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  1. #11
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,825

    Default Re: Positioning of shaft anode

    Quote Originally Posted by coopec View Post
    My boat will be in sea water but I didn't know that magnesium anodes should be used in freshwater.
    " An alloy much more active than zinc or aluminum is needed. Magnesium is the answer. A magnesium anode is a super activated metal which means it will protect more efficiently in fresh water. Traditional zinc or aluminum anodes are just not effective as they do not produce the voltage necessary to work properly.
    I dont know where you find this information but the reason zinc and aluminium are not used in fresh water is because they become passivated by an oxide layer, which remains even on returning to salt water,
    Aluminium, but not zinc, may be used in brackish water

  2. #12
    Join Date
    Nov 2013
    Location
    Perth WA
    Posts
    2,441

    Default Re: Positioning of shaft anode

    Quote Originally Posted by VicS View Post
    I dont know where you find this information but the reason zinc and aluminium are not used in fresh water is because they become passivated by an oxide layer, which remains even on returning to salt water,
    Aluminium, but not zinc, may be used in brackish water
    Sorry! Sorry! Sorry! (I should have given you the link to the source)
    http://martyranodes.com/freshwater-anodes

    But if you googled (say) the first line of my quote you would get the source. When I'm listening to music on the radio and I decide I like the song I take note of some words of the song and then google them. That gives me the title to the song.

    Google " All of a sudden the water tastes like wine" and tell me the name of the song!

    As far as understanding the chemistry of anodes I'll take your word for it : too technical for me!
    Last edited by coopec; 17-11-19 at 02:18.

  3. #13
    Join Date
    Nov 2013
    Location
    Perth WA
    Posts
    2,441

    Default Re: Positioning of shaft anode

    Can anyone comment on these devices? Do they do away with anodes?

    How To Fit An Electro Eliminator

    Fit an electro eliminator to the shaft to provide the best protection for the stern gear, and earth it to the hull. See how to fit an electro eliminator!

  4. #14
    Join Date
    Jul 2012
    Location
    Riyadh, Saudi Arabia
    Posts
    1,375

    Default Re: Positioning of shaft anode

    Quote Originally Posted by eddystone View Post
    I haven't yet had one fall off.
    I have. Imagine motoring for a few hours with the bloody thing rattling followed by a 'clonk' sound and then no more rattle.

    Whilst it's an improvement, you do wonder if it has damaged anything on the way.

  5. #15
    Join Date
    Jun 2001
    Location
    Corfu - mostly
    Posts
    5,415

    Default Re: Positioning of shaft anode

    Quote Originally Posted by langstonelayabout View Post
    I have. Imagine motoring for a few hours with the bloody thing rattling followed by a 'clonk' sound and then no more rattle.

    Whilst it's an improvement, you do wonder if it has damaged anything on the way.
    Same here, last year. An hour spent diving under the boat with a screwdriver to remove the surviving bolt, picking up some nasty scratches on the barnacles. Perhaps I shouldn't have left the anode on for a second season. Having no anode for a couple of months didn't seem to do the propeller any harm.
    Last edited by AndrewB; 17-11-19 at 09:13.

  6. #16
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    22,133

    Default Re: Positioning of shaft anode

    Quote Originally Posted by coopec View Post
    Can anyone comment on these devices? Do they do away with anodes?

    How To Fit An Electro Eliminator

    Fit an electro eliminator to the shaft to provide the best protection for the stern gear, and earth it to the hull. See how to fit an electro eliminator!
    Ships and large structures use impressed current to combat corrosion, although generally they also use anodes. The method works but might be overkill for a grp yacht.
    Answers to some technical queries at new website http://coxeng.co.uk

  7. #17
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,825

    Default Re: Positioning of shaft anode

    Quote Originally Posted by coopec View Post
    Can anyone comment on these devices? Do they do away with anodes?

    How To Fit An Electro Eliminator

    Fit an electro eliminator to the shaft to provide the best protection for the stern gear, and earth it to the hull. See how to fit an electro eliminator!
    No they do not do away with the sacrificial anodes, unless you fit an impressed current system of cathodic protection, with permanent anodes, instead.

    They are a means making the electrical connection to the propeller shaft instead of relying on a connection to the gearbox casing, there being a good electrical path through the gearbox internals and bridging the flexible shaft coupling.

    Dont know what instructions you were hoping to link to

  8. #18
    Join Date
    Nov 2013
    Location
    Perth WA
    Posts
    2,441

    Default Re: Positioning of shaft anode

    Quote Originally Posted by VicS;6974117.

    [I
    Dont know what instructions you were hoping to link to[/I]
    That was meant to be a test!! If you googled my comment it would have lead you to an article which explained how to do it.

    I once was a Lecturer (read teacher) of Accounting/Law/Economics etc and set an assignment. On the front cover I stated Your assignment must be your own work (Do not copy)

    When I got their assignments I googled the content on their assignments and found a whole lot of students (who were barely literate) had cut-n-pasted their assignment. Incredibly a few of them had submitted their assignments that were pinched from papers written by Emeritus Professors and so on! (Their jaws dropped when I fronted them and told them where they had copied their assignment from!!)

    I failed 15 of the 20 students but I was over-ruled by the Head of Department. (We won't have any students for next semester!)
    Last edited by coopec; 17-11-19 at 11:03.

  9. #19
    Join Date
    Aug 2013
    Location
    SW Leicestershire
    Posts
    1,169

    Default Re: Positioning of shaft anode

    Regarding zinc vs aluminium in brackish water. Fresh to salt water is a spectrum therefore, I assume, going from an estuary up a river the saline level will not only progressively diminish but also vary according to ebb and flow of tide. At what point do aluminium anodes become advisable? For myself, I don't have a choice as Darglow don't make aluminium anodes for the Featherstream prop and I don't want to mix zinc and aluminium.

  10. #20
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,825

    Default Re: Positioning of shaft anode

    Quote Originally Posted by eddystone View Post
    Regarding zinc vs aluminium in brackish water. Fresh to salt water is a spectrum therefore, I assume, going from an estuary up a river the saline level will not only progressively diminish but also vary according to ebb and flow of tide. At what point do aluminium anodes become advisable? For myself, I don't have a choice as Darglow don't make aluminium anodes for the Featherstream prop and I don't want to mix zinc and aluminium.
    I don't think I have ever seen any definite recommendations in terms of salinity

    This diagram from Wikipedia shows the usual accepted ranges for fresh , brackish and salt water.

    https://en.wikipedia.org/wiki/Bracki...ty_diagram.png
    Last edited by VicS; 17-11-19 at 11:57.

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