Was fairing putty protecting from electrolysis ?

Discussion in 'Sailboats' started by Kiss, Aug 22, 2016.

  1. Kiss
    Joined: Aug 2016
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    Kiss New Member

    I just bought a 38 cat ketch built in aluminium. I hired a team to put an antifouling paint. In preparation for the job to be done they sanded off the hull which had been covered with putty and faired. Two coats of primer and 3 coats of antifouling have been applied after all the putty had been removed.
    Now I wonder, was this a mistake to remove the putty ? Was is not a good protection against electrolysis ? Should I consider fairing the hull again to better protect it ? Which putty or filler should I use then ? If the aluminium is covered with putty, should I nevertheless use an aluminium primer and antifouling ?:?:
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Any non-conducting barrier prevents electrolysis. You have a total of 5 paint layers now, so it is safe to assume seawater doesn't come into contact with the aluminium.
     
  3. Kiss
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    Kiss New Member

    Thanks CDK, it reassures me.
     
  4. mydauphin
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    mydauphin Senior Member

    Every once in a while dive around your boat and make sure there are no hidden cracks in your fairing. I also use a capac ohm meter. My bare aluminum hull was treated with zinc chromate, then zinc chromate primer, then various epoxies then epoxy fillers, then another layer of Epoxy then comes the paint... but one scratch you are at the mercy of bad wiring at your favorite marina. Make sure you use galvanic isolators on your power feed.
     
  5. Kiss
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    Kiss New Member

    Thanks for this info. Excuse my little knowledge on the subject but when you say "one scratch and you are at the mercy of bad wiring at your favorite marina" does this mean that if I avoid marina, which I do, the presence of a scratch on the antifouling or a crack in the fairing will be less dramatic or not dramatic at all ? I will read more on galvanic isolators and be better prepared next time I go to a marina. I have saved the information and will see if I can do what you did with your hull next time I haul out. I really regret having remove the fairing. But, as I found out after buying that boat, **** happens !
     
  6. CDK
    Joined: Aug 2007
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    CDK retired engineer

    What the marina offers as "ground" or "earth" most of the time has an offset from the electrical potential of your boat. A damaged spot in the hull coating is prone to rapid electrolysis as soon as you connect to shore power, hence the need for a galvanic isolator.
     
  7. Tanton37
    Joined: Dec 2016
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    Tanton37 Junior Member

    Aluminum cat ketch

    Hey Kiss,
    Could you please contact me.......very interested in knowing more about your boat.
    Reach me at catketchme ATGMAILDOTCOM
    Cheers, David
     
  8. Ike
    Joined: Apr 2006
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    Ike Senior Member

    If you use a galvanic isolator or an isolation transformer, you should not have a problem with galvanic corrosion. Use appropriate anodes as well (often called zincs, but more often than not, not made of zinc)
     

  9. Scot McPherson
    Joined: Jan 2017
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    Scot McPherson Senior Member

    If the boat is aluminum, then the anodes really need to be made of zinc. An aluminum anode isn't going to be an anode at all on an aluminum hull.
     
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