Lightening Protection

[Howard]

Rather than hyjacking the nav lights thread, I figured it might be best to start a new one.

On the topic of lightening protection, I think we can all agree it's a good idea, the problem is how to do it. Do an Internet search on the topic and you eventually run across a study done several years ago by some professor in Florida that some view as gospel. Others contradict his findings. I think some guys are actually serious when they say their plan is to hover around someone with a mast taller than theirs. Hiding out in the crowd so to speak.

I spent quit a bit of time on this and came to the conclusion that the system you want is not a direct path that would encourage a strike, but rather one that if lightening does hit, provides a safe path to ground. The path has a "gap" in it that acts as a resistor. If actually hit, the jolt jumps the path and continues on to ground. Otherwise, it's not a good path and you may get passed over.

The idea I came up with was to run solid or braided copper wire down the inside of the mast to the base of the mast where it terminated at a plate. On the adjacent tabernacle was a corresponding plate that went to a ground (maybe a wide strip of copper attached to the bottom of the boat or to the side of the keel (Bronze bolt through the hull, or use a keel bolt or ???). The two plates are not connected, but are in close proximity to each other. Maybe an 1/8th inch or so. With this system, there would always be protection if the mast is up, but nothing to actually hook up.

Graham or others may know proven systems that work that would make this look dumb by comparison.

[Joel]

Howard , here is a link to a good article by John Payne

http://www.kp44.org/ftp/LightningStrikesOnboard.pdf (PDF)

Joel

[Charlie Jones]

Moved from Nav lights on P 22

or you could just fold the masts down and have a really low profile Grin

Frankly I've actually SEEN two boats get hit by lightning. One was a wooden boat, with a wooden mast, that was tied to a dock in between two plastic boats with masts at least 6 or 7 feet taller. Blew out the stuff at the top of the mast- otherwise didn't hurt the boat. The other was a fiberglass ketch on a mooring- lightning had been striking all around it into the water for at least 15 minutes when it took a shot to the mizzen mast- NOT the highest mast- the shorter one.

Laura and I have been anchored when severe thunderstorms were around and over us- In one we had 30 minutes of the most awesome lightning show I've ever seen- hitting the water within a hundred yards of us. We were ungrounded and totally unprotected- no problem. We sat through 5 different thunderstorms that night.

We have a friend who has a grounding strap down his compression post to his cast iron keel. His boat has been hit 3 times. And one time right beside him so strong it threw pieces of BOTTOM up into his cockpit ( he was in 4-5 feet of water)

Do what you feel comfortable with. I don't think ANYBODY can predict what lightning is gonna do or where it's gonna hit. Just do what you can, stay as far away from metal fittings as possible and hope it don't get cha. With our wooden mast and wood compression bulkhead, I'll be hanging some grounding cables off our shrouds as the best thing I can do.

[PAR]

I've been aboard two different boats during a strike, one protected the other not. The protected wooden ketch had a solid copper conductor (always use solid) attached to the mast and tipped, which ran down the mast, through the deck, eventually attached to a big ass plate on the exterior of the hull well below the waterline. The strike torched the conductor attachment clips and singed the wooden bulkhead it passed down on the interior and the connection at the plate was burned through, but no other damage, no leaks, holes or issues other then replacement of the BBQ'd pieces.

The other strike was on a 'glass production sailer with a deck stepped aluminum stick. The lightening traveled down the mast to the step on the cabintop, blew right through and arced to the centerboard pivot bolt and out to ground. It blew the step right off the boat and a substantial hole in the cabintop, which of course let the mast drop down into the cabin. The centerboard didn't drop off, though it cocked sideways and jammed the pin into melted plastic. The boat was leaking, the mast swinging wildly around inside the cabin nearly mashing Mike, who was below at the time. He was burned, Nick and I were singed and all off us knocked down and out. I was at the helm and aft, Nick at the companionway hatch. If I was out, I wasn't for long, though I was out of sorts for several minutes. Nick was worse for longer. Mike was in trouble and had difficulty doing anything other then remain in the  boat. He was out for a minute or two, before responding to ours calling if he was okay. The mast in the cabin made a lot of damage to the interior, basically acting a big ream, plowing through furniture, the inner liner, you name it.

We limped to shore bailing, pumps running and under jury rig with the headsail.

The "cone of protection" you've been reading about works and is the same technique NASA uses to protect the space shuttle and other launch equipment. NASA has done more for the furthering of the subject then anyone. There are several companies that specialize in protection systems. With the exception of a few, they all use the same cone of protection principles and you should too.

The gap idea you've come up with will permit the strike to find its own way to ground. You can rest assured it will not be as you hope, which is the nature of lightening. Provide a direct, uninterrupted path to ground, trust me. Replacing a few clips and some connections is cheap insurance if you're still able to wake up the next morning. For what it's worth, the chances of a lightening strike, is about one in a quarter million. It does happen and often with fatalities. I live in the lightening capital of the world. We get several thousand strikes in my area during an afternoon thunder storm. My odds are likely better for a strike then most and as a young man I enjoyed heavy weather sailing, which is inviting a strike.

[Tom Lathrop]

Many good thoughts so far.  Lightning protection is a good thing but not always easy to implement correctly.  Some boats just don't lend themselves to the best methods.  Making a direct (straight as possible) path from the mast top to the water can be difficult but usually possible.  Tying all metal rigging to ground is even harder to do well.  Running wires that connect stays, etc, together along the interior of the hull is a sure way to blow holes through the hull if the wire is run along the hull underwater. 

It is something of a catch 22.  Avoiding sharp sharp turns in bonding wire while avoiding running along the inside of the hull underwater can be a tough choice.

Reliance on the "cone of protection" to guarantee lightning protection is a mistake.  It is a good guide but no guarantee.  The so called cone is no more than a statistical average of probability of having a strike occur in a given spot.  Having been an engineer with Bell Labs, I have seen both the data and the actual apparatus used in developing the protection curve.  Given a large number of strikes, some will hit at all points surrounding the high conducting protective post or mast.  The cone just illustrates the probability of not getting hit at any point.

[PAR]

Tom's point should be well understood. There isn't any real 100% method of insuring you'll not get hit, but you can lower you odds of damage with some precautions and equipment.

Lightening by its nature is random. A friend living in Kentucky had the guy next door's barn struck and burn down. Well the next week, everyone was installing rods on their barns including my friend. He had two on his barn, one at each end and he got struck a few years later. Unfortunately, it struck the rain gutter he used to supply water to his cistern and caught the barn on fire anyway. He didn't lose the barn but was pretty pissed about the rods not protecting him.

Lightening can hit the pitcher on the pitcher's mound, but miss the 50' light poles and stands surrounding the field. A golfer can get a head strike, but the 40' tree next to him is missed. Or Charlie's example above on the ketch. Think of it as a teenage daughter and attempting to understand her next focus of interest or more importantly how accurately you can predict this.

[Howard]

On the practical then.....how to build a lightening protection system for a Princess cat-ketch boat.

The Florida professor I was thinking of was Ewen Thomson:

http://www.thomson.ece.ufl.edu/lightning/

Click on the sea grant pamplet.

Then there is this contemporary bit, which parallels the same notions as the John Payne article that Joel referenced:

http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.html

I don't know where I got the bit about the gap, but that isn't being mentioned anywhere in these articles, nor in most of the other ones on building lightening protection systems. To the contrary, they want to see as little resistance as possible.

This is where things start to break down and get fuzzy. I've heard before, and Paul referenced it too, that the conductor should be solid copper. Yet in the second article above, it mentioned this:

The main conductor carries the electrical current to the ground. Flexible, insulated compact-stranded, concentric-lay-stranded or solid copper ribbon (20- gauge minimum) should be used as the main conductor.

That doesn't sound like solid wire to me.

On to the Princess. Assumption here is unstayed birdsmouth wooden masts, so the only conductors down the mast that would normally be in place are the stainless sail track (unless you can find bronze), and any wiring for antennas or mast head lights (no stays). You gotta think the best place for the air terminal is the highest point, so that is the main mast. And the protection system on the main takes the jolt to the very front of the boat, as far away from the center of the boat (potential hiding place for crew) as you can get it. But then there is that secondary point...the mizzen. In the event you are in the cockpit trying to steer, you really don't want that to be struck, so the temptation would be to run all wiring for radios and lights up the main mast, but then that brings the whole electrical system into play, and the potential for the jolt to run around inside the boat. Eventually, all electronics go to the batteries, which are going to be as low as possible, which are then subject to a side flash through the hull.

So maybe all antennas and masthead lights etc. all go on the mizzen, which gets it's own grounding system in the aft end of the boat? How about right down the mizzen mast and tabernacle and through the centerboard trunk to a grounding plate? Could you line the bottom of the CB trunk with copper plates to act as grounding plate and reinforcement of the trunk for the CB to rub against? That gives you about 10 linear feet of grounding plate.

So the conductor is solid wire....4 gauge copper or ??????....which I think is about 3/16's in diameter. It extends at least a foot past the tip of the mast to be the highest point on the boat, and is ground to a pencil point tip (the air terminal). It comes down the inside of the mast to the base....and then what? For the mast to fold....there either has to be a terminal at the base, that makes a solid connection to another wire on the tabernacle, without making any curves or deviations from a straight line. Maybe the wire exits the mast at the top of the tabernacle and continues on?

On to the grounding plate. No grounding to "through hulls", but a bolt through the hull to a grounding plate isn't the same as a bronze through hull typically used for drains, etc. None up in the front of the boat anyway. What about the metal protective strip on the stem? What about extending that strip, or something like it right under the anchor well area, between the stem and front of the keel? A plate of bronze or copper, acting as both grounding plate and "grounding plate"....an abrasive keel protection strip for when you hit something or beach the boat. Bolt one to either side of the V bottom from the stem to the keel. The conductor down the tabernacle then gets split into two lines to make the transition from down to horizontal, forming a gentle curve and goes to two or three bronze bolts through the grounding plates on either side of the V hull?

And something similar being used for the mizzen?

[JeffM]

Good God, is this a scary topic!  I like more and more the idea of hiding in a mast forest AND dropping your own!  At the very least, I think I'll stay up north!

[Howard]

How about that St. Elmo's fire? That would be exciting!

[Tom Lathrop]

Howard,

The issue of solid versus stranded wire has to do with the fact that a lightning (no e in lightning) strike has the properties of broadband AC.  Before anyone yells that it is DC, let me explain.  The current pulse has an extremely steep wave front.  That is, the current builds up very rapidly in the initial surge.  That is why a lightning strike will be heard on any AM radio within range, regardless of the frequency it is tuned to.  All frequencies from DC to VHF are in the pulse.

A well known property of high frequency current is that it prefers to travel on the surface of any conductor.  So, a stranded wire has more surface and therefore less resistance to high frequency current than a solid wire of the same total cross section.  Whether this results in significantly better protection is something I don't know.

Florida State University operates the best laboratory I know of in lighting research. 

The only person I have known personally who was killed by lightning was a  Scout leader with his troupe on a camping trip in the mountains of western NC.  The troupe was sheltered under a tarp and under a tree.  They were in a forest so it would have been hard to avoid trees. He was wearing hobnailed boots and no one else was badly injured.  My conjecture is that he was hit by a side flash from overhead limbs to the tree roots with his boots making the path easier. 

I have worked on lightning damage in the telephone industry and studied it quite a bit but to say that I understand it would be  long stretch.

[Greg Luckett]

Good God, is this a scary topic!  I like more and more the idea of hiding in a mast forest AND dropping your own!  At the very least, I think I'll stay up north!

I live in Southwest Michigan on the big Lake.  A Catalina in the 30 to 35 foot range was hit two years in a row.  The first time she sank at the dock, the second time the yard folks caught her in time.  Needless to say, that owner sold her asap.

[Tom Lathrop]

Ray,

I see that you have been studying the book    All good information but I think we may be overdoing this issue for most of the small boats that we build.

Most of us will not be sailing our little boats in conditions that warrant extensive lightning protection.  We will mostly be going out in decent weather and close enough to shore to get off the water when lightning is threatened.  I don't mean that it is a non-issue but that it is not something to deter us from enjoying our little boats.  When in a threatening situation, we can make the proper decisions as skippers. 

I know of not a single situation in over forty years on the water in small boats, often in large racing fleets in thunderstorms, where lightning has caused a problem although I sail in the southern lightning belt.  I don't mean to say that lightning is not dangerous, just that we have many - many more more dangerous events to worry about, like driving to the lake.  More of us will probably die while sailing of a heart attack because we forgot to bring our nitro pills along than will be hit by lightning.  I do know of one of those locally.

At some point in either boat size or use, it makes sense to build in some lightning protection but I question whether it is practical or necessary in day sailers like our Core Sound and similar boats.  I will not be adding any to Lapwing and hope that I am not that one in several million that gets hit :-[ 

[PAR]

I have to agree with Tom. After sailing in many fleets, though some pretty nasty thunderstorms, for many years (hundreds of races), in about every conceivable size boat you can imagine, none were struck. Not mine nor anyone else's.

I've been struck, but also intentionally sailed in nasty weather in the lightening capital of the world, so it was just a mater of time for me. The vast majority of sailors will never get struck, even ones that seem to have crappy luck follow them around like the smell of a wicked fart.

If you sail as most do in fair weather and run for shelter when things get ugly, your odds are quite slim. If you prefer sailing through storms and testing you butt against the sea and mother nature, then protect your boat the best you can.

[Greg Luckett]

Par, I enjoyed that "crappy luck" comment.... ;D

[Ken_Potts]

  I'm with Tom - I won't be adding lightning protection to my CS17 (even though I HAVE been hit by it - But not in a boat).

  Having said that I wouldn't fault anybody for taking any precautions they feel comfortable with - Lightning hurts!

[Scott Dunsworth]

I wish I thought more about protection in the construction faise of my Belhaven. It will be a big chore to add it now. Very possible but a chore.

I have heard of people hooking a length of chain to the stays or mast and laying it overboard when caught out. If you had no chance to avoid the storm this might help but who knows.

Scott

[paul_stewart]

Ray,

Have you built (/planning to build) lightning protection into any Core Sound boats?  Any thoughts on design details for lightning protection for the CS20?

--Paul

[Tom Lathrop]

Ry,

For sure lightning protection is much simpler on a unstayed mast boat without stanchions and bow or stern pulpits.  There will be the boat wiring though.

Are you considering protection for both masts?  Would you do them individually, which I would favor as simpler and more effective?

[Ken_Potts]

  Try to remember that it's all a probability game.  I mentioned before that I've taken a lightning hit - What I didn't say is that I used to climb a lot and that's when I got it.  When my friends and I were hit it was pretty predictable.  We all knew we were dead.  There was no way out of our situation - We were on a knife-edge ridge and running for our lives when that bolt hit.  We were all generally careful about lightning but we were caught by a really fast moving storm that was unbelievably electrically active (It was terrifying/beautiful).  Given that we were able to run like (whatever) when we saw the storm coming instead of taking the time to reef and sail hundreds of yards to the nearest protection (the storm hit hard and fast) I'm not at all confident that I'd be able to get out of the way of a storm on the water, even fairly close to shore.

  Having said that, I'm an unofficial member of an unofficial club of eight (yes eight) of my close climbing buddies who've been hit by lightning.  We all made the right decisions given the situation and still got baked (fortunately not too badly).  I'm absolutely terrified of lightning as a result of my experience and I live in the #2 lightning fatality state (Hats off to Florida  ;D ).  BUT - Two of the members of my sparky club were in a "safe" place when they were hit - And they were hit

multiple times by that storm until in desparation they climbed up onto the (unsafe) ridge where the storm left them alone - They weren't safe until they did the WRONG thing.  Lightning is really unpredictable.

I haven't built lightning protection into my boat because based on my experience - And that of my really lucky (unlucky?) friends - I feel that I'd be walking a fine line between lightning protection and lightning attraction by trying to build an adequate path to ground on my boat.  I've chosen not to attract unnecessary attention.

  On a CS17 I think I might end up building structural flaws into the boat in the attempt to protect myself from the HUGE amount of electrical current.

I've made the decision as a man who's terrified of lightning that I'd rather sail this boat without lightning protection than try to build a direct path to ground into this hull with the additional mechanical stresses of a breach in the hull.  I'm talking purely about my boat and my experience here.  I'm just going back to the argument that every boat is a compromise.

[Greg Luckett]

Ken,

Ergo, my "medicinal brandy" solution.  There really is no right answer to the lightning avoidance.  Not having a grounded system tends to protect from attracting the multitude of weak streamer strikes, but gives no protection from the massive bolt.  On small boats there really is little difference between the mast pole and the water surface as far as lightning is concerned.  It is strictly a crap shoot.  All the lightning protection schemes for small boats are akin and as safe as me just hiding under a poncho.  Some of my best "religious" moments and promises to God were at those times.  I have had way too many close hits but so far not been hit.  When in the Seabees, I preferred getting shot at or mortared to being out in the lightning... the odds were better.  I had a really close call while on top of a volcano in Iceland.  It is amazing how fast some storms move and the faster they move, the worse the lightning.  Ever see lightning while in a snow storm??  Wierd stuff.

Darn, that "medicinal brandy" sounds good right now.  Is 8:18 AM too early? ;D