Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 19-04-2014, 13:17   #16
Marine Service Provider

Join Date: Oct 2011
Posts: 1,205
Re: Galvanic or Electrolytic Pit Corrosion Propeller

Aluminum anodes for brackish water, or for a boat that spend part time in salt and part time in fresh, or brackish water.

Anode FAQs

Lloyd

Quote:
Originally Posted by Hoofsmit View Post
Technically I'm sure you are correct, but we are trying to figure out the loss of material on a prop, not make a battery ! Or trying to electro plate our through hulls!
So do you think it is being caused by a stray current or poor quality prop material or ' bad' anodes?
I known magnesium anode mix is used in fresh water for anti galvanic corrosion protection and zinc rich in salt water.
I moored in a estuary where the salinity varied a lot dependant of rain full and tidal state and had both fitted for a season, the zincs sacrificed more than the mags.
__________________

__________________
FlyingCloud1937 is offline   Reply With Quote
Old 19-04-2014, 13:45   #17
Registered User
 
Hoofsmit's Avatar

Join Date: Jul 2013
Location: cornwall uk
Posts: 569
Galvanic or Electrolytic Pit Corrosion Propeller

Great link, explains a lot about the negative current impact on anodes and metals that need protecting

Thanks
__________________

__________________
Hoofsmit is offline   Reply With Quote
Old 19-04-2014, 20:38   #18
Registered User

Join Date: May 2012
Location: Western Wisconsin
Boat: O’Day Daysailer II, 17'
Posts: 572
Re: Galvanic or Electrolytic Pit Corrosion Propeller

Goudurix, have you changed engines or propellers on your boat?
__________________
westwinds is offline   Reply With Quote
Old 19-04-2014, 23:22   #19
Moderator
 
JPA Cate's Avatar

Join Date: Nov 2011
Location: aboard, cruising in Australia
Boat: Sayer 46' Solent rig sloop
Posts: 10,697
Re: Galvanic or Electrolytic Pit Corrosion Propeller

Goudurix,

If you have a bronze prop, and there is pink metal surrounding the pits, then you have had de-zincification on your prop, and this is caused by stray current. Could be poor wiring in the marina, or could be from your own boat.

I'm not an expert, but when I read how many zincs you're using, I wondered whether you are over-zinc-ed, which can cause problems, as well.

Perhaps the suggestion to find a qualified marine electrician to survey your boat for stray current is not a bad idea. You, yourself can check the electrical potential in various berths at your marina. This can be educational.

Good luck with it. i hope your prop's okay.

Ann
__________________
JPA Cate is online now   Reply With Quote
Old 21-04-2014, 03:05   #20
Registered User

Join Date: Aug 2011
Location: Zeebrugge, Belgium
Boat: Jeanneau Voyage 37 ft
Posts: 254
Re: Galvanic or Electrolytic Pit Corrosion Propeller

Thanks fot all your replies so far!
I am aware of the difference between galvanic corrosion/currents and stray current corrosion.

Unfortunately too late to send any pics of the prop; I put the boat in the water Saturday.

I heard about "over-zincing"; I have never measured the cathodic protection voltage of my system for which I would need a silver electrode.
The reason why I added 2 zinc discs to both sides of the propeller shaft strut, is that some years ago I observed purple-ish coloring of the strut, after I had connected the SSB auto-tuners RF ground to this bronze strut. There was already a copper mesh connected to it from the engine ground, thus serving also as the boat's (12V system) ground. Fearing problems due to the SSB (questionable) I did add the 2 bronze discs and put in high voltage capacitors (1 microF in total) between the ATU and the bronze strut to block any DC and ground loop voltage differences.

The zincs are branded and expensive.

As for the prop: there was no purplish coloring around the small pits. There was however, as every year, a difficult to remove calcified crust on the blades, indeed it made me think about barnacles - but could they cause the pitting?

As for the dock power system ground, I checked any leaks between this ground and the battery chargers output and 12V negative: infinite resistance. Tested for any faults in the 220V circuit of the water boiler - it seems OK.

There is definitely no connection between the dock power ground and ships ground or the engine (...I know...European rules not as stringent...) so I suspect adding in a galvanic isolator or isolation transformer would be unnecessary.

Jan
__________________
Goudurix is offline   Reply With Quote
Old 21-04-2014, 16:29   #21
Registered User
 
Celestialsailor's Avatar

Join Date: Nov 2006
Location: In Mexico, working on the boat
Boat: Hallberg Rassy 35. and 14ft.Whitehall pulling skiff.
Posts: 8,013
Images: 5
Re: Galvanic or electrolytic pit corrosion propeller

Quote:
Originally Posted by Cheechako View Post
How about the SSB ground plane... could it be getting to the prop somehow?
I did notice hauling out this time that where I placed my copper plate outside the boat, had a lot of bottom paint corrosion around it. Even though it was connected to a zinc. I am eliminating the copper plate for a KISS system to cure this.
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: Wow - what a ride!"

http://wwwjolielle.blogspot.com/
Celestialsailor is offline   Reply With Quote
Old 21-04-2014, 17:12   #22
Senior Cruiser
 
senormechanico's Avatar

Cruisers Forum Supporter

Join Date: Aug 2003
Boat: Dragonfly 1000 trimaran
Posts: 5,830
Re: Galvanic or Electrolytic Pit Corrosion Propeller

I installed a thin sheet of vinyl (to act as an insulator) beneath the zinc anode for all the bonding system and another one between the hull and keel cooler for the fridge. No paint burns.
__________________
Memento,homo, quia pulvis es, et in pulverem reverteris.
senormechanico is offline   Reply With Quote
Old 21-04-2014, 17:28   #23
Registered User
 
Celestialsailor's Avatar

Join Date: Nov 2006
Location: In Mexico, working on the boat
Boat: Hallberg Rassy 35. and 14ft.Whitehall pulling skiff.
Posts: 8,013
Images: 5
Re: Galvanic or Electrolytic Pit Corrosion Propeller

The paint burns I have go 12"s all around the 4"X10" copper plate.
__________________

__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming: Wow - what a ride!"

http://wwwjolielle.blogspot.com/
Celestialsailor is offline   Reply With Quote
Reply

Tags
corrosion, propeller, rope

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electrolytic conversion detection sandycohen Construction, Maintenance & Refit 2 29-06-2011 19:29
Shore Power and Galvanic Corrosion scalleia Electrical: Batteries, Generators & Solar 7 21-07-2010 20:05
The Galvanic Series and Corrosion GordMay Construction, Maintenance & Refit 8 22-05-2010 11:26



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 15:18.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.