Disappearing Zinc

  • September 11, 2012 7:40 PM
    Message # 1070125
    Deleted user

    OK Boys and Girls, put your tinfoil hats on and think!

    I got the best WestSail slip on the East Coast, well, kind of...... It’s 60ft long by 20 ft wide with 5 pilings down each side, The but end of the slip attaches to a 40' x 60'  deck with God knows how many pilings holding it to the bottom of Mattox Creek ,VA.

    I have 8 ft of water at normal low tides! Google Map it and you can see me in my slip! 

    The pier is 280+ feet out from shore and there is no AC power or H2O on the pier. So it’s a slip and nothing more. That’s why I say, “Best slip.... kind of.”

    I have two neighbors that haven’t moved their boats in three years! A Catalina 25 and a 28ft stink pot of some sort. The power boat is parallel to me in an equally impressive slip and the Catalina is inside the dance floor size deck 40ft away.

    Yes, 300 ft of dock, 8 ft MLW and only 3 boats! There’s a story behind this but it isn’t the purpose of this posting.

    Ever since my neighbors showed up to roust (rot, sink  -you get the idea...) my zinc on the prop shaft has been doing extra-extra duty. I go through them faster than I can put them on. In just a month, a brand new 4x1-inch collar on the shaft is pitted as if it was in the water for the better part of a year. 

    I’m guessing that my neighbor’s zincs are long gone and my poor little collar is absorbing all the stray electrons.

    Or could it be that one of my neighbor has his +'s and -’s miss wired?

    What to do?

    How about? 

    -If ask my power boat neighbor (God knows - he owes me for all the extra dock lines I’ve added to his mooring (his strategy is based on shoe laces, leftover yarn, and discarded clothes lines!) if I can attach a hefty wire from his engine block(s) to a junkyard hunk of zinc that I hang over his transom? His engine hatches are disintegrating to the weather, so a big wire snaking over the side wouldn’t detract from the lines of his hull.

    Crazy idea? I’m thinking about a length of # 4 cable and 5-10 lbs of zinc from the local scrap yard, wrapped tight and screwed tight to the cable/zinc, slung over his transom -  might help my poor little doughnut of electrolysis abatement.

    Any thoughts? 

    Or, can I just hang a hunk of zinc in the water off the dock,? Does it need to be grounded to something?  

    If so, suppose I get a 20-ft length of 3/4 pipe and drive it deep into Mattox Creek’s mud  and just attach a bunch of zinc what-evers on it? Grounding through the mud of Maddox Creek. Will that work?

    Any suggestions?

    Or do I need a #4 wire off my engine, hung over the side to a hunk of zinc? Maybe something like a battery jumper cable connection to disconnect when I go sailing? I don’t tie up fpr years at a time!

    And, “No” I can’t sink the stinkpot or Catalina, or disconnect their batteries.!  That wouldn’t be nice.

    Ed aboard Caprica #687

  • September 12, 2012 6:05 AM
    Reply # 1070538 on 1070125
    Anonymous member (Administrator)
    First fast answer / question - Can you move your boat and see what happens in the different location ?  - hard to fix the other boats.                
    Last modified: September 12, 2012 6:05 AM | Anonymous member (Administrator)
  • September 12, 2012 6:59 AM
    Reply # 1070579 on 1070125
    Don't delay.  If another boat has wiring problems, it can cause damage in a short time. 

    To prove it, you need a galvanic meter witha probe in the water.  Galvanic voltage will increase as you move it closer to the source.  One you identify the boat, enlist the help of the marina owner.  Unplugging the offender boat should make the galvanic voltage vanish instantly,thus providing conclusive evidence. 

    My own experience away from marinas is that zincs last as long as 18 months and as little as. 1 month.  No rational explanation why.  Not even location. 
  • September 13, 2012 6:46 AM
    Reply # 1071400 on 1070125
    First, adding zincs, ground rods, etc. is not solving your electrolysis problem.  That is just treating the symptoms and not the problem.  You really should identify the source of problem and fix that. 

    You haven't described the shore power setup. I presume you and/or your neighbors are using 110 AC?  Are any 110v wires hanging in the water? Are you and/or your neighbors using
    all 3 wires (black/white/green) wiring/cords for shore power?  How is the pier wired? Are the shore power outlets wired correctly (i.e. hot/gnd/neutral).  You can buy a 3 prong plug-in A/C wiring checker from RadioShack for less than $10 that tells you (via colored LED's) whether the power is wired correctly. It's a must have piece of equipment on my boat. When I move to different marinas the 1st thing I do after plugging into shore power is to plug my little checker in to see if the shore power is wired correctly.

    Electrolysis is caused by low voltage DC currents coming on board your boat on the shore power ground wire. Boats in a marina plugged into shore power all act as a giant battery.  They are all connected together by the green shore power ground wire, which is (or should be) connected to their DC grounds, engine block, and bonded underwater metals.  If the boats are in salt water then that forms an electrolyte and the dissimilar metals connected together act as a battery, causing corrosion.

    (After checking your own grounds) from your description as to the condition of the other boats I would suspect your neighbors likely have corroded terminals/ground bonds.  If you can't convince them their boats are slowly being eaten until/unless they clean up their electrical system the best you might do is just install a galvanic isolator on your boat.  That would be a much easier/cheaper solution than pounding pipe into the mud, buying zincs every month :)

    Here is some good info :  http://www.boatus.com/seaworthy/galvanic/default.asp

    Last modified: September 13, 2012 7:09 AM | Anonymous member
  • September 13, 2012 9:51 AM
    Reply # 1071549 on 1070125
    Deleted user

    I think most missed the fact you said you don't have shore power to the dock.
    but does the dock have lighting? if so, there could be issues hot or neutral leaking into the water.

    Is there an underwater power cable (charted)?

    If not, here are some of the routs for the Issue with DC current
    1.) wet salty dock lines have some potential (Steel line will make this much worse) this is in conjunction with the lighting or misswired boat, or shore power or other such bad things.
    2.) Is one of your seacocks or other zinks disconnected (or just connected)?

    Some solutions
    Hang a big zink fish connected to your (engine block)  protecting yourself.  Doing it on the other guys boat only protects him not you. Remember a circuit needs to be there for the fast corrosion of the zink.

    check your elec system.

    As for stray current (it is out there) but if you are changing the zink every month you have something else I believe.

    In Hawaii at fixed pier I had about 20  to 30 months between shaft zink changes (I am unbonded and have both shaft and a prop end nut zink)

    in CA at the dock, I remember about 12 to 14  (this was on a floating dock with wiring and I was using the shore power) = indirectly connected to others.

    Did have a month of OH no when a sailing Junk with the AC hooked Hot to its motor ground parked beside me and there was corrosion and even a shock from one of the his dock lines.  (He got it fixed right away when I asked him to have his electrical checked out, he got a shock getting aboard with a wet dock line so he did see there was an issue. So yes others can be an issue but if no dock power (= no connecting circuit) then you should not have issues with others +/- but your own system may have a break or a new connection (worn through insulation)??  a standard multi meter will do wonders for tracking it down.

    Hope this helps

    P.s. there is always a potential dc between the prop shaft and the water don't quote me (as I would have to look it up, but I remember 0.9+ volts) but at 0.0001 milliamp this is the potential between metals (should be the zink and the ss.  see http://en.wikipedia.org/wiki/Galvanic_corrosion
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