mV.
4) There's approx 100mV difference between DC ON and DC Off at the keel to engine bond. There is no specific circuit causing this. As I turned DC panel switched on, each had a % impact... issue must be on common wire, not out in branch circuits downstream of panel.

What do I do now???? Leave the keel to engine unbound?
Thanks for your comments/suggestions and sorry for the long post. Lots of data to communicate.

Thanks,
Zach
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Old 07-10-2016, 10:18   #2
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Re: Reference Cell Test Results, Help to Determin Resolution

answers on this electrolysis stuff is like pulling teeth... Not sure why my new thread didn't show in today's email push of new topics? maybe that would help get me info. I know there's others interested in knowing about this...
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Old 07-10-2016, 13:28   #3
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Re: Reference Cell Test Results, Help to Determin Resolution

I was waiting to find out what happen with the stray current problem in the bulge water?


When you say your moored, is there other boats around? Have you tested the water for stray AC and DC current coming from the other boats?


The next thing I would do before making any measurement using a haft-cell is the boat must be free of any stray current. Until that problem is fixed your wasting your time. IMO


I know you say the “Fish” is connected to the keel and therefor to the GROUNDING BUS. Please humor me and run the “Fish” directly to the GROUNDING BUS to see if it make a difference.
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Old 07-10-2016, 17:25   #4
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Re: Reference Cell Test Results, Help to Determin Resolution

Thanks for posting. It looks to me (not that I know much about it!) like good information you have, and it also looks like most of the stuff is in range (-900 ish) with the fish working and the keel bond in place.

I take it the through hull is unbonded?

Are the bond wires all in absolutely top condition, Ie minimal resistance?

Interesting stuff. Thanks for posting, and hopefully someone who knows more about the dark art of cathodic protection can wade in with some good info.
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Old 07-10-2016, 22:18   #5
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Re: Reference Cell Test Results, Help to Determin Resolution

everything that is bonded should have the exact same vaule.

if you only have zinc on the shafts. then you have a poor connection from shaft to rest of boat. which is why the shaft is showing higher. (the higher the more zinc). if you have brushes I would take sand paper or a file and clean them a bit. and measure every point you can, shaft, brush, wire attached to brush, etc. you'll probably see it change from shaft to brush. untill you clean it. I saw this a couple weeks ago on a boat. 30 secs with a file and both numbers synced somewhere in the middle afterwards. (shaft went down, boat went up, both now at same value)


I'm guessing your DC loads neg also come off the engine block? that could be the change there. you're probably picking up the voltage drop between the battery and engine block as current flows to the panel. if your DC panel fed came from battery it probably wouldn't see this change.

keep in mind you may have 200-300mv+ voltage drop between battery to panel with loads on. and now you are trying to measure MV between different things.
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Old 14-10-2016, 10:24   #6
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Re: Reference Cell Test Results, Help to Determin Resolution

Quote:
Originally Posted by Doodlebug View Post
I was waiting to find out what happen with the stray current problem in the bulge water?


When you say your moored, is there other boats around? Have you tested the water for stray AC and DC current coming from the other boats?


The next thing I would do before making any measurement using a haft-cell is the boat must be free of any stray current. Until that problem is fixed your wasting your time. IMO


I know you say the “Fish” is connected to the keel and therefor to the GROUNDING BUS. Please humor me and run the “Fish” directly to the GROUNDING BUS to see if it make a difference.
Hi doodlebug, Thanks. I'm over 100ft from another boat and since electrical potential decrease exponentially with distance, I highly doubt there's any meaningful potential getting to my boat from the others in the mooring field. I have also done some tests at anchor with nobody around and got very similar numbers. Why do you conclude I have a stray current problem?? I can connect the fish to the 'grounding bus', but I don't really have that. Do you want me to connect on the Battery monitor Shunt/terminal where all the negative DC leads AND the main bond/ground line is, which goes to the engine block or just at the engine block?
thanks
zach
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Old 14-10-2016, 10:45   #7
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Re: Reference Cell Test Results, Help to Determin Resolution

Quote:
Originally Posted by smac999 View Post
everything that is bonded should have the exact same vaule.

if you only have zinc on the shafts. then you have a poor connection from shaft to rest of boat. which is why the shaft is showing higher. (the higher the more zinc). if you have brushes I would take sand paper or a file and clean them a bit. and measure every point you can, shaft, brush, wire attached to brush, etc. you'll probably see it change from shaft to brush. untill you clean it. I saw this a couple weeks ago on a boat. 30 secs with a file and both numbers synced somewhere in the middle afterwards. (shaft went down, boat went up, both now at same value)


I'm guessing your DC loads neg also come off the engine block? that could be the change there. you're probably picking up the voltage drop between the battery and engine block as current flows to the panel. if your DC panel fed came from battery it probably wouldn't see this change.

keep in mind you may have 200-300mv+ voltage drop between battery to panel with loads on. and now you are trying to measure MV between different things.
Thanks smac999. I don't have brushes on my shaft.. Where can I get them? I can't find them for small shafts, just ships. I think that I need to get the brushes since there is clearly not a good electrical connection between the shaft and engine.

I don't understand your comments regarding the DC negative loads and potential at the engine vs the battery. Can you clarify? The engine and neg battery terminal is bonded with a heavy wire, so they should be equal potential. Negative DC panel lead(s) connect to battery monitor shunt along with bond wire from engine.

Can you isolate the DC system from bonds with a diode isolator (like a galvanic isolater) which will keep DC current off the underwater metal, but still allow short circuit connection?

Agree that all things bonded should be equal, assuming zero resistance. But there is some resistance in all wire and terminals.. how much potential difference is expected between different bonded items? Less than 10mV? Also keep in mind that the boat is floating and moving, so I take a reading on the engine, then a minute or 2 later at the keel. The readings may be slightly different b/c the boat is swinging. with the amount of lead and zinc I'm loosing, I know I have an issue in the hundreds of mV. So I've been kinda ignoring inconsistencies in values less then a few dozen mV. I just don't see the 400mV smoking gun I thought I would


thanks
zach
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Old 16-10-2016, 06:20   #8
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Re: Reference Cell Test Results, Help to Determin Resolution

Shaft Brush ➥ Marine Shaft Brushes

ProMariner Shaft Brush
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Old 16-10-2016, 10:11   #9
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Re: Reference Cell Test Results, Help to Determin Resolution

For several reasons,I decided I wished to dispense with the prop shaft zinc.
The shaft would need to be bonded to the rest of the system as the Volvo MD2020 transmission is electrically separated from the engine.
I had previously added an insulating flexible shaft coupler and bonded the thruhulls, so I got to thinking of ways to bond the shaft without a conventional brush.

Having a PSS shaft seal, I decided to do a little bit of sleuthing and found that the fixed carbon seal has extremely high conductivity and is also very high on the nobility scale !

The fix was to slip a small sheet of copper underneath the shaft log tube and solder a wire to the sheet and the bonding system.

Voila ! No more need for a shaft zinc, only the main centrally located zinc for the rest of the bonding system.
A check with a silver electrode showed all thruhulls and underwater metal are protected.
BTW, I have a homemade electronic circuit which monitors zinc voltage and is adjustable. It's been working for several years.
I adjusted the zinc to provide -0.700 volts to the system and it just stays at that setting regardless of the variability of the water.
The underwater metals are all in great shape while the single largish (2 LB) zinc now has lasted 3 years and counting with rather minimal loss of its metal.
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Old 16-10-2016, 16:30   #10
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Re: Reference Cell Test Results, Help to Determin Resolution

Well isnt that cool senor, 3 yrs now. I cant remember the last time I ref metered someones carbon block. Let me get this correct....you say "copper sheet under shaft log" but have you have made a mechanical conection to the carbon, long strip picking up both ends of the bellows?
Carbon makes contact with stainless collar then contects to shaft via set screws. Carbon is beefy, could thread a bolt into the bleed hole or blind thread a hole to accept the bonding lug.
I like it. Only concern is lack of use causing a poor connection leaving the shaft/ prop unprotected. That activity may pit the s.s. collar surface.
Am I confused to what youve done here.
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Old 17-10-2016, 06:29   #11
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Re: Reference Cell Test Results, Help to Determin Resolution

senor, I also like your little gadget. I have installed quite a few proper overboard zinc systems, zincs live on the dock and plug in via a good trolling motor quick connector. Most dont have a monitor.
I have two vessels that require special attention. One with an al. saildrive the other an al rudder. Both are independent/ isolated bonding systems to control these two metals (al./ rest of vessels exposed underwater metal) hence two overboard zincs.
It works all great but other than lifting zinc out for a visual its not something the owners can monitor with their limited understanding. These boats make me nervous as it doesnt take much to do tens of thousands damage and I'm not always around to watch.
Id be interested in your using your rig with a slight mod for my needs. Something you might like to play with?
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Old 17-10-2016, 10:53   #12
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Re: Reference Cell Test Results, Help to Determin Resolution

PM sent.
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Old 18-10-2016, 05:26   #13
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Re: Reference Cell Test Results, Help to Determin Resolution

Connecting anything to a PSS seems like a recipe for a bad outcome. Those stainless rotors crud up and pit easily. The carbon seal less so, but certainly not an ideal conductor.

Please enlighten everyone why you wanted to eliminate a simple zinc?
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Old 18-10-2016, 10:42   #14
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Re: Reference Cell Test Results, Help to Determin Resolution

When I purchased my 1995 boat, it was only 5 years old.
There was no bonding of anything, including the rudder gudgeon and related metal which had become Swiss Cheese. The prop was also damaged to a certain extent.
There was NO space on the prop shaft for a zinc, as the forward end of the prop had only about 1/4 inch of clearance to the cutless bearing.
The PO had thought he was protecting everything by hanging a fish zinc over the side connected to a shroud, and the only thing electrically connected to the rigging was a small dynaplate at the base of the mast.

I added a bonding system and a flexible shaft coupling to insulate the prop/shaft from the transmission to preserve the insulation which gave me enough space to add a shaft zinc to protect the prop. I also added a centrally located zinc for the rest of the boat's bonding.

Wanting to be able to use the previously posted circuit for the whole boat instead of having a separate shaft zinc to keep track of, I connected the PSS carbon graphite to the bonding system.

As far as conductivity is concerned, it's 1x10x5. It reads zero resistance with a DVM from the shaft to the bonding system connection.
The prop shaft measures the same negative voltage as the rest of the bonding system.

Electrical Conductivity for all the elements in the Periodic Table

As previously stated, a Volvo MD2020 has insulation between the engine and transmission with specific cautions against grounding the raw water cooled alloy transmission to protect it from galvanic action. Therefore, a zinc is necessary to protect the prop and shaft separately from the rest of the underwater metal.

By leaving the shaft flexible coupling in place and using the PSS as a shaft brush, I can protect the whole system with ONE long lasting zinc and have automatic voltage regulation for everything.
The zinc is less noble than everything else in the system, so I fail to see a problem.

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Old 18-10-2016, 10:55   #15
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Re: Reference Cell Test Results, Help to Determin Resolution

If you need a shaft brush, I have a spare you can have for the cost of mailing it.
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