Voltage Leak to Bonding System

[Gypsy Diver]

Hello. This relates to my 36-foot Island Gypsy trawler, 1984 vintage. She is experiencing a stray voltage leak in the bonding system. Measuring it right at the transom zinc bolt, I consistently get a reading of between 25 and 40 milliamps in the bonding system with my multimeter placed in series between the zinc bolt and the bonding wire. I disconnected the shore power and nothing changed. I turned off all the switches on my breaker panel and nothing changed.

[FONT=&quot]Would anyone have an idea as to the source of the leak?[/FONT]

 

[Comodave]

If you have all the A/C sources disconnected and any inverter turned off and you still have the voltage then it must be D/C. And D/C is what will eat your below the water metals quickly, sometimes very quickly. Does your meter show it as A/C or D/C? If it is indeed D/C then I would start by disconnecting the batteries and make sure it goes away. Then start adding things back and see when the voltage reappears. It will be a PITA to find most likely. I had about 40 volts A/C in the bilge water in a boat about 20 years ago. Turned out it was the PO, idiot, that swapped the neutral and ground coming off the back of the inlet. Also used 14 gauge wire which was crispy when I found it. New inlet and wired correctly and no more voltage in the bilge water.

 

[Gypsy Diver]

Thank you. I will try those things.

 

[SteveK]

The 25-40 milliamps makes me ask, is it possible you created a circuit for flow between dissimilar metals?

 

[Gypsy Diver]

Thank you for your kind and lucid responses, Mr. Comodave and Mr. SteveK. Pursuant to Comodave’s suggestion, I disconnected the AC power cable; I turned off the inverter and I disconnected both the positive and negative terminals from all batteries. In other words, I deprived the vessel of all intrinsic AC or DC power. Then, checking again for current between the copper bonding wire that is normally attached to one of the copper transom zinc bolts and that zinc bolt, my volt meter again registered about 35 milliamps of current. Reconnecting the batteries and all DC circuits made no difference. I would note that when I reconnected the AC shore power cable (which has its green wire passing through a brand new 30 amp galvanic isolator), the current reading at the transom moved up to about 50 milliamps.

The strange thing to me is that I don’t find any current flow between the bonding strap and any of the thru-hull fittings, nor at the prop shaft (placing the meter in series between the prop shaft wiper brush and the bonding strap).

In sum, I only find this stray voltage at the transom, between the bonding strap and one of the thru-hull bolts that hold the zinc onto the transom. Knowing nothing about such things, I am left wondering if the seawater (saltwater) at my marina isn’t slightly charged and is passing current into my boat.


Jerry

 

[O C Diver]

It occasionally happens that a nearby neighbor's boat is leaking AC into the water. Wondering if the flow might be coming in from outside.

Ted

 

[Comodave]

It occasionally happens that a nearby neighbor's boat is leaking AC into the water. Wondering if the flow might be coming in from outside.

Ted

That would be my next thing to check. Move your boat out of the marina and see what happens.

 

[porman]

I've got the same thing going on. If I disconnect the transom anode from the bonding system and put a meter in series I get 61 milliamps. If I put a clamp meter on the green (negative) wire on the shore power cord I get 61 milliamps with the anode reconnected to the bonding system. I suspect stray current is coming from an aluminum houseboat a few slips over. I put an electrical current detector used in swimming pools in the water next to it and it lit up like a Christmas tree. The marina management is working on the problem. This is a fresh water marina.

 

[Gypsy Diver]

I've got the same thing going on. If I disconnect the transom anode from the bonding system and put a meter in series I get 61 milliamps. If I put a clamp meter on the green (negative) wire on the shore power cord I get 61 milliamps with the anode reconnected to the bonding system. I suspect stray current is coming from an aluminum houseboat a few slips over. I put an electrical current detector used in swimming pools in the water next to it and it lit up like a Christmas tree. The marina management is working on the problem. This is a fresh water marina.

That could be dangerous in fresh water. I hope your marina management is taking it very seriously.

 

[porman]

They are. There have always been no swimming signs at the head of each dock. Right now it's Winter and the water is cold.

 

[CharlieO.]

I've got the same thing going on. If I disconnect the transom anode from the bonding system and put a meter in series I get 61 milliamps. If I put a clamp meter on the green (negative) wire on the shore power cord I get 61 milliamps with the anode reconnected to the bonding system. I suspect stray current is coming from an aluminum houseboat a few slips over. I put an electrical current detector used in swimming pools in the water next to it and it lit up like a Christmas tree. The marina management is working on the problem. This is a fresh water marina.

What is this electrical current detector you have? We have a few people that swim around our marina and it gives me the heebee geevees. I would like to be able to check around our vessel.

 

[porman]

tester

What is this electrical current detector you have? We have a few people that swim around our marina and it gives me the heebee geevees. I would like to be able to check around our vessel.

shockalert.com also check out electricshockdrowning.org for great information about this serious problem.

 

[Newtrawlerowner]

Thank you. I will try those things.

Also test your bilge pumps for voltage leakage. Place the positive lead in the bilge water (If you have any water in the bilge) and negative lead to green bonding system or even the engine. If shows voltage then disconnect battery or lift pump and switch out of the water. Great you-tube video here.

 

[Comodave]

I would take the boat out of the marina and see if the voltage is gone. If it is then it is the marinas problem, likely a leaky boat nearby. If the voltage is still there then unhook the batteries and if the voltage goes away start hooking things up one at a time and see when the voltage returns. You need to make a process and then work your way methodically through the process. Hopefully the problem will go away when you take the boat out of the marina and then the problem becomes the marinas. Good luck but don’t let this linger since if it a DC voltage it can quickly eat away your metals.

 

[porman]

In my case wouldn't my metals be protected since the stray current is going straight to the power pedestal ground?

 

[Comodave]

In my case wouldn't my metals be protected since the stray current is going straight to the power pedestal ground?

How can you be sure that is happening? I would not want to trust a $4K prop to say nothing of through hulls, shafts , etc.

 

[Mainship Pilot]

Sounds like you have a hot boat in the marina close by. I just moved slips due to a hot boat right next to me, owner has not been near the boat for many months. My zinc's were frying on a regular basis, after the move, all is well.

 

[Steve DAntonio]

You are turning off AC power but are you disconnecting the cord as well for the test? The cord's AC safety grounding wire is always connected, even with power off, as long as it is plugged in. If you disconnect the cord, and the current disappears or drops significantly, then your vessel is acting as a return path for leakage from another vessel.

Do you have a galvanic isolator?

More hear https://stevedmarineconsulting.com/wp-content/uploads/2019/09/Hot-Marina-Myth-CW-AugSept-2019.pdf