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Propeller Shaft Corrosion

Apr 11, 2018
6
Catalina 30 Waukegan Il
I am trying to chase down the cause of some corrosion / covering that has occurred in the last year on my propeller shaft. I added a new brass folding propeller, but I don't think that should cause this. It is in fresh water in Lake Michigan. Could it be electrolytic corrosion? there are some new boats around me in the harbor.

Any Suggestions on how to remove the corrosion.

Steve Goldman
1986 Catalina 30
Peenhonin
Waukegan, Il.
 

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Jan 21, 2018
18
Catalina 30 1620 Orange Beach, AL
The only corrosion I see it the Zinc on your prop shaft. Change the Zinc. The rest is only pond scum. Which can be cleaned off. Do you have a bronze shaft or stainless shaft? I will go down stairs and take a photo a bronze prop shaft that shows corrosion. They you will be able to really see what it looks like. Saltwater boat in a old marina with a electrical grounding problem.
 
Jan 21, 2018
18
Catalina 30 1620 Orange Beach, AL
Corrosion on prop and not showing is the corrosion on the interior portion of the prop that attaches to the shaft . The prop could wobble on the shaft like baby learning how to walk.
 
Jan 30, 2012
1,047
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
Steve -

More information would help but: First, as to galvanic corrosion (what you are calling electrolytic corrosion) make sure the anodes are magnesium - not zinc. Aluminum anodes will work too but magnesium is more active (i.e. electro negative.) All anodes provide a negative shift (we need about 200 mv negative for a fiberglass boat) - zinc works fine in salt water because salt water is far more conductive than fresh. So don't use zinc.

However, I see shaft shaft corrosion - and you report this is so without your propeller (probably not brass likely manganese bronze) showing signs of wasting. That suggests you really need to rule out the possibility of stray current.

Consult with a qualified - ABYC certified - electrician. He, she, they will measure your hull potential (batteries connected/unconnected, shore power plugged in/not plugged in, etc.) They will show you these measurements and explain them. With those measurements you will find the culprit pronto. And these measurements will rule out whether the problem source is you, your neighbor, or maybe even the moorage itself.

Charles
 
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Jan 7, 2011
1,843
Oday 322 East Chicago, IN
You are on fresh water I assume.

My SS shaft and bronze (or whatever it is) prop have a film of what I think it an organic material.

Your zinc looks different than the way mine deteriorates...but I use magnesium.

What is the dark spot directly in front of the zinc? Almost looks like a hole...but maybe just a shadow...

C8ADF295-5452-4CA7-88BB-6FDCFF36B73F.png

Greg
 
Jan 21, 2018
18
Catalina 30 1620 Orange Beach, AL
Charles is correct, it is called galvanic corrosion. Different industry, difference name. Same unfortunate problems. Here on the Gulf Coast, Zinc anodes are a life saver. Pay me now or pay somebody else latter.
 
Oct 29, 2012
260
Catalina 30 TRBS MkII Milwaukee
Had the same thing two seasons ago, power boat must have had lousy power hook up, when I hauled out, my anode was almost gone and shaft pitted. Thankfully he moved and I didn't have the same corrosion the next haul out. But I installed a galvanic isolator during winter lay up to not have to worry about bad neighbors
 
Oct 29, 2012
260
Catalina 30 TRBS MkII Milwaukee
BTW, the wm here finally stocks aluminum and magnesium anodes.
For years all the stocked was zinc
 
Mar 20, 2016
331
Beneteau 351 WYC Whitby
I installed a galvanic isolator ,cheaper off ebay made in England lifetime warranty ,and also install a flexible coupling which now electrically isolates the shaft and prop anode still looked new when I hauledRD%20Shaft%20Coupling.jpg
 
Jan 30, 2012
1,047
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
The ABYC rule concerning this situation is very specific.

The shaft needs to be un-isolated if you have shore power. If you use a shaft saver - use a jumper so the shaft is electrically connected to the motor. Safety green (the equipment grounding conductor) must be connected to DC negative, to the motor, and so necessarily to seawater via the shaft. This provides a second path to the shore power transformer ground rod via the water. If you isolate the shaft this secondary path is defeated.

For those with further interest there are several articles at http://www.qualitymarineservices.net/ under documents.

Charles
 
Mar 20, 2016
331
Beneteau 351 WYC Whitby
The ABYC rule concerning this situation is very specific.

The shaft needs to be un-isolated if you have shore power. If you use a shaft saver - use a jumper so the shaft is electrically connected to the motor. Safety green (the equipment grounding conductor) must be connected to DC negative, to the motor, and so necessarily to seawater via the shaft. This provides a second path to the shore power transformer ground rod via the water. If you isolate the shaft this secondary path is defeated.

For those with further interest there are several articles at http://www.qualitymarineservices.net/ under documents.

Charles
Then I guess every boat with a volvo penta sail drive doesn't meet ABYC as they are electrically isolated.Which ABYC standard is this ? Abyc wants ELCI GFCI main breaker to prevent what you say.Many people have died in marina's power running thru the water with boats leaking ,which is not what you want. Many clubs I visit have shore power detection and can tell if your boat is leaking when you plug in and will not let you until the source is found,which many times is battery charger or element in hot water tank
 
Jan 30, 2012
1,047
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
Right - you can't use the Volvo isolated seadrive as your vessel ground. But easy to comply with US AC rules
in that case. Just add a separate copper ground plate.

An RCD or ELCI trip threshold is too high to prevent electrocution - these are for equipment protection. They do a very good job too because if you had an AC to DC fault (together with a broken safety green - or if safety green was not connected to DC negative) it is unlikely a breaker would trip especially in a fresh water case.

Charles
 
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