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  1. #1

    Default electrical grounding to aluminum hull

    I am rewiring my aluminum boat. Should I ground the hull? I was thinking about running a wire from the negative side of my battery to a buss under the dash for my accessories.

    Thanks
    Bill

  2. #2
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    Default Re: electrical grounding to aluminum hull

    If you wan't a corrosion magnet... yes


  3. #3
    Admiral Dunaruna's Avatar
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    Default Re: electrical grounding to aluminum hull

    [colour=blue]Don't use the hull for ground, but bonding is o/k - depending on a few factors.
    Watch this space......................

  4. #4
    Commander studlymandingo's Avatar
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    Default Re: electrical grounding to aluminum hull

    Saltwater usage being one of those factors.
    The wetter, the better.

  5. #5
    Rear Admiral Boatist's Avatar
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    Default Re: electrical grounding to aluminum hull

    I would not use the hull to carry any current but to ground the engine to the hull is normal.

    I do not know about outboards but I do not think you will find an I/O that does not have some part of the engine bolted to the hull.
    Have some fun and enjoy the Great Outdoors.
    Love to fish out of Bodega Bay, California.

  6. #6
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    Current flowing through electrical connections, in particular dissimilar, metallic, electrical connections, causes electrolysis which is corrossive and destructive. A salt environment highly accellerates the process.

    To reduce the occurrence, the system needs one grounding point which is usually the neg batt term, where everything is connected in parallel Meaning separate wires go off to all the separate functions. Best to supply power the same way from the + terminal.

    The dashboard electronics can all be connected to an isolated (from the metallic hull) buss "terminal block" with one for + and another - power connections with a single wire (from each) representing the dash going back to the battery.

    Since the hull is metal I think it prudent to "safety ground" if you will, it to the single point neg bat term. If you let it "float" you never know when or if a static charge would build up that would be similar to a lightening bolt and the spark could destroy something sensitive (I realize the intensity is no where near as high, but the principle is the same; however, a distant lightening strike from a squall could trigger just such an event.).

    The engine is bolted to it and already serves as a safety ground for it but you might want another dedicated wire.

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  7. #7

    Default Re: electrical grounding to aluminum hull

    Mark,

    Thanks for explaining it to me. I was having a difficult time understanding why you should not ground each item under the dash directly to the hull since the motor is grounded just by its presence on the transom.
    I will run dedicated wires to the terminal blocks under the dash and make my connections for lights, depth finder, ect. at that point.
    I also recieved some (mis?)information regarding electrical current from the hull affecting the fishing while trolling.

    Bill

  8. #8
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    I spent many 10's of years working problems just such as this one on very high dollar toys, er ah things. Have a little training and experience.

    What we are talking about here is called "single point chassis ground". And what it does is insure that a piece of equipment isn't powered/signaled on a line powering/signaling another piece of equip which could inject noise into the second item on the line.

    What do you mean about current affecting fishing while trolling?

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  9. #9
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    One more thing Bill,

    If, for some reason you have interference on any of your dash electronics and by turning things off till the interference leaves you find something is the culprit, you can place a condenser (capacitor) across the + and - terminal blocks.

    Radio shack has them; a .1 microfarad cap at 50 or more WVDC would do nicely. Will be about the size of a nickel. What it does is short circuit high frequency signals right at the terminal blocks so that they can't get out of the power lead of one piece of equip and get onto the power leads of another.

    But, don't mess with it unless you have to and be sure it's electronics, not bubbles from the boat in the case of depth finder interference.

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  10. #10
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    Default Re: electrical grounding to aluminum hull

    [quote ]

    I was having a difficult time understanding why you should not ground each item under the dash directly to the hull since the motor is grounded just by its presence on the transom.
    [/quote]

    The motor is not grounded to the hull, it is bonded. They are 2 different things. You don't want your hull to be an electrical path to any device. Run individual ground wires to a grounding block and then run a single ground wire from that block to the battery if you have a lot of instruments/devices.

    As far as the whole lightning protection thing, a bonded motor or device to hull will not make a difference. Most people think a lightning rod on a house is meant to let the lightning hit it and send the lightning to the ground "safely".. not true. it exists to eliminate the build up of a charge in the first place which attracts lightning. If your house or boat is hit by lightning (directly) or very close vicinity no amount of grounding or bonding will help you.. the voltage and current of a strike are enormous.

  11. #11
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    You want them to remain at the same potential so that static electricity doesn't develop. You are moving a conductor (boat hull) through a dielectric medium (water) which develops static electricity. Improperly allowed to develop it can charge to thousands of volts and ruin the best electronics (if not protected against it).

    Agree on the purpose of rods on a house.

    Don't know your distinction between gnd and bond (with respect to the engine); both are synonyms.

    The engine is electricaly tied to the batt for power and power return (hence ground) through the engine's wiring harness. All the electronics in the boat and anything else electrical is driven from the battery....unless you have a dedicated APU like you'd have on a large boat.....then the APU is the point source.

    Therefore, since the batt is the origin of power, the battery is the best place to "reference" all electrical currents. Tieing off to the hull is just "referencing" the hull to the single point power source......that everything else within the hull if referenced to.

    Any technical library should be full of EMI (Electromagnetic Interference) facts and avoidances.

    HTH

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  12. #12

    Default Re: electrical grounding to aluminum hull

    Thanks for your input Mark & b00t.

    I notice on my boat that the bilge pump which is grounded to the hull at the transom is operational which indicates to me that the hull is grounded even though I have no other connection to the battery except the engine -- I have not yet run a dedicated ground wire.

    Also, in the past I have had interference on my depth finder when the engine is running (could be bubbles you mentioned) or when I am near another boater who is running his engine or depth finder ---- will the condenser (capacitor) you mentioned eliminate this (assuming it is not bubbles)? Is it placed on the culprit wiring or the depth finder?

    Finally, I have been told that any electrical current through the hull (static electricity?) might make the fish less willing to bite! (even though I am willing to take full responsibility for not being able to put fish in the boat!!)

    Thanks again for your information
    bill

  13. #13
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    Default Re: electrical grounding to aluminum hull

    Maybe that's why I don't catch fish, I have electrical current in my hull. I'm going to use that excuse anyhow, now if I could just come up with one for why I can't catch them from the dock either! 8)

  14. #14
    Fleet Admiral jtexas's Avatar
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    Default Re: electrical grounding to aluminum hull

    Fish are sensitive to electrical charge, some species more than others, and who knows how much is too much, but taking steps to minimize your electro-magnetic signature is more than mere superstition (at least I think it is).

    BTW, I can't quite put my finger on it, but "static electricity" somehow seems inconsistent with "electrical current"...
    It's all about the tools.

    "If the ocean is glass flat and the sun is shining, you open up the special memory compartment of your brain and start recording the smells, sounds, sights and feelings." -- Philster

    "Poets talk about 'spots of time,' but it is really fishermen who experience eternity compressed into a moment. No one can tell what a spot of time is until suddenly the whole world is a fish and the fish is gone. I shall remember that son of a b**** forever." -- N. Maclean

  15. #15
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    Default Re: electrical grounding to aluminum hull

    [quote ]
    I notice on my boat that the bilge pump which is grounded to the hull at the transom is operational which indicates to me that the hull is grounded even though I have no other connection to the battery except the engine ... in the past I have had interference on my depth finder when the engine is running ... [/quote]

    I would like to re-iterate that the wire between your engine block and your boat hull is used as a bond not a ground. All motors and instruments should have a direct path to the battery negative, not through the hull. There is no "ground" on the hull, only a poor path back to the only real ground (the battery negative).



  16. #16
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    Default Re: electrical grounding to aluminum hull

    I think the issue of "grounding" a boat to the water is poorly understood. You have some small as well as big fiberglass hulls with complete isolation between any electrical systems and the water. But some fiberglass hulls have bronze "grounding plates" on the outside of the hull, tied into the main negative buss in the boat.
    And then, as in this discussion, you have metal hulls, some, but not all of which, have a bond from the negative buss to the hull.

    Confusing.


  17. #17
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    Default Re: electrical grounding to aluminum hull

    i don't mean to 'steal' this tread, but i came across it while doing a similar search. I'm installing a permanent plastic tank in my aluminum boat w/ ob and it tells me to "connect an earh end ground wire from the fuel fill base to a likely grounding site such as the engin mount". It also says to "connect a grounding wire from the fuel sender." Can both of these grounds go to the negative terminal on my 12v battery?
    Doll Fin
    '73 Starcraft Mariner
    Restored 2006

  18. #18
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    Several answers here.
    ----------------------------
    Bill: Yes the capacitor is there for that purpose, ignition interference from you or another boat; anything electrical/electronic. However, any interference caused by hull disturbances (bubbles) will not be affected.

    Now, chasing noise (EMI) is an exacting science and basically every system has to be "tuned" to get rid of it.

    So for your boat, If you have a shielded power cable from the sounder containing: a (usually red) power wire, and (usually black) return wire for your depthfinder, put the ground and shield together on your - buss plate with one lead (as short as you can get it) of the capacitor. If no shield, it will do better than without the cap, but not near as effective. The other lead of the capacitor goes to the red lead and obviously they are on the + buss. This would be an optimum installation.

    What the capacitor does is to short circuit high frequency signals. Since it's connected across the power lines and the lines (up to the sounder) are shielded, most noise coming up through the boat's wiring is not allowed to continue up the wire to the sounder; it gets shorted out. The capacitor has no effect on your dc power so don't worry about it. 8)
    --------------------------
    swist: The plate on the outer side of your hull may be for your VHF antenna to insure a good reflective field off the water. Otherwise your engine, while in the water serves as a reference for your boat to the water and some people use it for that purpose; CB's especially.


    --------------------------------------
    Chesie, the first ground is "electrostatic" to prevent what I was referring to when I talked about static discharges....it's for no-fire safety and prior to removing the fill cap, you should touch the fuel nozzle to one of the screws mounting the filler tube to the boat which should pick up this ground (underneath) and discharge any static electricity. Otherwise, if here is some, and usually there is as you were rolling down the highway, or running across the water, you could have a spark when the nozzle touched the filler tube and possibly a resultant fire.

    The other line is to insure that you can run your fuel gauge. Since fuel sensors only require milliamperes to operate, and since it is an electrical device as compared to an electronic device, you can probably do that without worrying about it.

    HTH

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  19. #19
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    Default Re: electrical grounding to aluminum hull

    I recently purchased an aluminum boat which has some bad rot spots in the hull, all over, not just in one spot. I also found an old ground wire which ran from the battery - terminal to the hull. This must be the culprit as the amount of rot is substantial and the boat is a 1986. I will not be grounding anything from the hull when I rewire. Do not ground to the hull.

  20. #20
    Admiral Dunaruna's Avatar
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    Default Re: electrical grounding to aluminum hull

    [colour=blue]If you have an outboard, it's 'bonded' to the hull already - no if's or but's.

    It is the lifelong dream of the electrons to leave home (the negative terminal) and find heaven (the positive terminal). They will do this as fast as possible using the least path of resistance.

    'Grounding' cables supply that path. If you cabling/connection are substandard, the little electrons will use the 'bonding' system (the hull!).
    Watch this space......................

  21. #21
    Fleet Admiral Texasmark's Avatar
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    Default Re: electrical grounding to aluminum hull

    Couldn't have said it better myself, Duna,

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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