Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.

joost wrote:
Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.


My guess: if you see ACTUAL steel under a blister, the primer/basecoat
is faulty. If you see primer/basecoat under the blister, the top coat is
faulty.

Brian W

"Brian Whatcott" wrote in message
...
joost wrote:
Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.


My guess: if you see ACTUAL steel under a blister, the primer/basecoat is
faulty. If you see primer/basecoat under the blister, the top coat is
faulty.

Brian W

I agree with Brian.
Might try an epoxy barrier coat where you need to treat blisters. What I do
is only wait the minimum recoat time before applying subsequent coatings
including bottom paint. I've heard this allows the new and last coats to
chemically bond and since I haven't had any problems doing it this way I'll
continue.

mmc wrote:
"Brian Whatcott" wrote in message
...

joost wrote:

Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.


My guess: if you see ACTUAL steel under a blister, the primer/basecoat is
faulty. If you see primer/basecoat under the blister, the top coat is
faulty.

Brian W


I agree with Brian.
Might try an epoxy barrier coat where you need to treat blisters. What I do
is only wait the minimum recoat time before applying subsequent coatings
including bottom paint. I've heard this allows the new and last coats to
chemically bond and since I haven't had any problems doing it this way I'll
continue.




could be more unknown electrical leaks - esp if blisters are round.
Could also be 'salts' - we don't have products for it, but do have an
info page with links on it explaining it.
www.epoxyproducts.com/salt.html

paul oman
progressive epoxy polymers

could be more unknown electrical leaks - esp if blisters are round.
Could also be 'salts' - we don't have products for it, but do have an
info page with links on it explaining it.www.epoxyproducts.com/salt.html

paul oman
progressive epoxy polymers

Hmmm.... yes, the blisters are definitely round. And it happens only
at and below the waterline. Probably you are right and there are more
electrical leaks. Actually, I also found that there is a potential on
the hull, so something else must be leaking. It is a very frustrating
problem. It takes so much time to repair all those blisters and if I'm
unlucky I've to replace the propellor again too

Thanks anyway,
Joost.

On Sun, 3 May 2009 21:34:14 -0700 (PDT), joost
wrote:

could be more unknown electrical leaks - esp if blisters are round.
Could also be 'salts' - we don't have products for it, but do have an
info page with links on it explaining it.www.epoxyproducts.com/salt.html

paul oman
progressive epoxy polymers

Hmmm.... yes, the blisters are definitely round. And it happens only
at and below the waterline. Probably you are right and there are more
electrical leaks. Actually, I also found that there is a potential on
the hull, so something else must be leaking. It is a very frustrating
problem. It takes so much time to repair all those blisters and if I'm
unlucky I've to replace the propellor again too

Thanks anyway,
Joost.


An acquaintance had the same problem and painted, or partially painted
the boat several times - about once a year if memory serves. I asked
him several times whether he was sure that the hull was totally
isolated from the electrical system and he kept assuring me that it
was. His mate checked it!

After he had spent God knows how much money on yard costs he
apparently found another friend who repaired what ever problem was
leaking electricity and from what I hear (he's sailed for S. Africa)
is having no more paint problems.

I'm not a steel boat guy but I'd make very sure that the entire
electrical system IS isolated, radio grounds not forgotten and
remember that the engine has to be electrically isolated, before I
started looking elsewhere.


Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

An acquaintance had the same problem and painted, or partially painted
the boat several times - about once a year if memory serves. I asked
him several times whether he was sure that the hull was totally
isolated from the electrical system and he kept assuring me that it
was. His mate checked it!

After he had spent God knows how much money on yard costs he
apparently found another friend who repaired what ever problem was
leaking electricity and from what I hear (he's sailed for S. Africa)
is having no more paint problems.

I'm not a steel boat guy but I'd make very sure that the entire
electrical system IS isolated, radio grounds not forgotten and
remember that the engine has to be electrically isolated, *before I
started looking elsewhere.

Hi Bruce,

Thanks for that information. I'm happy to hear that I'm not the only
one with this problem. Ideally I would indeed like to isolate the
whole electrical system. Because what is happening now is that if
anywhere in the system a ground wire touches the hull, the return path
of the electricity goes through the sea water, to my prop, prop shaft,
engine and engine ground back to the battery.

Unfortunately, giving the starter and alternator a separate ground
connection is not an easy thing to do reliably. Therefore I'm now
thinking of connecting a separate wire from engine ground to the hull
(the engine isn't really ground. the resistance between hull and
engine measures 10 ohms). I think this is what is called 'bonding'.
WIth that extra wire, any leaking ground current can take an
attractive direct path back to the battery instead of going through
the sea water and creating expensive damage.

Any comments on this approach?

Thanks,
Joost

Paul Oman wrote:

...Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath....
Thanks,
Joost.
///
could be more unknown electrical leaks - esp if blisters are round.
Could also be 'salts' - we don't have products for it, but do have an
info page with links on it explaining it.
www.epoxyproducts.com/salt.html

paul oman
progressive epoxy polymers

What a helpful post!

Brian W

On Mon, 4 May 2009 02:32:51 -0700 (PDT), joost
wrote:

(old stuff snipped)


Hi Bruce,

Thanks for that information. I'm happy to hear that I'm not the only
one with this problem. Ideally I would indeed like to isolate the
whole electrical system. Because what is happening now is that if
anywhere in the system a ground wire touches the hull, the return path
of the electricity goes through the sea water, to my prop, prop shaft,
engine and engine ground back to the battery.

Unfortunately, giving the starter and alternator a separate ground
connection is not an easy thing to do reliably. Therefore I'm now
thinking of connecting a separate wire from engine ground to the hull
(the engine isn't really ground. the resistance between hull and
engine measures 10 ohms). I think this is what is called 'bonding'.
WIth that extra wire, any leaking ground current can take an
attractive direct path back to the battery instead of going through
the sea water and creating expensive damage.

Any comments on this approach?

Thanks,
Joost



O.K. here we go.

First of all the DC electrical system should be insulated from the
boat. No grounding, no nothing! The reason is that there is no
requirement that the DC system be connected to the boat and if it is
it can cause problems.

Usually the engine mounts insulate the engine from the beams on which
it is mounted and a plastic "flex plate" can be used to insolate the
propeller shaft from the engine.

Radios usually need a "ground plane" that is essentially the "ground"
side of the antenna circuit. This can be isolated from the hull by the
using capacitors. See recent post on rec.boats.cruising by Larry, et
al.

Assuming that you have a steel boat that is built properly the only
dis-similar metals you have in contact with sea water is the propeller
so with a completely isolated electrical system galvanic activity is
kept to the minimum.

You do still need zincs but the need is less.

Bonding - as there is no dis-similar metals then you do not need
bonding.

Lightning protection - as the entire hull is in contact with the water
and the mast and stays are not insulated from the hull the boat is
effectively grounded for lightening strikes.

Radios - Most radios use a "single sided antenna circuit" in other
words a wire leads from the antenna terminal on the radio case to an
antenna. the other side of the circuit is provided by a "ground wire"
to some sort of ground.

The ground side of the antenna circuit can be isolated from DC ground
by connecting it through a capacitor to the hull. See above.

Note: that some radio antennas are "two sided" and both the ground and
"hot" connections are made to the antenna. A "case ground" does no
harm in this case.

A.C. Power - AC power is more complicated and I won't go into it in
detail, but basically you can totally isolate an on board AC system
and treat it similar to the DC system but if you use "shore power" you
have different circumstances.

Commercial A.C. electrical power has connections to the physical
ground (the planet/ground/earth/dirt) and thus to a boat, through the
sea water. Because of this connection using commercial power (shore
power) without a ground circuit is extremely dangerous as standing on
a steel deck with bare feet and touching a live AC wire could very
well result in death.

Resolving this situation is fairly straight forward but in the
interests of brevity I'll not cover it here as it gets a little
complex - Isolation transformers 'n all that...

For good electrical/electronic information you can ping Larry over in
rec.boats.cruising as he is really knowledgeable (albeit outspoken).
There is another guy over there and I am embarrassed to say I don't
have his name (sorry mate) so you can get good information there.

Hope this helps.

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

Somebody wrote:
................................................. .......................
Unfortunately, giving the starter and alternator a separate ground
connection is not an easy thing to do reliably.
................................................. .....................

================================
It's very easy to do.

You need a cranking motor (starter) with an isolated ground which is
standard construction, if you specify it, and an alternator with
isolated field terminals as well as isolated DC output terminals.

Again, standard hardware, if specified.

All senders (oil pressure, water temperature, etc) must be 2 pole
units with insulated ground terminal.

The above give you an electrically insulated engine.

SFWIW, the above equipment is needed in the world markets since some
parts of the world use positive rather than negative ground.
====================================

"Bruce in Bangkok" wrote:

O.K. here we go.

First of all the DC electrical system should be insulated from the
boat. No grounding, no nothing! The reason is that there is no
requirement that the DC system be connected to the boat and if it is
it can cause problems.

Agreed. It is an absolute MUST on a metal boat..


Usually the engine mounts insulate the engine from the beams on
which
it is mounted and a plastic "flex plate" can be used to insolate the
propeller shaft from the engine.

Doesn't buy you much since sea water cooling will be involved.


Radios usually need a "ground plane" that is essentially the
"ground"
side of the antenna circuit. This can be isolated from the hull by
the
using capacitors.

Yep.

See recent post on rec.boats.cruising by Larry, et
al.

Assuming that you have a steel boat that is built properly the only
dis-similar metals you have in contact with sea water is the
propeller
so with a completely isolated electrical system galvanic activity is
kept to the minimum.

True.

You do still need zincs but the need is less.

True.


Bonding - as there is no dis-similar metals then you do not need
bonding.

Agreed.

Lightning protection - as the entire hull is in contact with the
water
and the mast and stays are not insulated from the hull the boat is
effectively grounded for lightening strikes.

No comment.

Radios - Most radios use a "single sided antenna circuit" in other
words a wire leads from the antenna terminal on the radio case to an
antenna. the other side of the circuit is provided by a "ground
wire"
to some sort of ground.

The ground side of the antenna circuit can be isolated from DC
ground
by connecting it through a capacitor to the hull. See above.

Note: that some radio antennas are "two sided" and both the ground
and
"hot" connections are made to the antenna. A "case ground" does no
harm in this case.

A.C. Power - AC power is more complicated and I won't go into it in
detail, but basically you can totally isolate an on board AC system
and treat it similar to the DC system but if you use "shore power"
you
have different circumstances.

Isolation transformers are an absolute necessity on a metal boat.

A transfer switch is required if an eng-gen is on board.
===============================
AC distribution on a boat, especially if an eng-gen is in service, is
a totally separate subject.
===============================

Commercial A.C. electrical power has connections to the physical
ground (the planet/ground/earth/dirt) and thus to a boat, through
the
sea water. Because of this connection using commercial power (shore
power) without a ground circuit is extremely dangerous as standing
on
a steel deck with bare feet and touching a live AC wire could very
well result in death.

No comment at this time.


Resolving this situation is fairly straight forward but in the
interests of brevity I'll not cover it here as it gets a little
complex - Isolation transformers 'n all that...

For good electrical/electronic information you can ping Larry over
in
rec.boats.cruising as he is really knowledgeable (albeit outspoken).
There is another guy over there and I am embarrassed to say I don't
have his name (sorry mate) so you can get good information there.

Hope this helps.

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

Lew