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.

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.

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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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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"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

Wilbur Hubbard wrote:


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

Hi Wilbur,

The steel boats that can cause problems
are the larger ones using impressed
current cathode protection. These guys
create a very strong electric field in
the vicinity of their vessel that can be
very difficult to protect from.

But the ordinary steel hulls (the
smaller guys you see in marinas)
shouldn't cause any more problems than
fiberglass or wooden boats using iron
keels with welded anodes. Which is
really no problems at all.

The biggest danger from other boats in a
marina is when they are un- or
under-protected and use shore power. But
even that can be easily dealt with.

Of all the things to complain about,
Wilbur. ;-)

Chuck

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Joe wrote:


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

Hi Joe,

Nick is measuring a voltage between his
hull and his negative wiring, with the
battery and AC power disconnected! It is
hard to attribute that to the water.
That's like measuring a voltage between
the water and the air.

Chuck

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On May 20, 1:39 pm, Chuck wrote:
Joe wrote:

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

Hi Joe,

Nick is measuring a voltage between his
hull and his negative wiring, with the
battery and AC power disconnected! It is
hard to attribute that to the water.
That's like measuring a voltage between
the water and the air.

Chuck

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That is weird, has to have a short to ground somewhere then.

Where do you think it is coming from?

His engine is grounded to the hull, he can claim it is not all he
wants to. Even if he has a flex joint in his shaft he has a steel
exhaust, which carries water through the flex joints and retains
enough moisture to cause a flow of electrons.

And IMO his engine should be grounded to the hull.

My guess is it's in the water, and at .6 V DC it not an issue, it's
normal.

Nick should measure a few slips in is marina. I had a big crewboat
here that had a rat's nest of wires so the owner of the crewboat & I
mapped the voltage in the whole marina. I wanted to make sure he was
not going to cause problems as he restored the boat.

On average it was .5 volts DC. We mapped the area and watched it over
time to see if anything changed, we cut the power to this side of the
marina completely and still had the voltage.

Joe

Joe wrote:

That is weird, has to have a short to ground somewhere then.

Where do you think it is coming from?

His engine is grounded to the hull, he can claim it is not all he
wants to. Even if he has a flex joint in his shaft he has a steel
exhaust, which carries water through the flex joints and retains
enough moisture to cause a flow of electrons.


I think something like that may be what
is happening, Joe. Two pieces of metal
in contact with some bilgewater or
cooling water could easily show a small
voltage between them.

Chuck

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On May 21, 5:05 am, Chuck wrote:

I think something like that may be what
is happening, Joe. Two pieces of metal
in contact with some bilgewater or
cooling water could easily show a small
voltage between them.


After sleeping on it, I have another suggestion. It may be the bottom
paint he's using. Might be high in copper content. Could cause the
blistering of the paint and the barrier as he described, and in the
fashion it is occuring.

Joe


Chuck