[Rhodes22-list] sailing and lightning (long reply)

Sat Jul 29 19:31:00 EDT 2006

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?" 
>
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