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Question for Nay

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  • Question for Nay

    Boat went in this week, still no clear answers to why my trim tab planes are recently pitting. My electrician came by yesterday and took some meter readings which showed I am marginally over zinc'd on my underwater metals. He did find my new Grocco raw water intake strainer was not grounded so the numbers were unhealthy for bronze. He added a ground to the block which corrected that. I am the 4th owner. My question is were the early (1981) boats bonded by the factory? Were shaft brushes ever installed?
    Thanks Nay.
    Enjoy,
    Tony

    1981 20 ft cuddy
    4.3L Chev V-6

  • #2
    Tony, I read your PM on this and below is a copy of the response

    "It seems you have been having this problem since the repower, is that right? To start, we used several different bonding strategies over the years and different models but they all basically used the engine block as the starting point. The very earliest hulls used a grounding bolt on the engine for all the grounds with the various fittings (strainer, thru-hulls, fuel fills, tanks, rudder ports and tillers, filters, etc) daisy chained together back to the bolt. Then we started using a dedicated bonding bus bar that was connected to the bolt and mounted on the side of the main stringer. The individual grounding wires were then connected to the terminal on the bus bar. I imagine over the years there were many manufacturer and owner mods done to the system but in general should still be be basically the same. For the life of me I cannot remember how we bonded the trim tabs, I'm thinking we didn't but used zincs mounted directly to them in addition to the shaft and rudder zincs.
    It may be quite possible that sometime during the repower one, or more, of the grounding lugs or wires became disconnected. Maybe there is a build-up of corrosion between the connectors and the fittings.
    I will pass along something that we discovered somewhat early in the production, the exhaust pipes need to be part of the bonding system also. At first I think they weren't because the thought was there were rubber hoses at each end and the galvanized pipe would be naturally isolated. That is true IF there was no water in the exhaust to make an electrical connection. We noticed that the zincs had to be replaced fairly often. With the boat sitting in the water, the pipes are always full so we started connecting them to the bonding system. I think we used high quality hose clamps and thick wire lugs.
    While a full bonding package couldn't hurt, your boat didn't have the problem before so a methodic check of the connectors, fittings and electrical system should identify the culprit. I'd verify that there is a stray current on your boat using a "standard cell" device to measure the current while the boat is in the water. Then measure the bonding continuity between all the metallic objects in the system. Lastly, I would disconnect the positive lead from the battery and using a multi-meter measure the voltage with the black lead connected to the bonding ground and the red lead connected to the disconnected positive battery cable to see if there is current flowing through the system. (Some people use a 12V light bulb with + and - leads connected. If there is voltage (or the lightbulb lights up) start pulling individual fuses (or disconnect the individual breakers, if used) until the voltage drops or the bulb goes out. Note which fuse or breaker was disabled when the voltage stopped and that should be a good starting point to secure the transient current.
    Let me know what you find out.
    Nay"
    If it doesn't say SHAMROCK, it doesn't say much


    '85 Shamrock 17'
    '68 Bertram 20' Bahia Mar

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    • #3
      Thanks Nay, I'm on it.
      My exhaust is all rubber, with dappars. Could the line be charged with water in a rubber hose?
      Enjoy,
      Tony

      1981 20 ft cuddy
      4.3L Chev V-6

      Comment


      • #4
        Originally posted by Tony View Post
        Thanks Nay, I'm on it.
        My exhaust is all rubber, with dappars. Could the line be charged with water in a rubber hose?
        I don't think so Tony but since your exhaust is all hose, I'm wondering, are the exhaust flanges connected to the bonding system?
        Nay
        If it doesn't say SHAMROCK, it doesn't say much


        '85 Shamrock 17'
        '68 Bertram 20' Bahia Mar

        Comment


        • #5
          The rudder port is the only grounded metal in the stern, which I put on nearly 20 yrs ago. The exhaust outlets are not the same brand. Boat was a diesel with a single outlet, which is likely the bronze one. The second one could even be non-metal, I can't recall and I just scraped and repainted this spring : < ( .... Provided I can get below the caulk, am I OK to daisy chain from the rudder port to the outlets?
          Enjoy,
          Tony

          1981 20 ft cuddy
          4.3L Chev V-6

          Comment


          • #6
            Originally posted by Tony View Post
            The rudder port is the only grounded metal in the stern, which I put on nearly 20 yrs ago. The exhaust outlets are not the same brand. Boat was a diesel with a single outlet, which is likely the bronze one. The second one could even be non-metal, I can't recall and I just scraped and repainted this spring : < ( .... Provided I can get below the caulk, am I OK to daisy chain from the rudder port to the outlets?
            I believe that would be fine to daisy chain them to the rudder port. Check for continuity all along the bonding system back to the ground base (normally the engine block or a dedicated buss). Also, ensure the fuel fill fittings and tanks are connected to the system.
            Corrosion on the trim tabs is still baffling me.
            Nay
            If it doesn't say SHAMROCK, it doesn't say much


            '85 Shamrock 17'
            '68 Bertram 20' Bahia Mar

            Comment

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