Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 07-05-2020, 19:18   #1
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Aluminium boat - stray current

We have a VDO leak detector gauge (this one) that is often on one red negative on our newish-to-us boat. Obviously on an aluminium vessel this isn't good (although from the detents I presume that means about -12.5mA?).

An electrician doing other jobs said it could take a long time to find, but that there is a lot we could test without paying for his expensive time, but (for other reasons) he didn't specify what tests we could do.

The best I've found is to ensure all the switchboard is off (except for the detector itself!), and perform the test as each switch is turned on and this hopefully narrow the problem area.

Not being on the boat at the moment (covid)...
  • are there any other tests?
  • what would you do to find out where the problem in the line(s) are if it can be narrowed?
  • where the problem may be if the switchboard is off, yet it still indicates a leak - batteries terminals??

Thanks
__________________

mcarthur is offline   Reply With Quote
Old 07-05-2020, 23:15   #2
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 3,563
Images: 7
Re: Aluminium boat - stray current

Remove the negative which goes from the batteries to the engine and see if it goes away. If so you might want to consider a battery switch in the negative as a precaution when the boat is not in use.

I have heard of folks having a solenoid to do this except when the engine is being cranked but you also have to isolate the alternator and run a negative return from it to the batteries.
__________________

RaymondR is offline   Reply With Quote
Old 08-05-2020, 02:55   #3
Registered User

Join Date: Nov 2019
Posts: 1,302
Re: Aluminium boat - stray current

Quote:
Originally Posted by RaymondR View Post
Remove the negative which goes from the batteries to the engine and see if it goes away. If so you might want to consider a battery switch in the negative as a precaution when the boat is not in use.

I have heard of folks having a solenoid to do this except when the engine is being cranked but you also have to isolate the alternator and run a negative return from it to the batteries.
Yes . Isolate the negative

Typical leaks are dc motors carbon brush dust , engine sensors , alternators and electronics

Helps to have two people when searching for a leak



Many times I spend hours , days looking for a leak and in the end the leak was right before my nose in a predictable location
slug is offline   Reply With Quote
Old 08-05-2020, 12:43   #4
Registered User

Join Date: Nov 2018
Posts: 212
Re: Aluminium boat - stray current

One of the frequent areas for "leakage" is in the VHF radios and HF antenna tuners. VHF antennas quite often have the shield of the coax connected to the outside of the antenna. The antenna mount connects it to the mast. The shield is also connected to -12v at the radio. This problem is solved by using an inner-outer DC block in the coax. Pasternak, among others, sells them.

Some HF antenna tuners have the RF ground point which connects to your RF ground also connected to -12v. Inserting a capacitor between the tuner ground connection the ground itself eliminates the DC path.
Bycrick is offline   Reply With Quote
Old 08-05-2020, 17:12   #5
Registered User

Join Date: Jun 2009
Location: Dunedin, New Zealand
Boat: Ganley Timerider
Posts: 33
Send a message via Skype™ to Al Walker
Re: Aluminium boat - stray current

Recently dealt with stray current issues on our steel yacht. I installed a SeaBis unit, not cheap, but well worth the money spent. It's an Australian outfit (just Google them), and Glen Bishop there is very helpful and knowledgeable.

Our boat was already set up with a solenoid, isolated alternator, etc, but we still developed issues (carbon build-up on the alternator, moisture in nav lights). Now we have the SeaBis monitoring for stray current all the time, and we can see when stray currents are present. Not surprisingly, often in heavy weather or heavy rain, the issue clears with the weather.

Glen has a lot of information on his website, but it takes a wee bit of wading through.

I never really gave it much thought before, but seeing what a fairly minor case did to our underwater paintwork, and potentially to the steel, I'm very comfortable with spending the money on the monitor.
Al Walker is offline   Reply With Quote
Old 09-05-2020, 16:54   #6
Registered User
 
Oceanride007's Avatar

Join Date: Jun 2013
Location: Gladstone Qld.
Boat: Custom Perry Passport 41, steel
Posts: 455
Re: Aluminium boat - stray current

I see another thread, https://www.cruisersforum.com/forums...rk-188167.html
where you asked a similar question.


As you can imagine Ships had earth faults long before resistance testers were available.
Here is a simple explanation for traditional 12V DC Earth Lamps, attachment below.



2, 12V lamps incandescent lamps in series between Neg and positive will give half brilliance. If another wire between the 2 lamps was connected to ships hull thru a normally open toggle switch and there was a earth fault. Then to test, press the toggle, one lamp will burn brighter than the other. The low brilliance lamp will indicate the polarity of the circuit in fault.



Now you may not be burning any more milliamps or amps because the circuit is not completed, normally. But these faults were always treated seriously. A completed circuit could be sad for paint, hull, CB tripping. A non completed circuit on AC shore supply could be a danger to swimmers.



Have seen ships with so called Earth Lamps on every DC and AC Busbar, these days they measure resistance, one reason is that a detection circuit could be fitted to raise alarm.
Attached Thumbnails
Click image for larger version

Name:	P1010559.jpg
Views:	26
Size:	400.5 KB
ID:	214712  
__________________
Oceanrider.
"The floggings will continue until morale improves"
Oceanride007 is offline   Reply With Quote
Old 09-05-2020, 20:51   #7
Registered User

Join Date: Sep 2007
Location: Queensland, Australia
Boat: None at present--between vessels. Ex Piver Loadstar 12.5 metres
Posts: 1,180
Re: Aluminium boat - stray current

if you are connected to shore power you MUST use a isolation device in the mains feed. I used a 2.5 kva isolating transformer--because I got it cheaply from a military surplus store, but it was big and had its own locker. There are capacitive isolators that function well and are much smaller and more cheaply bought. NEVER let your vessel become part of the AC mains supply earthing system. It will provide the best earth in the entire system and the stray currents from all over the place will exit via your hull or propeller into the salt water and destroy your vessel--as happened to an aluminium trawler in Tasmania, with loss of life.

Your radio and radar earth plate, and any other electrical communications receiving or transmitting equipment must have a good earth--but it must NEVER become part of any other earth on the vessel--that should have its own earthing system. I never let the vessel become any part of a return leg, including the mast. ALWAYS run a separate negative rail. You can use a heavy conductor and connect more than one device to it--provided that the currents are well within the current carrying capacity of the wire.
Mike Banks is offline   Reply With Quote
Old 10-05-2020, 02:05   #8
Registered User

Join Date: Jan 2020
Location: Sweden
Boat: Swan 57
Posts: 29
Re: Aluminium boat - stray current

I think Mike Banks above described it very well. I use a Victron Isolating Transformer which is excellent. Even though my yacht is GRP many such yachts has had their foot rails, folding props and other expensive items destroyed.
Many aluminium yachts at anchor or at the dock, hang a hefty zink anode in a copper wire connected to the aluminium hull, over the side for prevention.
Hermia II is offline   Reply With Quote
Old 10-05-2020, 15:05   #9
Registered User

Join Date: Mar 2015
Posts: 8
Re: Aluminium boat - stray current

I also fitted a SeaBis (stray current detector) to my steel yacht as mine was blowing hand sized patches of good paint off at the waterline and showing clean etched metal when the paint came off. I eventually solved all my stray current issues and now my electrics are completely "above ground". I had issues in both engine battery and house battery circuits. In the engine circuit it was the usual suspects of a perminant negative bolted to the engine block without an isolator and non isolated alternators. I also had a normally closed fuel solanoid that required negative current to the engine block to be open. That had to go and I built a pull knob and cable that starves the engine of fuel.
In the house battery circuit I had to replace the VHF antenna with a ground plain independant version and there was some other stuff I cant remember as all repairs were done bit by bit over time as changes were made.

My advice would be to isolate house and engine circuits and disconnect both leads from the engine battery and see if there are faults in the house system. To sort this out with the SeaBis system of diagnosis you have to begin disconnecting wires from the negative bus bar leaving each one off. It must be noted that if you have three faults your sray current detector won't show "all clear" until the third wire is off. You may then have multiple wires off. You may even have them all off and still be showing a fault so you will need to begin disconnecting things like bilge pumps or wires from your positive bus bar. Once you have reached "all clear" begin touching wires to the bus bar one at a time. If they are not causing the fault put them back on. If they cause faults tag them and leave them off. You then have to work out where the wires go or what's not working to find out what was causing the fault. It could even be a chafed or submerged wire
I notice the fault alert that started this thread was a positive warning showing so I wouldn't be sure that this is an earth issue. Your electrician is right this can take some time but it's worth the effort
Taswildlife is offline   Reply With Quote
Old 10-05-2020, 16:55   #10
Registered User

Join Date: Apr 2020
Boat: Amel 53, Super Maramu
Posts: 242
Re: Aluminium boat - stray current

Chasing down stray currents is always such fun (not!) that I was intrigued to hear about a new product/web site on the subject, the "SeaBis" mentioned in previous postings. So I checked out the website.

Being someone who believes that clear writing equals clear thinking, I was horrified trying to understand what the writer was trying so unsuccessfully to convey. But... heck, not everybody is a gifted writer, so I waded through though it until I came to this statement:

Quote:
Rust cause:

Air carries stray current causing rust. Preventing stray current reduces rust. Use SeaBis!
Really??? Total puesdo-scientific BS! This is so far from scientific reality I just dropped the whole effort. That, and his insistence that an AC power connection can NEVER be the source of a DC stray current problem just reflects a total misunderstanding of issues.
SVHarmonie is online now   Reply With Quote
Old 11-05-2020, 17:27   #11
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Re: Aluminium boat - stray current

Quote:
Originally Posted by RaymondR View Post
Remove the negative which goes from the batteries to the engine and see if it goes away. If so you might want to consider a battery switch in the negative as a precaution when the boat is not in use.

I have heard of folks having a solenoid to do this except when the engine is being cranked but you also have to isolate the alternator and run a negative return from it to the batteries.
Hmm, I'll look that up - it was all English, but when put together I didn't have a clue what you said
mcarthur is offline   Reply With Quote
Old 11-05-2020, 17:28   #12
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Re: Aluminium boat - stray current

Quote:
Originally Posted by slug View Post
Yes . Isolate the negative

Typical leaks are dc motors carbon brush dust , engine sensors , alternators and electronics

Helps to have two people when searching for a leak

Many times I spend hours , days looking for a leak and in the end the leak was right before my nose in a predictable location
Ouch, that sounds annoying and time consuming over all. She's a new boat to us and lots to learn - and find! Thanks
mcarthur is offline   Reply With Quote
Old 11-05-2020, 17:29   #13
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Re: Aluminium boat - stray current

Quote:
Originally Posted by Bycrick View Post
One of the frequent areas for "leakage" is in the VHF radios and HF antenna tuners. VHF antennas quite often have the shield of the coax connected to the outside of the antenna. The antenna mount connects it to the mast. The shield is also connected to -12v at the radio. This problem is solved by using an inner-outer DC block in the coax. Pasternak, among others, sells them.

Some HF antenna tuners have the RF ground point which connects to your RF ground also connected to -12v. Inserting a capacitor between the tuner ground connection the ground itself eliminates the DC path.
No HF, but VHF could be it (AIS and radar complicates it too). Thanks for the tip on Pasternak.
mcarthur is offline   Reply With Quote
Old 11-05-2020, 17:36   #14
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Re: Aluminium boat - stray current

Quote:
Originally Posted by Oceanride007 View Post
As you can imagine Ships had earth faults long before resistance testers were available.
Here is a simple explanation for traditional 12V DC Earth Lamps, attachment below.

2, 12V lamps incandescent lamps in series between Neg and positive will give half brilliance. If another wire between the 2 lamps was connected to ships hull thru a normally open toggle switch and there was a earth fault. Then to test, press the toggle, one lamp will burn brighter than the other. The low brilliance lamp will indicate the polarity of the circuit in fault.

Now you may not be burning any more milliamps or amps because the circuit is not completed, normally. But these faults were always treated seriously. A completed circuit could be sad for paint, hull, CB tripping. A non completed circuit on AC shore supply could be a danger to swimmers.

Have seen ships with so called Earth Lamps on every DC and AC Busbar, these days they measure resistance, one reason is that a detection circuit could be fitted to raise alarm.
That's what John from Morganscloud said too. I'd hoped tracking then was easier . Similar to the advice on tracking down propane leaks (not!) - wander round with a candle and when you're dead, you've found the leak.
mcarthur is offline   Reply With Quote
Old 11-05-2020, 17:38   #15
Registered User

Join Date: Mar 2012
Location: Australia
Boat: 50' aluminium power cat
Posts: 96
Re: Aluminium boat - stray current

Quote:
Originally Posted by Mike Banks View Post
if you are connected to shore power you MUST use a isolation device in the mains feed. I used a 2.5 kva isolating transformer--because I got it cheaply from a military surplus store, but it was big and had its own locker. There are capacitive isolators that function well and are much smaller and more cheaply bought. NEVER let your vessel become part of the AC mains supply earthing system. It will provide the best earth in the entire system and the stray currents from all over the place will exit via your hull or propeller into the salt water and destroy your vessel--as happened to an aluminium trawler in Tasmania, with loss of life.

Your radio and radar earth plate, and any other electrical communications receiving or transmitting equipment must have a good earth--but it must NEVER become part of any other earth on the vessel--that should have its own earthing system. I never let the vessel become any part of a return leg, including the mast. ALWAYS run a separate negative rail. You can use a heavy conductor and connect more than one device to it--provided that the currents are well within the current carrying capacity of the wire.
Thanks Mike. She's an older European boat, and apparently few have isolation transformers. It's one of the first things I'll be checking post-covid!
__________________

mcarthur is offline   Reply With Quote
Reply

Tags
boat, current

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Stray current and antifoul failure/ delamination joemac4sail Electrical: Batteries, Generators & Solar 9 04-01-2020 23:55
Stray Current Detector Ian R Electrical: Batteries, Generators & Solar 12 27-12-2018 20:02
Stray Current MartinMayer Electrical: Batteries, Generators & Solar 32 10-01-2011 05:48
How to Measure Stray Current in the Water erict Electrical: Batteries, Generators & Solar 11 03-12-2010 12:07
Stray Current Corrosion . . . Boracay Electrical: Batteries, Generators & Solar 29 29-09-2010 06:13

Advertise Here


All times are GMT -7. The time now is 21:49.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.