Corrosion from Galvanized Chain

So, I learned something new tonight. "White Rust". The white powdery coating on the galvanized chain. It is the galvanizing rusting. Once the gavanizing is "rusted through" then the steel can oxidize and rust in the reddish brown we see on bare metal rust.

Harvey
SleepyC :moon

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That white rust, aka zinc oxide, is a sign that the zinc in the galvanized coating is doing its job. Somewhere else on the chain, or on some ferrous metal in conduction with the chain, is an exposed surface where iron would be rusting EXCEPT that the zinc on the chain, being more active electrolysiswise, is "rusting," aka oxidizing, instead. That's why it is refered to as a sacrificial coating. And when it is gone, baby, the chain itself is next!

Yup, same zinc oxide found in ointments used to protect skin from sunburn.
 
Like the "Zincs" on the boat. 8)

The most regular rusty place on the chain was near the end, where it had been connected to a stainless swivel. That area has some places with some regular rust mixed in with the white rust.

Harvey
SleepyC :moon

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hardee":1lhksf4d said:
Like the "Zincs" on the boat. 8)

The most regular rusty place on the chain was near the end, where it had been connected to a stainless swivel. That area has some places with some regular rust mixed in with the white rust.

Harvey
SleepyC :moon

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Sounds like an area with high abrasion. Not at all sure how the presence of some SS might influence rusting or loss of zinc. A mix of rust and zinc oxide suggests local electrolysis cells. Too many things going on to know.
 
Dave, I'm just guessing here. The Stainless Steel swivel attached between the galvanized anchor and galvanized chain ==> dissimilar metals??

AND the end of the chain at the anchor would get more abrasion from bottom contact, roaming with the angle of pull from the boat, although I would think there would be more length than the 5-6 feet.

Harvey
SleepyC :moon

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Hi again Tom,
I was reading this anchoring discussion and it rattled my old brain.
The weight of the chain was in the boat when I got it from the dealer. He thought that the boat balanced better with a lot of bow weight. However I forgot that Tom has added some other mods that increased the weight of the boat. To get the RPM up perhaps a prop with a little less pitch would be a help. Other brats will have good ideas as to the size. Tom painted the bottom because he kept the boat in the water. Bottom paint also adds drag, so prop size may be the answer.

Fred Messerly
 
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