Diver finds Halos in bottom paint

I have a diver clean the bottom of the boat every month. Yesterday he notified me that there is a halo around one of the underwater lights. The halo effect is usually caused by the bottom paint eroding due to stray current. Typically, most prominent with black bottom paint with high copper content; just what I have. So guess what I'm doing today.... Anyone else have to deal with this?

Checking bonding wires!!! Fun.

Not.

I spent a couple of hours on the boat checking potential and current between the hull zinc and various points around the boat. The problem per the diver is on the starboard side but interestingly the readings on the port side were concerning.
I ran the testing with dock power up and running then again with the dock power disconnected - negligible differences, so I'd say the isolation transformer is good. I bought a Silver Chloride cell from boatzincs.com yesterday - more to follow.
Thoughts on this?

I think were thinking same...It could be external to you.

Are there any new residents/boats next to or close to you? How about any recent electrical work on the dock?

Any history on the same readings?

I'm still trying to understand what it's telling me.....
I have a new neighbor on my port side - 42' Carver.
Empty slip to the starboard side.
I put one side of the DVM on the hull zinc bolt and took all of the measurements with reference to that.
The odd thing is everything bonded to that hull zinc should have been near zero current and voltage.
The port propshaft is bothersome as that is the same side I saw all of the galvanic corrosion when we rebuilt the running gear last year. There was a different boat (a real garbage scow) there before and now the Carver.
Hopefully the silver chloride test cell will tell a better story.

But the haloing is on the starboard side - I double checked with the diver when I saw the readings.

More to follow unless someone here has an epiphany

]p]

ttmott said:

I'm still trying to understand what it's telling me.....
I have a new neighbor on my port side - 42' Carver.
Empty slip to the starboard side.
I put one side of the DVM on the hull zinc bolt and took all of the measurements with reference to that.
The odd thing is everything bonded to that hull zinc should have been near zero current and voltage.
The port propshaft is bothersome as that is the same side I saw all of the galvanic corrosion when we rebuilt the running gear last year. There was a different boat (a real garbage scow) there before and now the Carver.
Hopefully the silver chloride test cell will tell a better story.

But the haloing is on the starboard side - I double checked with the diver when I saw the readings.

More to follow unless someone here has an epiphany

Click to expand...

Unfortunately electricity in water is like water in an old house, it will take the path of least resistance and come out far from where it entered. I would agree the port side is most concerning, Odd that the starboard engine has a negative potential?

Maybe move over to the next slip or other temporary location and repeat? That would at least let you know if it is local to your slip, or your boat.

dtfeld said:

]p]


Maybe move over to the next slip or other temporary location and repeat? That would at least let you know if it is local to your slip, or your boat.

Click to expand...

I really like that idea. First I'll wring out the boat where it is then move it and do it again. There are several empty slips even further away.
The good news is I think I've eliminated that expensive isolation transformer being the issue - I think.

TTMott, very interested in this thread as I am chasing something similar. When I hauled the boat 4 months ago, yard said I had an electrolysis issue. I'm getting 220 MV between zinc and port engine. Any sources to share to learn more about this issue and how to troubleshoot?

Thanks

LMBoat said:

TTMott, very interested in this thread as I am chasing something similar. When I hauled the boat 4 months ago, yard said I had an electrolysis issue. I'm getting 220 MV between zinc and port engine. Any sources to share to learn more about this issue and how to troubleshoot?

Thanks

Click to expand...

I'm wrestling with the findings also. One would think, if everything was bonded and very low resistance through that bonding, that there would be zero current and potential measurable. These are low numbers however. Even if the numbers are low with the boat passing DC current between metal parts under water we have a problem.
The diver did confirm that my zinc's are going away way too fast.
I have a feeling this is going to turn into a science project....
I bought this to further isolate the issue -
https://www.boatzincs.com/corrosion-reference-electrode.html

I understand also that it is DC current that causes these galvanic and electrolysis issues.
Things I have read point to malfunctioning DC chargers, defective bonding and, external stray current coming through the AC shore power ground or through the water.

In the meantime…maybe add some hanging zincs. Cheap insurance until you can work this out. Getting it easily connected to your bonding system might be a challenge.

https://www.boatzincs.com/hanging_anode_zinc.html

If you haven't searched "Steve D'Antonio", you might look for info there. Interesting stuff.

ttmott said:

I understand also that it is DC current that causes these galvanic and electrolysis issues.
Things I have read point to malfunctioning DC chargers, defective bonding and, external stray current coming through the AC shore power ground or through the water.

Click to expand...

Tom, the one thing I found when I went through some of this is the bonding plate and it's bolts had resistance to them. Meaning the bolts were not completely adhered to the bonze. Also disconnect the ground on the charger and do the test again. Of course use the new test lead and test the docks ground as well. If your dock doesn't have GFCI wiring then most likely there is a grounding issue as well. Your problem is very well a multitude of small issues surrounding the boat and none by themselves may be worth looking at but when put together there is a problem. That's the hardest to find and seems like where you are at. And to your point, there seems to be more of an issue with the port engine then the starboard from your findings.

When you get your grounding probe, you can check both sides of the boat by moving the probe around your boat and leave the pos probe connected. If there is a stray current issue you should pick that up by moving the probe. Albeit a hard issue to track down. Good Luck!

More today. I enlisted my slip neighbor, and we did everything again. Then went around the other boats and turned off their power and disconnected their power cables and redid all of the measurements. No significant change in any of the values.

Here is something interesting - yesterday I got 240 mV on the port propshaft and then today got 71 mV. Same setup. I then rotated the propshaft and it jumped up to 320 mV. We are going - what the??
So, I think when you rotate the shaft the gear oil coats the bearings and gears creating an insulating layer further removing the bond to the engine block; what else could it be?
We also took readings while shutting down all of the DC powered things using the circuit breakers. Then completely shut down the DC on the boat. No change in readings.
Then took readings with the UW lights on and off with no significant change in voltage. Remember the haloing is around the starboard UW light.

So, here we are with the Port side of things definitely carrying a higher potential and current than the starboard side.
Confirmed that the dock and slips AC power isn't contributing as far as the measured potential within the boat's metal and hull zinc.

Next is the Silver Chloride test cell.

As a side observation, my slip neighbor's Cabo has shaft brushes to ensure his shafts are bonded. I may look into some shaft brushes after this is all done and understood.....

Just a quick question, when you were going around to other boats in the marina, turning off their power and unhooking their cables - do they mind that someone is doing that? Just curious, would be a no-no where I keep our boat.

FootballFan said:

Just a quick question, when you were going around to other boats in the marina, turning off their power and unhooking their cables - do they mind that someone is doing that? Just curious, would be a no-no where I keep our boat.

Click to expand...

We are pretty close; a quick text was in order.

After I typed that in, I regretted. Hope I didn't offend.

From post#3, I'm surprised that your underwater lights aren't bonded. I had new Ocean LED's installed when I took delivery of my boat in May of 2013. A few months later I noticed the LED housings were pitted. It was October and was heading to FLIBS so figured I would quiz the Ocean LED folks since I had just spend a ton on them. First thing they mentioned was to check the bonding. Well, he was right, there was no bonding. Called the yard that installed the lights and they added bonding wires the next day. No more pitting. Still pissed that it happened in the first place.

I took some time today and ran through some testing with the Silver Chloride test cell I received yesterday.
The booklet that came with the cell is very informative both on how to test but how to interpret the results.
There are four tests:
Test 1, Measurement of the Hull Potential - This test measures the potential between the boat and the test cell through the primary grounding plate. Boat construction determines what the hull potential range should be. For fiberglass boats with inboard engines the range is -550 millivolts to -1100 millivolts DC (-0.550 volts to -1.100 volts). Readings within the range indicates the underwater metal is protected against corrosion. Readings below (more positive) reveals the metals are under-protected and may be corroding. Readings above (more negative) indicate the metals are over-protected. This test is done with shorepower disconnected and batteries disconnected. This is your baseline for all testing.
Test 2, Bonding System Verification - This is taking individual measurements of each metal component exposed to raw water. These measurements should match exactly the Hull Potential measurement test. This verifies the bonding system fully connects all of the metals to the hull anode.
Test 3, Checking Galvanic Isolation - This test verifies the boat metal elements exposed to the raw water are isolated from the shorepower AC Ground, cable TV Ground, and any other ground connection to the shore systems. A boat that is not galvanically isolated can create electrical interaction through the water with other boats or other underwater metallic structures. A shift over 10 mV from the hull potential reading indicates the anodes are interacting and being consumed by nearby underwater metals and a shift of over 100 mV indicates significant leakage due to another boat charging the water and/or failure of the galvanic isolator (or isolation transformer).
Test 4, Checking for and finding any stray current - This test looks for significant voltage changes to the Hull Potential Voltage as AC and DC power is turned on and various electrical devices are exercised. This test requires water to be added to all the sumps and the pumps turned on and off also. We are looking for a potential shift of over 10 mV. Isolating any sign of leakage is the process of going back and switching on the power to devices (AC and DC) one at a time and seeing changes with the device off and on.

OK - as you can see in the chart I made below there are only three things of any concern that I need to address - so far. I still have to complete the bonding test of the forward things, the stray current testing, and crawl back there and test the UW lights. No smoking gun yet but more to follow.