Grounding or bonding issue???

On haul out yesterday it was apparent that my prop, rudder and metal rudder bracket were thickly coated in a hard scale. None of the other boats hauled today at our marina had this. It was very easily dissolved with a light muriatic acid solution but obviously I have an electrical issue. There does not seen to be any corrosion on these parts but something is wrong and I want to correct it. We are in fresh water but this likely doesn't matter. Where do I start?? Any suggestions would be very much appreciated.

I have just my sterngear bonded to a single zinc plate on the transom and a Drivesaver to isolate it from the engine. Never had a problem in 20+ years. BUT, always heavy barnicle growth on the metal skeg bar by the end of the year, right over the bottom paint. Last year I decided to change that and was told by Pettit that applying copper base bottom paint over even primed metal neutralizes the paint right away. They said a barrier coat or non-copper paint was needed for metal. This spring I coated my skegbar with two coats of epoxy (2nd thickened) and this year not a single barnicle on it. They were right.

We don't know if your boat is moored or has dockside power or if your changed anything this year.

I believe the OP has a fresh water boat.

I'd consider getting a corrosion analysis performed by a competent technician who utilizes a silver/silver-chloride (Ag/AgCl) reference electrode. We had one done last summer and it took about one hour. Money well spent. Here's a link that may help.

Corrosion Reference Electrode Product Specifications

Yes I am in fresh water, no barnicles here. I am on shore power in the marina except when out on the water as my refrigerator is 12V and the battery charger needs to keep topping up the batteries. I haven't changed anything significant, new chartplotter and VHF. Did add a bow thruster as well and funnily enough no coating on it at the bow of the boat. Larry, I will see if someone in this area does this type of analysis, seems reasonable. Thanks all.

Quick Check

LaBomba said:

Yes I am in fresh water, no barnicles here. I am on shore power in the marina except when out on the water as my refrigerator is 12V and the battery charger needs to keep topping up the batteries. I haven't changed anything significant, new chartplotter and VHF. Did add a bow thruster as well and funnily enough no coating on it at the bow of the boat. Larry, I will see if someone in this area does this type of analysis, seems reasonable. Thanks all.

Click to expand...

When you are plugged into your shore power, with a clamp type ammeter check your shore power cord for current flow. Simply clamp around your shore power cord while it's plugged into to the boat. Any current indicates leakage to ground through something on your boat. Any current flow is a dangerous condition in fresh water.

Scary, thanks I will try that, I have a clamp type digital amprobe. I assume I need to shut off all boat powered equipment, battery chargers etc. to do this test?

LaBomba said:

Scary, thanks I will try that, I have a clamp type digital amprobe. I assume I need to shut off all boat powered equipment, battery chargers etc. to do this test?

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No actually turn everything on...the check is to see that all equipment using power is returning it out the neutral back to source ground rather than out through the bottom of the boat....thus the "zero" reading signifying all is "good".

Greetings,
Mr. ps. OK, ya got me. Everything on? What about something that cycles like your fridge? THAT alone will cause fluctuating/different readings will it not and I suspect we're talking milli amps here. Would have to be a damn sensitive instrument I would think.

RT Firefly said:

Greetings,
Mr. ps. OK, ya got me. Everything on? What about something that cycles like your fridge? THAT alone will cause fluctuating/different readings will it not and I suspect we're talking milli amps here. Would have to be a damn sensitive instrument I would think.

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Not really you are checking the power coming in through the cord cancels out the power going out and if not zero...then it's leaving via the water...

http://assets.bluesea.com/files/resources/application_briefs/clamp_meter.pdf
•
Check for current leakage. When clamped around cables which include both the hot and neutral wires, there should be no
current reading. If a significant current reading exists, it indicates a fault condition. Using the clamp feature around a shore
power cord can reveal potentially deadly AC current leakage into the water surrounding the boat.

Greetings,
Mr. ps. Thanks but still doesn't make sense to me. If everything is off and there's still a power flow THEN you have a leak. If everything is on and cycling, power is flowing but some is doing mechanical work and some is given off as heat/light etc. How do you know how much, if any is leaking?

RT Firefly said:

Greetings,
Mr. ps. Thanks but still doesn't make sense to me. If everything is off and there's still a power flow THEN you have a leak. If everything is on and cycling, power is flowing but some is doing mechanical work and some is given off as heat/light etc. How do you know how much, if any is leaking?

Click to expand...

whatever it reads is what you are leaking....you may be locked into DC thinking...with AC this test is the recommended one...very basic but a start...

try this for explanation...

https://www.bluesea.com/resources/1381

Greetings,
Mr. ps. OK, gotcha BUT you would only be able to detect leakage IF there was an ELCI or a GFCI on board-correct?

RT Firefly said:

Greetings,
Mr. ps. OK, gotcha BUT you would only be able to detect leakage IF there was an ELCI or a GFCI on board-correct?

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No I don't think so...IF you had a ELCI...it would trip if you had leakage..the reason they exist.

If you DON'T have one...and you get a reading on your power cord...you have an issue that needs correction.

You won't get a reading if you have a fault that is leaking back out the green wire...so that one thing this test doesn't get I think....the test is more for leakage into the water.

Greetings,
Mr. ps. I never was very good at electricity. I'm stumped if there are more than 2 wires. Thanks.

Let me give it a try:

AC current from the shore power outlet goes down the black wire (I am using DC terms but bear with me) to the various appliances on the boat and then back up on the white (neutral wire). If you have any kind of fault- a short to ground in an appliance or wire then the current comes back on the green- the ground wire.

If you put an AC clamp on ammeter around all three wires you should see zero amps. The incoming black cancels out the outgoing white (or green).

But if you have a leak to the water (typically in the bilge) then some of the current will leave the boat through the water and there will be less current in the white or green wire and your clamp on ammeter will show some current.

It is a crude but effective test for AC leaks to the bilge.

But having said all of the above, AC leaks to the bilge don't cause what you are seeing. And I am not sure it is an electrolysis issue at all.

David

And to drive home the point, less than 1 amp leakage into the fresh water can kill a nearby swimmer. Just do the test, take our word for it, and get help if your reading is not really close to 0 amps. And yeah, maybe nothing to do with the scale buildup.

With your shore power disconnected, and your inverters, and generators output isolated, use an ohm meter between your AC neutral and ground.

You should see an infinite reading.

If you do not you need to find and resolve the issue.

psneeld said:

No I don't think so...IF you had a ELCI...it would trip if you had leakage..the reason they exist.

If you DON'T have one...and you get a reading on your power cord...you have an issue that needs correction.
>>> good and simple test to perform, thanks for the reminder

You won't get a reading if you have a fault that is leaking back out the green wire...so that one thing this test doesn't get I think....the test is more for leakage into the water.
>>> this fault (actually either fault) should trip shore power GFCI on the shore side if installed ... which leads me to the questions below ...

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If there is a working GFCI on the shore side of shore power connection, is it really safe to assume that there is no AC current leak into the water and/or ground on a connected boat?

What is the impact of boat's galvanic isolator on shore GFCI's ability to detect the faults?

An ammeter will tell you how many amps/milliamps are being drawn through the power cord. Any equipment that is on and functioning will add to the total. The meter will only read zero when there is no electron flow.

Psneeld is very correct of course. Some others are mudding the water. I suggest if you don't understand electrical AC and/ or DC you hire a marine electrician that is ABYC certified before someone gets hurt. According to BoatUS 11 people drown each year in US most in fresh water around boats with faulty wiring. First of all, all current flow is the same in all branches of the circuit. In AC the black and white wires are equal and the green is 0. You don't lose amps unless there is a path to ground, intentional or otherwise. Amps don't disappear or evaporate they flow back to source. See Kirchhoff's circuit laws - Wikipedia, the free encyclopedia

Second The clamp meter will show any current that is going to the green wire if there is a fault! In AC the green wire should carry 0 current in a perfect world. All grounds should measure zero volts if all is well AC/DC. House electricians some times don't understand this in marine applications. We had/have this condition in our marina and found it was Air conditioning units not properly bonded and the docks terminal ground was not sized properly to carry the load (volt drop) Suggest you read Nigel Calder's boat book before you disagree with anyone. I hope this helps. It is difficult to explain electrical physics via printed word. The Blue sea references and more are easy to understand.

Guys, some of you are really missing the point from a practical sense. You have the concepts absolutely correct, but in practicality you can miss the problem entirely.

If you put your current clamp on the green wire, unless you have a REALLY big problem its probably going to read zero anyway.

Thats because most current clamps are just not designed to pick up miliamp sized currents all that well.

Your current clamp might be rated for 0-200 amps but that doesen't mean it actually works at near zero amps. I do not care what the label says. I do not care what the specifications from the manufacturer say. I do not care what Wikipedia says, or what a electrical engineer learned in college. I care about the reality of the field.

People that deal with very small currents (like utility guys in the Meter, Relay or SCADA shop(s)) have special very low range current clamps. Little itty bitty things, not the standard electricians clamp. For those that doubt this, try it some time. Set up a test circuit. We did, when I worked as a meter/relay tech at our local utility. Meter techs deal in 0-5 amp circuits every day . We found that it was darn near impossible to actually read sub amp currents accurately using standard electricians current clamps.

Greetings,
Mr. ks. That's exactly what I was alluding to in post #9. I would THINK a meter would have to be VERY sensitive to detect milli amps. I fully realize the problem in that milli amps CAN kill.

ksanders said:

Meter techs deal in 0-5 amp circuits every day . We found that it was darn near impossible to actually read sub amp currents accurately using standard electricians current clamps.

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Clamp on ammeters are a great tool to have on a boat. Make sure you get one that will read DC as well as AC. Be careful sometimes the specs imply the unit will give DC current readings, but on some of the cheaper units this can only be done using the meter as a conventional multimeter not via the clamp facility.

The big advantage is that they will read currents without breaking the wire.

On DC currents they seem to be OK to about the +/- 0.1 Amp level with a bit of care.

For the OPs problem I would be looking carefully at the Bow thruster. A simple solution that may work is to consider isolateing both the + and - sides of the bow thruster when it is not being used.

If the "scale" is from galvanic action it may suggest that your boat is providing a connection to the marina's A/C earth grounding system allowing any stray voltage leaking from other boats to dissipate through yours. Isolating the two systems can be simple if the shore power is only used for battery charging, but if it's a live aboard situation it would be more complex ($$). Either way, if this problem is significant/corrosive I would contact a licensed marine electrician for a proper evaluation.

Do you have anodes of any kind on your boats running gear? If so, it sounds to me like they may be leaching onto your props.

Just to clarify...galvanic corrosion is strictly the action between 2 underwater metals.

Stray current corrosion is just that...either AC or DC....

Stray current on the marina's green wire shore power ground can be blocked with a galvanic isolator for between $100-$400 or isolation transformers that I think start around $600 for a 30A service.

And yes ...again...a clamp ammeter around a shore power cord will show zero unless there is current lost to the water...Kevin Sanders is correct in the fact that depending on how sensitive your clamp meter is....will determine just how little stray current you may be able to detect that you are losing overboard.

And to clarify, a clamp ammeter will show zero if there is zero draw, meaning no devices are using any electricity, or the draw is too low for a common meter to read.

sanjuanjohn said:

And to clarify, a clamp ammeter will show zero if there is zero draw, meaning no devices are using any electricity, or the draw is too low for a common meter to read.

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No...it will show zero if there are no leaks...meaning normal 30 or 50 amp draw will still show zero on the clamp meter around the shore power cord...

Now take it to your panel and put it around just the black or white or red wire going to your panel and it will show what ever you are drawing...but around a normally functioning boat/shore power cord and the clamp meter will show zero even.... with the cords/panels maxed out with draw.

I know I just did it a couple weeks ago when I upgraded to 50 amp shore power and was running all my checks.

That's why if you want to use a clamp meter and determne what an appliance draws...you have to have an adapter where the wires are split so you can just wrap the clamp around ONE wire, not the cord.