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