Stray Current?

rpell1@msn.com

rpell1@msn.com

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Sep 25, 2008
464
Catalina 30 MKIII Varuna Boat Club
We are having a "discussion" at our Club about whether or not being continuingly hooked up to shore power can cause problems for other boats in the marina? My '97 MKIII has a galvanic isolator and I am using a Hubbell 30amp power chord. The shore outlets have been checked for polarity and there are no problems there. My contention is that my boat is not contributing to any of the problems. Opinions please?
 
justsomeguy

justsomeguy

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Feb 20, 2011
7,993
Island Packet 35 Tucson, AZ/San Carlos, MX
www.powerandmotoryacht.com

Stray Current Test

Story and photography by Capt. Vince Daniello Damaging and dangerous stray current can come from a chafed bilge-pump wire or a wet terminal strip near bilge water, electrical equipment leaking power into a grounded case, improper electrical work on your boat or on the dock, or innumerable other...
www.powerandmotoryacht.com www.powerandmotoryacht.com
 
B

Benny17441

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May 24, 2004
7,131
CC 30 South Florida
It is like the Covid-19 it was good at the last time tested. 12V leakage should not be a problem. The life span of the sacrificial anode in the prop shaft should provide reasonable evidence of whether there is an ongoing problem.
 
jonelli

jonelli

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Jun 2, 2014
589
Catalina 30 mkII - 1987 Alamitos Bay Marina, LB, CA
I’m no expert, but I’ve asked a few people about this too because one of my dock neighbors mentioned something that they were having issues losing bolts to their out drive.
After asking someone with experience, I was responded with smiles and a response like “it’s been claimed many times but usually never proven”, and to just look at your zincs. If there was a problem with your boat, your zincs would show it.
Anyway, that’s the basic gist of the response I got.
 
weekendrken

weekendrken

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May 7, 2011
281
C - 30 # 3573 Lake NormanNC formerly Bflo NY
RP

Two things are necessary for stray current to cause a problem.
#1) The 12v negatives need to be bonded to the shore power ground (green) behind the panel ABYC *requires* this. The purpose is safety in case there is AC leakage to somewhere on the boat or into the water. The path to ground bleeds it off before someone is electrocuted.
#2) The green ground needs to be connected to "earth" i.e., tp the power stanchion and to an earth grounding rod.

You have #2) broken by using a GI. That protects both you from others', and everyone else from your stray current if you are leaking.

We have one IC30A forum member (a land based electrician) who REFUSES to bond the 12v neg to shore earth because he contends that his boat is safe from electrocution (has an ELCI breaker installed) and he refuses to spend the cash for a GI.
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Benny17441 said:
12V leakage should not be a problem.
Click to expand
12V leakage certainly is a problem! Quoting from the book that comes with the boatzincs.com reference electrode, the "Corrosion Reference Electrode User's Guide," page 9,

"The most common sources of electrolytic corrosion in the marine environment are:
  • Stray DC currents leaking from defective wiring or equipment in contact with bilge water within a vessel;
  • ...."
From a safety perspective, probably not a problem.
 
Mechone

Mechone

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Mar 20, 2016
594
Beneteau 351 WYC Whitby
I have a GI , ELCI and surge protection on my A/C . My GI has a display showing if you ever have A/C or DC leakage. I'm on my 3rd year same anode on prop and can still read Martyr on it. Before installing GI ,I would get rust spots on my cast iron keel.
We also have the docks GFI protected. If one boat leaks it shuts the whole dock down . Most common leakage is the element on hot water tank ,then battery charger
 
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Jackdaw

Jackdaw

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Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
If you have a GI you are a good actor.

For years I was the only boat at WYC with proper shore power setup. Per AYBC, my AC earth and DC ground were bonded. Every year, I checked my sacrificial anode on my prop shaft. Every year, it looked like new.

last year, some new boats with home-brew AC systems arrived. And my anode suffered.

so this year.
6DA435D9-8977-44C9-AB12-5967A29300C8.jpeg


but having one of really more like a CoVid mask. It’s not for your protection as much as being kind to others.
 
Last edited:
Mechone

Mechone

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Mar 20, 2016
594
Beneteau 351 WYC Whitby
Jackdaw said:
If you have a GI you are a good actor.

For years I was the only boat at WYC with proper shore power setup. Per AYBC, my AC earth and DC ground were bonded. Every year, I checked my sacrificial anode on my prop shaft. Every year, it looked like new.

last year, some new boats with home-brew AC systems arrived. And my anode suffered.

so this year.
View attachment 184475

but having one of really more like a CoVid mask. It’s not for your protection as much as being kind to others.
Click to expand
A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.
What you are saying is totally not true ,its to protect your boat as well as others. Also if you don't have a display it's not ABYC compliant
 
Johnb

Johnb

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Jan 22, 2008
1,421
Hunter 37-cutter Richmond CA
Mechone said:
A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.
What you are saying is totally not true ,its to protect your boat as well as others. Also if you don't have a display it's not ABYC compliant
Click to expand
I believe that there is no longer a requirement to have a display as long as the unit is fail safe. The changing standards are confusing.
https://www.deimarine.com/media/wysiwyg/documentation/GI_Liability.pdf is a good read.

One way or another, a ground fault interrupter, as close to the incoming power connection as possible remains a huge safety asset.
 
Jackdaw

Jackdaw

.
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Mechone said:
A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.
What you are saying is totally not true ,its to protect your boat as well as others. Also if you don't have a display it's not ABYC compliant
Click to expand
Of course it to protect your self as well as others, you're over-reading my point.

And BTW, to be AYBC complaint, modern fall-safe GI isolators DO NOT need a display.
 
Mechone

Mechone

.
Mar 20, 2016
594
Beneteau 351 WYC Whitby
Johnb said:
I believe that there is no longer a requirement to have a display as long as the unit is fail safe. The changing standards are confusing.
https://www.deimarine.com/media/wysiwyg/documentation/GI_Liability.pdf is a good read.

One way or another, a ground fault interrupter, as close to the incoming power connection as possible remains a huge safety asset.
Click to expand
True ,mine is 3 years old and fails safe ,however without a display you do not know its failed and is now not protecting your boat as it is now possibly passing current, The ELCI which I also have is only measuring a balance on neutral and hot on A/C that you are using . If the boat beside you has a leak and bad ground ,it travels thru the water to your boat and thru your ground ,eating your anodes as your GI has failed safe
 
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