Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-29-2018, 08:21 AM   #1
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,513
Magnesium sacrificial anodes

I was reading ABYC E-02 about cathodic protection and saw the following note:

2.7.4 Magnesium anodes shall not be directly

coupled to the surface to be protected without dielectric

shielding.

Does anybody have more explanation, details or info about this?
All anodes are magnesium on my boat so the question.

L
__________________
Advertisement

Lou_tribal is online now   Reply With Quote
Old 01-29-2018, 09:24 AM   #2
Senior Member
 
Capecodder's Avatar
 
City: Cape Cod, MA or Fort Myers, FL
Country: USA
Vessel Name: Osprey
Vessel Model: Her Shine. Newburyport
Join Date: Dec 2013
Posts: 352
I find this company helpful with my Anode questions.
BoatZincs.com (978-841-9978) - FAQs
__________________

Capecodder is offline   Reply With Quote
Old 01-29-2018, 10:03 AM   #3
Guru
 
kthoennes's Avatar
 
City: Sioux Falls, South Dakota
Country: USA
Vessel Name: Xanadu
Vessel Model: Mainship 37 Motor Yacht
Join Date: Oct 2013
Posts: 1,038
I'd be interested in the explanation on that if you get one. I used magnesium on our boat currently (one transom plate on mounting studs and one "baseball" anode on each prop shaft). Fresh water, Missouri River. I was surprised how much loss there was after a single season, but I know the loss rate is much faster with magnesium.
kthoennes is offline   Reply With Quote
Old 01-29-2018, 04:52 PM   #4
TF Site Team
 
City: Westerly, RI
Country: USA
Vessel Name: N/A
Vessel Model: 1999 Mainship 350 Trawler
Join Date: Jan 2014
Posts: 1,833
https://www.corrosionpedia.com/defin...lectric-shield

I wonder if it is an issue with dissimilar metals?
Shrew is offline   Reply With Quote
Old 01-29-2018, 05:17 PM   #5
TF Site Team
 
Bacchus's Avatar
 
City: Seneca Lake NY
Country: US
Vessel Name: Bacchus
Vessel Model: MS 34 HT Trawler
Join Date: Nov 2014
Posts: 2,919
Standing by for explanation???
All anodes are dissimilar and don't see how they work without being connected electrically to the material to be protected... AFAIK? ???

We are in fresh water and use all alum anodes.
__________________
Don
2008 MS 34 HT Trawler
"Bacchus"
Bacchus is offline   Reply With Quote
Old 01-29-2018, 06:05 PM   #6
Guru
 
Northern Spy's Avatar
 
City: Powell River, BC
Country: Canada
Vessel Name: Northern Spy
Vessel Model: Nordic Tug 26
Join Date: Feb 2012
Posts: 3,023
A guess. The passive current in the "system" is driven by the galvanic potential of the metals. Too high of a potential would create a proportionally higher current. The dielectric shield would force the current distribution over a greater area, protecting more of the parent material and making the anode last longer.

I'm making an educated guess based on a few maintenance projects I did with impressed cathodic protection of waterfront facilities at a mill.

Occasionally, the diver would find issues all around the pilings or fixed barge float where the shields fell off, but the metal under the anode was perfect.

Keep in mind with impressed current, you ran electricity through the anodes on purpose, so you could consume them really quickly if they weren't shielded.
Northern Spy is offline   Reply With Quote
Old 01-29-2018, 06:19 PM   #7
Guru
 
kthoennes's Avatar
 
City: Sioux Falls, South Dakota
Country: USA
Vessel Name: Xanadu
Vessel Model: Mainship 37 Motor Yacht
Join Date: Oct 2013
Posts: 1,038
Quote:
Originally Posted by Bacchus View Post
Standing by for explanation???
All anodes are dissimilar and don't see how they work without being connected electrically to the material to be protected... AFAIK? ???

We are in fresh water and use all alum anodes.
I had the same thought. In a previous life I worked for my father's commercial diving company. We did a lot of work on traveling water screens at power plants -- essentially giant conveyor belts with heavy wire mesh across steel frames, set across power plant cooling water intake canals. In high corrosion environments we typically welded aluminum anodes to the frames of the steel traveling water screen baskets (the aluminum anode was cast around a mild steel rod that stuck out a few inches on each end for the welded attachment). No dielectric barrier there...
kthoennes is offline   Reply With Quote
Old 01-29-2018, 06:27 PM   #8
Guru
 
Northern Spy's Avatar
 
City: Powell River, BC
Country: Canada
Vessel Name: Northern Spy
Vessel Model: Nordic Tug 26
Join Date: Feb 2012
Posts: 3,023
The ones I recall with were dipped in plastic (like plastidip). You cut away the plastic to expose as much of the anode that you wanted to. The plastic remained on the side you were attaching it to. You could cut away more depending on the current reading on the reference anode. Very primative. I'm sure they are much more sophisticated now.
Northern Spy is offline   Reply With Quote
Old 01-29-2018, 07:49 PM   #9
Guru
 
kthoennes's Avatar
 
City: Sioux Falls, South Dakota
Country: USA
Vessel Name: Xanadu
Vessel Model: Mainship 37 Motor Yacht
Join Date: Oct 2013
Posts: 1,038
I'm thinking of those anode fish now that some smaller boaters use, those zinc or aluminum things cast to look like fish that you just toss and hang overboard. The other end of the cable usually has a clip on it like a battery jumper cable. What are you supposed to do with that clip? Well here:

https://www.fisheriessupply.com/mart...zinc-cmgrouper

Here's the product directions. Hmmm. (Well duh, yeah, don't clip it to a battery terminal, ha!):

Using the cable on a cleat, secure the Grouper's weight below the bottom of the hull before attaching the alligator clip to outboard or outdrive mounting bolt, or to rudder or strut ground strap, etc.
Clip to grounding strap, where possible, or to a component wired to the boat's common DC ground
Do NOT connect to battery
kthoennes is offline   Reply With Quote
Old 01-30-2018, 07:09 PM   #10
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,513
Spend two days to seek for information but did not find anything conclusive. Only thing I found that it was recommended to have the anode isolated from the support and connected to the piece to protect in one single point.
Wish to see one of our corrosion expert chime in!

L
Lou_tribal is online now   Reply With Quote
Old 01-30-2018, 07:18 PM   #11
Guru
 
boatpoker's Avatar
 
City: Whitby, Ontario
Country: Ontario
Vessel Name: DIRT FREE
Vessel Model: Benford Fantail 38
Join Date: Sep 2012
Posts: 2,502
Quote:
Originally Posted by Lou_tribal View Post
I was reading ABYC E-02 about cathodic protection and saw the following note:

2.7.4 Magnesium anodes shall not be directly

coupled to the surface to be protected without dielectric

shielding.

Does anybody have more explanation, details or info about this?
All anodes are magnesium on my boat so the question.

L
Suggest you re-read that. They are referring to aluminum and steel hulls only.
__________________
If you can live with the consequences, go for it - wg
Y'am what y'am an' thats' all that y'am - Popeye
I had an allergic reality - Jillie the Bean
boatpoker is offline   Reply With Quote
Old 01-30-2018, 07:24 PM   #12
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,513
Quote:
Originally Posted by boatpoker View Post
Suggest you re-read that. They are referring to aluminum and steel hulls only.
I can believe you but this is not mention in E-02.

Here is the section where I saw this:

2.7.3 Only one current path shall be provided from

each anode to the cathodic bonding system.

NOTES:

1. Sacrificial anodes may be mounted directly on

the metal to be protected.

2. Zinc galvanic anodes may be applied directly to

aluminum, steel and non-metallic hulls without shielding.

3. Better current distribution will be obtained with

a dielectric shield between the anodes and metals to be

protected providing the anode is electrically connected to

the metal being protected.

2.7.4 Magnesium anodes shall not be directly

coupled to the surface to be protected without dielectric

shielding.

L
Lou_tribal is online now   Reply With Quote
Old 01-30-2018, 07:39 PM   #13
Guru
 
boatpoker's Avatar
 
City: Whitby, Ontario
Country: Ontario
Vessel Name: DIRT FREE
Vessel Model: Benford Fantail 38
Join Date: Sep 2012
Posts: 2,502
Quote:
Originally Posted by Lou_tribal View Post
I can believe you but this is not mention in E-02.

Here is the section where I saw this:

2.7.3 Only one current path shall be provided from

each anode to the cathodic bonding system.

NOTES:

1. Sacrificial anodes may be mounted directly on

the metal to be protected.

2. Zinc galvanic anodes may be applied directly to

aluminum, steel and non-metallic hulls without shielding.

3. Better current distribution will be obtained with

a dielectric shield between the anodes and metals to be

protected providing the anode is electrically connected to

the metal being protected.

2.7.4 Magnesium anodes shall not be directly

coupled to the surface to be protected without dielectric

shielding.

L
Don't know where you are getting that from but here is a photo of the appropriate section of the 2013 standard which is the latest edition of E-2.
Attached Thumbnails
Click image for larger version

Name:	abyc.jpg
Views:	28
Size:	80.2 KB
ID:	72552  
__________________
If you can live with the consequences, go for it - wg
Y'am what y'am an' thats' all that y'am - Popeye
I had an allergic reality - Jillie the Bean
boatpoker is offline   Reply With Quote
Old 01-30-2018, 07:44 PM   #14
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,513
Quote:
Originally Posted by boatpoker View Post
Don't know where you are getting that from but here is a photo of the appropriate section of the 2013 standard which is the latest edition of E-2.
Oh mine is the 2001 version, need an update
Thank you!

L
__________________

Lou_tribal is online now   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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





All times are GMT -5. The time now is 07:27 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×