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think I found my electronic gremlin

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  • think I found my electronic gremlin

    I began noticing strange signs of metal corroding/dissolving on my boats transom area a few years ago. First was a 10lb A-B-C extinguisher which was mounted to one side of the rear inspection hatch that has the 2 holes for lifting it out. The alum body of this extinguisher just below the handle, began to dissolve to the point that it resembled the fur on a scared cat. I had never seen anything like this nor had a local company who had decades of experience selling and servicing fire extinguishers. Bought a new one, added a couple layers of red paint and re-installed. Not long after I noticed some new pitting to the tailing edges of my Bennett trim tabs. Drew a blank after hiring an electrician to test my marina. I did not run the engine during the testing. Perhaps he could have picked up the current at the back of my boat if he had. That was a few yrs ago. Boat has been stored and not used.

    I ran the engine at home 2 weeks ago and found one of my fuel valves seized and broken. In taking off the steel bracket which is attached to the transom with 2 s/s screws, and holds the plate to which the 2 fuel valves are attached to, I realized the steel plate was rusting badly and showed some similarities to the aluminium fire extinguisher. I had painted it with grey Tremclad enamel years before. Then a black ground wire dropped from one of the screws holding the mounting plate. So I must have installed it this way, Lord knows what I was thinking. I might have been planning on running a wire to the engine where the grounds should be. Can,t remember at this point. There was no way for the current to go but into the transom, which would explain why the trim tabs were pitting 2 feet away. The extinguisher is not connected to the transom, other than touching it by leaning up against it. The raw alum. was probably the least noble metal available and the current jumped from the transom? Hopefully this saga will help someone down the road. In circumspect, I probably should have installed a negative bus bar at the transom. Between downriggers, nav. lights, trim tabs etc, would have made sense.

    Last edited by Tony; 09-29-2022, 04:14 PM.
    Enjoy,
    Tony

    1981 20 ft cuddy
    4.3L Chev V-6

  • #2
    Glad you found an issue. My first thought is, "What are your zincs looking like?" I run T-20's on my tabs. If you had that much gong on it is likely your zincs are severely degraded/spent.
    C Rhodes
    26' Mackinaw - 1990
    351 Indmar (1990-2006: Great Engine)
    351 PCM (2006 - Current)
    Southport, NC

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    • #3
      I actually keep my old zincs for comparison over the past years. I saw some recent pitting on the tabs themselves, but not so with the zincs. I use one set of 3" pancake zins on tabs, 2 X shaft zincs, and one 4 or 5" pancake on the rudder. Frankly they all look reusable, but I don't. Also my season is 6 months at the dock in brackish salt water, and 6 months on my trailer at home.
      Enjoy,
      Tony

      1981 20 ft cuddy
      4.3L Chev V-6

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