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If
you have any additional questions that should appear here, please send us
an email.
Frequently
asked questions about our products
We specialize in the manufacture of the following items:
·
SiedarcTM -
spark-promoting grounding electrodes embedded in Marelon through-hulls;
·
HStripTM
– 0.5 ft2 tinned solid copper grounding strip.
As a service we also address some commonly held misconceptions and more
general questions that have little to do with our products.
SiedarcTM
Q.
Has any testing been done?
A. Yes.
We (Ewen Thomson, Ken Elder and Richard Cohen) conducted some tests with
a 10 kV voltage source using KENNICK Inc.'s generator. One of the experiments was as
follows. An electrode was placed
with its tip about 4 mm above the surface of sea water from the Gulf of
Mexico as shown in the photo on the left. The galvanized steel water tank was
24" in diameter. The rings on
the bottom of the tank are spaced at about 1" intervals to give an
idea of scale.
  Photo by Ken Elder, KENNICK Inc
The
picture on the right shows the sparking extent for one test. Note that the ~15" diameter of the
sparks is about 100x larger than what would be expected between flat
plates. A particularly interesting
feature of the sparks is their occurrence in the air just above the water surface. Similar tests done with
immersed electrodes resulted in entirely different phenomena - a glow
discharge rather than spark formation occurring over a much smaller
distance (~ 1/2" diameter).
Despite
the low voltage of these experiments, the observed mechanism of spark
channel formation in the air just above the water surface is consistent
with other scientists' interpretation
of much larger sparks and actual lightning.
One explanation is that the sparks attach to charges on the surface
of the water. This observation is the
reason why we suggest that our SiedarcTM electrodes should be
installed just above the water surface.
Q.
Can the electrode survive a 100% lightning current?
A. No lightning conductor can withstand 100%
of all lightning strikes. The main
problem is overheating from long continuing currents, that occur in about
half of all lightnings and are responsible for fire ignition. Physically, there is about a 10V voltage
across the electrode-discharge interface.
Hence for a charge of say 10 C, the electrode tip is subject to 100
J of heating. However, once the tip
starts melting, no further temperature increase is possible since the metal
vapor disperses. Without going into
further proprietary details, we pay careful attention to these factors in
the design of our electrodes. As a
starting point, we adopted an engineering approach and designed each
electrode to the same specification as that advocated by NFPA 780 for an
air terminal for a Class II lightning– a 1/2" diameter solid
copper rod with a shaped tip. Tin
electroplating is added for superior corrosion resistance and compatibility
with connectors inside the boat.
Q.
Why
is the electrode/cable connection overengineered?
A In our experience, the weakest link of
any lightning protection system is each connection. To make the best possible connection to
each SiedarcTM electrode we get each one rotary swaged using the
same process as that used for standing rigging. Were it not for the tin in the connecting
cable, it would be almost impossible to discern where the cable begins and
the connector begins after the swage.
Q.
Do current or pending standards allow for sparking grounding
electrodes?
A. ABYC TE4 allows for supplemental
grounding conductors, as does the 2008 version of NFPA
760 Ch. 8. These can have a water-contact area of
less than 1 ft2, including zero.
HStripTM
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Question
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Answer
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What is significant about an area of one square
foot?
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Not much
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What do you recommend for the through-hull
penetration?
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Great caution
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Why do you recommend 1/0 or 2 AWG cable
whereas ABYC says #4 is adequate?
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Less margin of error
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Can I lower drag by embedding the strip flush
with the hull?
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To a point
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Why should the ground strip be made of solid
tinned copper?
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Safety & reliability
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Q.
What is significant about an area of one square foot?
A. One square foot is a nice round
number. It turns out (see Concepts)
that a typical lightning current flowing uniformly out of a 1 ft2
ground area immersed in salt water generates a fairly low voltage of about
11kV. However, even in sea water
sideflashes have caused hull damage when there was too large a distance
between the mast and the grounding surface and the connecting cable was too
close to the hull. In fresh water
the voltages generated are large enough to cause sideflashes from multiple
conducting fittings. As Thomson,1991
concludes "the 1 ft2 is shown to be hopelessly inadequate
to prevent sideflashes in fresh water". In fact, of more importance than the area
is the shape of the grounding surface.
A square 1 ft2
plate has a grounding resistance of 0.36 ohm. In contrast, our HStripTM with
dimensions of 0.36" x 2" has only half the area but less
resistance (0.29 ohm). Also, if we
split the traditional one square foot area into two strips, we can place
each near the periphery of the boat to allow for externally-routed
connections but still have a total area eqaul to that required in the
standards.
Q.
What do you recommend for the through-hull penetration?
A. Each
through hull penetration is a potential source of water leakage into
the hull and, in a water soaked hull, the connection through the hull
couples the lightning current into this hull moisture. The result can be multiple blow outs from
the hull moisture through the gel coat and into the water, where the extent
of damage depends on the whim of the lightning. Since the internal damage is invariably
masked by the hull coating, it is very difficult to ascertain this. So, for each hull penetration we
recommend careful attention to the hole treatment to ensure as large a
layup of insulating and waterproof insulation between the hull and the
connector. We also use proprietary
techniques in our connector design to minimize the risk of sparks forming
from the connector.
Q.
Why
do you recommend 1/0 or 2AWG cable whereas ABYC says #4 is adequate?
A. Many years ago the recommended cable size
for down conductors in standards was #8 AWG. This changed after the publication of
earlier scientific calculations of heating in cables in Thomson,1991
showing that a large lightning current could cause #8 copper cable to
melt. In addition, actual
observations indicated failure of #8 gauge wire. So #4AWG was chosen based on these
heating curves. However, other
research performed by Dr. John Tobbias indicated that even #4 gauge copper
shielding wire could rupture at large current owing to the magnetic pinch
effect. So we recommend 1/0 or 2 AWG
gauge for all major connections.
Q.
Can I lower drag by embedding the strip flush with the hull?
A. Since the sharp edges of the HStripTM
are designed to form sparks, these should remain exposed. However, 1 mm (.04") or so should be
enough for this purpose. So, yes,
but leave about 1 mm protruding.
Q.
Why should the ground strip be made of solid tinned copper?
A. With the price of copper heading into the
stratosphere, a cheaper product could be made using sintering to introduce
cavities into the metal.
Unfortunately, despite many opinions to the contrary, this does not
lower the resistance when used as a lightning ground. The scientific explanation comes directly
from the definition of ground resistance
where the symbols have their
conventional meaning. The dot
product in the denominator means that only the perpendicular component to the current density J contributes to the total
current. Merely increasing the total
surface area of S does not increase the current I and has negligible effect
on the electric field E. So the resistance of a solid immersed
conductor is theoretically the same as the resistance of one that has a
pitted surface. One very undesirable
consequence of filling a grounding conductor with holes is that there is
now less metal so that the resistance of the conductor itself is larger and
hence it is more likely to heat up when lightning flows through it. Add in the water that is inside the
holes, and we now have the potential for some of the current to flow inside
confined pockets of water. It takes
little imagination to work out what is likely to happen if this water
reaches its boiling point.
As for tinning, we tin plate all of our cuprous
metals, including brass and bronze, to improve their corrosion
resistance. This is consistent with
our philosophy to make all of our products to the highest possible
standards. And if we do not like the
standards, we rewrite them!
Common misconceptions & questions
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Question
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Answer
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Reason
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If I add a chimney brush to my mast I will not be struck
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Wrong
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Reputable scientists have much to say on this score.
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A temporary system is adequate
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No
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It needs to be deployed first
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Liability is less if nothing is done
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Wrong
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A good lightning protection system
lowers the chance of injury.
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A protection system just attracts lightning
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No
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Florida marine surveyors
should know.
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Can I reduce my insurance premium?
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Not yet
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A good LPS decreases the risk of injury & damage, but standards
are needed.
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Lightning always takes the shortest path to ground.
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Wrong
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Tortuosity in lightning channels reflects how air breaks down in short
spurts.
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How do I protect a steel ship?
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With care
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Sideflashes through the hull are not a problem, but crew and
electronics protection still is.
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A
temporary system is adequate?
Here is
a first hand account from Joe & Kathy Siudzinski's report from 27 October, 2003, when they
encountered some "Evening Unpleasantness". The full account plus additional analysis
is here.
It's getting darker, and
lightning starts appearing.
The wind drops off and eventually goes back to the north, but there is LOTS
of lightning coming in from the west.
Using the radar, I pick out a big cell moving fast towards us and after
plotting it I decide to go north to avoid it because there is a lot of
lightning to the south. This works, barely, as all this horrible stuff
passes a couple of miles behind us. Now, this isn't just inter-cloud
lightning, this is huge massive bolts coming down and hitting the water!
We try to compare notes with the other two boats - even though we are very
close, we can barely hear each other on either the VHF or SSB. Anyway, the
boat in front goes south while we and the one behind us continue
northwards. Big mistake.
To make a long story short, we spent eight hours surrounded by lightning
and occasionally some incredibly heavy rain. Why we didn't get hit, I'll
never know, because we repeatedly ended up right smack dab in the middle of
the storm cells.
I was too chicken to go out there
and install my home-made grounding rod (battery cable terminated in a
copper water pipe which I strap onto the mast) as by the time I realized
there was lightning it was too late.
I put our backup GPS, a compass, and a hand-held VHF into the BBQ (Faraday
Cage). Should have put one of the computers in there also.
Kept the radar and engines going the whole time, the boat nicely steering
itself on autopilot. Winds weren't too strong after the initial lashing,
maybe up to 20. Kept the mainsail up and on the fourth reef and locked dead
amidships with the two preventers and mainsheet.
This was one of the most awesome and spectacular events in my life - if we
weren't right inside these humongous thunderstorms, I would have loved
watching it. As it was, those sizzling bolts coming down into the water not
far from the boat were the most fearsome things I've ever witnessed. This
was continuous incessant lightning and not just a bolt here and there - it
was daylight out there! The smell of ozone permeated the air. Would you
believe I forgot that I now have a camcorder on board!
Anyway, I spent the time alternating between setting the engines and
autopilot to what I thought would avoid the major upcoming nasties (totally
unsuccessful in this) and then curling up next to Kathy on the bunk down
below. A pillow over the head minimizes the flashing lights. I think we
both got religion last night.
While in the middle of one of the last nasty chunks of thunderstorm that I
failed to avoid, I bit the bullet and turned the boat south and after we
got out of that one we were able to avoid the few remaining nasties.
It was over with by 2am.
At least the boat got washed.
The other two boats came through unscathed, but each caught with a man on
deck stowing sails when the winds hit.
Kathy's doing fine, figuring it's just another strange ritual one goes
through when sailing a boat across the ocean.
Liability is less if nothing is done?
There
is a belief amongst some manufacturers that if they install a lightning
protection system that then fails they are more liable than if they had
done nothing at all. There is no obligation to do this as standards
are not mandatory and are intended mainly to improve personal safety, not
to assure it. However, there is solid evidence
that even perfunctory adherence, such as grounding a mast to keel bolts,
decreases damage. Hence this
argument would tend to fail the "due diligence"
requirement.
Gary
Crist J.D. addresses this argument in "When lightning strikes"
published in Golf Course Management, pp. 21-22, April 1996 as
follows: "Many people incorrectly believe that liability is best
avoided by doing nothing. Those who assert this illogical argument believe
their approach disassociates them from the hazard, rendering them not
responsible for any resulting damage or injury. Such thinking is
legally incorrect, to say nothing of its utter insensitivity."
While Dr. Crist was referring to lightning hazards on golf courses, the
same reasoning applies to lightning protection of boats.
Other
legal points are raised by Krupnick et al. in "Lightning injuries:
Electrical, medical and legal aspects" pp. 157-194, by Andrews,
Copper, Darveniza and Mackerras (eds.) CRC Press, 1992. Specifically,
they point out on page 158 that although the phenomenon of lightning is
beyond man's control and therefore correctly deemed an "Act of
God", when someone in a position of responsibility does not take
reasonable measures to protect against injury and damage they may be held
liable. They state "It is generally held that if injury or
damage results from the lightning strike and, concurrently, an act of
negligence committed by a responsible person, such person cannot escape liability
if the injury or damage would not have occurred except for the persons
failure to exercise due care."
In
the context of lightning and yachts, it would seem that a lightning
protection system is a reasonable measure to take to insure the safety of
all on board. Perhaps the best argument against the do-nothing
approach is that liability claims only follow after costly damage or injury
and the best way to minimize the risk of these is to install the best
system possible.
A protection system just attracts
lightning?
A
common, and dangerous, misconception is that an ungrounded mast is
less likely to get struck than one that is grounded. It is dangerous
because this is frequently given as a good reason to leave a boat with no
protection system. The point was
addressed in a University of Florida research project whose conclusion was
a resounding "No" based on the experiences of marine surveyors: grounding a sailboat mast does not
cause an increased risk of a lightning strike".
Educational materials in the form of a pamphlet
and video
are available on line, and the section concerning grounding vs. no
grounding is here.
Note that in this survey and its discussion in the pamphlet,
"grounding" and "lightning protection" were
synonymous. Specifically, one of the questions asked of the surveyors was
"How many of these sailboats had a lightning grounding system, that
is, had the base of their mast
bonded to the keelbolts or a ground plate under the boat".
In fact, finding the answer to this question was one of the primary
objectives of the University of Florida
study. Theoretical arguments without experimental data are of limited
use because of the complexity and lack of understanding of the attachment
process. For example, recent work at New Mexico Tech indicates that
the upward going streamer is preceded by short (~microsecond
duration) current pulses rather than suddenly turning on. And
who could have predicted from theory that blunt
lightning rods work much better than sharp ones? So we attempted to get
some data by saturating the Lake Lanier
and Lake Norman
areas with posters requesting that we be notified if anyone was struck by
lightning. Unfortunately, no notifications came in. So the
surveyor's survey was the less-desirable alternative.
However, if anyone has a strong desire to add a lightning protection system
that is insulated from the water, the new NFPA
standard allows for this possibility. After considering the
problems of both galvanic corrosion and, even worse, electrolysis in a
marina where ground leakage currents are flowing in the water, we
included the provision for an air gap to break the circuit to any immersed
grounding conductor. This has the additional benefit of not
introducing AC ground fault current into the water, which is a major cause
of electrocutions. The air gap should be within 8" of the
grounding conductor and its breakdown voltage should be between 600V and
15kV. Since SiedarcTM
grounding electrodes are preferentially placed above the waterline, this
means that we can construct a NFPA-compliant system with multiple grounding
points that is electrically isolated from the water. See the Seminars page information about the NFPA
standard.
Can I reduce my insurance
premium?
An effective LPS lowers the risk of damage and
decreases insurance claims in several ways:
(1) In a well grounded and bonded system, the
risk of personal injury, and therefore a liability claim, is
decreased. Cost/benefit ratios can be very small. For
example, the cabin space below a deck-mounted mast and above a keel bolt is
at high risk of a connecting spark, a risk that can be virtually eliminated
by adding a bulkhead below the mast and connecting the mast base vertically
to the keel bolt.
(2) Although the survivability of
electronics systems is extremely difficult to guarantee, a network of
lightning conductors that surrounds the systems provides a good
shield. Also, measures such as
common cable harnesses, twisted wire pairs, and transient suppressors
used, for example, in telecommunication facilities are likely to increase
the chances. A frequent problem is that all electronics systems are
incapacitated, include the CDI system in outboard motors. Any
protection system that helps to ensure that key propulsion and control
systems are functional after a lightning strike will decrease the risk
of both personal injury and loss of the boat.
(3) According to Boat US the cost
of repair to a submerged boat is about 40% of the boat value. Hence
if a lightning strike blows out a through-hull transducer, the resulting
hole could form the basis of a very expensive claim. While the risk
of this happening cannot be eliminated, appropriate protective measures can
significantly lower this risk. As an example, consider a fisherman
with a metal superstructure surrounding the helm and the usual cluster of
instruments. Invariably the speedometer or fish finder is located in
the hull directly below the instrument cluster and connected to it via
narrow gauge wires. A likely path for a lightning strike is down the
VHF antenna into the instrument cluster, down the narrow gauge wire to the
speedometer transducer, and into the water. Since the transducer has
not been designed with lightning in mind, a blow out is probable.
The above reasons would appear to dictate an
answer of "Yes" to the question "Can I reduce my insurance
premium?" In actuality, it is much more complicated as any
premium reductions would need to be assessed according to guidelines
relating risk abatement to lightning protection measures. For
example, a boat either has a carbon monoxide detector or it does not, but
the same cannot be said of a LPS since each boat is different and the type
and degree of protection depends on the individual boat type.
For example, in a small open boat the main concern is to avoid a direct
lightning strike to a person, but in an offshore fisherman an equally
pressing need is for survivability of propulsion and control. To
further complicate matters, a LPS should always be installed during
manufacture but this adds costs that will probably not be recouped by the
owner in reduced premiums. On the other hand, the insurer also has
the prerogative of raising deductibles and denying coverage and so can
further influence the decision of the owners, and through them the OEM's,
to demand adequate protection.
Our dream ship is 55'-75' long
and made of steel. If you were to own such a vessel, how would you protect
it?
A steel hull means that the risk of holes being blown through the hull
present in fiberglass and wooden boats is virtually eliminated, although it
is possible that a through-hull could still blow out or some damage to the
hull surface could occur at the exit points. The remaining concerns
are then protection of (i) crew, and; (ii) electronics. Crew
protection reduces to two further cases (a) direct strikes, and; (b)
sideflashes.
(i) (a) Crew protection from direct strikes The objective here
is to ensure that lightning does not attach to any place on the deck, that
is, where a crew member might be standing. As an illustration of an
effective but extreme measure, NASA at Kennedy Space Center suspend a
catenary wire above a sensitive installation, for example a launch
gantry, to intercept the lightning via an upward-going streamer and
divert the lightning channel away from the gantry. A similar
technique can be used if a ship has multiple masts supporting a wire.
Vertical conductors afford some protection for the surrounding area
by attracting lightning attachment to their top, or, more accurately, by
preferentially launching an upward-going streamer to intercept the
downward-going leader. This concept has been summed up in the
term "cone of protection". However, in
practice the cone is rather leaky as it is based on probability rather than
certainty - a better name for it would be the "sieve of
protection"! Hence nearby lightning rods lower the risk of
nearby attachment, but do not eliminate it. Much better protection is
afforded inside metallic stays. In the case of a passage maker with a small
aft mast the area inside the stays could be considered well protected, but
almost no protection is offered outside this area. Anchoring during a
thunderstorm on this ship would be a hazardous occupation. Note that
the mechanism for lightning attachment is unaffected by the material used
in the hull and whether the mast(s) are grounded or not.
(i) (b) Crew protection from side flashes A sideflash
is a spark that travels (usually) between the main lightning conductor and
a nearby conductor - water (both in water tanks on the boat and the water
it is floating in) and crew members both being considered conductors.
However, if the lightning attachment point, for example a mast, is
not connected to a grounding conductor in the water then
a major sideflash may be more vertical than horizontal and carry a large
proportion of the lightning current - several tens of kiloamps.
Sideflashes can also occur in a boat whose main lightning conductor IS well
grounded. As a result of the high voltage caused by the
lightning current, discharges may form between the main conductor and any
nearby conductors. Bonding is the answer to this problem, but the
bonded conductor is then raised to the voltage of the lightning and this needs
to be taken into account. Not that this is bad - birds can perch on
high voltage lines without injury - but it may create problem areas near
the water, which is closer to "ground" voltage, especially in
fiberglass and wooden hulls. In fact, in order to prevent
sideflashes the whole boat needs to be raised to the potential of the
lightning conductor. This is much easier to do in a steel or aluminum
ship since the whole hull can be incorporated into the bonding system.
However, if the cabin and pilothouse are fiberglass or wood, separate
conductors need to be added for the main down conductor system and the
bonding system. When adding these care needs to be taken that the
conductors do not cause galvanic corrosion of the hull.
(b) Protection of electronics Lightning damage to
electronics is a major problem since the combination of low-voltage
equipment such as computers, remote transducers (e.g. weather instruments,
radar, radio antennas), and close lightning is a very bad mix. To
make matters worse, a direct strike is not necessary - electronics can be
blown from nearby lightning as a result of induced currents flowing off
masts, etc. Devices such as transient voltage protectors are designed
to limit voltages entering electronic circuits and the incorporation of
these on circuit boards significantly increases their chances of surviving
a close or direct strike. In addition, equipment layout and the harnessing
of interconnecting cables is crucial. There are some
fundamental principals that need to be followed to reduce the risk of
damage, but it can never be reduced to zero. As in all types of
lightning protection, it is a case of improving the odds. From my
past work on sailboats, the chance of damage to at least some
electronics was more than 90%, and to all electronics, 40-70%.
A "protected" boat in this study was considered to be
one with a grounded mast. This minimal level of protection improved the
odds in fresh water, but there was no difference in salt water.
Hence merely grounding the mast was not enough to improve the
survivability of electronics. I have no data on relative
electronics damage in steel hulled ships. From a theoretical point of
view, a fiberglass superstructure between a metallic mast and a steel
hulled ship can be regarded as an insulating filling in a conducting
sandwich. If no precautions are taken, both the bottom of the mast
and the top of the steel hull may simultaneously launch multiple sparks to
complete the lightning's path to ground.
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