Zinc sacrificial anodes for painted aluimin hull saltwater use

Discussion in 'Boat Design' started by the brain, Feb 19, 2017.

  1. the brain
    Joined: Sep 2016
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    the brain Senior Member

    I now think I know what the two round pieces that are bolted to the inside of my late 1980s armstronge engine bracket. attach image

    ?1.how do you know when the zincs are wornout and need replaceing? or do they completely dissinagrate? I've read replace when it shrinks by50%

    in my case undetermined orginal size.

    ?2. must zincs be used in pairs? like the OB engine only has one correct?

    ?3.if I have functioning zincs inside the engine bracket I assume it's not nessasary to attach more zincs to hull because basicalley my engine bracket is now part of the hull.
    addsionalley my hull is painted (acrillic emanale orginale paint) outside only the inside of hull is bare aluimin.

    the zincs inside the engine bracket are deepely pitted ( I was told, my used brakect was never exposed to saltwater) the zinc on the OB engine appears a dustie greyish cover of corrosion.

    these brakect zincs appear to be builtin I don't see a bolt to turn to remove and replace these zincs?

    Thanks for the surport STB

    dam there a lot of zincs to choose from at this site

    hows this look for a brakect zinc replacement?

    Attached Images

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  2. the brain
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    the brain Senior Member

    anyone w/ advice
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    1. Given enough time they will disintegrate completely.
    No real reason to replace them at 50% other than a commercial one.

    2. No need for pairs, other than a commercial one.

    3. The zinc on your outboard engine is important, the others aren't.
  4. the brain
    Joined: Sep 2016
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    the brain Senior Member

    ?1.there are three different types of anodes

    ?2.for saltwater use which type is for aluimin used in mainly saltwater ocasionalle freshwater?

    ?3.the metal that is used in any anode is it just a softer version of the same material?

    ?4.Will two different type anodes have a counter productive effect?
    like since I don't right now know what anodes I currently have on both engine and engine bracket mite be best to remove and replace so I know?

    Thanks STB
  5. Scot McPherson
    Joined: Jan 2017
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    Scot McPherson Senior Member

    The one that deteriorates the fastest is probably the one that's most important. It's clearly giving up more material therefore is the one that's doing the job. You don't need to replace them at any given percentage of loss, but definitely before it either falls off or disintegrates completely.

  6. Barry
    Joined: Mar 2002
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    Barry Senior Member

    For aluminum in salt water use zinc

    No, the metal is different, zinc, magnesium etc

    The anodes that you listed of will not create any significant counter productive corrosion. As your boat does not look like that it will sit in water continually for months at a time, and the hull is painted, there should not be much deterioration of the anodes in any case.

    The engine anodes are important, as mentioned by CDK, especially if you have a bronze/brass prop. For the price, just by the OEM ones.

    For the engine bracket, buy zinc

    The picture was not the best, but they look like they are in good shape on the bracket.

    Don't paint the anodes
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