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Grounding Plates

Discussion in 'Bristol' started by bmccuej, Jun 5, 2016. Add this thread to a FAQ

  1. bmccuej


    Joined Aug 4, 2010
    3 posts, 0 likes
    Hunter 27
    US Fairhaven
    I have a 1979 Bristol 29.9, the boat does not have a grounding plate on the hull. About half the sailboats I see while on dry dock do have ground plates mounted to the hull. Does anyone know what triggers the need for a grounding plate?

  2. Don S/V ILLusion

    Don S/V ILLusion

    Joined Sep 25, 2008
    4,601 posts, 74 likes
    Alden 50
    US Sarasota, Florida
    what is it you want to achieve? An effective counter poise for an HF radio or a so-called Lightning ground?

  3. Skipper


    Joined Oct 9, 2008
    1,076 posts, 67 likes
    Bristol 29.9
    US Dana Point
    Grounding plates in your boat size are mostly for lightning.
    The DC grounds through the engine/prop shaft.
    All 8 of your stays/shrouds, the 7 bronze thru hulls, the engine, and the mast are all bonded together. The wires are visible on all except the mast, where there is a wire-attached metal plate under the base.
    With your internal ballast, you can't exit lightning through the keel as there are no bolts. Bristol exits the lightning through the shaft and 7 thru hulls. It also keeps the rig at the same electrical potential as the ocean.

  4. Bill Roosa

    Bill Roosa

    Joined Jun 6, 2006
    6,640 posts, 59 likes
    Hunter 40.5
    US Harrington Harbor North, MD
    would agree with Skipper, they are for (and Don) so-called lightning protection. That method has not been conclusively confirmed to be effective BTW. Also there are better high frequency (HF) radio grounds then a sintered bronze plate a few feet below the surface. Your HF radio will push out a stronger signal if your ground crosses the water surface during transmit. (think fin attached above the water line but projecting into the water) Your VHF does not need a radio ground for its signal. It does need one for the chassis ground though but that can be the normal bonding wire.

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