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    Galvanic Isolation-gctid816061

    Hello guys.

    Query my boat has always suffered from galvanic corrosion. I have a galvanic isolator on the boat that i have yet to test but assuming it is working I have another question.

    There is a ground wire from my breaker panel attached to my through hull in mid bilge. Should it be connected? Seems to me that it defeats the purpose of the isolator. Comments appreciated
    John McLellan White Rock BC
    "Halifax Jack"
    1999 2855 383 stroker BII
    MMSI 316004337

    #2
    There are several sorts of "Grounds" you need to worry about (and that get improperly described) on a boat. They are all at the same potential or so very close that people try to think of them as ONE circuits. The reality is they are several different circuits that are normally at the same potential, but each serves as very important role.

    SAFETY GROUND: This is the EARTH GROUND that makes all those 3rd prongs functional on your tools. They hold the chassis of those tools at the same potential as the earth. It serves as an emergency path to earth ground when things short out internally. Safety Ground is tied to Neutral

    AC NEUTRAL: This is the RETURN PATH for the AC power coming from your local power grid. This SHOULD be at the same potential as your SAFETY GROUND, but doesn't have to be and on a boat in the water, it is very likely not. They call this a floating ground.

    BOND: Also electrically the same potential as the SAFETY GROUND, but serves to keep all of your rusting bits (which generate DC) at the same potential and provide a path for your various zincs to sacrifice themselves in the anodic process. (saving your important cast iron, bronze and aluminum bits from all that fancy stainless and carbon steel).

    DC GROUND (more accurately the NEGATIVE RETURN) is there to feed DC current back to all your DC motors, starter, lights, etc. Since you have no chassis, you need an equally sized NEGATIVE RETURN to match the highest loads on the POSITIVE DC circuits. This is at the same potential as your AC Neutral side, but since its DC it never cares.

    On a boat, a Galvanic Isolator shunts any DC found on your AC Safety Ground and Neutral to your Bond Ground. This only protects you from the other boats in the marina that are rusting away, AND protects THEM from you. Without a Galvanic Isolator, YOUR zincs are being burned off to counteract corrosion going on anywhere on your docks. that's probably not why you bought them and the reason they have value.
    Custom CNC Design And Dash Panels

    iBoatNW

    1980 CHB Europa 42 Trawler- "Honey Badger"

    Comment


      #3
      "SomeSailor" post=816086 wrote:
      There are several sorts of "Grounds" you need to worry about (and that get improperly described) on a boat. They are all at the same potential or so very close that people try to think of them as ONE circuits. The reality is they are several different circuits that are normally at the same potential, but each serves as very important role.

      SAFETY GROUND: This is the EARTH GROUND that makes all those 3rd prongs functional on your tools. They hold the chassis of those tools at the same potential as the earth. It serves as an emergency path to earth ground when things short out internally. Safety Ground is tied to Neutral

      AC NEUTRAL: This is the RETURN PATH for the AC power coming from your local power grid. This SHOULD be at the same potential as your SAFETY GROUND, but doesn't have to be and on a boat in the water, it is very likely not. They call this a floating ground.

      BOND: Also electrically the same potential as the SAFETY GROUND, but serves to keep all of your rusting bits (which generate DC) at the same potential and provide a path for your various zincs to sacrifice themselves in the anodic process. (saving your important cast iron, bronze and aluminum bits from all that fancy stainless and carbon steel).

      DC GROUND (more accurately the NEGATIVE RETURN) is there to feed DC current back to all your DC motors, starter, lights, etc. Since you have no chassis, you need an equally sized NEGATIVE RETURN to match the highest loads on the POSITIVE DC circuits. This is at the same potential as your AC Neutral side, but since its DC it never cares.

      On a boat, a Galvanic Isolator shunts any DC found on your AC Safety Ground and Neutral to your Bond Ground. This only protects you from the other boats in the marina that are rusting away, AND protects THEM from you. Without a Galvanic Isolator, YOUR zincs are being burned off to counteract corrosion going on anywhere on your docks. that's probably not why you bought them and the reason they have value.
      Excellent explanation, SS, but it appears you missed his second question, one I'd like answered too.

      "hfxjack" post=816061 wrote:
      There is a ground wire from my breaker panel attached to my through hull in mid bilge. Should it be connected?
      Our motorsailer had all the brass, bronze and SS thru-hulls (attached to plastic hoses) all bonded with a #8 copper wire to the engine. The first time we pulled it, we had dark rings around all the metal thru-hulls. I removed the wires and the rings never came back. Was it a good idea to remove them?
      "B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
      MMSI: 367637220
      HAM: KE7TTR
      TDI tech diver
      BoD Puget Sound Anglers North Olympic Peninsula Chapter
      Kevin

      Comment


        #4
        "CptCrunchie" post=816120 wrote:
        Excellent explanation, SS, but it appears you missed his second question, one I'd like answered too.

        "hfxjack" post=816061 wrote:
        There is a ground wire from my breaker panel attached to my through hull in mid bilge. Should it be connected?
        Our motorsailer had all the brass, bronze and SS thru-hulls (attached to plastic hoses) all bonded with a #8 copper wire to the engine. The first time we pulled it, we had dark rings around all the metal thru-hulls. I removed the wires and the rings never came back. Was it a good idea to remove them?
        Didn't miss it. Just hoped you'd see what I was saying in terms of separate circuits, that should be at the same potential.

        Thru-hulls should all be bonded together. That BOND system (circuit) should be 100% at the same potential. The boats NEGATIVE RETURN path (sometimes referred to as DC GROUND) is a SEPARATE circuit that should be at the same potential at all times. Those two SEPARATE circuits are tied together somewhere, and that should be a buss bar. If you disconnected it right there and saw current flow (and you will) you would be able to know whether there is DC leaking somewhere, or if DC generated on your screws, shafts, struts, rudders, outdrives or other is bleeding onto your NEGATIVE RETURN. This goes equally for your AC SAFETY GROUND and NEUTRAL. If you're seeing current flow there, you may be getting DC from other boats or the rusting dock itself.

        You have to think of them as SEPARATE systems. Then you can break down what you might be seeing and what is causing it. Simply disconnecting the two systems does nothing. Depending what direction (polarity) of that DC current, you could know whats causing. Otherwise you're just giving up on the offending circuit and you'll pay the price one way or another later.
        Custom CNC Design And Dash Panels

        iBoatNW

        1980 CHB Europa 42 Trawler- "Honey Badger"

        Comment


          #5
          If your boat has always had this problem i would suspect something added or modified improperly by the previous owner. You could start inspecting the obvious stuff, any new to the boat gadgets you didn't install yourself, look for alterations to the wiring harness and non factory connections. Some Sailor is right about the separate ground systems and if at some point changes or additional connections for devices have been made improperly to the wrong grounding location it could cause a ground loop to develop and amplify due to the building resistance of an aging boats ground system. Check out all the grounds you can find, they should go to central connection points not anywhere that seems convenient. DC systems should be separate from AC with no sharing grounds. Your A/C neutral connection is another one too look into, sometimes it is bonded to ground inside the panel (if you have one) and sometimes its not, you need to check this out and find out what abyc code requires and what your galvanic isolator requires, the random ground wire to your panel is suspect. It might be a bit of work but going through your wiring cleaning tightening and lubricating all the connections you can find will work wonders for your boats electrical health and keep it reliable for years, I would start there and see what happens. This is a complex subject, you'll likely get enough info here to make your brain hurt, good luck !
          1990 3888 Bayliner, Twin 351's

          Comment


            #6
            Hmmmmmm..... Not quite sure I'm asking the right question.

            Why would I want to connect a wire to a metal thru-hull that isn't connected to anything other than the fiberglass hull and a plastic hose? The PO did that. Where and how would it leak current? Moreover, what might the gray rings around the thru-hulls be when they were all connected to the engine? Would that be zinc bits? Head intake, galley saltwater intake, sink drains, AC/heat pump intake, etc. The thru-hulls seemed fine, but the fiberglass and bottom paint all around them were degraded, almost pitted. When I removed the wires, it never happened again. So, should a wire have been a there to begin with?

            PS: I only removed the wires attached to the thru-hulls. The rest of the systems were professionally installed.
            "B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
            MMSI: 367637220
            HAM: KE7TTR
            TDI tech diver
            BoD Puget Sound Anglers North Olympic Peninsula Chapter
            Kevin

            Comment


              #7
              "CptCrunchie" post=816157 wrote:
              Why would I want to connect a wire to a metal thru-hull that isn't connected to anything other than the fiberglass hull and a plastic hose?
              Why? Because if that metal fitting fails, you will sink the boat. Think of that metal fitting as a single plate in a very large battery. As current flows from one piece of metal to another through an electrolyte (water) electrons are transferred through a process called redox. A less noble metal will reduce its total mass (corrode) and a more noble metal will add those electrons (oxidize). That bronze thru-hull, if it was the ONLY piece on metal on the boat and with no other DC flowing around it, would NOT benefit from bonding. Sailboats can often leave bonds out because they have very little ferrous metal or stainless in the water and very small DC systems.

              Power boats should bond everything and pile on zincs to protect themselves (sacrificial). All metal thru-hulls should be bonded.

              Galvanic corrosion will not affect paint or gelcoat. If you're seeing degradtion, it's likely because chemicals being poured down that through hull are staining it.

              The virtues of thru hull bonding is controversial at best, but as a general rule, very well understood and very basic electro-chemistry at work. Keep everything at the same potential at all cost is the best guarantee.

              Here's a last thought. If you have ANY rust on your boat (risers, fittings, block, exhaust), where do you think the electrons went?
              Custom CNC Design And Dash Panels

              iBoatNW

              1980 CHB Europa 42 Trawler- "Honey Badger"

              Comment


                #8
                "SomeSailor" post=816186 wrote:
                "CptCrunchie" post=816157 wrote:
                Why would I want to connect a wire to a metal thru-hull that isn't connected to anything other than the fiberglass hull and a plastic hose?
                Why? Because if that metal fitting fails, you will sink the boat. Think of that metal fitting as a single plate in a very large battery. As current flows from one piece of metal to another through an electrolyte (water) electrons are transferred through a process called redox. A less noble metal will reduce its total mass (corrode) and a more noble metal will add those electrons (oxidize). That bronze thru-hull, if it was the ONLY piece on metal on the boat and with no other DC flowing around it, would NOT benefit from bonding. Sailboats can often leave bonds out because they have very little ferrous metal or stainless in the water and very small DC systems.

                Power boats should bond everything and pile on zincs to protect themselves (sacrificial). All metal thru-hulls should be bonded.

                Galvanic corrosion will not affect paint or gelcoat. If you're seeing degradtion, it's likely because chemicals being poured down that through hull are staining it.

                The virtues of thru hull bonding is controversial at best, but as a general rule, very well understood and very basic electro-chemistry at work. Keep everything at the same potential at all cost is the best guarantee.

                Here's a last thought. If you have ANY rust on your boat (risers, fittings, block, exhaust), where do you think the electrons went?
                +1

                The exception is wooden boats. There's been some research over the years that shows that bonded, metal thru-hulls in a wooden hull can create a small galvanic cell at the interface between the wood and the metal. This will slowly eat away at the wood. Keep in mind that in order for this to occur there has to be some moisture between the thru-hull and the wood. So the wood degradation will be less with a properly sealed, bonded thru-hull.

                Here's a good article on bonding:

                https://www.google.com/url?sa=t&rct=...DP5Lie59Vjju5Q
                1999 3788, Cummins 270 "Freedom"
                2013 Boston Whaler 130 SS
                Anacortes, WA
                Isla Verde, PR

                Comment


                  #9
                  There are some pictures in this post of bottom paint being affected - I have seen this on a number of Sea Rays where the bonding was insecure and they had rafted often with portable gensets - in one case an IO boat lost most of its outdrive integrity over a couple of months as well (34' Rinker I think).

                  http://www.thehulltruth.com/boating-...hru-hulls.html
                  Northport NY

                  Comment


                    #10
                    "Norton Rider" post=816189 wrote:
                    The exception is wooden boats. There's been some research over the years that shows that bonded, metal thru-hulls in a wooden hull can create a small galvanic cell at the interface between the wood and the metal.
                    This is true. Also... if your thru-hulls are reacting with your BOTTOM PAINT, then you have definitely got a problem. BUT...it's not there. Bottom paint is usually (assuming copper based here) conductive. It's like a giant conductive skin on your hull. If its reacting around your thru-hull then the bottom paint is grounded somewhere... that's not good. Someone has painted right over or onto something that is bonded. THAT is improper. It's cosmetic, but if you insist on painting up to a bonded component, then use a non-metallic biocide paint around the thru-hull and then conductive bottom paint at least 1" from any metalic parts (thru-hulls, outdrive, rudders, transducer, etc).
                    Custom CNC Design And Dash Panels

                    iBoatNW

                    1980 CHB Europa 42 Trawler- "Honey Badger"

                    Comment


                      #11
                      "SomeSailor" post=816244 wrote:
                      ... if your thru-hulls are reacting with your BOTTOM PAINT, then you have definitely got a problem. BUT...it's not there. Bottom paint is usually (assuming copper based here) conductive. It's like a giant conductive skin on your hull. If its reacting around your thru-hull then the bottom paint is grounded somewhere... that's not good. Someone has painted right over or onto something that is bonded. THAT is improper. It's cosmetic, but if you insist on painting up to a bonded component, then use a non-metallic biocide paint around the thru-hull and then conductive bottom paint at least 1" from any metalic parts (thru-hulls, outdrive, rudders, transducer, etc).
                      When we bought the boat, all the thru-hulls were painted with - what was then legal - 70% copper bottom paint. I sanded all of them, though not down to the bare metal, then repainted them with the same bottom paint. Hmmmmm......

                      Guess I know now how the rings were formed. B)
                      "B on D C", is a 1989 2459 Trophy Offshore HT, OMC 5.7L, Cobra OD, Yamaha 15hp kicker. Lots of toys! I'm no mechanic, just a blue water sailer and woodworker who loves deep sea fishing.
                      MMSI: 367637220
                      HAM: KE7TTR
                      TDI tech diver
                      BoD Puget Sound Anglers North Olympic Peninsula Chapter
                      Kevin

                      Comment


                        #12
                        I've read a fair amount on this subject...there are two trains of thought and the way I read it, it comes down to this:

                        1) Offshore boat: corrosion is due to galvanic action: bond through hulls

                        2) Marina boat: corrosion is due to stray currents from leaky ac systems. isolate through hulls

                        You still need the proper system in place for the ac feed (Isolation transformer or galvanic isolator) and DC negative connection to the AC 'ground' but it sounds like you have that under control.

                        Chay

                        Comment


                          #13
                          "CptCrunchie" post=816120 wrote:
                          "SomeSailor" post=816086 wrote:
                          There are several sorts of "Grounds" you need to worry about (and that get improperly described) on a boat. They are all at the same potential or so very close that people try to think of them as ONE circuits. The reality is they are several different circuits that are normally at the same potential, but each serves as very important role.

                          SAFETY GROUND: This is the EARTH GROUND that makes all those 3rd prongs functional on your tools. They hold the chassis of those tools at the same potential as the earth. It serves as an emergency path to earth ground when things short out internally. Safety Ground is tied to Neutral

                          AC NEUTRAL: This is the RETURN PATH for the AC power coming from your local power grid. This SHOULD be at the same potential as your SAFETY GROUND, but doesn't have to be and on a boat in the water, it is very likely not. They call this a floating ground.

                          BOND: Also electrically the same potential as the SAFETY GROUND, but serves to keep all of your rusting bits (which generate DC) at the same potential and provide a path for your various zincs to sacrifice themselves in the anodic process. (saving your important cast iron, bronze and aluminum bits from all that fancy stainless and carbon steel).

                          DC GROUND (more accurately the NEGATIVE RETURN) is there to feed DC current back to all your DC motors, starter, lights, etc. Since you have no chassis, you need an equally sized NEGATIVE RETURN to match the highest loads on the POSITIVE DC circuits. This is at the same potential as your AC Neutral side, but since its DC it never cares.

                          On a boat, a Galvanic Isolator shunts any DC found on your AC Safety Ground and Neutral to your Bond Ground. This only protects you from the other boats in the marina that are rusting away, AND protects THEM from you. Without a Galvanic Isolator, YOUR zincs are being burned off to counteract corrosion going on anywhere on your docks. that's probably not why you bought them and the reason they have value.
                          Excellent explanation, SS, but it appears you missed his second question, one I'd like answered too.

                          "hfxjack" post=816061 wrote:
                          There is a ground wire from my breaker panel attached to my through hull in mid bilge. Should it be connected?
                          Our motorsailer had all the brass, bronze and SS thru-hulls (attached to plastic hoses) all bonded with a #8 copper wire to the engine. The first time we pulled it, we had dark rings around all the metal thru-hulls. I removed the wires and the rings never came back. Was it a good idea to remove them?
                          Depends. If lightening strike can occur, then leave them. If not, cutting the bonding wires is preferable IMHO.
                          www.boatyardgm.com
                          www.pacificyachtimports.net
                          2002 Carver Voyager 57
                          "Making Waves"
                          3988 250 Hinos
                          "The Dark Side"
                          Alameda, California

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