Lightning protection

Discussion in 'Electrical Systems' started by missinginaction, Sep 8, 2013.

  1. missinginaction
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    missinginaction Senior Member

    Well, I've finished up my wiring but before I close up the panels I thought I'd ask a question or two regarding lightning.

    I know I can't protect against a direct strike.

    I understand that it is considered good practice by some to tie metal located high on the boat together and bring a cable down to a grounding plate or to the main engine where any lightning strike would (hopefully) take the easy path to ground and bypass (again hopefully) most or all of the boats current carrying wiring.

    I have a couple of stainless rails on the flybridge, one on the bow, a bimini frame, two vhf antennas on stainless steel mounts and an aluminum rub rail. For the purposes of this discussion I'm going to omit the rub rail from the grounding as it would be difficult to get a wire to.

    My thinking is to tie all of these items together using AWG 6 cable. Bringing the flybridge rails, the bimini and the vhf antenna mounts to a separate bus bar via the 6 ga. cable. Tie this upper bus to a second bus near the lower helm where I can tie the bow rail in and then run an additional length of cable back to a common ground point. The final bus (final ground) has the rail/antenna ground and the AC redundant ground (green or bare) connected to it. I can ground this to my engine or perhaps drill a couple of holes in the hull and install a grounding plate.

    This final ground would run parallel to the boats DC and AC wiring but be separate from any current carrying wire. There is another DC grounding bus handling all the DC current carrying wire.

    I realize that this set up is often skipped by a lot of boat owners but I'm just looking for some opinions on the value of going the extra step and installing this.

    Thanks,

    MIA
     
  2. SamSam
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    SamSam Senior Member

    There are lots of sites on the web explaining things. I had listed some but then the computer glitched and lost them all. One thing I wanted to say is this seems to be a popular opinion...
    http://www.pearson35.com/projects/lightning.htm
     
  3. missinginaction
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    missinginaction Senior Member

    Thanks Sam. I looked over that Pearson link. I'm wondering about the worth of a lightning rod an my powerboat. The VHF antennas would be the highest points and I'm thinking that if they were struck the charge would of course blow out the radio but since the antenna mounts are stainless steel and would be grounded perhaps the main part of the charge would choose the least resistive path to ground and travel through the antenna into the mount and through the awg6 wire. The radio could be replaced for $150.00.
     
  4. jonr
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    jonr Senior Member

    Non direct strikes can cause a lot of problems too. I use several different surge protection devices. Disconnecting things that aren't in use also helps.
     
  5. SamSam
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    SamSam Senior Member

    Lightning is like voodoo, very mysterious.

    I'm thinking an antenna might do good to attract the bolt but not to convey it to the water, and the path of least resistance wouldn't necessarily be the antenna. The strikes pulse, it's not just one solid blast. If you're driving in a good storm each flash is sometimes like a strobe light for 5-6 pulses and the antenna might disappear in the first pulse, leaving the lightning to find something else.

    Running it through the engine also doesn't seem like a good idea. At work, when welding on machinery is done they are very careful not to hook the ground lead to where current will pass through bearings and such to prevent arcing across the internal parts of the bearings or electronics.

    Although this doesn't tell you much about protection, it's kind of exciting...
    http://www.boatus.com/seaworthy/swlightning.asp

    This place seems to give some info..
    http://www.marinelightning.com/Information/GroundingConcepts.htm#Lightning
     
  6. JSL
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    JSL Senior Member

    Check out ABYC TE-4, it is fairly clear and detailed.
     
  7. CDK
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    CDK retired engineer

    MIA, your reasoning in post #1 is sound. I assume you have a rudder and perhaps some zinc in the water, so you probably don"t need a ground plate. But installing one does no harm of course.

    The vhf antennas are always a weak spot in lighting protection; they eagerly pick up electrical fields because of their shape. The set has one or more semiconductor devices that limit the voltage between the core and the coax shield, but when they conduct the electric charge is dumped in the ground lead of the radio set. Grounding the antenna mounts cannot prevent a dead radio, but keeps large discharges out.

    The quote about Dynaplates is nonsense. They conduct very well and if they receive a current load that vaporizes the trapped water, there has been a direct hit.
     
  8. SamSam
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    SamSam Senior Member

    I noticed that about the Dynaplates
    I mean, their whole reason for being is to offer a low resistance to current flow. But I let it go as I figured that wasn't the point. The point is all the 'trapped ' water being instantly turned to steam by such a large discharge of power causing the plate to explode and putting a hole in the hull. Whether that happens or not is debatable, but as a theory it sounds plausible.

    At another site it was saying a strike destroys those type plates, and that it was common for wooden boats to have large problems with lightning strikes that discharge through the hull as opposed to discharging through a ground plate, as the water in the planks reacts the same way, more or less exploding and destroying planks.

    With the info so varied and theory like, with statements like 'lightning protection systems actually increase your chances of a strike by offering a path of least resistance', a lot of people just go with the majority of boats and don't do anything, kind of like the ostrich head in the sand thing.

    Here's the TE-4 regs that JSL mentioned, the only site I could find that was free. I've no idea if they are current or not. They also say nothing about the sintered metal ground plate question.

    http://www.marinesurveyorschool.org/seminar_files/Lightening Protection.pdf

    Here is a good article from the 90s i think, talking about the shortcomings of the then current standards. In particular it talks about having only 1 ground plate, the resultant primary conducter having to be run through the boat as opposed to directly overboard, and the likelyhood of damage from side flashes because of it. Apparently if lightning discharges though fiberglass, say to an anchor chain, it will carbonize the laminate, not only weakening it in the meantime but providing a discharge path for the future. Although the carbon provides a path of least resistance, it actually has too much resistance for such high discharge loads, so if it is hit again, much worse hull damage is experienced.

    Lightning is voodoo. Black Magic.

    http://www.iamimarine.org/iami/exchange.pdf

    .
     
  9. JSL
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    JSL Senior Member

    Based on some first hand experience it is best that there be a dedicated ground plate... using boat parts (rudder, engine, etc) might not be a good idea. I heard of one case where the 'juice' went via the engine - gear - shaft - prop. .... it did not go well.
     
  10. SamSam
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    SamSam Senior Member

    Yes. They all mostly recommend grounding those things to the plate, but not so the strike goes through them to the plate.

    Although some did say the rudder and prop shaft and keel bolts are great for lightning grounds, I believe one even said to route it through the engine, I don't think I'd do it.
     
  11. Yobarnacle
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    Yobarnacle Senior Member

    I have been going to sea on steel vessels continuously since 1966 and never has MY ship/s been struck by lightning. The masts are welded to the hull, a closed circuit.

    I was always a believer in the grounded "antenna" radiates away electrical potential so lightning CAN'T strike. See the diagram for "cone of protection".

    Other types of lightning arrestors systems can be read about here.

    http://en.wikipedia.org/wiki/Lightning_arrester
     

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  12. missinginaction
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    missinginaction Senior Member

    Thanks everyone and especially sam and JSL for the reference and link to the TE-4 information.

    Based on what I'm reading it would seem that my original idea needs some modification. Since I'd have to run cable horizontally and there would be bends in the cable the original idea doesn't look attractive.

    However I can modify my plan to run a 4awg cable to a grounding plate mounted forward, directly under the antennas and helms (straight down) and then run a secondary awg6 cable back to the main bonding bus which will ground back to the engine. This would seem to be the best course given the information at hand.

    Then, when the storm hits, I'll just throw out the anchor and go in the berth and put a pillow over my head. :eek:

    I wonder weather it would be worthwhile to step the vhf antennas (put in a horizontal position) in the summer when the boat is docked and I'm somewhere else?
     
  13. Ike
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    Ike Senior Member

    Ewen Tompson is probably the number one expert on lightning and lightning protection. Below are links to many different pages on his web site. Below that are some other good links on lightning.


    Ewen Thompson's Website on Lightning http://www.marinelightning.com
    The Science Of Lightning Protection http://www.marinelightning.com/science.htm
    Non-technical Article on lightning protection http://www.marinelightning.com/Information/
    GroundingGuide.htm
    Technical Lightning Grounding Information http://www.marinelightning.com/Information/
    GroundingConcepts.htm
    A New Concept for Lightning Protection of Boats http://www.marinelightning.com/EXCHANGEOct2007Final.pdf

    L-36.com A collection of articles on lightning protection http://l-36.com/lightning.php
    Michael Kasten on Lightning Protection http://www.kastenmarine.com/Lightning.htm
    NASD on Lightning http://nasdonline.org/document/209/d000007/boating-lightning-protection.html
    Cruising Resources On lightning http://cruisingresources.com/Lightning_Protection
     
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  14. MikeJohns
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    MikeJohns Senior Member

    Michael Kasten has a good article based on Thompson's work here:

    http://www.kastenmarine.com/Lightning.htm

    We received one strike at anchor in a steel boat at night We had no problems whatsoever and didn't even know it had been us that had been hit until we were told the following day.

    Some numbers for the reality of strike rates are given for the US here:

    http://www.boatus.com/seaworthy/swlightning.asp

    I wonder how many metal boats (like we experienced) are hit and never even know. No side flash no fried electronics when you have a faraday cage same as a car being struck, again most people just wouldn't know.

    One posibility is that the schooner Nina was struck and sunk by lightening and that all the electronics including EPIRBs were knocked out in the hit.
     

  15. jonr
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    jonr Senior Member

    Interesting. Is it advisable to keep a second EPIRB/PLB in a metal box?

    I wish I had done this :-(. It took out the antenna and the radio.
     
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