anodes

Discussion in 'Boat Design' started by rfleet1066, Oct 25, 2012.

  1. rfleet1066
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    rfleet1066 rfleet1066

    Gosh, fellows. I am more confused now. I did contact McDuff, waiting for reply. When engineering in unknown territory, I always consider margin of error and how overkill might cost more, but satisfy the requirement. Can I over-protect?

    Ryland
     
  2. rsimon
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    rsimon Junior Member

  3. rsimon
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    rsimon Junior Member

  4. CDK
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    CDK retired engineer

    Nothing dramatic will happen if you install more zinc than necessary for protection. The electrodes are sacrificial, but as long as the integrity of the paint layer is not impaired by scratches, the wear rate stays low.

    I've noticed an increase in marine growth on metal surfaces (stainless rudders) bonded to the hull, so it seems certain organisms follow the path of the galvanic protection current. But I found no evidence that it is proportional to the amount of zinc used.
     
  5. michael pierzga
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    michael pierzga Senior Member

    Yes... being over anoded is just as bad as under anoded. I can usually spot "over anoded " condition by the bubbling paint..burn..near the anode.

    The mcduff literature is good and should allow you to make an initial installation. Plenty of technical literature available on the internet.
     
  6. gonzo
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    gonzo Senior Member

    I suppose that if you consider the hull as a galvanic cell, then the names get inverted.
     
  7. Dhutch
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    Dhutch Junior Member

    The hull is always in the cell.

    The cell is
    - Hull (the cathode)
    - Sacrifical anode (the anode)
    - Water you floating in (electrolite)


    Daniel
     
  8. rfleet1066
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    rfleet1066 rfleet1066

    good explanation

    That's the best explanation of this subject for my needs. Is it possible to over do it? Is even distribution a factor? Does every dissimilar metal attachment (coolers, thrusters,drives, etc.) need separate protection?

    Ryland
     
  9. Dhutch
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    Dhutch Junior Member

    My field of knowlage is narrowboats, simple boats, in fresh water.

    The main issue there certainly is the dissimilar metals, stainless propshaft in the main. I understand the throw is in feet not meters which on a narrowboat gives you issues as other than the stern theres very few places you can put then they wont get knocked off.


    Daniel
     
  10. CDK
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    CDK retired engineer

    If water were a good conductor, a single electrode would be enough. Unfortunately that is not the case. When paint damage occurs 10 ft from the zinc, the galvanic protection will still be fairly effective, but with a second damaged spot near the zinc, there is no current left at 10 ft.

    Dissimilar metal attachments must be protected with electrodes in close proximity, especially if light alloy is involved.
     
  11. michael pierzga
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    michael pierzga Senior Member

    Yes. Struts, shafts, thrusters, sea chests, rudders. All metal pieces.

    How much ? is a good question. For instance an anode located in fast moving water is less effective , but subject to waterflow erosion. You may need two anodes instead of one.

    Best is not to get all worked up and stressed about anodes. Your hull wont melt in one year is you miscalculate. Follow the Mgduff recommendations, Give it your best shot then every year observe the anode erosion and adapt. Rudder anodes burn fast, prop nut anodes erode fast, sea chest anodes erode fast...hull anodes last for years.
    When your boat is alongside a concrete steel reinforced dock, you will notice that the dockside anodes wear faster than the sea side ones.
     
  12. Frosty

    Frosty Previous Member

    No you cant over do it. I had a 60 footer in the sea and it had 5 1 kilo anodes down each side 2 on each side of the rudder and a shaft anode.
     
  13. rfleet1066
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    rfleet1066 rfleet1066

    Should electrical systems have an isolated ground or neutral, or is the hull not compromised by that?

    Ryland
     

  14. CDK
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    CDK retired engineer

    That topic has been discussed here numerous times.
    What you do or don't in the hull has no effect on the outside world.

    There is however one exceptional situation: using a metal hull as the return for very high currents does cause corrosion due to the voltage differential.
     
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