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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On Jun 16, 8:37?am, Bil wrote:

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

Cheers

Bil

Did I somehow miss a mention of the boat's hull type? If Al's boat is
a wooden hull, magnesium would be entirely unsuitable regardless of
any fresh water considerations.

As mentioned above, the zinc's are not a good choice in freshwater
cause of the forming of zinc-patina.
Magnesium will probably be gone too fast. Better would be aluminum-
anodes.

Fair winds,
Len.