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Galvanic corrosion

Discussion in 'Technical Discussion' started by learjett2, Dec 21, 2017.

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  1. learjett2, Dec 21, 2017
    #1
    learjett2

    learjett2 New Member

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    Pros/cons on cathodic protection on 42' motor vessels? Presently costing me approximately $750. per year,between zincs and diver. Considering monitoring or possible impressed current system.
    42'Ocean Alex 1988 sedan berthed in a basin with brackish water surrounded by steel bulkhead that has not been maintained .
    Any inputs appreciated!
  2. Capt J, Dec 21, 2017
    #2
    Capt J

    Capt J Senior Member

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    How many times per year are you changing your zincs?

    A galvanic isolator helps considerably with zinc life a lot of times. I have a 62' Sunseeker in a marina with boats on both sides with a 3' wide finger pier and the zincs last a year or longer even. The owner also runs 400 NM a month or more at 28 knots in saltwater, boat sits in saltwater.

    I would say 4-6 months is standard life for zincs.

    Also, how old is your shorepower cable and does ANY of it sit in the water?
  3. learjett2, Dec 21, 2017
    #3
    learjett2

    learjett2 New Member

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    I'm at the low end,4 months, definitely nothing in the water and good electric cable. I have a Xantrec inverter/charger not sure if it has an isolator?
    Thanks for the input.
  4. Capt J, Dec 21, 2017
    #4
    Capt J

    Capt J Senior Member

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    No it does not. It's relatively easy to install a galvanic isolator and they're about $400 and do help.
  5. Capt Ralph, Dec 21, 2017
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    On the other hand, 2 maybe 3 sets of zincs and I'm assuming normal dive service (regular bottom cleaning).
    $750 / year is pretty good.
  6. Capt J, Dec 21, 2017
    #6
    Capt J

    Capt J Senior Member

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    Are you SURE the zincs are wearing down that fast? There was a diver here that got on drugs and was charging all of his customers for zincs and they weren't even changed nor needed to be changed....he just billed them for invisible zincs. Also, if you're using Camp zincs that's part of the problem......use Reliance or another brand of zincs......Camps are cheap ingredients.
  7. JWY, Dec 22, 2017
    #7
    JWY

    JWY Senior Member

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    +1 on the galvanic isolator. How often are you having the diver check the zincs? Zinc replacement every 4 months seems excessive. Have you checked the water for stray current? Have you considered aluminum alloy anodes? Do you have sufficient zinc coverage (props, shaft, thrusters, tabs, engines, heat exchangers, etc.)? Have your diver take a picture of the zincs to show the wastage before replacement, that way comparative photos may reveal whether there is a problem or not.

    Judy
  8. baltimore bob, Dec 22, 2017
    #8
    baltimore bob

    baltimore bob Member

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    Galvanic isolator absolutely!
  9. Fishtigua, Dec 23, 2017
    #9
    Fishtigua

    Fishtigua Senior Member

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    My zincs were going haywire and I found it was the bloody phone landline that was iffy and leaching over the boat. Got an isolator shortly afterwards.
  10. learjett2, Dec 23, 2017
    #10
    learjett2

    learjett2 New Member

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    The reason I posted originally was because the port shaft zinc's were half gone while the starboard looked almost new, after 4 months.A little bilge crawling revealed the port grounding strap was gone,water cooled shaft log had a tab welded right on top so easily broken, repaired so we'll see if it makes a difference. Definitely thinking Galv isolator and shaft wiper's to insure good connection.
    Thanks to everyone for input.DCL
  11. Bill106, Dec 25, 2017
    #11
    Bill106

    Bill106 Senior Member

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    Yep, the standard phone/cable TV shore inlets do pass through a ground from the shore side effectively bypassing galvanic isolators and isolation transformers. To make matters worse, disconnecting the small grounds usually trashes the signals so a lot of folks leave them connected. A small 1:1 isolation transformer takes care of the issue.