Shaft Anode Question?

Terry in Naples · Apr 26, 2015

Yes, many times zincs last a few months. Depends on lots of things, not grounded on the boat, stray current from a dock, salinity of the water, probably many others. I replace mine every 3 months, i

njlarry · Apr 27, 2015

Mine was missing after three months as was the heat exchanger zinc. This year I am adding a galvanic isolator and a second shaft zinc. Also will test zincs with volt meter connected to the shaft and a zinc held over the side. Reading should be near zero.
I am sure you know to be careful swimming in marinas given the AC shock hazard. Hope you test the waters with a meter first.

Charles Erwin · Apr 27, 2015

". . . . Also will test zincs with volt meter connected to the shaft and a zinc held over the side. . . ."

Here is a diagram showing the test set up. The numbers in this diagram are referenced to a zinc probe.

Galvanic isloation is just about mandatory if you are having zinc rapid wasting - and maybe even if you do not have rapid wasting. You don't know who your neighbor may be from time to time. Additional zinc probably won't hurt. You are shooting to achieve replacement at about 9 12 months time.

Charles

John Murphy · Apr 27, 2015

Pateco, A VERY SIMPLE solution to your problem is ameliorated thusly: very stealthally abscond w/ one of your significant-others nail polish. On the replacement zinc, paint over the pathway of the screws/bolts. I have done this the past few years and after 1 year in the water, I still have both sides of my STILL ATTACHED zinc in the amount of your picture. This year, I have also painted the inside pathway. We'll see how long this lasts. DO test the waters for stray current in marinas. Several people have been electrocuted from stray current from the dock elect. plugs or other boats. Fair Winds... LT. MRF, SN, USPS

Davidasailor26 · Apr 27, 2015

John Murphy said:
This year, I have also painted the inside pathway. We'll see how long this lasts. DO test the waters for stray current in marinas. Several people have been electrocuted from stray current from the dock elect. plugs or other boats. Fair Winds... LT. MRF, SN, USPS

What do you mean by "inside pathway"? I hope you don't mean the surface of the zinc that mates against the shaft, as that would block the electrical connection and nullify the zinc's protection.

+1 on testing the water for voltage before swimming, or preferably don't do this at a marina. Search the archives for ESD if you're not convinced on why.

Ken Cross · Apr 27, 2015

Wow, I'd be really concerned about a zinc in need of replacement so soon. I get 2 years in our really large marina. In fact I once went 3. Once I switched to a composite prop, the zincs looked like new after 2 years. We'll see how our new to us boat does, but I know it was in the water at least 2 years and they looked pretty good when I redid the bottom and replaced them anyway.

John Murphy · Apr 27, 2015

Ken Cross, You are a lucky sailor. On The Chesapeake Bay ( 50/50 salinity) corrosion is rampant. Fair Winds and Following Seas,...and May your Jib Always Draw !! MRF

Scotty C-M · Apr 27, 2015

My zincs go almost that fast. I've often wondered if a zinc with that type of surface is still effective.

I thought David was making an appropriate clarification.

By the way, stray electricity causing ESD is a big problem in fresh water. Much less so in salt water. Yes, you can get into trouble if you touch an improperly grounded metal in salt water, but not just by being near it - as is the case in fresh water. Google "Electric Shock Drowning" and you can learn a lot about it. A must read for fresh water sailors, and important for all of us.

http://www.boatus.com/seaworthy/magazine/2013/july/electric-shock-drowning-explained.asp

Ron20324 · Apr 27, 2015

I don't know what John meant about "pathway", and I see nothing wrong with what David wrote in reference to the "quote" that he referred to... only with what post 9 said.

Ralph Johnstone · Apr 27, 2015

Pateco, until you can determine if you have external current causing increased loss to your zincs, install another zinc close to the first on a section of shaft which has been cleaned. Double the zinc surface area and roughly cut the corrosion on each in half.

If that's not possible, wire up a zinc fish to your engine block and throw over the side (the fish, not the engine). Check the resistance between your shaft and the engine block connection to ensure you have a good electrical path.

mitiempo · Apr 27, 2015

One possible reason for a short zinc life is not having a galvanic isolator. When you plug into shore power your boat is connected to all others in the marina through the green AC ground. This means that if your neighbors zincs are gone your zincs are protecting the underwater metal on his boat. If one of your neighbors has a wiring issue the problem only gets worse.

fstbttms · Apr 28, 2015

pateco said:
This anode was installed only last August. It has only been in the water 7 months. Is it normal for them to go so quickly in salt water?

I consider 7 months to be at the low end of the normal anode lifespan range. Install another on the shaft and you will replace both less frequently.

fstbttms · Apr 28, 2015

njlarry said:
I am sure you know to be careful swimming in marinas given the AC shock hazard. Hope you test the waters with a meter first.

Electric Shock Drowning (ESD) is virtually unheard of in saltwater. As a real-world example, I do boat bottom cleaning in saltwater marinas in the Bay Area. Have for 20 years. To my certain knowledge, not one diver has been injured or killed due to ESD during the over 1,000,000 in-water hull cleanings that have been performed here during that time.

I'd say that you are at much greater risk simply driving to your marina than you are diving in it.

fstbttms · Apr 28, 2015

Ken Cross said:
I get 2 years in our really large marina. In fact I once went 3. Once I switched to a composite prop, the zincs looked like new after 2 years.

An anode that lasts that long is not doing its job. FYI.

fstbttms · Apr 28, 2015

mitiempo said:
When you plug into shore power your boat is connected to all others in the marina through the green AC ground.

Almost. Your boat is in electrical contact with all the other boats on that particular shore power circuit, not every boat in the marina.

fstbttms · Apr 28, 2015

pateco said:
What is a Galvanic Isolator?

Almost always a good idea.

http://www.boatus.com/seaworthy/galvanic/

Ken Cross · Apr 28, 2015

These things

pateco said:
Mitiempo,

What is a Galvanic Isolator? I am currently docked behind a private home in Pompano Beach FL. The only other boat that should be on the same ground is the property owners small sailboat shown forward of the Stargazer in the picture below.

QUOTE]

Here is a link:
http://shop.sailboatowners.com/search.php?kw=galvanic isolator

They work, but I understand it isn't uncommon to see them internally shorted which renders them useless. They can be easily checked with a multimeter.

Ken

Shaft Anode Question?

.

.

.

.

Attachments

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.