Check out this prop shaft anode

[fstbttms]

Originally Posted by boatpoker

I'd suspect metallurgical contamination of the anode given that there was no mention of shaft or propeller corrosion.

I hadn't considered that before.

[kingofcary]

Folks .... no shaft or prop corrosion. Again, the 'chunks' that came off anode occurred from wrench to get 1st turn. As previously mentioned must be internally degraded ... whether by metallurgical contamination or electrolytic or galvanic corrosion I sure don't know. Thanks ...

[boatpoker]

Originally Posted by fstbttms

I hadn't considered that before.

I've seen people cleaning anodes with steel wire brushes, a possible source of contamination ?

[Celestialsailor]

It sounds like there might be different factors that can cause problems. Another consideration might be a new neighbor who does not have a properly installed electrical system.

[fstbttms]

Originally Posted by boatpoker

I've seen people cleaning anodes with steel wire brushes, a possible source of contamination ?

I've never known that to be the case and I've been cleaning anodes with steel brushes for 28 years.

[fstbttms]

Originally Posted by Celestialsailor

It sounds like there might be different factors that can cause problems. Another consideration might be a new neighbor who does not have a properly installed electrical system.

As previously mentioned- electrolytic corrosion. But almost always due to a problem aboard the boat in question.

[boatpoker]

Originally Posted by Celestialsailor

It sounds like there might be different factors that can cause problems. Another consideration might be a new neighbor who does not have a properly installed electrical system.

I've heard that dozens of times when doing corrosion surveys and have always found the corroding vessel to be the source of it's own issue.

[Celestialsailor]

Originally Posted by fstbttms

As previously mentioned- electrolytic corrosion. But almost always due to a problem aboard the boat in question.

Originally Posted by boatpoker

I've heard that dozens of times when doing corrosion surveys and have always found the corroding vessel to be the source of it's own issue.

good to know...thanx for the education.

[Goodxcharly]

There is no advantage to changing them late other than $2 or $3.

[plittle2005]

Is the boat in salt, brackish or fresh water?

The advice these days seems to be: use aluminum, not zinc, for salt & brackish, and magnesium for fresh. My aluminums get used up (50%) in one 6-month season on the brackish Hudson River, whereas my previous zincs showed almost no deterioration.

[boatpoker]

Originally Posted by plittle2005

Is the boat in salt, brackish or fresh water?

The advice these days seems to be: use aluminum, not zinc, for salt & brackish, and magnesium for fresh. My aluminums get used up (50%) in one 6-month season on the brackish Hudson River, whereas my previous zincs showed almost no deterioration.

Thats because your zinc anodes were not working. Zinc anodes develop a calcareous coating in fresh or brackish water which acts and an insulator and renders them useless. Aluninum anodes are the only ones that work in all waters.

[Cynara]

Are you in a marina or at anchor. In my opinion if your plugged into a dock the zinc should have been gone a long time ago. I replaced our zincs about every 9 months. Inspect your through hulls very carefully