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12v grounding Dynaplate and hull zincs?

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  • 12v grounding Dynaplate and hull zincs?

    24' Fiberglass OB powerboat. Dual batteries, one starting, one deep cycle accessories. All electrical and lightning (t-top) grounds connect to a dynaplate mounted to the underside of the boat. First, is that correct 12v grounding?
    Second, my brass thru-hull and brass drain plug have deteriorated from apparent electrolysis. The boat is on a trailer mostly but stays in the water for a few weeks at a time during the summers in the keys. Is the grounding causing this electrolysis and what is the remedy? Would a hull zinc connected to the brass thru hulls solve this. And should they be connected to the dynaplate ground or isolated?

  • #2
    Re: 12v grounding Dynaplate and hull zincs?

    grounding plates are ok, and any vessel that stays in the water needs sacrificial zincs in numerous places,

    the biggest problem with a moored vessel are the boats in your proximity,boats that use battery chargers constantly and have not wired their boat correctly,

    the electrolysis from others is what you need to protect you boat from, and you do that with numerous zincs connected to any metal on your boat that is submerged


    • #3
      Re: 12v grounding Dynaplate and hull zincs?

      My thru hulls were all connected/grounded to the ground plate which ultimately grounds to the OB motor that has zincs that we have replaced periodically. Would I be wise to add hull zincs also? Maybe a zinc grouper to drop in the water when at the dock connected to the grounding system?


      • #4
        Re: 12v grounding Dynaplate and hull zincs?

        Originally posted by nautihabits
        My thru hulls were all connected/grounded to the ground plate which ultimately grounds to the OB motor that has zincs that we have replaced periodically. Would I be wise to add hull zincs also? Maybe a zinc grouper to drop in the water when at the dock connected to the grounding system?
        by all means, if you are having problems, the drop in zincs would help,


        • #5
          Re: 12v grounding Dynaplate and hull zincs?

          [colour=blue]With all due respect, X man, it ain't that simple.

          To clear up an often misunderstood and misquoted term -

          Galvanic corrosion is the reaction that occurs between an anode (i.e. Zinc) and a cathode (i.e. StainlessSteel).
          Electroylsis is reaction that occurs between an anode and a cathode when an external electrical source is applied.
          They are two different processes. Both can occur in the marine world. The damage caused by both is visually similar, the fix is not.

          There is a distinction between bonding & grounding. Bonding is for giving lightning somewhere to go other than your heart and grounding is for electrons to go to the negative post of the battery(s). You need both. DO NOT rely on the bonding system to ground, you must have a clear path to battery negative, not through the outboard and zincs and plates etc.

          If you are getting brass damage in only a few weeks, you have serious issues. I would begin by testing all of your electrical toys and ensure a good ground path. Then I would be doing a bit of investigation on the boats that are moored near you. Does the marina pen have shore power?

          To combat electroy;lis, the surface area (and type) of anode is crucial depending on the surface area and type of cathode. Simply adding anodes can make the problem worse.
          Watch this space......................


          • #6
            Re: 12v grounding Dynaplate and hull zincs?

            OK, so the bonding for lightning (dynaplate) should NOT be connected to the grounding (- battery) system, Is that correct?
            And my brass hull fittings, should they be bonded or grounded to anything or are they protected by the OB motor zincs and should stand alone?
            Right now all bonding and grounding is tied in together. Is that causing me the problems? When boat is in the water it is at dock behind a house. No shore power however neighbors have electrical davits and power at the seawall.
            Thank you for the explanation.


            • #7
              Re: 12v grounding Dynaplate and hull zincs?

              [colour=blue]Grounds and lightning plates should not be connected. Usually, brass does not need anodes - usually.

              I am hesitant to advise you further because this subject can become very complicated and from my side of the computer screen I don't know the full story. You need a local tech to properly advise you.

              Your brass damage concerns me, it points towards an external influence.

              What condition are your anodes in? Be specific. What is your prop made of and what condition is it in?
              Watch this space......................


              • #8
                Re: 12v grounding Dynaplate and hull zincs?

                Believe me I have been all over the internet and am as confused now as ever about the subject, so I know it is complicated.
                I'll give you as concise a picture as I can of my set up. I have a 24 SeaRay Laguna (open fish) with a 250 hp Yamaha w/ stainless prop.
                One starting battery that the main + lead from the motor is connected to and one deep cycle battery that is charged by the yamaha accessory battery charging lead.
                Both batteries connect to a switch (off/1/both/2). Always turn to 1 (starting battery) to start and run the boat (have rellay never had to use "both" to crank but as a safety measure).
                The deep cycle battery has a cable that runs up to the console where it connects to a seperate on/off disconnect switch. The other pole of the disconnect runs to a terminal block that then powers all of the acessories (radios/gps/lights/pumps etc.) through a series of breakers and switches. So, I think that the starting and accessory systems are independant of each other. I am able to run accessories with the starting system shut off and visa versa.
                The grounds are all connected at terminal blocks and to both battery - terminals. They also connect to a dynaplate on the hull at aft and are connected to the brass thru hull fittings via copper leads/wires.
                As for the "lightning" protection. The more I read the less I think I have afforded by my setup but here it is. The boat has an alluminum T-top. Under the console the t-top, steering helm, rails etc are bonded together with a heavy alluminum wire that runs to the previously mentioned exterior dynaplate that the ground also connect to in the aft bilge compartment.
                I don't think I have a current leak coming from within the boat itself but I have no idea about the surrounding waters. The zincs on the OB motor deteriorate somewhat and we replace them when it is indicated. The brass deterioration is a mystery. Is my setup causing this? I have experienced some pitting also on the nosecone of the lower unit that contacts the water when trimmed up. Any input and suggections are very appreciated. Thanks.


                • #9
                  Re: 12v grounding Dynaplate and hull zincs?

                  [colour=blue]Do you have any form of mains (110/120v) system in your boat?

                  How often do the anodes deteriorate - 6 months - yearly - every two years? BTW, when over half of the anode is eaten away is the time for replacement.
                  Watch this space......................


                  • #10
                    Re: 12v grounding Dynaplate and hull zincs?

                    Only 12v dc on the boat. Even remove batteries to charge if needed.
                    The skeg zinc we probably replace yearly when appropriate and the bracket zinc may go two years or more. Boat is only in the water 24 hrs a day for 8 - 10 weeks out of the year and trailered to and fro the remaining months. We keep an pretty watchful eye on the zincs.


                    • #11
                      Re: 12v grounding Dynaplate and hull zincs?

                      I have found this site to be informative on the subject:
                      It advised the following:
                      Bonding and Electrolytic Corrosion Due to Hot Marinas
                      Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine.

                      It's worth understanding the reason. In an increasing number of marinas, there are substantial DC electric currents running through the water. If your bits of immersed metal are bonded, the electric current will take the lower resistance path offered by your boat in preference to the water near your boat, and the current will flow into one of your bits of metal, through your bonding wires, and then out another bit of metal. The anodic bit of metal or thru-hull that has the misfortune to be on the "out current" side of the current running through your bonding system will also become "out metal" and will disappear, sometimes rapidly.

                      Your zinc is only intended to protect against the modest galvanic potentials and therefore currents that are caused by the dissimilar metals that are immersed and electrically connected together on your own boat. Your zinc is incapable of supplying enough galvanic potential to protect against substantial DC currents that may be flowing in the water. These DC currents in the water will cause electrolytic corrosion to your bonded thru-hulls or metal parts.
                      Maybe this is what is occurring and I need to isolate my thru-hulls and drain plug / run all my dc - to the bateries and engine only / and maybe forget the dynaplate all together?


                      • #12
                        Re: 12v grounding Dynaplate and hull zincs?

                        [colour=blue]I agree with the above but I think the first step is to confirm whether or not your mooring is 'hot'.

                        If it were my boat I would seek the advise of a marine lightning specailist to ensure that the protection is adequate (apparently, S.E. Florida is the lightning capital of the world!). I would also isolate the grounds from the dynaplate, that would include checking that all grounds are not substandard (they could be 'using' the plate).

                        BTW, you can literally dip the probes of a DVM in the water and check for voltage. Connect the positive to the batt and probe the water with the negative (in and around the plate/anodes etc). Anything over 1 volt is a concern.
                        Watch this space......................


                        • #13
                          Re: 12v grounding Dynaplate and hull zincs?


                          For now I am replacing the the thru-hull that got eaten up and leaving the underwater metals "isolated" (not bonded) from one another.

                          The more I read it seems like the dynaplate is a waste of time for my application and more for grounding high powered radio equip. and not lightning protection. I am getting rid of it rather than replace it because mine is covered with hard scaley marine growth.

                          The engine it seeems should supply sufficient ground for the VHF and GPS I have on the 25'.

                          I will consult further on the lightnong issue and proper protection.

                          And when I go back to the keys in May probe the water at the seawall or get a specialist to come and test.

                          Thanks. Nautihabits.