Hull Electrode for Lightening

Discussion in 'Multihulls' started by Owly, Mar 9, 2017.

  1. David Cooper
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    David Cooper Senior Member

    Testing of wires in clothing has already been done for people working on live power lines (where it works fine), but I've never heard anything about any attempts to extend the idea to normal clothing where it ought to save lives. There was a case in which someone had a burn from lightning right down his front, but it left a two inch gap where it jumped into the metal strip in a banknote in his pocket (which it likely destroyed).

    As for your mast being unstayed, that makes no difference to the potential viability of using a mesh of conductive paint on the outside to lead the current outwards and round the hull instead of passing through it. And you may not need to do the whole hull - just a band right round it where the mast is could be enough to prevent the current going through the boat and blasting a hole through it below the water line.
  2. Sparky568
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    Sparky568 Junior Member

    Testing of wires in clothing has already been done for people working on live power lines (where it works fine), but I've never heard anything about any attempts to extend the idea to normal clothing where it ought to save lives.

    In what universe would this make sense??
  3. Owly
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    Owly Senior Member

    I would suspect that stainless steel would do as well, nor would it have to be mesh..... Stainless foil simply glued to all the surfaces. I can just imagine climbing into a "farady berth" with all my electronics, closing the mesh door and cowering there in terror in one of those incredibly violent thunderstorms I've seen. The mesh door would keep out both insects and damaging electromagnetic waves ;-)........... Makes a great mental image... hugging my Ipad, chart plotter, and other sensitive toys as the world outside goes crazy for an hour or so.

  4. Ike
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    Ike Senior Member

    It's simple enough. Just google "how to build a faraday cage" and many sites tell you how to make one. There's some youtube videos as well. No it doesn't have to be copper but some metals work better than others. Even ordinary aluminum foil will work.
  5. Owly
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    Owly Senior Member

    I suspect that it does make a difference, as the steeply angled pathway provided by metal stays and shrouds provides the main path for lightening on a stayed mast as the chain plates terminate very close to the water line as compared to the mast step. In this case the stays do not exist, but the mast step is within a few inches of the water with only the thin plywood hull between. That makes the mast an almost perfect lightening rod, in contrast to an stayed where the step may be 6' or more from the ground plain provided by the water surface.
    The lower the resistance of the circuit to ground, the less likely the current is to seek additional or alternative paths.
    I built a set of grounded pliers many years ago to pull spark plug wires off of a running engine. A ground wire went to a ground clamp which would be clamped right to the engine block. You could then pull off wires with impunity, holding the pliers in your bare hands, watching the spark jump to the pliers with your bare fingers mere inches away. This is only about 40,000 volts, compared to millions, but the bite is enough that many people I demonstrated this to were afraid to try it.
    The idea here is that providing an excellent low resistance path to ground should minimize the danger of lightening seeking other pathways and the resulting collateral damage.

  6. Owly
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    Owly Senior Member

    I wonder how many lives per year are lost to lightening? I can't imagine buying special clothing to protect for lightening........ It's not like seat belts or air bags. We get into airliners knowing that if anything goes wrong we have zero chance of survival. Do you know anybody who was killed by lightening? I lost two friends......... and their horses, that way, but I suspect that few people could name an acquaintance who died or was injured by lightening. Most of us can tell stories of boats that were lightening damaged however.

  7. jorgepease
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    jorgepease Senior Member

    I was curious ...

    2015 Lightning Deaths:

    Florida: One death in Bonita Springs on May 13 and another in Port Orange on June 26.
    Iowa: One death in Moscow on May 4 and another near Palo on June 20.
    North Carolina: Two deaths total on April 9. One in Cary and another in Anderson Creek.
    New Mexico: One death in Carrizozo on May 15.
    West Virginia: One death in Fayetteville on June 1.
    Arkansas: One death in Benton County on June 13.
    Florida: One death in Largo on June 19.
    Alabama: Two deaths total on June 23 in Opp.
    Arizona: One death on June 27 in Mogollon Rim, Northern Arizona and another in Benson on June 30
    Texas: One death on July 2, victim initially struck May 21 in Port Lavaca
    Alabama: 12-year-oil girl passed away July 7, after being struck by lightning on July 5.
    South Dakota: One death on Juy 12 on a disc golf course in Spearfish.
    Lightning Facts

    NOAA says that during the 10-year period of 2004-2013, 33 people were killed and 234 were injured by lightning strikes annually.

    On average, lightning strikes are fatal to about 10 percent of people who are struck. The remaining 90 percent survive, however they often suffer from an array of long-term, often debilitating symptoms.

    No place outside is safe when thunderstorms are in the area. If you hear thunder, lightning is close enough to strike you. Immediately move to safe shelter, a substantial building or inside an enclosed metal-topped vehicle.

    Below are some additional facts about lightning:

    25 million - Average U.S. cloud-to-ground lightning strikes per year
    50,000 degrees (F) - Temperature that lightning can reach
    1,800 - Average number of thunderstorms on earth at any given moment
    100 - Number of times lightning hits earth per second
    5-10 miles - Distance lightning can strike away from a thunderstorm
    The energy of a lightning bolt can exceed the power of a nuclear reactor
    Average lightning strike can light a 100-watt bulb for more than 3 months
  8. David Cooper
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    David Cooper Senior Member

    Ever since I heard about the metal strip in the banknote having an impact on the path taken by the current in a lightning strike, and the business of lightning flowing over the skin if it's wet rather than going inside the body, it's seemed obvious to me that it needn't take much modification to ordinary outdoor clothing (at very little extra cost) to reduce the damage done to people by lightning strikes, although you'd obviously need to make sure you aren't designing anything that attracts a strike, not least because it often leads to permanent hearing damage.

    But the important point for this discussion is that the current tends to flow round the outside if routes are provided to allow it to do so, and that should apply equally to a boat. If you provide alternative paths from where a mast reaches the deck to take the current out to the sides and down to the water from there, most of it should follow those two paths rather than continuing on down the mast - the electrons all repel each other strongly and will branch away readily if such paths of low resistance exist. However, I know someone who keeps parrots, and he has a large outdoor cage for them which was struck by lightning a few years ago (while the birds weren't in it). There was a piece of metal designed to hold some kind of perch that came into the middle of the cage from one side, and current flowed along it before jumping to the ground underneath where it scorched it, this happening right in the middle of what ought to serve as a good Faraday cage.

    I've also been reading things that suggest it isn't safe to touch two points of a Faraday cage while you are inside it in case there's a voltage difference between those points, which again suggests that Faraday cages can't be guaranteed to work, although perhaps that only applies when they aren't sufficiently complete. What I would do then is try to provide a number of safe paths for the current to follow round the outside of the hull, but I'd still want to create one from the bottom of the mast down to a grounding plate to guard against the possibility of a current flowing down that route and jumping through the hull. We heard earlier in this thread an account of lightning not following the route provided for it and exiting through the rudder instead, but most of the current probably did still follow the provided path to the grounding plate and, unsurprisingly, left no sign of having done so. The more paths you provide for the current, the more likely it is that it will stick to those and not jump out onto paths you haven't planned because you'll be reducing the strength of the current every time you split it, making it harder for it to jump across gaps onto any unplanned paths. You certainly can't rely on it following one single planned path as all the electrons are trying to repel each other off that path if they get the chance to do so, and that's why you would do well to push the odds in your favour by providing multiple planned paths. I suspect most of the current would follow the paths furthest out due to the powerful repulsion force that makes a Faraday cage work, so I'd try to give them enough conductor to travel through that it can survive a strike without vaporising in case the boat has to take a series of strikes.

  9. oldsailor7
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    oldsailor7 Senior Member

    A fellow sailor had his boat in a dock next to mine. He had rigged a copper wire from his mast shroud down to a metal plug in his keel to earth any lightning strike.
    He was hit by lightning and the bolt travelled down to the water line an then out sideways through the hull sideways into the water, blasting a hole in the side and his boat sank at the mooring. :(
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