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Grounding Plates

Discussion in 'Technical Discussion' started by NEO56, Aug 31, 2014.

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  1. NEO56, Aug 31, 2014
    #1
    NEO56

    NEO56 Member

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    There's a boat currently on the market, and rumor has it that there was an electrical fire onboard. I called a buddy of mine who is familiar with the boat, and he confirmed that indeed there was a fire, and a hole had to be cut into the deck to put it out! In our conversation, I told him of a sport fisherman that was two years old, and was being offered way below actual value, when I pressed the broker as to why, he confessed that the boat had been struck by lightning, and fried most of the wiring on the boat. I mentioned that the boat probably didn't have a grounding plate installed. I was then told that he hadn't seen a grounding plate on a new boat in 15-20 years! Somebody please straighten me out....I can't even conceive of having a boat without a grounding plate....what's up with this guys?
  2. Capt J, Aug 31, 2014
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    Capt J

    Capt J Senior Member

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    No, I don't see them and haven't seen them in a very long time. All if usually see is a plate zinc on the transom, rudder zincs, trim tab zincs and sometimes shaft zincs. But typically the shafts are tied into the transom zinc. But no grounding plates.
  3. NEO56, Aug 31, 2014
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    NEO56

    NEO56 Member

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    O.K. J, So where does all of that energy go when lightning strikes the boat? What about the energy inside the boat?
  4. Capt J, Aug 31, 2014
    #4
    Capt J

    Capt J Senior Member

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    From boats I've seen that have gotten hit by lightening, both boats SF with tuna towers and both boats got hit 2 different times. Both of those boats had grounding plates and both times on both boats, everything got fried electrically, from electronics to the microwave. There is such a HUGE amount of electricity from a lightening bolt that no #4 wire is going to dissapate, that the grounding plates cannot dissapate it fast enough. I'm no expert on this, but perhaps that is why builders have stopped building boats with grounding plates....at least under 100'. I'm not sure what builders do on the larger ones.
  5. Opcn, Aug 31, 2014
    #5
    Opcn

    Opcn Senior Member

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    Like a lightning rod, the purpose of a grounding plate is to keep your boat from getting struck by lightning, not to prevent damage in the case of a lightning strike. Lightning happens because the charged water droplets in the cloud create an electric field and force the charges down in the water/soil column. This creates a charge differential between the cloud and the ground/water. It's basically a giant capacitor with a high internal resistance. The grounding plate or lightning rod is a conductor that passes electricity on through to the gap at a slow speed and discharges the capacitor before it can build up enough charge to catastrophically discharge in the form of lightning, which heats the air until it forms a plasma and the resistance plummets.
  6. captholli, Aug 31, 2014
    #6
    captholli

    captholli Senior Member

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    Grounding plates AKA Dyna plates were primarily used on composite builds for counterpoise for Single Side Band radio installs up until a few years back until builders started glassing in large suface area's of wire mesh In F/B brows or deck overheads and then that was attached to a wide flat copper strap and run to any large grounded chunk of iron such as a motor then transferring to the vessels bonding system. Lightning strikes on today's composite vessels will take the least resistive path to earth/ ground usually through the vessels electrical ground & bonding system.
  7. NEO56, Aug 31, 2014
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    NEO56

    NEO56 Member

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    So, from these responses, can I safely assume that a lightning strike will mean replacing all electrical items, T.V.'s, Instruments, Radar, Radio's, Microwaves, etc.?
  8. AMG, Aug 31, 2014
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    AMG

    AMG YF Moderator

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    Where I live, most of the damage from lightnings are coming through the shore power connections...
  9. Opcn, Aug 31, 2014
    #9
    Opcn

    Opcn Senior Member

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    Yes. Surge protectors can be used on individual components to give them a chance of surviving a strike, but it is not a guarantee.

    the physical wires for your low voltage applications might actually survive. The transformer at one end and the doodad at the other will surely be burnt out, but you might not have to repull the wire.
  10. captholli, Aug 31, 2014
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    captholli

    captholli Senior Member

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    No way to 100 % protect your vessel from lightning. It's a crap shoot at best. There's all sorts of "Static Discharge / dissipaters on the market, ( Brass toilet brushes) mounted at the highest point of the vessel that create a " Static aura" around your vessel or so the manufacturers claim . Kinda like voodoo or Santeria I figure as the facts don't back the manufacturers claims. Certain types of equipment onboard is more susceptible to millions of volts no matter what pitiful surge protector is in line and electronic power supplies found in most multi input voltage marine electronics and t.v.s cable boxes etc. Are highly susceptible to hits. Induction wound motors seem to take the brunt of lightning hits also , washers, dryers, dishwasher etc. I've been aboard several vessels after the fact of being struck by lightning and the forensics of tracing the path of the strike or hit more than likely begins with a antenna hit and the electrical path that it took to earth (burnt and melted wiring) was more than obvious.
  11. NEO56, Aug 31, 2014
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    NEO56

    NEO56 Member

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    Thanks captholli, So in a live aboard situation, when an electrical storm heads your way you run around the boat and un-plug everything you can...and carry battery powered GPS, and any other battery powered device useful for getting home as back up (assuming your on the hook near a Bahamian island). Would killing 90% of your Breaker Panel help? Shut down everything but the inverters? And I'm guessing that you Insurance won't pay to replace everything that get's fried?
  12. captholli, Aug 31, 2014
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    captholli

    captholli Senior Member

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    Just like your land yacht ( Prevost) keep as much as u can on a power strip, room to room TV and electronics wise and unplug anything that you can to isolate them from the electrical hard wired system. Not at all convenient unless u make a concerted effort to make things like power strips accessable to unplug in a hurry. Turning breakers off at the panel will not isolate your equipment from the neutral or ground of the circuit.
  13. NEO56, Aug 31, 2014
    #13
    NEO56

    NEO56 Member

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    O.K. That makes sense...but will shutting down my breaker panel (most of it) save my panel, and most of the wire heading for it?
  14. Capt J, Aug 31, 2014
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    Capt J

    Capt J Senior Member

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    Are you kidding??? No, you do as you normally do in your own home and find bigger things to worry about than the 1 in 100,000 chance your boat is going to get hit by lightening.
  15. NEO56, Aug 31, 2014
    #15
    NEO56

    NEO56 Member

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    That's what I like about you J, you cut through the crap. But I'm thinking that if I'm anchored off of an Island in the Bahamas...guess what? I'm the tallest structure for miles around, and with my luck, my odds aren't 100,000:1 of being hit. They're like 2:1 of being hit! As I've mentioned in previous posts, I don't know jack about electrical systems. And as a result electricity scares me. I've been known to shut off the entire power to a house to install a ceiling fan! (Seriously...not kidding)
  16. Capt J, Sep 1, 2014
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    Capt J

    Capt J Senior Member

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    I've gone through LOTS of lightening storms on deliveries over the years. Some of them even on Sportfish with a big old Tuna Tower! You keep on moving and just hope it's not your lucky day. That being said none of the boats I've ever ran or have taken care of have ever been hit with lightening. I personally only know of 2 that have and both of them twice in the same spot, in the last 30 years.