[Rhodes22-list] Lightning mitigation

Sat Jul 14 11:22:37 EDT 2012

Hi All,

Following is a repost of a summary of some research I did a few years 
ago on lightning.  Much is still valid today even if some of the links 
aren't.

-- 
Cheers!
John Lock
~~~~~~~~~~~~~~~~~~
s/v Pandion - '79 Rhodes 22
Lake Sinclair, GA
~~~~~~~~~~~~~~~~~~

JULY 2006 -

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.

-- 
Cheers!
John Lock
~~~~~~~~~~~~~~~~~~
s/v Pandion - '79 Rhodes 22
Lake Sinclair, GA
~~~~~~~~~~~~~~~~~~

On 2012-07-14 00:51, peter klappert wrote:
> Just to bring you all up to date and ask a question (or two).
>
> Did I mention that the day I discovered the damage the Tampa Bay Times reported that Tampa has lost its (completely unofficial) status as lightning capital of the world?
>
> I may as well get to the important question right away, then rattle on for anyone interested in the patient's health. So here's the question:
>
> What kind of lightning mitigation does the R22 have? For example, it might be heavy guage wire or cable connecting the shrouds to centerboard or some other metal below the waterline.
>
> Does anyone know? Or has anyone done or modified this sort of thing on their boat?
>
> Here's the latest news. If I had more time I could make this shorter, but it's past midnight and the marine electrician is due at 8 A.M.
>
> The damage to Aeolia is, of course, more extensive than I knew when I sent the list under the subject "Major Electrical Problems." But it's not much more extensive, just quirky and seemingly patternless.
>
> There is no visible damage to hull cabin or rigging, but most electronics are fried, as are running and anchor lights; the VHF aerial apparently got melted out of its mast-top mounting. So far wiring seems to be ok, with some fuses blown and some not. The outboard's electric starter is gone, but the motor starts manually and runs like a purring cat. Both main & Genoa look to be like new--I was concerned because of their proximity to metal.
>
> I'll know a lot more after this weekend and hope to have Aeolia out on Tampa Bay sometime next week.
>
> The concensus among those I've talked to is that having the boat elevated on the lift and the aluminun lift itself increased likelihood of my boat being either struck or damaged by a strike nearby. Still, the total height of Aeolia on the lift, including 2-foot VHF aerial, is only about 36-37 feet above mean high tide.
>
> One leg of dock wiring is shorted, but that may be unrelated. Aeolia was not on shorepower at the time and the hull made no direct contact with metal--it was on the carpet-covered PT lumber of the lift bunks. Odds are that was part of the problem.
>
> Obviously I need to make sure the lift is grounded (never thot to wonder or doubt it until this happened) and the guy who built the dock is looking into what might be possible and legal by way of a lightning rod on a pole. His power boat has a 24' metal antenna and has never been struck. My next door neighbor docked his C & C 34 behind his house for many years without incident. Lightning strikes--or damage, at least--among the big sailboats on the other size of Apollo Beach (in Bal Harbor) are reputed to be rare.
>
> G'night!
>
>
>
>   
>
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