Here is problem that has me puzzled, and looking for any ideas.

Today we hauled our boat, and I noted the prop appears to have some
electrolysis or other corrosion stress to it. The prop is 2 years
old, Bronze on a SS shaft. When hauled, its color is ink black and it
has these small 'corrosion worms' all over it. Each 'worm' appears to
be corrosion, is about 5/8" long and about 1/32" wide. There is one
about every 2-3 square inches.

I do not know the cause of this, and will have to investigate if it is
something on my boat leaking, or something from a neighboring boat.

Now, here is what puzzles me. The shaft zinc does not show any signs
of undue wear. I would think that if I had some electrolysis issue,
the shaft zink would be one of the 1st things to go...

Any ideas?

(BTW, the boat has unbounded underwater fittings, and all other Bronze
parts look normal)

Thank you in advance
-al-

Al Thomason wrote:
Here is problem that has me puzzled, and looking for any ideas.

Today we hauled our boat, and I noted the prop appears to have some
electrolysis or other corrosion stress to it. The prop is 2 years
old, Bronze on a SS shaft. When hauled, its color is ink black and it
has these small 'corrosion worms' all over it. Each 'worm' appears to
be corrosion, is about 5/8" long and about 1/32" wide. There is one
about every 2-3 square inches.

I do not know the cause of this, and will have to investigate if it is
something on my boat leaking, or something from a neighboring boat.

Now, here is what puzzles me. The shaft zinc does not show any signs
of undue wear. I would think that if I had some electrolysis issue,
the shaft zink would be one of the 1st things to go...



Hello Al,

Offhand, this doesn't sound like
electrolytic corrosion.

That the zinc shows no sign of wear is
not necessarily a good thing, BTW. You
want to make sure the zinc is making
good electrical contact with the shaft.

It may be a form of self-corrosion,
perhaps caused by biofouling. While
copper alloys (bronzes) are generally
good at discouraging fouling, a certain
amount of galvanic corrosion seems to be
required for this process to occur. Was
there a lot of growth on the prop? Had
it been coated with anything? Fresh
water or salt? Prop in the mud and muck?
Is it a high-speed cigarette boat or a
clunky sailboat? For how long has the
prop been idle? Etc.

Sulfide-polluted seawater can produce a
black film on the prop.

Your best strategy is to contact the EPA
immediately and cordon off the marina
..... just kidding. You might contact the
manufacturer of the prop and see if they
can provide any further insights.

Sorry I can't give you a better answer.

Chuck

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Chuck,

Thank you, will call the manufacture Monday. Good suggestion, as I
understand this prop is a type of "bronze" proprietary to the
manufacturing.

On your other questions: Boat is a trawler style boat. Fresh water,
on the river about 1 day from the sea. It was last used in December
after we finished Christmas Ships and I took her over for the 'Winter
major work' (Am restoring her)

There was minumual fowling on the prop when hauled (river slime). The
shaft zinc does show wear, but it is inline with the other zinc's and
what I would call 'normal' given its two year service. No mud baths
for the prop, nor sand. Rather slow turning (cruise at 500-600 Shaft
RPM), Prop is Osborn propeller works in BC. Shaft unknown SS.

Another interesting data point, that perhaps leads more to it being
something with the prop alloy its self: The Prop nuts are Bronze, and
showed none of this Blacking!

There is no disfigurement to the prop, in fact the Black almost looks
like it has been anodized, if such a thing is possible with bronze.
Scrape down a small area, and the prop is not overly 'pink' under.
But I tell you , the black prop is a little disturbing looking, no
wonder I can not catch any spring salmon :-)


On Sat, 16 Jun 2007 08:58:57 -0400, Chuck
wrote:

Hello Al,

Offhand, this doesn't sound like
electrolytic corrosion.

That the zinc shows no sign of wear is
not necessarily a good thing, BTW. You
want to make sure the zinc is making
good electrical contact with the shaft.

It may be a form of self-corrosion,
perhaps caused by biofouling. While
copper alloys (bronzes) are generally
good at discouraging fouling, a certain
amount of galvanic corrosion seems to be
required for this process to occur. Was
there a lot of growth on the prop? Had
it been coated with anything? Fresh
water or salt? Prop in the mud and muck?
Is it a high-speed cigarette boat or a
clunky sailboat? For how long has the
prop been idle? Etc.

Sulfide-polluted seawater can produce a
black film on the prop.

Your best strategy is to contact the EPA
immediately and cordon off the marina
.... just kidding. You might contact the
manufacturer of the prop and see if they
can provide any further insights.

Sorry I can't give you a better answer.

Chuck

Al Thomason wrote:


There is no disfigurement to the prop, in fact the Black almost looks
like it has been anodized, if such a thing is possible with bronze.
Scrape down a small area, and the prop is not overly 'pink' under.
But I tell you , the black prop is a little disturbing looking, no
wonder I can not catch any spring salmon :-)

I'm still leaning toward copper sulfide
formation, Al. Didn't catch it before,
but you said the other underwater
bronzes are unbonded, and therefore
freely eroding (at a very small rate, of
course). That could explain why only the
prop was affected. The previous prop
never had this black film in the same
location?

Chuck

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On Jun 16, 10:35 pm, Al Thomason wrote:


Thank you, will call the manufacture Monday. Good suggestion, as I understand this prop is a type of "bronze" proprietary to the manufacturing.

On your other questions: Boat is a trawler style boat. Fresh water,
on the river about 1 day from the sea.

Do you mean genuine fresh water or brackish? If you're a day's
steaming from the sea, you may be in genuine fresh water.

If the water is truly sweet (ie no salt), zinc anodes are not v
effective.

Magnesium is better than zinc as a sacrificial anode in sweet water.
Your prop manufacturer will be able to advise further.

Cheers

Bil

Bil wrote:


If the water is truly sweet (ie no salt), zinc anodes are not v
effective.

Magnesium is better than zinc as a sacrificial anode in sweet water.
Your prop manufacturer will be able to advise further.


It is a matter of degree, of course.
Just about any dissolved minerals will
make "freshwater" conductive and a zinc
anode effective. The more pure the
water, the less the opportunity for
corrosion involving the prop/shaft
galvanic couple. The magnesium will go
quite quickly if the boat ventures into
seawater.

If the zinc is (has recently been)
active, it will have a shiny appearance.
If it has been inactive, it will be
dull, off-white (covered with zinc
oxide), and possibly fouled. If
inactive, it must be scoured to remove
the oxide. It will not clean itself and
will be ineffective until it is cleaned.

If the manufacturer believes the
symptoms point to insufficient anodic
protection (which seems unlikely to me),
some simple tests can be conducted to
test that theory.

Chuck

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Chuck wrote in news:1181997953_10245
@sp12lax.superfeed.net:

That the zinc shows no sign of wear is
not necessarily a good thing, BTW. You
want to make sure the zinc is making
good electrical contact with the shaft.



You mean we're NOT supposed to put the zinc around a protective rubber
sleeve to "save it"?.....(c;

(Seen that...I left when they started arguing it was the best thing to do.)

Larry
--
http://www.spp.gov/
The end of the USA and its Constitution....RIP

Larry wrote:


You mean we're NOT supposed to put the zinc around a protective rubber
sleeve to "save it"?.....(c;

(Seen that...I left when they started arguing it was the best thing to do.)

Larry

You've seen too much, Larry. They know
and they're not happy! ;-)

Chuck

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I agree with other posts, if you are in fresh water the Zinc anode will
become covered with a hard white deposit and consequently be ineffective .
I have a magnesium anode on a ss wire ( bonded to the engines) which I hang
over the side at the stern when I moor in freshwater for any length time e.g
a month or two and pull it in when I go to sea.

Many European sailors who venture into the canals and rivers do this.

Alec


"Al Thomason" wrote in message
...
Chuck,

Thank you, will call the manufacture Monday. Good suggestion, as I
understand this prop is a type of "bronze" proprietary to the
manufacturing.

On your other questions: Boat is a trawler style boat. Fresh water,
on the river about 1 day from the sea. It was last used in December
after we finished Christmas Ships and I took her over for the 'Winter
major work' (Am restoring her)

There was minumual fowling on the prop when hauled (river slime). The
shaft zinc does show wear, but it is inline with the other zinc's and
what I would call 'normal' given its two year service. No mud baths
for the prop, nor sand. Rather slow turning (cruise at 500-600 Shaft
RPM), Prop is Osborn propeller works in BC. Shaft unknown SS.

Another interesting data point, that perhaps leads more to it being
something with the prop alloy its self: The Prop nuts are Bronze, and
showed none of this Blacking!

There is no disfigurement to the prop, in fact the Black almost looks
like it has been anodized, if such a thing is possible with bronze.
Scrape down a small area, and the prop is not overly 'pink' under.
But I tell you , the black prop is a little disturbing looking, no
wonder I can not catch any spring salmon :-)


On Sat, 16 Jun 2007 08:58:57 -0400, Chuck
wrote:

Hello Al,

Offhand, this doesn't sound like
electrolytic corrosion.

That the zinc shows no sign of wear is
not necessarily a good thing, BTW. You
want to make sure the zinc is making
good electrical contact with the shaft.

It may be a form of self-corrosion,
perhaps caused by biofouling. While
copper alloys (bronzes) are generally
good at discouraging fouling, a certain
amount of galvanic corrosion seems to be
required for this process to occur. Was
there a lot of growth on the prop? Had
it been coated with anything? Fresh
water or salt? Prop in the mud and muck?
Is it a high-speed cigarette boat or a
clunky sailboat? For how long has the
prop been idle? Etc.

Sulfide-polluted seawater can produce a
black film on the prop.

Your best strategy is to contact the EPA
immediately and cordon off the marina
.... just kidding. You might contact the
manufacturer of the prop and see if they
can provide any further insights.

Sorry I can't give you a better answer.

Chuck

Thank you all for your comments.

Yes, we are in very fresh water here. The zincs do not show the White
oxidization mentioned, but they are also not shinny. They are more a
dull gray and slightly ruff surface. There is some measure of wear
on them, but very little.

Though currently moored in fresh water, we do make trips to the coast,
and use in salt water. This will increase in the coming years.

I will look into the Magnesium anode for over the side. There was on
board a 'fish shaped' item which I remember was used in just such a
way. I assumed it was zinc, but perhaps it is actually magnesium.

Am going to call the Prop supplier Monday, will report what they say.
Again, to me the troubling thing is that only the Prop shows this
blackening... The rudder, cutlass tube, even the prop nut all are OK.

-al-


On Sun, 17 Jun 2007 13:31:24 +0100, "Alec"
wrote:

I agree with other posts, if you are in fresh water the Zinc anode will
become covered with a hard white deposit and consequently be ineffective .
I have a magnesium anode on a ss wire ( bonded to the engines) which I hang
over the side at the stern when I moor in freshwater for any length time e.g
a month or two and pull it in when I go to sea.

Many European sailors who venture into the canals and rivers do this.

Alec