Sacrificial anode for aluminum hull?

Discussion in 'Boat Design' started by nopeda, Mar 28, 2017.

  1. nopeda
    Joined: Aug 2013
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    Location: GA

    nopeda Junior Member

    Hi,

    I have a197? 43' aluminum hull houseboat on a freshwater lake near Atlanta, GA. AFAIK it has never been out of the water. It's located in a fairly large marina. I've been told that steel hull boats should have a sacrificial anode applied to help keep the hull from breaking down, but recently someone said that aluminum boats should have one also. Is that true, and if so can anyone tell me just how to do it or suggest a page or video that explains to how to apply one to aluminum hull boats in fresh water?

    Thank you for any help!
    David
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

  3. Barry
    Joined: Mar 2002
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    Barry Senior Member

    You have stumbled on an anomaly

    Generally all aluminum hulls should have anodes attached in salt water and ABYC quantifies the difference of various materials in Table 1, E2, Galvanic Series of Metals in Seawater wrt to a Silver Chloride Cell

    To protect aluminum in sea water, zinc appears next and then magnesium/mag alloys. But Magnesium can produce IN SEA WATER a corrosion potential above -1200 mv. In Sea water and referenced to the silver chloride cell. This potential can create alkali corrosion.

    So then the natural conclusion would be then to install zinc anodes, BUT in 2.7.1.3 notes, the table omits Zinc as being an anode for freshwater protection.

    But the table allows magnesium as an anode material which according to 2.10.1 Note

    Summary,
    One table, referenced to seawater, suggests that only Zinc would be the anode choice due to magnesium's higher than desired potential difference, IN SEAWATER, and the other table omits zinc as being a suitable anode in fresh water.

    Obviously, sea water conducts electricity better than freshwater so PERHAPS a magnesium anode would do the trick. You would almost have to hang one over the side of the boat with a multimeter attached and see what the potential difference is in the water that you are in to be sure.

    There are you tube videos that show how to do this.

    Perhaps Private Message CDK on this question.

    Or perhaps, just search for anode suppliers as they often have recommendations of their alloys under various conditions.
    But be sure that you find a specific reference to an aluminum hull.

    Perhaps in freshwater, no anodes are required.

    Or perhaps in freshwater, the mag anodes due to the lack of an electrolyte, the sea water, will not produce a more than -1200 mv differential
     
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