Single pole and 2 pole conflict

Discussion in 'OnBoard Electronics & Controls' started by watchkeeper, Nov 8, 2010.

  1. Bglad
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    Bglad Senior Member

    "With aluminim you don't want to see readings at or above 1050 mV because the aluminum may suffer alkali corrosion from too much zinc ionic current. In addition, your anti-fouling paint will begin to suffer as well."

    I am interested to know if anyone has actually had this problem with zinc. An expert I know says overprotecting aluminum with zinc is not possible since zinc's volatge potential is only between -980 and -1030. It should not be able to overprotect aluminum.
     
  2. michael pierzga
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    michael pierzga Senior Member

    I dont know...Im not an electrical engineer. Classic Signs of OVERPROTECTION are deterioration of the paint system. The electric field generated is too powerful. Many times even on a correctly protected yacht you will see this paint system damage around the anode. The paint system on a metal boat...or any boat is expensive, difficult to renew and provides critcal protection to the substrate. I think the key element in the Anode discussion is to be aware. Just like the electrical system isolation. Be aware.
    The anode field is scientific. When a production yacht is built ,the builder consults a professional and establishes the correct anode density for " Perceived" use and location. Many things could change over the life of the yacht. It could for instance be in a highly charged marina environment or fresh instead of salt water, add additional metal mass below the waterline...a bowthruster for instance . My life is boats, Ive never lived in a house. I find it very difficult to receive pro...scientific advise..when on the road or servicing in unknown shipyards.
     
  3. CDK
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    CDK retired engineer

    Are you sure about the currency or did you mean peseta's?:D

    Last month I bought a piece of zinc, almost 18 kg. Paid 20 euros which is twice the market price, but the guy had to cut it from a large sheet.

    I cut it to the proper size with a plasma cutter, drill holes and have anodes for the rest of my boat's life.
     
  4. michael pierzga
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    michael pierzga Senior Member

    Ahhh..pesatas..remember back in the old days ...800 pesetas for a nights dockage !! Its now 6 and a half euros per square meter per night !! Remember the Duro...5 pesatas...5 duros 25 pesatas...the nickname duro ,for 5 peastas, was because that was the salary for a hard days work. Duro means Hard....cinco duro's, 25 pesatas... was a weeks hard work.

    Be careful with homemade anodes CDK...your could be playing with fire. Assuming your anode stock is the correct alloy, drilling a hole thru the alloy as a mounting grounding point, is virtually usless. Your anodes will indeed last forever !!!!!!!!!!!!!! A Marine anode consists of a metal bar...steel..placed in a mold with Zinc alloy anode material poured around this steel bar or plate. This steel insert now has perfect large surface area, electrical conductivity with the Anode material. Next, with a steel fastening and steel star washer, not stainless steel, your attach this anode to the boat via the steel mounting insert. . You now have a perfect, hull to anode, electrical connection.
    If you bore a hole thru pure anode alloy stock, drive a fastening thru and mount, you have a very low surface contact, poor electrical..metal to metal connection. As soon as the anode begins to do its job this "Fastening to anode" connection with be attacked and eroded..the anode will erode away from the fastening..the anode will become loose and completely lose its electrical connection to the hull. It may indeed last a long time or it make simply fall off the bottom .
    You may be able to retrieve this fallen anode from the bottom of the harbour, harvest the mussles from it skin, cook in white wine and garlic,...serve with fresh bread and reuse the anode.

    And Its true...anodes. MGduff...are expensive. 8x 225mm flush pie plates, 2.5 meters of bar stock anode, propeller anode and two rudder anodes...plus a few little guys inside...I dont like to renew then until its the correct time. Surprising how many yachts simply throw out.
     
  5. gonzo
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    gonzo Senior Member

    Anodes can be of different metals. Zinc is one of them. In fresh water magnesium is often used, also aluminum. Painting aluminum like Adhoc says is not bad, however there can't be any break in the coating. Our experience shows that it is safer to spread corrosion over a large surface rather than concentrating it in a very small area. I don't design metal boats, but maintain and survey them.
     
  6. aranda1984
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    aranda1984 aranda1984

    On electrical isolation and stray current

    Corrosion Monitors and Bonding.

    Larger metal boats, especially those with extensive electrical systems, should have a corrosion monitor installed. Corrosion monitors allow you to keep tabs on AlumaNaught’s hull potential, enabling you to be sure that its zincs are working properly, know when they need replacement and identify overprotection and stray-current corrosion.
    On still larger craft, the isolated fittings (eg. bronze seacocks) should be connected to their own completely separate and isolated secondary internal bonding system.
    The bonding conductors on these secondary system must be insulated.
    Even the Zink anodes for this separate system must be completely isolated from the metal hull.
    Dual- metal corrosion monitors are available to monitor the hull anodes and to monitor the secondary-bonding system. A reliable monitor, such as that made by Electrocatalytic of Union, New Jersey, is important.

    Stray current corrosion.

    Stray current corrosion is the most dangerous form of corrosion to which any metal boat can be subjected. The voltages generated by dissimilar metals alone in salt water are measured in millivolts. Stray currents from faulty wiring (on board or shore power) can reach more then 100 volts. Not only do these high voltages pose a serious electrocution hazard (particularly AC current) but they also can eat away large portions of metal hulls in just weeks, sometimes days (even at just a few volts, as compared to millivolts for galvanic corrosion). It is vital that the electrical system on all metal boats complies precisely with American Boat and Yacht Council Standards.
    There is just no point in building a strong beautiful hull only to have it eaten away by stray electrical currents.

    Vital Isolation Transformer.All metal boats (except small runabouts, canoes and skiffs) should be fitted with isolation transformer at their shore-power inlet. If properly wired and installed, the isolating transformer nearly guarantees that faulty shore-side wiring cannot somehow short to the hull.
    Failure to install an isolation transformer is asking for serious trouble the first time your AlumaNaught or Iron Maiden spends a few days at an incorrectly wired dock (and there are plenty of those around)
    Simple galvanic isolators help in this regard and may be adequate for metal runabouts with shore-side connections to a battery charger, but they are not sufficient insurance for larger metal boats. At this writing, the only marine UL-approved isolation transformer being manufactured comes from Charles Marine Products (Rolling Meadows, IL).

    Isolate Electric Wiring From Hull. Great care must be taken with the DC system as well to ensure that it’s entirely isolated.
    All wiring, both positive and the return negative wires must be fully isolated from the hull.
    The sole exception is that the DC negative bus must be bonded to the hull.
    This is best accomplished as follows:
    For aluminum hulls, weld a 3/8” x 4” (10 x 100 mm) aluminum lug to a convenient frame or hull stringer. Bolt ¼” x 4” stainless flat bar to this lug, with two ¼” stainless bolts with lock washers. Attach a 00 cable, from the negative bus, to the stainless bar at least 3” clear from the aluminum, with a stainless bolt, with lock washer. Paint all bolts, the stainless bar, adjacent aluminum, and the terminal fitting of the 00 cable with three coats of marine warmish to seal out moisture.
    For steel hull, weld the ¼” stainless flat bar directly to the hull framing.
    At first glance, isolation of the DC system seems relatively easy to accomplish, but there are many potential pitfalls and hidden paths to short the negative return to the hull structure.
    One of the most commonly overlooked paths is the engine block.
    Most automotive alternators (commonly found on marine engines) use the engine block as the negative ground. This can short the negative to the hull through the engine-mount bolts.
    Be certain to install isolated-negative return marine alternators for engines and generators in metal boats. Then go to the next step and float the engine on rubber mounts, with a flexible rubber coupling to the shaft. This further isolates the engine from potential shorts to the hull.
    Another item often overlooked is engine instruments. Many of the standard senders (transducers) also use the engine block for negative return. Again, be sure to use only senders that have isolated negative returns.
    Still another potential path for shorts is hose with embedded wire reinforcements. Should the wires wear through and make contact at both ends, again you have a potential electrical path to the hull.

    AC Bonded to DC Bus. Like the DC electric system, the AC system must be completely isolated from the hull and from the DC system itself. Once again there is one and only one mandatory exception: the AC system green wire ground, from the isolation transformer (or the galvanic isolator on small boats) must be bonded to DC negative bus. AC wiring must not make electrical contact with any other portion of the hull or DC wiring.


    The above data was taken from the book : The Elements of Boat Strength for Builders, Designers and Owners, by Dave Gerr. …
     
  7. CDK
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    CDK retired engineer

    Check your book! Is this the correct wording or did you improvise?

    No professional will EVER express a current in volts.
     
  8. gonzo
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    gonzo Senior Member

    If we are talking about voltage it will be whatever the supply is. Probably 440V maximum.
     
  9. CDK
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    CDK retired engineer

    Pls read the 1th sentence of my post #38.
    As you pointed out in post #62, you're no electrical engineer.

    BTW The proper word is "electrode", not anode. The zinc/magnesium/aluminum is a cathode, the boat's metal parts form the anode.
     
  10. apex1

    apex1 Guest

    Always impressive to read, how much they can charge you. The rest of the sailing world pays substantially less than you.

    To the rest of your copy and paste "advice", I am sure that the experts like CDK can learn a lot from that.............being only a few decades in business:p

    Regards
    Richard
     
  11. michael pierzga
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    michael pierzga Senior Member

  12. aranda1984
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    aranda1984 aranda1984

    Hi CDK.

    You wrote: "Check your book! Is this the correct wording or did you improvise? No professional will EVER express a current in volts."

    ...This is the exact wording in his book. I never questioned it since the way I read it, he is talking about stray current and in that context, the voltage can reach 100V, across the hull's resistance and that way it will create the so called stray current.

    I bought his statement of 1oo V, because at this voltage if you have DC you see bubles on the plates as the hydrogen and oxygen is being separated from the water and if it is AC, you are already boiling the water if sufficient current is available.

    We are talking about drastic failures here.

    I don't argue with the less then perfect wording, because he is on the ball with everything else, which is important to prevent the loss of the base metal in your boat.

    He is a Naval Architect, not an Electrical Engineer. I didn't even question his statement. I understud what he meant.
    I guess it is like speed reading or reading a word with scrambled letters.

    By the way IMHO the book is an incredible source of material for those who are interested in this sort of things.

    I have also learned something from him.

    I used to run a couple of long bus bars in many of my DC applications.
    (The largest was a full sized hybrid locomotive, 600VDC at 1000A.)

    The bus bars were insulated by a 1/16" insulator and clamped together. Various size capacitors were installed across to prevent any problems.(especially in PWM applications.)
    The negative bus bar was grounded to the chassy or hull or frame at one point, depending on what I was working on.

    Yes, I was using automotive gear... single wire!

    Regards,

    Stephen I. M.
     
  13. CDK
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    CDK retired engineer

    Nothing cryptic. Keep the junction dry and no galvanic action will take place.
    A thin smear of liquid neoprene or Sikaflex around the contact area is all you need to maintain contact during the electrode life.

    The remark about nomenclature was just a remark: everybody calls them anodes. But that doesn't make it right.
     
  14. CDK
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    CDK retired engineer

    Stephen, I am not familiar with the book or the author, so I will not comment on it. But whenever I note such blatant nonsense, I get a bit cautious about the rest of the text.
     

  15. michael pierzga
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    michael pierzga Senior Member

    CDK...a forum is intended to be a gathering point for a wide ranging group of interested people to share experience an observations. Cryptic, Pedantic ..ANODE CATHODE nonsense simply fogs the issue...volts amps ? You have just created uncertainty for any reader who has been recommended David Gerrs fantastic reference book.
    You may decide to go your own way on yachts, you may chop up zinc to install on your yacht..I can only observe that you are playing with fire. To advocate to a reader that its possible to create a waterproof underwater joint that achieves electrical bond and allows the anode to stand free of the substrate is irresponsible . If you are advocating a zinc to substrate bond, then you should review all available literature so that you may discover that this is BAD PARCTICE.
     
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