Negative Hull Bonding

Discussion in 'Boat Design' started by Katoh, Jul 8, 2011.

  1. Katoh
    Joined: May 2010
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    Location: A.C.T

    Katoh Senior Member

    The original position of batteries were at the stern adjacent to the motor, These were located in open boxes, a bit to exposed for my liking. I can move all my electrical forward under cover which will also tidy up the mess of cables all over the transom. Now I will have just have 2 cables 4awg in conduits leading to the engine bay and of course the motor control harness.
    The original wiring on the Volvo had the motor bonded to hull Green Wire and then Also a Black wire of equal size from negative side post on the starter to the hull also. Both of these also piggybacked another smaller wire that fastened on the transom shield.
    For the life of me I cant see how the hell your going to achieve 0v
    Doesn't matter how well you try an isolate that motor to the hull Its always going to read something. Unless your boat is Glass, but im talking about aluminium.
  2. Mark Cat
    Joined: Jun 2011
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    Location: Michigan

    Mark Cat Senior Member


    I agree, Volvo Penta, for example, have a "vision" of how they want to protect the Volvo engine and other components from corrosion, but do not address it from a practical electrical systems standpoint.

    I actually requested ABYC contact Volvo to find out what the system plan was on maintaining this "isolation" relative to ABYC corrosion, bonding and electrical considerations. Volvo's stance was more is addressing their needs and not the builders when it can to a "disclaimer". So the responsibility for correctly designing the system would ultimately reside with the builder.

    Any Volvo people can confirm or shed more light on this?

  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The Volvo people aren't completely wrong either.

    As previously established it is near impossible to isolate the drive from the hull, but by not connecting the wire, a low resistance path to the hull is avoided.
    There is galvanic interaction between the different metals of the drive, but to reduce that the drive has its own zinc.

  4. Katoh
    Joined: May 2010
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    Location: A.C.T

    Katoh Senior Member

    I am starting to read this differently now, and this is only an assumption.
    What if the Volvo people meant 0v between there motor, leg, whatever and the hull itself. The only way to achieve this is through good bonding, not isolating.
    If these people wanted 0v from there part going back to an active terminal then shouldn't have negatively bonded there own equipment.
    I personally think we are reading this wrong, and what we should be striving to accomplish is total bonding of the hull so it doesn't matter what parts we choose we should get a reading of 0v. Of course if we go from any part to an active terminal it should read 12v, but I dont think that's what their talking about.
    The fact is you can only do this while the boat is in water! On trailer boat outside of water would give you a reading of 0v no matter what, put it in water and start with your ohm meter, I believe yo will get some interesting readings.
    I have been toying with idea of setting up a simple circuit, maybe a light on the dash so when a stray current does happen or a leak from the positive, the light will come on. I can not seem to work that out. Suggestions Please.
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