Revelations about zinc electrodes.

Discussion in 'Boat Design' started by CDK, Jan 7, 2011.

  1. CDK
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    CDK retired engineer

    That is a problem I wasn't aware of.

    My experiment revealed that in the vicinity of an active electrode, there is aggressive oxidation of steel not connected to the protected object.
    I can imagine that ionized seawater is split into Na and Cl ions. The freed Na is immediately linked to oxygen, also a product of the electrolysis, but the chlorine ions may be responsible for the breakdown of wood.

    Please note that electrolysis only takes place if the zinc electrode's current has a short electrical path to metal parts it is connected to. That may be a shaft or rudder if the electrode is mounted on the wood nearby, but the most logical path is to the steel strap or fasteners.

    What could be the idea behind zinc electrodes on a wooden hull?
     
  2. mark775

    mark775 Guest

    Jeez, Michael - You're just picking a fight!
    We fishermen not so stupid, eh Ollie? We always call da thing a zinc.
    "Anode" comes from Greek "ana", which means "up" and "cathode", "kata", which means "down". (actually, way up and way down) but what about in the case of a battery being discharged, the positive terminal is the cathode, while for the same battery being recharged, the positive terminal is the anode. Since defined in terms of function, rather than structure (In my book) look at the problem in terms of current flow. If confused, remember what CDK said about a CRT. Current only flows in one direction there and IMO we can use that as a baseline, if needed.
    If we can come to terms with whether current is flowing to a zinc or from it, the question is answered. Does it matter? I vote for the use of the word "zinc" to avoid the problem.
    As far as the copper bushings, let's just say CDK didn't say "US style", but they are quite common that way here.
    Gonzo, That thread on Wiki pedia, which I'm not even going to look at, is a direct attack, in itself, and you know it. For shitsake, lighten up and listen to CDK and we might learn something. I have lots of experience with zincs (I dare say, it would be hard for someone to have more at my age) and I didn't know about painting the bolts or the backside. I also wouldn't have known the etymology of "ana" and "kata" if it weren't for this thread, but let's move on and learn some more.
     
  3. gonzo
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    gonzo Senior Member

    I am not sure if I read the post right. Are you saying I quoted Wikipedia?
     
  4. mark775

    mark775 Guest

    No, I just saw a thread "wikipedism" or something like that. I assumed it was just a hit on people using Wiki knowledge. If not, I apologize and will go look.
     
  5. CDK
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    CDK retired engineer

    For you education Michael:
    http://www.boatzincs.com/b-6.html

    In fact the not so cleverly designed ones with an iron strap are all labeled "European style" at boatzincs.com.
     
  6. viking north
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    viking north VINLAND

    CDK, this was a discussion on another forum(wooden hulls, bonding, zincs) and i thought it would be a good idea to re introduce it here as the discussion seemed to be more related to zincs and metal hulls but i'm sure that many members here possibly have wooden hulls. The theory is that on wooden boats metal thru hulls should not be internally bonded to the common bond point in the hull when zincs are installed as the electrical activity associated with the resultant circuit breaks down the wood fibers at and in close proximity of the thru hulls. I could expand upon this but as a rule the more input the better. Geo.
     
  7. CDK
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    CDK retired engineer

    No need to expand. It is very clear what happens.
    The zinc is internally bonded to an unpainted thru hull, so there is a closed circuit and the electrode starts generating a current the moment the boat reaches the water. Especially in seawater the current can be quite substantial and the electrolysis products (ions) will attack the organic material around the metal parts.

    My advice is to mount zinc electrodes ON the metal parts that need protection and keep them from becoming active by meticulously painting these surfaces.
     
  8. BertKu
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    BertKu Senior Member

    Thank you Gonzo and CDK, I have learned something. like I said in thread 58 "My conclusion is that one has to be damn carefull what kind of bolts to use when mounting the zinc. " Now I learn, that I have to paint them.

    I am building a wooden boat and I was planning to connect every metal part to the sinc part. Like we were used, to have a central earth point in electronic equipment. I am never too old to learn. carry on folks, I am learning. (But don't be upset if we sometimes put some humor in the conversation)
    Bert
     
  9. MatthewDS
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    MatthewDS Senior Member

    Interesting discussion about the composition of marine anodes. My only comment is that anodes installed on the steel parts of the marine facilities that you folks tie up to have a very different composition.

    A typical marine anode for installation on a pile or wharf is primarily aluminum, with under 10% zinc, and trace amounts of other elements like Iron, Cadmium, Silicon, and Tin.

    I believe that the different composition is designed to result in a longer life, typically measured in decades, at the expense of the complete protection that a pure zinc anode would provide.
     
  10. rwatson
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    rwatson Senior Member

    Apologies Bert, just for you and any other academics in this thread, I incorrectly read "Zinc Oxide" as the deposit on the cathode.

    Blame it on my eyes and using bitmapped screen shots, but the deposit is
    Zinc hydroxide Zn(OH)2

    Thought I should correct my error in the interests of future generations :)
     
  11. viking north
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    viking north VINLAND

    Bertku, to prevent breakdown of the wood fibers at or near a wooden hulls metal thruhulls the trend amoung wooden boat owners is #1 paint the outside surface of the thruhull. #2 Do not bond the thruhull at all to the inside common bonding point. I.E. I'm not sure if you decipered that info from the comments above. I mentioned back in post #25 and again in post # 82 with the hope there would be more discussion on it as some wooden boat owners have a different take. But from all the info i have researched on the subject to bond or not to bond metal thruhulls on wooden hulls the overwelming trend seems to be not to bond. It is not a problem for me as i have a GRP hull just because of my age, finances, don't want the high maintenance but thought it was an important point for wooden boat owners and seems it does apply to your project. Geo.
     
  12. Wynand N
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    Wynand N Retired Steelboatbuilder

    Very nicely put Mark.
    In electroplating as I mentioned in my earlier post, we manipulate the the positive and negative charges to the cathode and anode depending of task in hand. Getting the anode to shed some ions to the cathode (workpiece) it is usually positively charged.
    However, if we want to shed from ions from the cathode - such as electro-cleaning of workpiece - the cathode gets positively charged...

    In the end in my primitive view is also "does it matter?" since the results are the same. IOW, sacrificial anode (zinc) will protect the boat's more noble materials and with no sacrificial anode, something immersed on the boat will turn to an anode instead sacrificing itself to protect the next hierarchy up the galvanic scale.
     
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  13. BertKu
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    BertKu Senior Member

    Thank you Viking for the info. I misunderstood the word "bonding" as gluing, while now I understand it is electical connecting, Got the picture. Thus I should not connect the two keels to each other. But I will be running my DC motors in the keels and thus I will have to electrical isolate them from the metal keels. I better start doing some more research, as we have lightning cabling, DC motor cabling and galvanic prevention. In anyway, thanks for the hint.
    Bert
     
    Last edited: Jan 11, 2011
  14. BertKu
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    BertKu Senior Member

    CDK, you are probably the most knowledgeable on this subject. What would you do, if you were in my shoes.

    I haven't made my mind up to build the keels from Stainless steel 316 or from mild steel and then powder coating them.
    The experimental box I have made from mild steel.

    Here is my question:

    Would you electrical connect the whole lot, included the lightning down cable from the mast and both keels and make the minus of the batteries to the central earth point. Put on the powder coated keels the zincs, each keel a zinc. Put a zinc on the 30 mm shaft and a small zinc on the rudder.

    OR

    Would you have the DC motors and batteries and electronics floating.
    Don't connect the keels to each other and have the lightning cable electrical connected to the metal keels only. We have to bear in mind that a lightning strike will have short burst, up to 40 of them per strike and up to 40.000 Ampere in each short pulse, flowing down wards and will form an electrical field. If I don't earth my electronics to the same central point I will blow the electronics , because of the energy induced by this field.

    OR

    Re-route the lightning surge via the mast wires and this will form a Faraday cage. Make the connection for the lightning outside the hull, to the seawater. Have the electronics and batteries floating or earth the electronics via the keels. Have the minimum zinc mounted, this in view that I will be having the boat only for a few hours per week-end into the sea.

    The problem is that those three subjects are interrelated to a certain extend. Zinc and stray currents, DC motors and lightning
    Bert
     

  15. BertKu
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    BertKu Senior Member

    That cost you a beer, but apology accepted, we were not even aware of the mishap. But you are right, for those people doing the future search, it is better to have it corrected.
    Bert.
     
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