Stray current (voltage leak) problem on steel boat.
 

Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

All wiring that I can see is doubled with the positive wiring going back
to 2 main battery isolator switches with single pole appliance switches
in the circuit at the switch board. The negative wires all come back to
a bus then to the battery.

The only things that do not go through the main isolator switches are
the solar panels (via the regulator) and the bilge pump.

There is a Plasmatronics solar charge controller between the solar
panels and the house battery which appears to regulate the charge on the
negative wire...

There is also a sophisticated charging regulator for the heavy duty
alternator (can't remember the brand). Manages the boost, absorption, etc.

Back to the multimeter testing, when checking voltages, I am able to
measure a voltage between the +ve and -ve wires of approx 13.4V. I can
also measure a potential between the -ve wire and the hull of 0.6V with
the -ve being at a higher potential than the hull. This then gives a
voltage between the +ve wiring and the hull of 14V.

With everything double wired I would not have expected any connection to
the hull and thus not be able to measure any voltage between either the
+ve or -ve wires and the hull.

To add to this, when checking with the ohmmeter between the -ve wiring
or engine block and the hull, I can measure a resistance (indicating a
connection ) with the meter in one polarity but open circuit with the
polarity reversed.

I have a limited electronics background from many years ago and this
suggests to me that somewhere there is a diode passing current between
the -ve wiring and the hull. The 0.6 volt drop plus the dependence of
polarity in measuring a resistance between the hull and the -ve.

I am suspecting something to do with my solar panels as their frames are
screwed directly to a SS bimini and hence the hull... (Can solar panels
leak to their frames???)

This voltage was measurable both with the boat on the hard and in the water.

What I don't understand is how the hull can be at a lower potential than
the -ve wiring. I also don't know whether there are any diodes
connected to the panels as the controller has a mosfet switch in it to
prevent battery drainage back through the panels.

Is it possible that instruments (depth sounder, autopilot head, etc)
could be leaking to the hull?

Sorry for the long winded post but hoping to get to the bottom of this
without paying a sparkie a fortune to do it for me...

Any suggestions?

Thanks for any assistance.
Cheers,
Nick.

Stray current (voltage leak) problem on steel boat.
 

nick wrote:
Snip

Any suggestions?

Thanks for any assistance.
Cheers,
Nick.

Hi Nick,

The obvious next step is (fortunately)
an easy one: disconnect the solar panel
and regulator and measure again.

Some solar panels do contain diodes.

Whether that is the cause of your
corrosion problem is possibly a
different matter.

Chuck

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Stray current (voltage leak) problem on steel boat.
 

Hi Nick,

A boat electrical system has a lot of details, and
the devil lies somewhere in those details. If
you are going to find the problem, you need to be
able to draw a _detailed_ schematic of your boat
wiring including the 12V DC system, and the 120V
AC dock power.

Based on what you wrote below, I drew a basic
schematic of your 12V DC system, but it does not
have enough detail to determine where the problem
is. It did generate some questions that may help
you put a finger on where the problem lies.

1) Where is the "Safety Ground" for your 120V AC
dock power, and how is it hooked up to your hull?

2) Is your boat hooked up to dock power when it is
in the water?

3) Where are your 120V AC neutral and safety
ground connected together? And are they connected
to, or isolated from your 12V Ground?

4) If you disconnect your solar cells completely,
what voltage and resistance do you measure between
the 12V ground and the hull?


nick wrote:
Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

All wiring that I can see is doubled with the positive wiring going back
to 2 main battery isolator switches with single pole appliance switches
in the circuit at the switch board. The negative wires all come back to
a bus then to the battery.

The only things that do not go through the main isolator switches are
the solar panels (via the regulator) and the bilge pump.

There is a Plasmatronics solar charge controller between the solar
panels and the house battery which appears to regulate the charge on the
negative wire...

There is also a sophisticated charging regulator for the heavy duty
alternator (can't remember the brand). Manages the boost, absorption, etc.

Back to the multimeter testing, when checking voltages, I am able to
measure a voltage between the +ve and -ve wires of approx 13.4V. I can
also measure a potential between the -ve wire and the hull of 0.6V with
the -ve being at a higher potential than the hull. This then gives a
voltage between the +ve wiring and the hull of 14V.

With everything double wired I would not have expected any connection to
the hull and thus not be able to measure any voltage between either the
+ve or -ve wires and the hull.

To add to this, when checking with the ohmmeter between the -ve wiring
or engine block and the hull, I can measure a resistance (indicating a
connection ) with the meter in one polarity but open circuit with the
polarity reversed.

I have a limited electronics background from many years ago and this
suggests to me that somewhere there is a diode passing current between
the -ve wiring and the hull. The 0.6 volt drop plus the dependence of
polarity in measuring a resistance between the hull and the -ve.

Sure sounds like a diode to me too. Now the
question is where is the diode.

I am suspecting something to do with my solar panels as their frames are
screwed directly to a SS bimini and hence the hull... (Can solar panels
leak to their frames???)

This may indeed be the problem. Disconnect the +
and - leads from the solar panels and retry your
measurements between -Ve and the hull. If the
solar cells have have anything to do with the
problem, this will show it.

This voltage was measurable both with the boat on the hard and in the
water.

What I don't understand is how the hull can be at a lower potential than
the -ve wiring. I also don't know whether there are any diodes
connected to the panels as the controller has a mosfet switch in it to
prevent battery drainage back through the panels.

The answer is simple. Somewhere your +Ve is
connected through a fairly large resistance to
your hull, and there is a forward biased diode
between your hull, and your -Ve. Draw the circuit
diagram I just described, and you'll instantly see
what I mean. The question is where is the diode
connection from hull to -Ve, and where is the
leakage resistance from the +Ve to the hull.

Solar cells are themselves just a diode, however
there are usually many cells in series to produce
a usable voltage output.

Is it possible that instruments (depth sounder, autopilot head, etc)
could be leaking to the hull?

Anything is possible at this point. _Something_
is causing the problem.

Sorry for the long winded post but hoping to get to the bottom of this
without paying a sparkie a fortune to do it for me...

Any suggestions?

Thanks for any assistance.
Cheers,
Nick.

Good luck with it, and let us know when you find
the problem.

Don W.

Stray current (voltage leak) problem on steel boat.
 

On Thu, 17 May 2007 12:16:04 GMT, nick
wrote:

Is it possible that instruments (depth sounder, autopilot head, etc)
could be leaking to the hull?

Sorry for the long winded post but hoping to get to the bottom of this
without paying a sparkie a fortune to do it for me...

The leakage could be almost anywhere.

Probably the fastest way to find it is to start by disconnecting or
turning off all of the DC circuits. Hopefully that makes your leakage
voltage disappear. If not, start at the batteries and breaker panel.

Next step is to start turning things on one at a time until the
voltage reappears. That will indicate the offending circuit or
component.

Stray current (voltage leak) problem on steel boat.
 

On May 17, 7:16 am, nick wrote:
Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

All wiring that I can see is doubled with the positive wiring going back
to 2 main battery isolator switches with single pole appliance switches
in the circuit at the switch board. The negative wires all come back to
a bus then to the battery.

The only things that do not go through the main isolator switches are
the solar panels (via the regulator) and the bilge pump.

There is a Plasmatronics solar charge controller between the solar
panels and the house battery which appears to regulate the charge on the
negative wire...

There is also a sophisticated charging regulator for the heavy duty
alternator (can't remember the brand). Manages the boost, absorption, etc.

Back to the multimeter testing, when checking voltages, I am able to
measure a voltage between the +ve and -ve wires of approx 13.4V. I can
also measure a potential between the -ve wire and the hull of 0.6V with
the -ve being at a higher potential than the hull. This then gives a
voltage between the +ve wiring and the hull of 14V.

With everything double wired I would not have expected any connection to
the hull and thus not be able to measure any voltage between either the
+ve or -ve wires and the hull.

To add to this, when checking with the ohmmeter between the -ve wiring
or engine block and the hull, I can measure a resistance (indicating a
connection ) with the meter in one polarity but open circuit with the
polarity reversed.

I have a limited electronics background from many years ago and this
suggests to me that somewhere there is a diode passing current between
the -ve wiring and the hull. The 0.6 volt drop plus the dependence of
polarity in measuring a resistance between the hull and the -ve.

I am suspecting something to do with my solar panels as their frames are
screwed directly to a SS bimini and hence the hull... (Can solar panels
leak to their frames???)

This voltage was measurable both with the boat on the hard and in the water.

What I don't understand is how the hull can be at a lower potential than
the -ve wiring. I also don't know whether there are any diodes
connected to the panels as the controller has a mosfet switch in it to
prevent battery drainage back through the panels.

Is it possible that instruments (depth sounder, autopilot head, etc)
could be leaking to the hull?

Sorry for the long winded post but hoping to get to the bottom of this
without paying a sparkie a fortune to do it for me...

Any suggestions?

Thanks for any assistance.
Cheers,
Nick.

I've measured the stray current in my marina and found an average
voltage of .5 DC. Most marinas will have some stray voltage. Anyone
can take a meter and put one end to the ground terminal on your shore
power and one lead in the water and see if there is any stray
voltage.

What condition were your zincs in?

from this old boat:
******************
How much zinc

The amount of protection a zinc anode provides depends on its surface
area. The zinc surface area needed varies with the kind of metal being
protected and with the chemical make-up of the water, but you can use
1% of the surface area of the protected metal as a starting point.
Check the protected metal frequently. If it shows signs of corrosion
despite the zinc, you need more surface area.

Zincs should be replaced when about half of the anode has been lost to
corrosion. Ideally we want that to occur not more frequently than
annually. The longevity of a sacrificial zinc anode is a function of
its weight. When a zinc lasts less than a year, you need one with more
weight.

Normally, however, you are not faced with determining the appropriate
anode size (other than diameter for a zinc shaft collar). Rather, you
are simply replacing depleted zincs with new ones of the same size.
Check all zincs at least annually and replace all that are half
depleted.
******

Joe

Stray current (voltage leak) problem on steel boat.
 

On May 17, 7:16 am, nick wrote:
Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

Nick it could also have been a bad priming job before or when the
barrier coat was applied. Paint over dew ect...ect.. The welds are
always areas that harbor moisture.

Could also be stray voltage from a nearby fiberglass hull effecting
your hull. You would be suprised how many idiots use car type battery
chargers without grounds to keep the batteries charged. I've seen
zincs boiling on glass boats before.

Are you zincs welded on or bolted?

I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

No it is not. It will make contact with the hull via the shaft and
shaft tube.


snip


Any suggestions?

As others stated, turn it all off and measure, power up one at a time
and measure.

Good luck, let us know what you found.

Joe

Thanks for any assistance.
Cheers,
Nick.

Stray current (voltage leak) problem on steel boat.
 

Joe wrote:
On May 17, 7:16 am, nick wrote:
Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

Nick it could also have been a bad priming job before or when the
barrier coat was applied. Paint over dew ect...ect.. The welds are
always areas that harbor moisture.

Could also be stray voltage from a nearby fiberglass hull effecting
your hull. You would be suprised how many idiots use car type battery
chargers without grounds to keep the batteries charged. I've seen
zincs boiling on glass boats before.

Are you zincs welded on or bolted?

Yeah, I saw the wiring on a fishing boat just up the jetty from me...
it was frightening, masses of wires just twisted together with no
insulation tape or terminal strips, etc... Who knows what he's pumping
out.. and there are quite a few fishing boats there and odds are that
others will be just as dodgy.

My anodes are bolted on. They are on studs welded to the hull.


I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

No it is not. It will make contact with the hull via the shaft and
shaft tube.

I looked into that and the shaft has a thick spacer made of some kind of
plastic between the gearbox and the tube which isolates the engine from
the shaft.

snip


Any suggestions?

As others stated, turn it all off and measure, power up one at a time
and measure.

Good luck, let us know what you found.

Joe

Well, I'm getting a bit confused now. I disconnected my solar panels
completely from the wiring, totally disconnected the batteries and
insulated the solar panels from the hull as an added precaution. I was
able to measure ~0.8v between the -ve wiring and the hull. I don't
understand where this can be coming from.

I suspect I'd be wasting my time looking for the source of this
potential and would be better off looking for the connection or path
between the wiring and the hull.

At least I know now that my solar panels aren't to blame...

I've just bought a book that covers marine electrical, stray currents,
corrosion, bonding, etc in great detail so I'm going to digest this in
the hope that I'll better understand what I'm looking for.

Will update this when I make some progress.

Thanks everyone for your input. Don, I don't use shore power and the
boat has no AC wiring. It's purely a DC think but thanks for the thought.

Cheers,
Nick.

Stray current (voltage leak) problem on steel boat.
 

nick wrote:


Well, I'm getting a bit confused now. I disconnected my solar panels
completely from the wiring, totally disconnected the batteries and
insulated the solar panels from the hull as an added precaution. I was
able to measure ~0.8v between the -ve wiring and the hull. I don't
understand where this can be coming from.


Hi Nick,

If I understand correctly, you believe
none of your -ve wiring should be making
contact with the hull. Also, none of the
"appliances" have metal cases or
cabinets that make electrical contact
with the hull? A sal****er moistened
piece of plywood could do it.

With the batteries disconnected, I would
look for something making contact with
sal****er, the hull, and the -ve wiring.
The bilgepump, depth sounder, and
knotmeter are three critters with those
characteristics that come immediately to
mind. No SSB ground connection?

BTW, what do you measure between the
hull and +ve with the batteries
disconnected?

Again, it is by no means clear that
whatever is causing the voltage reading
you observe is also the cause of your
paint problem.

Good luck!

Chuck


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Stray current (voltage leak) problem on steel boat.
 

On May 20, 8:31 am, nick wrote:
Joe wrote:
On May 17, 7:16 am, nick wrote:
Hi All.

I don't know if anyone can help with suggestions here but I'll give it a
whirl.

I hauled out my boat last week to do the bottom paint and discovered
substantial blistering of the paint. I attacked these with a high
pressure cleaner initially and that stripped most of the loose paint off.

In places bare metal was exposed, in others it was back to the primer or
undercoat. It was particularly evident around welds and through skin
fittings (metal ones only) and even around the anode bolts.

Nick it could also have been a bad priming job before or when the
barrier coat was applied. Paint over dew ect...ect.. The welds are
always areas that harbor moisture.

Could also be stray voltage from a nearby fiberglass hull effecting
your hull. You would be suprised how many idiots use car type battery
chargers without grounds to keep the batteries charged. I've seen
zincs boiling on glass boats before.

Are you zincs welded on or bolted?

Yeah, I saw the wiring on a fishing boat just up the jetty from me...
it was frightening, masses of wires just twisted together with no
insulation tape or terminal strips, etc... Who knows what he's pumping
out.. and there are quite a few fishing boats there and odds are that
others will be just as dodgy.

My anodes are bolted on. They are on studs welded to the hull.





I had a shipwright and a very experience boat painter look at the hull
and both confirmed a stray current problem, albeit relatively minor.
Interestingly, both said I had TOO MANY anodes on the hull and that this
in itself can cause a problem.

I have since done some quite extensive reading on the subject on the net
and in some books and all confirm the diagnosis.

So, armed with a multimeter I set about doing some testing but first a
basic description of my electrical system.

The boat has a large house battery and a decent engine battery plus 180
watts of solar panels. The engine has a standard alternator (30A I
think) plus a heavy duty 120Amp alternator mounted on it.

The engine is isolated from the hull via rubber engine mounts.

No it is not. It will make contact with the hull via the shaft and
shaft tube.

I looked into that and the shaft has a thick spacer made of some kind of
plastic between the gearbox and the tube which isolates the engine from
the shaft.



snip

Any suggestions?

As others stated, turn it all off and measure, power up one at a time
and measure.

Good luck, let us know what you found.

Joe

Well, I'm getting a bit confused now. I disconnected my solar panels
completely from the wiring, totally disconnected the batteries and
insulated the solar panels from the hull as an added precaution. I was
able to measure ~0.8v between the -ve wiring and the hull. I don't
understand where this can be coming from.

I suspect I'd be wasting my time looking for the source of this
potential and would be better off looking for the connection or path
between the wiring and the hull.

Again, here in this marina the average voltage in the water is .5
volts DC.
If your marina is of any age the discarded metal in the water can
create stray voltage.

Joe

At least I know now that my solar panels aren't to blame...

I've just bought a book that covers marine electrical, stray currents,
corrosion, bonding, etc in great detail so I'm going to digest this in
the hope that I'll better understand what I'm looking for.

Will update this when I make some progress.

Thanks everyone for your input. Don, I don't use shore power and the
boat has no AC wiring. It's purely a DC think but thanks for the thought.

Cheers,
Nick.



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Stray current (voltage leak) problem on steel boat.
 

"Joe" wrote in message
oups.com...
Again, here in this marina the average voltage in the water is .5
volts DC.
If your marina is of any age the discarded metal in the water can
create stray voltage.

Joe


You people and your dumb metal boats, the problems you cause. To make a
battery one needs two dissimilar metals and salt water. You have that in
abundance in a marina what with aluminum hulls, steel hulls, various
zincs, bronze fittings, stainless steel fittings, copper paint, etc.
Steel boats are a menace because steel acts as a cathode so you have to
have all these sacrificial anodes (zincs) attached to protect it from
slowly being eaten away and plated on more noble metals.

Would you allow somebody to pull into the slip next to you and commence
to start sandblasting your hull? I doubt it, but that's about what is
happening to your boat's bottom and sundry metal fittings when a steel
boat parks its ugly ass next to your superior and inert fiberglass boat.
Marinas should be required by law to install active cathodic protection
and all metal boats should pay enough more for their slips to pay for
the costs associated with the protection.

Wilbur Hubbard