eletric ground for metal hull

Discussion in 'Metal Boat Building' started by luso, May 26, 2006.

  1. luso
    Joined: May 2006
    Posts: 16
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    Location: florida usa

    luso New Member

    Hello I'm new to this forum.
    My wife and I are rebuilding a 52' metal hull schonna for 6 years.Unbiliveble how much works it is,just finishing the internal framing.
    Houpe you guis can help us .We have a yanmar diesel generator,misssing the rear end, found one at northentools[ pulley driven] but was told that it needs to be ground.How could I ground the system without creating a eletrolisis to the hull?
  2. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    To ground or not is a debatable subject, but I think there is a clear path.

    In reality unless you have massive currents flowing connecting the hull to the negative of your electrical system and to the Nuetral of your generator will not cause any Electrolysis.
    For electrolysis you need a differential voltage and you just will not get this given the very low ohmage of the hull. (Plus the hull tends to be isolated by the paint system but we won't go there).

    The only proviso is that the prop shaft should be bonded as well otherwise there is a slight risk that the isolated shaft could contact internal wiring and cause electrolysis although the risk is minute.

    In the marina with a bonded hull you must use an isolating transformer or a galvanic isolator otherwise the hull can become an anode to a faulty shore power installation or a faulty neighbouring vessel.

    I hope this helps, you will find a lot of confusing and poorly researched material on this topic.
  3. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    There should be only one grounding point for your entire electrical system. On most boats it is the engine block. All other grounds lead to that point. Most accepted standards say don't use the metal hull as a ground as it will lead to galvanic corrosion. Some people will say this is not true. It's been debated for many years. I think the standards are right. On larger boats like yours the builders usually put in a groundiing strip, usually a large cable or metal bar running the length of the boat which is connected to the block. All ground wires go to the gorounding strip.

  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    In the new Pro Boatbuilding there is a letter to the editor about a previous article and it mentions that "using the engine block as the DC ground is problematic" and can lead to "ground loop currents that in turn can lead to stray-current corrision on board the vessel" and "the fact that the ABYC still refers to the engine block as the primary negative reference simply points out that the standards need updating". As Mike says, there is a lot of confusing material on the subject. Sam
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