Click for Cheoy Lee Click for United Click for Lurssen Click for Docktail Click for Burger

Galvanic corrosion

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

You need to be registered and signed in to view this content.
  1. learjett2

    learjett2 New Member

    Joined:
    Dec 15, 2017
    Messages:
    5
    Location:
    San Francisco ca
    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

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    9,932
    Location:
    Fort Lauderdale
    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

    learjett2 New Member

    Joined:
    Dec 15, 2017
    Messages:
    5
    Location:
    San Francisco ca
    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

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    9,932
    Location:
    Fort Lauderdale
    No it does not. It's relatively easy to install a galvanic isolator and they're about $400 and do help.
  5. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    5,291
    Location:
    Jax FL
    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

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    9,932
    Location:
    Fort Lauderdale
    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

    JWY Senior Member

    Joined:
    Feb 22, 2004
    Messages:
    1,010
    Location:
    Ft. Lauderdale
    +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

    baltimore bob Member

    Joined:
    Sep 22, 2013
    Messages:
    304
    Location:
    Baltimore, Maryland
    Galvanic isolator absolutely!
  9. Fishtigua

    Fishtigua Senior Member

    Joined:
    Jul 20, 2007
    Messages:
    2,335
    Location:
    Guernsey/Antigua
    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

    learjett2 New Member

    Joined:
    Dec 15, 2017
    Messages:
    5
    Location:
    San Francisco ca
    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

    Bill106 Senior Member

    Joined:
    Jan 9, 2010
    Messages:
    368
    Location:
    Beaufort NC
    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.

Share This Page