[Rhodes22-list] Reposted on Lightning (reply of 7/30 1:12pm)

[Arthur H. Czerwonky]

All,
I am reposting this reply from Ewan FYI.  I was told the first copy was quite garbled.
Art


Dear Art,

Thank you for forwarding this lively and interesting discussion.  Since it contains so many points of view,  it is impracticable for me to address all of them.  For example, of the four "INTERESTING FACTS" mentioned below,  I would agree with just one of them - 
Being caught out in a sailboat during a lightning storm does not mean you are going to be struck.
However, even this one comes with a  disclaimer.  Compared with being in a marina close to other boat masts, being caught out in a thunderstorm increases your probability of being struck by perhaps a factor of five or ten.   The empirical evidence for this estimate is Boat US insurance statistics.  Specifically, lightning damage to catamarans is twice that to monohulls. The brief explanation for this is that catamarans are wider and so there is less protective effect from neighboring masts in marinas. 

My best attempt at addressing the relevant issues are  contained in my web pages at www.marinelightning.com , that have been updated very recently.  But even here I realize that there is so much information scattered over  so many pages that it is difficult for the lay sailor to come to grips with the most important concepts, and why should anyone believe what I have to say, as opposed to, for example, the bristle brush salesmen who have a much cheaper product that, if you believe them, may actually prevent lightning from striking  in the first place?   (For one answer to this see http://www.marinelightning.com/AirTerminals.htm .  For another, Boat US have a photo of a seriously listing catamaran whose bristle brush is still intact at mast head following a lightning strike.  )

Here is an overview:

The home page www.marinelightning.com summarizes our approach, as having  a foundation in peer-reviewed science,  being consistent with observations of actual damage, and  being considered by the lightning protection committee of the National Fire Protection Association for inclusion in the 2007 version of NFPA 780 (see pages 21-28 in http://www.nfpa.org/Assets/Files/PDF/ROP/780-08-ROP.pdf   ).

Perhaps the most straightforward explanation is that on  http://www.marinelightning.com/science.htm .  After a brief historical introduction, the relevant lightning discharge processes are described and reasonable solutions are proposed.  A key point here is that we attempt to build a marine lightning protection system that simulates that on a building - with multiple air terminals, down conductors on the outside, and multiple grounding terminals around the perimeter.  Note that this is a very different scheme than the commonly used one of a single cable through the middle of the boat that terminates in a single one-square-foot ground plate, which is a good way to maximize the risk of sideflashes.

Products that have been developed to a commercial stage are described on http://www.marinelightning.com/products.htm These include the Siedarc (TM) grounding electrode, the GStrip (TM) 1 square foot grounding strip, and the ZzapStrap (TM) bonding strap for a boat on a boat lift.   The prices on all products are less than or comparable to those on similar products available elsewhere.  For example, a Siedarc (TM) electrode with  4' of cable is $215 compared with $419 for the single-electrode Strikeshield model CSSB-15.   The CSSB does come with a mast-mount connector, but otherwise the two are very similar.   Internal connections for the Siedarc can be made with  inexpensive heavy duty lugs.  

As you can  tell from the above, the installation of a reasonably effective lightning protection system is not trivial, and every boat is a custom job.  However, there are huge cost/benefits  for a one design such as the Rhodes 22  if the manufacturer is motivated to add this feature during production.  A complete system should be possible for a few percent of the cost of a new boat.  This is where your discussion group may be able to make a difference.  If you could convince General Boats ( 252-482-4372) that you, the customer, would like to see this feature on your boat then something is likely to happen.  Once a system and components have been designed for new builds, retrofits should be possible at an affordable price.   

I would really like to help.  Since I have a commercial interest in this, it is inappropriate for me to post anything directly on your message board.  However, please feel free to quote me in any way that you feel is appropriate, and let me know if there is  anything else I can do to .

Best regards,
Ewen Thomson.

Arthur H. Czerwonky wrote:

Dr. Thompson,

We have a discussion in progress on lightning, and how skippers of the Rhodes 22 fleet could best provide protection for crew, boat, and electronics in the event of a lightning accompanied storm underway.  The below 'wisdom' is a poor substitute for your studied insights for sure, but does this approach hold any promise for effectiveness?  The '35 foot conductor from mast head to the copper plate' would probably have to be 4 gauge.  Does this solution make sense?

Would appreciate your suggestions.
This reminds me of the first lightning protection system for my Mirage 5.5.  The maiden cruise in July 1986 was to Cumberland Island, GA, in the depth of a thundery summer. The new boat had not come with lightning protection since the builder assured me "we don't add that because it just attracts lightning".     So I cobbled together  a temporary system consisting of two fairly large aluminum plates attached to copper braid.  The theory was that one end of the braid would be wrapped around the mast and the two plates thrown over each side just before a thunderstorm.  Remember this was 1986, long before I realized that tinned copper braid is likely to corrode any aluminum it comes in contact with, and is likely to self destruct during a lightning strike.  In any event, and, with 20/20 hindsight, completely predictably, the plates never did get deployed.  When the inevitable storm rolled in we were nowhere near the boat, which was maybe just as well.  We were onshore at Cumberland Island holed up in the visitor's center watching the unprotected boat swing wildly at anchor as a lightning strike nailed one of our close neighbors.  Lesson learned:  Don't rely on a temporary system.  Soon after that my Mirage had what was, at that time, a state-of-the art system consisting of an aluminum rub rail along the centerline that was connected to bow pulpit, chainplates, iron keel, and aluminum rub rail.  See http://www.thomson.ece.ufl.edu/lightning/video.html for a video tour.  This system is now due for an upgrade.  Even though the boat spends the majority of its life on a trailer, the aluminum rub rail is corroding.  Besides, it is in the middle of the boat rather than near the waterline and so is scheduled to be pulled off and replaced by six electrodes just above the waterline.  Also, the connections were not up to par and will be beefed up to be at least as good as #4 gauge copper wire.   The design constraints are tight given the limited interior space of the Mirage 5.5, and the main problem is not how to do it, but how to do it most simply, with the least cost, and acceptable aesthetics.

There are a couple of interesting  postscripts to the 1986 discussion/argument concerning lightning protection.  The question as to whether the act of grounding a mast increases the risk of a lightning strike was a valid one.  While a scientific explanation based on electrostatic theory  predicted that bridging the short gap between mast base and water should have an insignificant effect on the electric field at mast head, that is, an answer in the negative, it would be nice to get some empirical answers. So Sea Grant funded a two-year research program in part to get an answer.  The results  are published in a Sea Grant bulletin (SGEB17 - see http://www.thomson.ece.ufl.edu/lightning/SGEB17.html or http://nsgl.gso.uri.edu/flsgp/flsgpg92001.pdf ) and presented in a video ( http://www.thomson.ece.ufl.edu/lightning/video.html )  The answer to the strike probability question is given  at http://www.thomson.ece.ufl.edu/lightning/SGEB17.html#Attachment   In another development, the builder,  Ken Fickett of Mirage Manufacturing,  has since become a staunch advocate of  lightning protection and close collaborator.  We are just completing the first installation of a complete system on a  Great Harbor 47 which we plan to write up for publication in PassageMaker. 


R,

Art Czerwonky

-----Forwarded Message-----
  
From: "Arthur H. Czerwonky" <czerwonky at earthlink.net>
Sent: Jul 29, 2006 6:31 PM
To: The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
Subject: Re: [Rhodes22-list] sailing and lightning (long reply)

John,

Helpful insights on a nebulous potential problem.  This could be a logical approach - about 35' of insulated heavy gauge cable run up the mast on the main halyard connected so as to project the top end about 12" above the masthead, connected to the other end with a copper plate welded/soldered and crimped, which would be put into the water near one of the upper side stays.  The top end would best have a 'spear' type end attached.  It would be used when strike probability is high, otherwise stowed forward.  Thoughts?

Art



-----Original Message-----
    
From: John Lock <jlock at relevantarts.com>
Sent: Jul 29, 2006 3:12 PM
To: The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
Subject: Re: [Rhodes22-list] sailing and lightning (long reply)

At 03:31 PM 7/28/2006 -0700, Tootle wrote:
      
http://www.cdc.gov/nasd/docs/d000001-d000100/d000007/d000007.html

And since John Lock would rather read than sail, maybe he should reasearch
this one.
        
That is an incorrect statement.  I would rather be sailing!  But 
since I am nowhere near water and don't have a boat, well...

I already did some research on the subject because it concerned me 
when the sailing bug first bit (not long ago).  Here are some salient 
facts and observations that I have found valuable - YMMV.

First, there are two schools of thought on adding lightning 
protection to your boat:

1) Lightning is a random and poorly understood phenomenon.  Trying to 
avoid or control it is probably futile and the results will be random 
and poorly understood.

2) Doing something is better than doing nothing and maybe it will 
help.  Besides it's a cool project.

I suspect that both points of view have merit and which one you 
subscribe to probably says more about your personality than your 
technical skills ;-)

SOME INTERESTING FACTS _

* Boats in saltwater are more likely to be struck than boats in 
freshwater, due to saltwater's higher conductivity.  However, boats 
struck on freshwater are more likely to be severely damaged due to 
the higher current loads in the strike itself.  (All this being 
relative to the small likelihood of getting hit in the first place.)

* Powerboats are potentially more dangerous in a storm than 
sailboats, because their lower profile means a greater amount of 
current is needed to make a strike.  So, if you're out in a typical 
fiberglass runabout and get struck, poooof.

* Being caught out in a sailboat during a lightning storm does not 
mean you are going to be struck.  There are many accounts of people 
witnessing water strikes very near their boats.  Many other factors 
are involved in setting up a lightning strike.

* Boats with lightning protection systems "may" be more likely to be 
struck, but experience less damage.  There only seems to be anecdotal 
evidence of this, but the theory seems sound.  That is - if you give 
lightning somewhere to go, it may hit you first, but be dissipated 
more readily (see more on this further down).

SOME MYTHS TO BE DEBUNKED -

"Mooring your boat among boats with taller masts will protect you"

Lightning is seeking it's best path to ground.  Height (or the 
distance of the "air gap") is only one factor.  Other factors - such 
as mast/keel composition, deck or keel stepped masts, presence of 
other grounding objects near the waterline, etc - will ultimately 
decide the lightning path.  For example, a lead-keeled, keel-stepped 
boat may be more likely to be struck than a deck-stepped, centerboard 
boat with a taller mast.  And you can't survey all those boats you've 
parked amongst, so it's false security.

"Clamping jumper cables on a shroud and dangling the other end in the 
water is good enough"

While that sounds good on the surface, it is in fact a very bad 
idea.  The problem is that you are depending on relatively small 
surface areas to conduct a helluva lot of current.  The connection 
points between the shroud and the mast and the jumper cable clamp and 
the shroud are not sufficient to conduct the amount of current a 
strike produces.  However, you have increased the likelihood of a 
strike by providing a grounding path.  I would strongly discourage 
this practice. (There is also a similar method, which involves 
wrapping the anchor chain around the mast.  Same problem.)

"Adding a good lightning protection system will protect me and my boat"

Well, maybe...  There is at least one documented case of a 
well-protected boat being sunk by a strike.  The mast and all the 
shrouds were grounded via heavy copper cable to a copper plate 
epoxied onto the bottom of the hull.  However, there was some 
moisture behind the plate.  When the strike occurred, that moisture 
was instantly vaporized into steam and exploded the plate off the 
hull (with obvious results).

SOME GOOD IDEAS IF YOU PLAN TO ADD A LIGHTNING SYSTEM -

* Use nothing but heavy-gauge (#4 or larger) copper conductors.  All 
other materials will corrode or provide inferior conductivity.

* Keep all leads as straight as possible.  Any sharp bends or kinks 
will defeat the purpose.

* Provide lots of contact surface.  Snaps, hooks, turnbuckles, etc. 
will not conduct the current loads you get in a typical strike.  Use 
large connecting plates, bolts, and flat washers, clean connecting 
surfaces and seal from weather.

* If you have a system installed, don't do anything to defeat it if 
you're caught in a storm.  For example - don't hold onto the backstay 
while you pull up the swim ladder or fiddle with the outboard.  You 
may involuntarily become an integral part of the lightning system (as 
Bill E. so eloquently described :-) )

VARIOUS LIGHTNING PROTECTION SYSTEMS -

There are basically three commercially available systems in use at 
varying costs and perceived effectiveness.  Again, this assumes that 
you subscribe to the "something is better than nothing" school of thought -

1) Complete grounding systems - the mast, shrouds, motor, electronics 
and any other conductive materials are wired into one or more 
grounding leads, which go thru the hull to a flat copper plate 
affixed to the exterior.  Yep, that means you have to drill one or 
more holes to bring the conductor thru and (as shown in the example 
above) must be mounted with great care to eliminate all possibility 
of moisture behind the plate.  These systems are usually 
professionally installed, custom designed for each boat, and cost 
mucho bucks.  See 
http://www.marinelightning.com/Information/GroundingGuide.htm for 
some details on this.

2) Static dissipators - These are like inverted stainless steel 
"whisk brooms" attached to the top of your mast.  The theory is that 
the many small metallic points offered by the strands of the device 
will dissipate charges gradually as they build up, rather than 
allowing potentials to increase to the level of a full strike.  There 
seems to be little evidence that this actually works, since it's 
supposed to prevent a strike.  So... you could say if you don't get 
hit, it must be working!  They are cheap and have the added benefit 
of keeping birds off your masthead.  See example at 
http://www.yachtgard.com/lightning.html

3) Mast grounding systems - These work on the same principal as #1 
above, except the focus is entirely on the mast, rather than the 
whole boat.  The idea being that if lighting strikes the mast (most 
likely point), we should give it somewhere to go before it can cause 
any damage.  In concept, this is similar to the "jumper cable" method 
mentioned earlier, but approaches the problem in a more realistic 
manner.  A large copper conductor is bolted to the mast and attached 
to heavy copper cable, which can be removed and attached when needed, 
leading into the water.  The water-end usually has some kind of 
device attached to increase its surface area in contact with the 
water.  See http://www.strikeshield.com/ for a commercial example.

There are many online resources on lightning and boats, protection 
systems, theories, rumors, innuendo... hey, after all it IS the 
Internet ;-)  Try a search on "lightning protection for sailboats" 
and you'll get plenty to confuse you further.

And finally, to Mike W: there are two problems with your system - an 
aluminum plate (1) with a right-angle bend in it (2).  You'd be much 
better off with a flat copper plate attached to the conductor without 
any bends.  I don't know what the physical constraints inside the 
trunk are, but there you have it.

Cheers!

John

"Ever wonder what the speed of lightning would be if it didn't zigzag?"