Hull protection

Discussion in 'Powerboats' started by Mik the stick, Nov 22, 2014.

  1. Mik the stick
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    Mik the stick Senior Member

    I understand the need for Zink sacrificial anodes even on a wooden boat. What I don't understand is that a steel boat can be protected by spraying on hot zink then painting it. If the paint is scratched the zink protects the steel however when open to seawater it is also a sacrificial anode. Therefore the whole bottom of the boat is a thin sacrificial anode isolated from contact with sea water by the paint. Have I got this right? I looked very closely at a WW2 wooden seaplane tender and could see nothing which looked remotely like a zink anode. I noted the paint above LWL was very smooth and bright, below LWL was dull and rough.
     
  2. gonzo
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    gonzo Senior Member

    A wooden tender won't react to salt water like a steel hull will. Am I missing something in your question?
     
  3. DCockey
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    DCockey Senior Member

    Sacrificial anodes on wood????? :confused:
     
  4. TANSL
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    TANSL Senior Member

    No throughout the hull itself but in some areas should be fitted: shaft / propeller / rudder
     
  5. gonzo
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    gonzo Senior Member

    Sacrificial anodes in wooden boats protect the fasteners.
     
  6. TANSL
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    TANSL Senior Member

  7. DCockey
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    DCockey Senior Member

    Do metal objects need to have an electrical connection to an anode to be protected by the anode?
     
  8. gonzo
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    gonzo Senior Member

    The water connects them. It is an electrolyte.
     
  9. DCockey
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    DCockey Senior Member

    There needs to be a complete circuit between the sacrificial anode and the metal it is protecting. Electrons need to be able flow from the sacrificial anode to the metal it is protecting.
    http://www.cathodicprotection101.com/
     
  10. TANSL
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    TANSL Senior Member

    DCockey, you are quite right but as well say Gonzo, salt water acts as the electrolyte and connects them. Salt water completes circuit.
     
  11. DCockey
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    DCockey Senior Member

    So how does a sacrificial anode protect fasteners in a wooden boat? The wood is a very poor conductor so the fasteners are not connected to the anode.
     
  12. TANSL
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    TANSL Senior Member

    If the fasteners are not in contact with water, needless to protect them. Here you are absolutely right: have you nailed it.
    Another way to protect metals against maritime oxidation is to paint them with a suitable paint. Maybe that would avoid using sacrificial anodes in many places.
     
  13. TANSL
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    TANSL Senior Member

    After three minutes thinking on the subject, I really do not know if someone, on some wooden boat, will ever put anodes to protect the fasteners. Looks like hunting flies with cannon, maybe not worth it.
    In areas close to the seacocks and another hole in the hull, with metallic elements, sacrificial anodes are placed. Once placed, they also protect fasteners. I can think of no other explanation.
     
  14. gonzo
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    gonzo Senior Member

    The main problem in wooden boats is the interaction between lead or cast iron ballast and bronze or galvanized fasteners. Zincs are placed in the areas where the dissimilar metals are close. For example, through hull fittings, keel/hull joint and propeller shaft. All those metal parts can be connected together.
     

  15. TANSL
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    TANSL Senior Member

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