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Thread: Is this over zinced?

  1. #1
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    Default Is this over zinced?

    The zinc is attached to the base of the prop which is 2.5". The zinc is for a 2.5" shaft and prop of expected size. My prop is 13".
    After 1 week in salt water there was a fine whitish scale on most of the prop. I easily removed it with acid.
    I was thinking about painting half the zinc to halve it's size.

    too much zine for bronze prop?.jpg
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  2. #2
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    Default Re: Is this over zinced?

    This is ringing a bell.
    A few months (?) ago, a thread appeared ...someone had one of these pod /electric drive gizmos...the zinc had gone crazy overnight or something.
    The culprit was maybe a freshwater anode , "zinc" , used in saltwater or a short in the ground?
    This does not look too nutty.
    A pic of the white scale may have been helpful.
    Too Much anode , on a wood boat, is usually expressed as damage to the wood!!!,,,which is where the danger is.
    Run your fingers )carefully) dalong the edges of the wheel (prop) for any roughness appearing. look for discolorization of the bronze.It looks good from here anyway.
    If I were an electric nerd, I'd say puy some tester thingy on it...but I dunno what all that means frankly.
    Maybe a laniolin spray fer nex time ?
    bruce

  3. #3
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    Default Re: Is this over zinced?

    Aren’t fresh water ‘zincs’ magnesium, which is farther out on the galvanic scale?

  4. #4
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    Default Re: Is this over zinced?

    Quote Originally Posted by JimConlin View Post
    Aren’t fresh water ‘zincs’ magnesium, which is farther out on the galvanic scale?
    deja voodoo

  5. #5
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    Default Re: Is this over zinced?

    The zinc in that photo looks like it's been in the water a lot longer than one week. I'd say that something is definitely amiss, but I don't have a lot of experience with a bronze prop on stainless shaft in aluminum drive housing situations.
    "Visionary" is he who in every egg sees a carbonara.

  6. #6
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    Default Re: Is this over zinced?


  7. #7
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    Default Re: Is this over zinced?

    Yes, my first issue was the motor was shipped with a magnesium anode which fizzed away after 3 days in salt water. Before this I was unaware of different anode materials. Now I've put a regular zinc anode on but there's more activity going on than I'd expect (pits in the zinc anode) and the light colored, thin scale on the prop after 7 days in salt water. I know about over zincing a wooden boat but wonder if over zincing can create enough electricity to do the scaling and pitting. The boat was at a crowded marina with lots of live aboards.
    The edges of the blades are smooth.
    I might paint half the zinc for the next week in the water. If there's any scale I'll photo it. Thanks!
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    When we remember we are all mad, the mysteries disappear and life stands explained.

    Mark Twain

  8. #8
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    Default Re: Is this over zinced?

    I don't think "painting" the anode is a good move. Next you may have the aluminum flaking away.
    My bet is a leak from the marina.
    Can you disconnect your own batteries easily enough?
    Hang a six pak of aluminum empties overboard?
    electric boats....bullwinkle ...that trick never works
    bruce

  9. #9
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    Default Re: Is this over zinced?

    Something doesn't make sense. Is that an aluminum drive? Aluminum is less noble than bronze or zinc and there is no way to isolate it 100% with an exterior coating. The magnesium you took off that got wasted quickly says to me a really hot marina or possible bonding/grounding issue and the aluminum is now sacrificial.

  10. #10
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    Default Re: Is this over zinced?

    I'd bet theres lotsa stray current in the marina and its eating up the zinc.

  11. #11
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    Default Re: Is this over zinced?

    I hope it's stray current.
    The boat is a plywood sharpie sheathed with Dynel and epoxy.
    The only electrical device onboard is the A.C. motor which is power is disconnected by relay when not in use.
    The shore power cord is connected to the battery charger which was only plugged in once for a few hours during the week's stay.
    The aluminum motor case came with a (powder?) coating and I've painted it with Aluminum hull boat anti fouling.
    The motor case has it's own smaller zinc bonded to the mounting bolts.
    Thanks for the opinions.
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    When we remember we are all mad, the mysteries disappear and life stands explained.

    Mark Twain

  12. #12
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    Default Re: Is this over zinced?

    The relay shuts off both the pos and neg?
    One may think the neg battery post is moot, it may not be , insofar as electrons running the wrong way .
    Dis connect the battery entirely, pos and neg., don't just turn a switch.

  13. #13
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    Default Re: Is this over zinced?

    Something is making electricity there...
    Get a voltmeter and start checking things. It's pretty easy to find if there is stray current, connect the meter between the shaft and the water.

    It is pretty common, and your own boat could even be the culprit.

  14. #14
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    Default Re: Is this over zinced?

    hmmm, I don't know if the switch breaks both + and - poles. Easy enough to find out.
    I've tried a volt meter measuring in between the zinc and a copper pipe dangled in the water, Just showed small varying readings.
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    When we remember we are all mad, the mysteries disappear and life stands explained.

    Mark Twain

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