Ewan Thomson Reply "Lightning" Fw: Re: Fw: Re: [Rhodes22-list]
sailing and lightning (long reply)
Arthur H. Czerwonky
czerwonky at earthlink.net
Sun Jul 30 21:32:19 EDT 2006
Forwarded FYI.
Art
-----Forwarded Message-----
From: Ewen Thomson
Sent: Jul 30, 2006 1:12 PM
To: "Arthur H. Czerwon Subject: Re: Fw: Re: [Rhodes22-list] saili reply)
Dear Art,
Thank you for fo Since it contains so me to address all of th FACTS" mentioned below,&nbs -
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. Compar being in a marina close to other boat masts, being caught out in a
perhaps a factor estimate is Bo lightning damage to catamar brief explanation for this is that cata there is less protective effect from neighboring ma marinas.
My best attempt at addressing the relevant issues a in my web pages at www.marinelightning.com , that h updated very recently. But even here I realize that there is much information scattered over so many pages that it is difficul t for the lay sailor to come to grips with the most important
concepts, and opposed to, for example, much cheaper product that, if you bel prevent lightning from striking in the first answer to this see [1]http://www.ma rinelightning.com/AirTerminals.htm . For another, Boat US have a photo of a seriously listing catamaran whose bristle brush is still
intact Here is an overvi The home page [2]www.marinelightning.com summarizes our approa as having a foundation in peer-reviewed science, being cons istent with observations of actual damage, and being considered by
th Protection Associatio 780 (see pages 21-28 in [3]http://www.nfp a.org/Assets/Files/PDF/ROP/780-08-ROP.pdf ).
Perhaps [4]http://www historical intro processes are described and reaso key point here is that we attempt to protection system that simulates that on a buildin multiple air terminals, down conductors on the outside, and multip le grounding terminals around the perimeter. Note that this is a
very through the one-square-foot ground plate risk of sideflashes.
Products described on [5] include the Siedarc ( square foot grounding strip, and for a boat on a boat lift. Th than or comparable to those on similar pr elsewhere. For example, a Siedarc (TM) electrode wit cable is $215 compared with $419 for the single-electrode Str ikeshield model CSSB-15. The CSSB does come with a mast-mount c onnector, but otherwise the two are very similar. Internal conn ections for the Siedarc can be made with inexpensive heavy duty
lugs. As you can tell from the above, the installation of a 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 system should be po boat. This is where you difference. If you could con that you, the customer, would like to s boat then something is likely to happen. Once components have been designed for new builds, retrofits shoul possible at an affordable price.
I would really li in this, it is inappro your message board. Howeve way that you feel is appropriate, an anything else I can do to .
Best reg 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 Mirage 5.5. The maiden crui Island, GA, in the depth of a thundery su not come with lightning protection since the builder "we don't add that because it just attracts lightning". &n So I cobbled together a temporary system consisting fairly large aluminum plates attached to copper braid. The the ory was that one end of the braid would be wrapped around the mast
and the thunderstorm. Remember tinned copper braid is likely t contact with, and is likely to self dest strike. In any event, and, with 20/20 hindsig predictably, the plates never did get deployed. When t inevitable storm rolled in we were nowhere near the boat, which was
mayb up in the wildly at anchor as a neighbors. Lesson learned:&n system. Soon after that my Mirage had state-of-the art system consisting of an aluminum the centerline that was connected to bow pulpit, chainplate iron keel, and aluminum rub rail. See [6]http://ww w.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
ma corroding. near the waterline and replaced by six electrodes just above connections were not up to par and will be least as good as #4 gauge copper wire. The d are tight given the limited interior space of the Mirage 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 discussion/argument concernin question as to whether the act of groundi risk of a lightning strike was a valid one. W explanation based on electrostatic theory predicted the short gap between mast base and water should have an ins ignificant effect on the electric field at mast head, that is, an
answer in answers. So Sea Grant to get an answer. The res bulletin (SGEB17 - see
[7]http://www.thomson.ece.ufl.edu/lightning/SGEB17.html or
[8]http://nsgl.gso.uri.edu/flsgp/flsgpg92001.pdf ) and presented in
.html ) The answer to the strike probability question is given&nb sp; at [10]http://www.thomson.ece.ufl.edu/lightn ing/SGEB17.html#Attachment In another development, the buil der, Ken Fickett of Mirage Manufacturing, has since become a st aunch advocate of lightning protection and close collaborator. We are just completing the first installation of a complete system
on a&nbs publication in PassageMake
R,
Art Czerwonky
-----Forwarded Message-----
From: "Arthur H. Czerwonky" [11]<czerwonky at earthlink.net>
Sent: Jul 29, 2006 6:31 PM
To: The Rhodes 22 mail list [12]<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 [13]<jlock at relevantarts.com>
Sent: Jul 29, 2006 3:12 PM
To: The Rhodes 22 mail list [14]<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
[15]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
[16]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 [17]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?"
__________________________________________________
Use [18]Rhodes22-list at rhodes22.org, Help? [19]www.rhodes22.org/list
--
Ewen M. Thomson, Ph.D.
Marine Lightning Protection Inc.
3215 NW 17th Street< Gainesville, USA
Phone: +1 352 373-3485
Emai URL: [21]www.marinelightning.com
Innovative scie yachts.
References
1. 3D"http://www.marinelightning.com/AirTerminals.htm"
2. 3D"http:/ 3. ="http://www.nfpa.org/Assets/Files/PDF/ROP/780-08-ROP.pdf"
4. 3D"http://www.marinelightning.com/science.htm"
5. 3D"http://www.marinelightning.com/products.htm"
6. 3D"http://www.thomson.ece.ufl.edu/lightning/video.html"
7. 3D"http://www.thomson.ece.ufl.edu/lightning/SGEB1 8. 3D"http://nsgl.gso.uri.edu/flsgp/flsgpg92001 9. 3D"http://www.thomson.ece.u=/
10. 3D"http://www.thomson.ece.ufl.=/
11. 3D"mailto:czerwonky at earthlink.net"
12. file://localhost/tmp/3D"mailto 13. 3D"mailto:jlock at relevantarts.com"
14. file://localhost/tmp/3D"mailto 15. 3D"http://www.marinelightning.com/Inf 16. 3D"http://www.yachtgard.com/lightning 17. 3D"http://www.strikeshiel=/
18. 3D"mailto:Rhodes22-list at rhodes 19. 3D"http://www.rhodes22.org/list"
20. 3D"mailto:ewent at marinelightning.com"
21. ="http://www.marinelightning.com"/
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