Lightening Protection

[Tom Lathrop]

Ken,

Great story of your brush with fickle lightning.  When you say you were all hit, I assume you mean that you were all in the electric field of a nearby hit.  I have also been on high rocky ground when one of those quick storms came up and was frightened to think that this was the hard place next to a rock.  A bolt did hit nearby but I only had my hair to prickle.  Soil conductivity is so high in such rocky terrain that your body looks pretty inviting to a lightning stroke. 

Liz and I were racing our Windmill when we were caught in one of those near electric fields and our hair jumped straight out.  Looked funny but neither of us laughed.  We had already capsized and brought the boat back upright and were bailing after taking the sails down.  The mast was wood but the halyard was stainless cable.  The lightning found a more inviting target and hit elsewhere.  None of the 200+ boats were hit although most might have been capsized.  I've sailed through many storms over the years, have been very near several bolts on land,  and am still lucky to not have been hit or actually seen another boat hit. 

[Charlie Jones]

;D Greg- remember- it's after 5 SOMEWHERE  ;D

[Greg Luckett]

Hey!  You're right, Charlie.  Thanks for reminding me.

I remembered something else about lightning.  When it would hit the Frigate I served on, the ship would make a strumming sound all over, and the Twidgets would go crazy getting our electronic gear back up and online.  I was a Boiler Tech. using analog, pneumatic control systems, so it did not affect propulsion as badly.  I did see some awesome sparks zinging around in the fireroom but if you blinked you missed the sight.  The sounds lasted longer.  We got some St. Elmos fire around the generators too.  No one ever got hurt from it as far as I can recall.

Oh, and I really hated going up on the stacks in the storms.  I think that is when I began to prefer being shot at to daring the lightning.

[Tom Lathrop]

Careful now Greg,  I was a Twiget. If that is what you called the ET's, on DDR 874, radar picket destroyer.  Seen a lot of that stuff there too.  St Elmos is a great sight.

[Greg Luckett]

Yep, Tom.  Twidgets = ETs and related fields, like Snipe = Marine Engineering related, Deckapes covered Gunners and Bosuns, and Airdales covered the Aviation related fields.  Of course, you could have an Airdale that was also a Twidget.  When I went to the Bees, all that passed away like an old dream unless I had to ride a boat or ship or plane....LOL.  Heck, I still have nightmares that I am being forced back into a ship's boilerroom for duty. ;D

[Ken_Potts]

  Greg,

  I agree with the medicinal brandy strategy.  I think prudence is the best course of action and if the first shot doesn't suffice it should be followed by more as necessary

  Tom,

  I haven't had to deal with lightning on the water yet but your mention of the windmill incident almost makes me shiver (okay, it DOES make me shiver  ).  I've had a few close brushes - Not quite hair-standing-up but I have felt the buzzing precursor to lightning and been spared.  Eek!  As you said the incident I mentioned was ground-flash, not a direct hit but there was definite current flowing.  We were trying to maintain separation as we ran towards what we believed to be safety but my friend at the front of the group tripped and fell at one point.  The second in line caught up with her and just as I ran up on him the lightning hit (we were all bunched together at exactly the wrong moment).  She was on her hands and knees in a puddle and saw electricity arcing between her arms and up to her upper chest.  I was intently trying to pick out each step on the rough trail so I was looking down when the bolt hit and I got to watch the twin arcs from ankle to ankle and from knee to knee.  If I remember correctly the friend who was in the middle didn't remember seeing anything - He just hit the ground.  I can't believe that Heather (up in front) survived with all that current so close to her heart but fortunately nobody suffered any lingering physical effects (at least two out of the three of us are really, really afraid of lightning now though ) One thing that may have helped us was that we were totally drenched by that time and maybe the majority of the current might have travelled through the sheet of water that was coating us.

  Ray,

  I think you're right - I think I was wrong with the structural compromise comment.  I would make decisions about lightning protection differently if I were building boats to sell - But like you I've opted not to add protection to my daysailer.  In my mind there are enough non-obvious factors to lightning protection that I'd rather concentrate on getting off the water in time than risk attracting unnecessary lightning strikes with a protection scheme that might not ultimately keep the bottom of my boat (or the top of my skull) intact - I'm not saying YOU can't effectively implement lightning protection, I'm saying I can't

  In the end I retreat to Greg's strategy and I'm careful to provision my boat with proper amounts of grog or a reasonable substitute.  I once worked for a man who's sister was forever crippled by a lightning strike she suffered in her house.  I know that's a statistically insignificant event but I'd rather fry sailing than watching Gilligan's Island...

[Charlie Jones]

Ken- one of my favorite quotes of all time is on Webb Chiles website- has some bearing here.

"Live passionately, even if it kills you, because something is gonna kill you anyway"

Think about it.

Oh, and my mother was struck by lightning inside a house when she was much younger- she was putting a chunk of wood into a wood stove when the bolt came down the stove pipe, and knocked her down

[Ken_Potts]

  That's a great quote Charlie!

  And I think it's entirely unfair that your mother had to deal with that stress while also dealing with cold.  Thundersnow ought to be illegal - Sure we're always subject to some form of mortality but I'd like it if we could either be taken out by lightning on a warm summer day or cold in a blizzard - It just seems to be unfair to get smacked by lightning while trying to keep warm.

  Ray,

  I'm not arguing against lightning protection.  I'm arguing against complicating the construction of my personal boat based on lightning protection.  when my friends and I were hit in the mountains we made all the right decisions.  Afterwards we discussed the issue passionately ad nauseum and came to the conclusion that we didn't have enough information to keep from getting hit that day - It happened because it happened.  Lightning is funny stuff and it IS possible to attract a hit that otherwise wouldn't have happened by trying to provide a good connection to ground.  In trying to provide a good connection to ground I might introduce a 90 degree turn in the wiring that would cause the bottom of my boat to be blown out in a strike that might not have happened if I just buried my head in the sand regarding lightning danger and built my boat per design.  I'm not arguing against the experts in the field because they are experts and I am not and I am certaainly not advocating avoiding lightning protection.  I am just sharing my direct experience with the unpredictable nature of lightning and my decision to basically bury my head in the sand.  I'm not saying I'm any safer than someone who implements a sound lightning protection strategy - I'm just saying I'm enjoying life until that final bolt barbecues my brain - Preferably on the water and not on the couch   How many of us have lightning-proofed our houses?

  Maybe the best course of action is to make sure that the masts are in an area of the boat where it is safe to blow a hole through the hull (the mast would not be stepped near a watertight compartment). After the hit one could jury rig a new mast step and limp home.

[Howard]

Charlie: One of my favorite quotes was from Joycelyn Elders, Surgeon General under Bill Clinton. "We're all gonna die of something".

I'm still on Princess sized boats, not day sailors. On an extended cruise, you don't pick and chose when you go out. You are always out. You stay on a boat long enough in lightening prone areas and you will find yourself in harm's way. If you are 5 miles from shore, those storms come up quick. You can't outrun them to shore. And who is to say you are safer in the back of an anchorage or at a marina than out on the water? Back to hiding out in the crowd again.

Ray's mention of using a band of copper down the outside of the mast sounds like a simple and somewhat elegant solution to the conductor. Would make the transition from mast to tabernacle in a straight line a with a good connection easier. The mizzen would be above the cone of protection, so yes, it gets the same treatment.

They need to both be connected to the same underwater grounding strip? If so, a long strip of copper running from stem to stern could be used.

Do the electronics get their own grounding strip? Leave them out of the lightning system, but grounded just the same? Otherwise, if it jumps into your electric system, it's going to try to find a way out.

[Tom Lathrop]

The overwhelming consensus of the prophets is also that lightning dissipators (Bottle Brush air terminals) that claim to prevent ligtning strikes have no basis in fact either and simply dissipate the money in your pocket.

.

Ray,

The bottle brush and the porous grounding plate are two of my favorite straw men.  I don't think the brush is better than a single sharp conductor or the porous plate better than a solid bar of the same dimensions.  There are good electrical theories behind this belief but I won't bore you with them.

[Charlie Jones]

I know many offshore fishermen who put a spare GPS and a spare hand held VHF into a metal box while underway. Then IF they get hit and the electronics gets fried, the metal box acts as a Faraday cage and hopefully they'll have the basics left.

We will be doing the same aboard Tehani with our back up hand held GPS and VHF.

[Tom Lathrop]

That will work Charlie, but you should wrap them is something like bubblewrap to hold them off the metal surface.  In the near field of a strike, some current will flow in the box case and that means a voltage drop, which means the possibility of a shock to anything bridging the voltage drop.

[Charlie Jones]

good point Tom, duly noted-thanks

[paul_stewart]

Great discussion, rich in ideas, points of view, experiences, and pros & cons; much appreciated!

Regarding...

A long thin ground plate is in fact and deed more conductive than a square one.  Lightening discharges from the edges,  so the ground plate would be a fore and aft 1 1/2 inch wide copper bar at least 1/32 inch thick screwed and 5200'd to the bottom of the boat with no fairing to fair awaay the transition.

The hard part is the electrical connections of the masts to the plate. ...

I think the easiest though not most attracitve solution would be to xcrew a half inch by 1/8 inch copper conducter down the entire outside of the mast after epoxy coating the mast ...

Ray, on the CS20 #103 we recently installed a stainless steel keel guard from bow to stern (3/4" x 1/8" x 22' in 4 sections).  Type-304 stainless steel is certainly has greater resistance than copper,  but....   Could this metal strip also serve as a grounding plate, I wonder.   Given that it is there anyway, would it be pointless to connect it to a copper strip running up each mast?    Any thoughts about that?

A half-baked idea that could leave us ... umm... half-baked?  I can see it now: a stike on the main mast, the keel guard on the bow flashes to 5000 degrees, the epoxy in the bow seam vaporizes, ...  oops. 

Picture at picasaweb.google.com/danceswithsandybottom/CS20_Flip__20080123/photo#5158900109286544658

http://picasaweb.google.com/danceswithsandybottom/CS20_Flip__20080123/photo#5158900109286544658

[Mike Vacanti]

Paul,

I've been following your progress on the CS 20, the workmanship looks very nice. I was wondering why you decided to make the keel band from 2 different type of stock? If the half-oval was from Jamestown I know that it is very expensive, was the flat stock used because it was hidden from view and cheaper?

Thanks

[paul_stewart]

Mike,

Yes that's exactly right.  The unpolished flat stock (3/4" x 1/8" x 6',  type 304 SS) came from McMaster-Carr for about $3/foot.  Initial sticker shock at JD strongly suggested that we should use this unpolished flat stock and drill, counter-sink, bevel (half-oval), and polish it ourselves.  Sure, why not.  In a moment of insanity I gave in to temptation and bought one section from JD (1/2" x 1/8" x 6' half oval) for the bow.  The other 3 sections came from McMaster-Carr.  During the installation we abandoned the idea of beveling and polishing the flat stock (for now, anyway)  --only because on further thought it didn't seem necessary!

That's the story, for whatever it's worth.  I'm speaking from genuine inexperience here.

The forum and all comments and suggestions are much appreciated !!!     

There's no way I'd get this boat built if I were doing it alone.  Fortunately, my son (Alan) and I make a good team  -- he's a budding boat builder/designer, experienced sailor, and engineering student at NCSU.  And I contribute something too, but I can't recall what it is.  We're having a great time on this project.  Icing on the cake if she floats.

[Mike Vacanti]

Paul,

Thanks for your reply, if you don't mind I have another question. It looks like the machine screws holding the keel band in place are screwed into an oversized hole in the keel that was then filled with epoxy. Is there a nut buried in the bottom of the hole and is the green goo on the screw threads some sort of release agent? That looks like a very long lasting approach to the problem of rot around fastener holes.

Regards

[paul_stewart]

Mike,  please see reply in "Re: Core Sound 20: Hull #103". 

http://www.messing-about.com/forums/index.php?topic=5825.msg50077#new

[Greg Luckett]

I agree as it will make it easier to sort out these threads.  Lots of good info floating around.

[Howard]

Last question. On completing the path from conductor to grounding plate, you now have to design a path through the hull to the grounding plate. Literature all says no 90 degree turns, yet most of the literature also references the use of keel bolts, bolts through the hull, etc.

A grounding wire down the tabernacle could be looped around under the washer and nut of a copper bolt, or a longer section of bolt left proud and the wire clamped to it. But at the bolt's terminal is that 90 degree bend on the grounding plate. Or when you build the hull, you could include that grounding wire through the hull to a bolt terminal (no soldered joints).

Lastly, holes through a plywood hull need to be drilled oversize and backfilled with epoxy, then drilled out again. Is that jolt going through the hull going to melt my epoxy? If so, will using a copper bushing (small piece of copper pipe or fitting) inside the epoxy as a sleeve for the wire or bolt to pass through and caulking that with 5200 or something work?

On the topic of electronics, I wasn't as concerned about the electronics as I was in keeping the jolt out of them. Wiring is going to be found inside the cabin and a strike to the electronics brings the potential of it running around inside the cabin, looking for a way out. Side flashes and all that. Maybe you keep the wiring running forward below the sole near keel bolts? A safe spot inside the cabin then would be on side bunks, feet up off the sole.

From there.....I like the plan where you down a couple shots of rum and hit the sack. Either you wake up when it's over or you don't.  ;D