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  1. #1
    Ausfish New Member
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    Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Is there anyone out there who might be able to advise me as to what is the effects of using stainless steel or galvanised screws (zinc coated) onto an aluminium boat hull in regards to electrolysis. Ie, will the stainless steel and gal break down before the aluminium or the other way around. I don't want to end up with holes in the hull like I have been told lead sinkers sinkers can do.

    Thanks in anticipation.

  • #2
    Ausfish Bronze Member
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Jack,
    There is lots of stuff about this on ausfish. Go search for more.
    In summary (my version anyway):

    Don't use zinc-cadmium or zinc-galv screws/bolts in alumnium ever. Depending on lots of things, they will amalgamate (and dissolve) with the aluminium in weird ways - all bad.

    Use S/S (only 316 if below the waterline) and use duralac (a tube costs up to $30 but lasts forever if you are careful with the lid etc) in the hole, the bolt, washer and nut.

    If selftapping screws in, first tap them, then remove, put duralac in the hole, then reinsert the screw.
    If no duralac, then use marine sikaflex. If no sikalfex and desperate, use neutral cure roofing silicon - but use something - you will be amazed at how fast the hole and surrounding area corrodes (white powder...) and bubbles...and it gets worse quickly, evenutually leading to pinholes around chines and keels.......
    Even if you don't use your boat often, you can still watch the corrosion happen in the comfort of your carport (though a bit slower.....).
    Note that it is the aluminium that will break down - though the screws/bolts and fittings may discoulor and gradually break down also.

    An alternative often forgotten about is to use marine grade (sealed end) aluminium rivets - these are available at serious bolt shops - though even blunnings now carries some. But even then use duralac or something......particularly below the waterline or on the hull.

  • #3
    Ausfish New Member
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    alcam,
    Thank you very much, this is very helpful.
    Many Regards, Jack

  • #4
    Ausfish Gold Member
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Jack,

    Visit this website:

    www.tefgel.com.au

    It may solve your problems.

    White Pointer

  • #5
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    You can get away with using ordinary aluminium pop rivets.... as long as you drive the remaining steel mandrel out of the rivet with a punch the fill the rivet with sealer such as sicaflex.

    bed everything on some sort of sealer...........if using rivets get sealer under the head of the rivet...... silicon is not good... polyeurathane is far better...... sicaflex is king...... bostic gold isnt bad.

    As for zinc plated hardware.......even just out in the rain the zinc goes off pretty quick....... if you put an unprotected zinc plated steel screw in an aluminium boat......I would expect to see corrosion in weeks........steel and aluminium not good at all.

    cheers

  • #6
    Ausfish Premium Member
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Quote Originally Posted by oldboot View Post
    You can get away with using ordinary aluminium pop rivets.... as long as you drive the remaining steel mandrel out of the rivet with a punch the fill the rivet with sealer such as sicaflex.

    Good idea. Sealed rivets have a steel mandrel = VERY BAD!

  • #7
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    You can get aluminium rivets with aluminium shafts....but... if you dont seal the hole in the rivet it will retain water and salt...and will be a source of rapid corrosion.

    Just make sure you catch the mandrel when you punch it out.

    I sometimes put a slack bit of gaffa tape over the back of the rivet to catch the mandrel.

    cheers

  • #8
    Ausfish Addict Noelm's Avatar
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    there is a whole host of Marine Pop rivets available that are suitable for Aluminium, and no need to get rid of the centre, they are also waterproof, only thing worse on Alloy than steel/zinc plated is Brass, that is a certain no no!!!

  • #9
    Ausfish Bronze Member Steboe's Avatar
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Quote Originally Posted by Noelm View Post
    there is a whole host of Marine Pop rivets available that are suitable for Aluminium, and no need to get rid of the centre, they are also waterproof, only thing worse on Alloy than steel/zinc plated is Brass, that is a certain no no!!!
    Where i can I buy sealed aluminium rivets with an aluminium shaft in a packet of 100 or less, the sealed rivets at bunnings have a steel shaft

    Ken

  • #10
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    try "The bolt king" at capalaba.

    cheers

  • #11
    Ausfish Bronze Member suzygs1000's Avatar
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    Thumbs up Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Hi,

    Zinc is next to aluminium on the galvanic table, therefore there should be very little chance of corrosion if you use galvanised fittings on aluminium

    I built an aluminium trailer a little over two years ago, and all the fittings on it are galvanised ie bolts, nuts, axles, discs, springs, multi roller fittings.


    After two years of use, there is no sign of corrosion around any of the fittings!

    It may happen eventually, but I am keeping an eye on it.

    I always use Duralac with stainless bolts or screws.

    I have never had a problem with al rivets with al mandrels.

    Dave.

  • #12
    Ausfish Addict FNQCairns's Avatar
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Quote Originally Posted by Steboe View Post
    Where i can I buy sealed aluminium rivets with an aluminium shaft in a packet of 100 or less, the sealed rivets at bunnings have a steel shaft

    Ken
    I get mine from whitworths

    cheers fnq



  • #13
    Ausfish Bronze Member suzygs1000's Avatar
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    Bias boating also sell them in a couple of different sizes singly.

    Dve.

  • #14
    Ausfish Addict Noelm's Avatar
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    Re: Electrolysis with zinc & stainless steel screws on aluminium boat hull

    OK, first off, forget Bunnings, we are talking Marine here, so off to a yacht ot Boat supplies place you go, and you will be able to buy them as easy as pie!

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