another good reason to not have any alleged lightning protection---stu--if i misspelled something --please blame it on my boatkat, as he isnt a gud speeler and his speeelchix broakd....
Lightning Protection Question...
- Thread starter Nik
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As a possible solution to this quandry, for those that want to do this on a dagger board boat; how about (utilizing some ideas from the replies), but diverging as well. The DB trunk is not a tight fit, since the DB is hollowish (made to fill and sink) using a long electricains bit to bore top to bottom, pull some copper wire of appropriate size up through the hole, screw and epoxy/ laminate sheet copper (14 / 16ga) about 4-6" wide around the bottom (greater than 1sqft). At the mast step, but on the mast have a 1/2 - 5/8 copper bolt that attaches to / through the mast and run wire to the top, attached to a typical barn lightning rod. I think this design would minimise the directional changes. When the DB is up the 3' of wire could be neatly coiled, when down it would be out of the way. Just some further ideas. Any one see faults in this process?
To all, thanks for the words of wisdom and direction this has taken. Yes, I am familiar with both sides of the argument of having or not having. But these opinions are typically written by "PROFESSIONALS / EXPERTS" and we all know how that really works in real life. Here we now have another lucid understanding of the pros and cons. All six of our cats / kats were broken; and are now fixed. To thse tht hve isus wth splng errs, pls gt a lif, ths is a frndly frm; Lt's kp it tht wy. I posted this to get opinions on what others are doing out there now. In 25+ years of sailing, I never experienced a strike; though, I have felt a "change in the air", years ago when I did some racing. Nor, have I known any one to have been struck. As for now, if I see dark clouds... I run like HELL for port. Thanks again to everyone.
Nik
To all, thanks for the words of wisdom and direction this has taken. Yes, I am familiar with both sides of the argument of having or not having. But these opinions are typically written by "PROFESSIONALS / EXPERTS" and we all know how that really works in real life. Here we now have another lucid understanding of the pros and cons. All six of our cats / kats were broken; and are now fixed. To thse tht hve isus wth splng errs, pls gt a lif, ths is a frndly frm; Lt's kp it tht wy. I posted this to get opinions on what others are doing out there now. In 25+ years of sailing, I never experienced a strike; though, I have felt a "change in the air", years ago when I did some racing. Nor, have I known any one to have been struck. As for now, if I see dark clouds... I run like HELL for port. Thanks again to everyone.
Nik
before you bore
You might want to think about what a piece of copper wire vaporizing inside of your daggerboard would do to it. Perhaps running it along the aft edge would be more sensible?
You might want to think about what a piece of copper wire vaporizing inside of your daggerboard would do to it. Perhaps running it along the aft edge would be more sensible?
Keep in mind that any advice in this thread involving underwater structures might only apply in salt water. And then they only apply if you do a good job getting the charge to the underwater structure. What you will usually read is that the structures need to be "about 1000 times larger" to work in fresh water. Lets see... how big are those plates going to need to be?? You want me to drill a hole for a wire in the bottom of my Mac and then mount a plate
A fairly small wire like 8 gauge is able to easily withstand the current of a strike because the time frame is so short. The problem with small wires is that their "inductance" (inductance is basically resistance for very short time frames) is too high so lightning uses air as it a lower resistance path. Larger wires have lower inductance and this is more the reason you need larger diameter wires.
Someone mentioned the marine lightning protection web site (Dr. Thomson). In my opinion, that is the best place to read in detail. Go look up his patent if want more detail.
In my opinion, the arguments about grounding increasing your chances of getting struck carry about the same weight as the argument that the number 13 is unlucky.
A fairly small wire like 8 gauge is able to easily withstand the current of a strike because the time frame is so short. The problem with small wires is that their "inductance" (inductance is basically resistance for very short time frames) is too high so lightning uses air as it a lower resistance path. Larger wires have lower inductance and this is more the reason you need larger diameter wires.
Someone mentioned the marine lightning protection web site (Dr. Thomson). In my opinion, that is the best place to read in detail. Go look up his patent if want more detail.
In my opinion, the arguments about grounding increasing your chances of getting struck carry about the same weight as the argument that the number 13 is unlucky.
Bill Rossa mentioed the dangers of exploding wires. If you have never witnessed such an event I can understand the casual attitude. There is enough energy in a lightning strike to fuse sand into glass in a few micro seconds. I have experienced electrical shocks from 115 volt circuits and I have seen the effects of a 6600 volt line using a man for a conductor. The special effects people in Hollywood sometimes come close in the make-up in a horror film.
My house was struck by a minor discharge 30 years ago. It smashed a wall switch and a light bulb and broke a little concrete outside. A dead tree in my back yard a 150 feet from the house was struck by a large discharge and large chunks of bark landed a few feet from the house.
Just as not all gunshots are the same neither are all lightning strikes.
My house was struck by a minor discharge 30 years ago. It smashed a wall switch and a light bulb and broke a little concrete outside. A dead tree in my back yard a 150 feet from the house was struck by a large discharge and large chunks of bark landed a few feet from the house.
Just as not all gunshots are the same neither are all lightning strikes.
My personal view is that taking a spark that just travelled half a mile or more through highly resistive air and trying to steer it the way you want it to go for its last couple of feet is mostly a fool's errand. (Which is not to say that I never go on fool's errands.)
It is hard to generalize on lightning protection as strikes are not created equal. What may work for a low intensity hit may blow up at higher intensity. The problem we have with a sailboat and lightning is that our slow speed usually will not allow us to get out of the way of large thunderstorms. Heading for port may also not be an option as we sail in shallow waters and faced with strong winds we rather face a thunderstorm out where we may have some sea room. I follow statistics and they point out that it is safer to be on a sailboat during a thunderstorm than on a golf course near it.
Ionized air is not highly resistive.. it is a pretty good conductor. There is no reason to not believe lightning doesn't follow the physics we already know about. If you want to channel lightning, you have to compete with ionized air. If you provide a better path, "chances are" that the lightning is likely to take it.
When lightning is traveling through wire, there can be a huge amount of energy flowing in the wire - but not necessarily delivered to the wire. Power delivered in the wire is simply based on the current and resistance. Its a condition where whatever power delivered causes a temperature rise based on the thermal characteristics and also that in the short time frame, no heat is leaving the wire. The energy of lightning strike is usually delivered in the multiple millisecond time frame. In this condition, the heating of say an 8 gauge wire is really not that high - way less than required to melt the wire. A 12 or 16 gauge wire would be a different story..
Benny, my situation is similar on a lake. When the storms come in, the power boats get to the ramp first - and I'm stuck waiting. I don't even try anymore.
When lightning is traveling through wire, there can be a huge amount of energy flowing in the wire - but not necessarily delivered to the wire. Power delivered in the wire is simply based on the current and resistance. Its a condition where whatever power delivered causes a temperature rise based on the thermal characteristics and also that in the short time frame, no heat is leaving the wire. The energy of lightning strike is usually delivered in the multiple millisecond time frame. In this condition, the heating of say an 8 gauge wire is really not that high - way less than required to melt the wire. A 12 or 16 gauge wire would be a different story..
Benny, my situation is similar on a lake. When the storms come in, the power boats get to the ramp first - and I'm stuck waiting. I don't even try anymore.
As to protection:
It is thought that the protection of a higher mast (or tree or whatever)only extends in a cone about 45 degrees out. Therefore, essentially, if you are outside the rigging, you are outside the cone of protection, which is why short masts get hit surrounded by higher masts.
Next time you are in a plane, look out the window and imagine you are a lightning bolt looking for a place to zap. A few feet difference in height is pretty insignificant.
It is thought that the protection of a higher mast (or tree or whatever)only extends in a cone about 45 degrees out. Therefore, essentially, if you are outside the rigging, you are outside the cone of protection, which is why short masts get hit surrounded by higher masts.
Next time you are in a plane, look out the window and imagine you are a lightning bolt looking for a place to zap. A few feet difference in height is pretty insignificant.
we tries to speel correctly--lol--this lightning thing isnt very easily dealt with but the trip thru the gulf in the middle of days of lightning was a gas--the winds were awesome and the sailing was very very fast--it was a bit scary as hell...but there wasnt a single moment we didnt pray or wonder if we were gonna be done in by sea gods angry enough to kill us or ditch the boat--but we were only ones out there and did not get hit....we did get a ditch bag together--we were all 3 skeered...LOL..but how do you find immediate shelter 60 mi from shore when going 5-10 kts?? at 0200??or your kat either...
lol....
Energy delivered to a wire
I agree with the physical discription Walt brought forward. Energy is delivered to the wire based on the well known Ohm's relation. Which is why you use larger conductors, don't use solder, and do want to have clean tight low resistance mechanical connections throughout. With that said 2.23 geggawatts of energy is a lot of current and voltage. Millions of both. Even the low resistance of a wire will cause significant heating of it, probably vaporize parts/most of it and the ionized metal will continue to provide a low(er) resistance path to ground till the event is over.
Can you "control" a lightning strike through your boat? Not in the triditional sense so you can sleep through one and not get up to check on it. But you can increase your odds of successfully allowing lightning aboard (read no dead people, and no holes in the hull)? I think so.
One interesting concept is whether to ground the mast or not. Seems to most that grounding provides a better (lower resistance) path to ground and would encourage lightning strikes. verses ungrounding the mast and presenting a higher resistance path. The insurance companies have been keeping statistical info on such stuff (their business you know) and they have documented that grounded boats (in salt water) do in fact get struck more often than ungrounded boats. The ungrounded boats that do get struck are more often total losses as the lightning "has its way with them" Which is why the insurance companies recommend/require grounded boats for coverage. To me that is the end of the debate as all I can do is increase my odds of surviving a strike by grounding.
A 2 ohm path to ground from lightning rod to keel would absorb P=I^2 * R=millions^2*2=some meaningless first digit and 12 zeros=?000000000000 watts. The fact that the wires survive at all is a mystery. Clearly there are multiple paths reducing the watts absorbed to just millions of watts. Which is why I am a proponent of fore and back stay, mast and shrouds all being grounded.
I agree with the physical discription Walt brought forward. Energy is delivered to the wire based on the well known Ohm's relation. Which is why you use larger conductors, don't use solder, and do want to have clean tight low resistance mechanical connections throughout. With that said 2.23 geggawatts
of energy is a lot of current and voltage. Millions of both. Even the low resistance of a wire will cause significant heating of it, probably vaporize parts/most of it and the ionized metal will continue to provide a low(er) resistance path to ground till the event is over. Can you "control" a lightning strike through your boat? Not in the triditional sense so you can sleep through one and not get up to check on it. But you can increase your odds of successfully allowing lightning aboard (read no dead people, and no holes in the hull)? I think so.
One interesting concept is whether to ground the mast or not. Seems to most that grounding provides a better (lower resistance) path to ground and would encourage lightning strikes. verses ungrounding the mast and presenting a higher resistance path. The insurance companies have been keeping statistical info on such stuff (their business you know) and they have documented that grounded boats (in salt water) do in fact get struck more often than ungrounded boats. The ungrounded boats that do get struck are more often total losses as the lightning "has its way with them" Which is why the insurance companies recommend/require grounded boats for coverage. To me that is the end of the debate as all I can do is increase my odds of surviving a strike by grounding.
A 2 ohm path to ground from lightning rod to keel would absorb P=I^2 * R=millions^2*2=some meaningless first digit and 12 zeros=?000000000000 watts.
The fact that the wires survive at all is a mystery. Clearly there are multiple paths reducing the watts absorbed to just millions of watts. Which is why I am a proponent of fore and back stay, mast and shrouds all being grounded.
Somebody say it was? On the other hand, the force needed to ionize a half mile of air is, in the jargon of physics, really big, and that's what we're trying to channel through little bits of wire. It's a little like trying to steer a runaway bus by carefully placing pebbles on the road.
I would think you could find something on the Internet to back to this up?? I didn't try but if someone knows of a reference, I would appreciate the link. Some that I know of somewhat related:
http://www.kp44.org/ftp/A_CriticalAssessment_of_the_US_Code_forLightningProtection_of_Boats_IEEE.pdf
http://www.marinelightning.com/
In the first reference, the paper wasn't really trying to determine if grounding vs non grounding made a difference. There were more boats struck with grounding but any boat which had a connection between the mast to to keel was thrown into the "protected" category. Maybe there are just more boats in Marina's (where most strikes occur) that have the mast connected to the keel? We don't know and I don't think can make conclusions. The one conclusion is that the damage in an ungrounded boat is higher.
The second reference
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Catamarans generally do not have a metal keel in the water attached to the mast. Ie, they are always ungrounded. Yet.. they have twice the number of lightning strike claims. A conclusion here would be that simply being wide is more important than grounding or not.
Finally on the wire gauge, cant really argue with perceptions based on millions of amps (I think numbers are more like 30K amps), but I may try and calculate the actual heating in a 8 gauge wire using real numbers. In the first reference, Thomson says that 8 gauge wire is marginally adequate for the currents possibly meaning the temperature in the wire gets somewhat close to the melting point. As mentioned, I think the more important reason for needing larger wire is because of the lower inductance. Regardless of the wire itself being able to withstand things, a poor connection can be a localized source of big heat - big heat in small area = not good. Its important also to note that while the power in the wire is huge, the time frames are short. The temperature rise is proportional to power delivered * time.
"Grounded boats get struck more frequently than ungrounded boats." How frequently do boats of any flavor get struck? People walking on the beach and or on the golf course or hiking in the mountains also get struck by lightning. Millions of people doing all manner of outdoor stuff do not get struck by lightning what are they doing right versus the folks that do get fried?
No, but catamarans do have twice the surface area of other boats for the most part. I'd bet if you looked at the statistics, and the boats actually hit, the narrower catamarans, like the Gemini or Iroquois, were hit less often than wider cats. I'd also bet that larger boats are hit more often than smaller ones...
I saw this useful comment on the topic and thought i would post for further discussion http://www.sailnet.com/forums/seamanship-articles/19179-lightning-strike.html
Just a follow up regarding will wire burn up in a lightning strike.. lots of details.. but I guess I need to back up what I said..
First, the equation I'm using is delta temp * mass * specific heat
is equal to
Power * time or I*2 * R * time
This assumes that all the energy into the volume stays in the volume because of the short time frame (ie, none of the heat generated exits the volume)
The total equation for temperature change is then:
delta Temp = I**2 * R * delta time / ( mass * C )
Mass = density * volume = density * area * length
For copper, density = 8.8e3 kg/m**3
C = 287 J/Kg*C = specific heat of copper
Delta time assumed is 7e-4 seconds (summation of a bunch of 2 usec pulses over a much longer time frame)
For a "typical" 30KA peak current lightning strike, the temperature rise in one meter of wire is
gauge / resistance / mass / temperature rise in C
----------------------------------------------------------------------
10 / 3.3e-3 / 4.63e-2 / 158 C
8 / 2.1e-3 / 7.35e-2 / 99.6 C
6 / 1.32e-3 / 1.16e-1 / 25.0 C
4 / 8.31e-4 / 1.85e-1 / 9.84 C
2 / 5.22e-4 / 2.94e-1 / 3.90 C
The last column "delta T in C" is the temperature change in Celsius due to the power deposited in the wire.
For much stronger strike of 100 K amps,
gauge / resistance / mass / temperature rise in C
----------------------------------------------------------------------
10 / 3.3e-3 / 4.63e-2 / 1750 C
8 / 2.1e-3 / 7.35e-2 / 1110 C
6 / 1.32e-3 / 1.16e-1 / 278 C
4 / 8.31e-4 / 1.85e-1 / 109 C
2 / 5.22e-4 / 2.94e-1 / 43.3 C
Note that the temperature rise in the wire does not depend on the lenght. Longer wire will have larger volume/mass so you end up with the same temp rise no matter what lenght.
If you believe the numbers (I have no reason not to)... for a 30KA lightning current, the temperature rise in even 10 gauge wire is only 158 C. Copper melts at 1084.6 C.. so no problem.
For the much stronger 100KA lightning current, you can see that 8 gauge wire has increased temp by 1110 C - ie, its melted. But 4 gauge wire has only increased in temp by 109 C - not much at all.
Other than digging through text books, here is the only place I can find a reference on the method used.
http://www.eng-tips.com/viewthread.cfm?qid=253435&page=1
The time of 7e-4 seconds comes from an assumption that there are about 350 pulses over 35 msec and each pulse lasts 2 usec. 350 pulse * 2 usec = 7e-4 second (from some reference I will find is someone REALLY wants to know).
First, the equation I'm using is delta temp * mass * specific heat
is equal to
Power * time or I*2 * R * time
This assumes that all the energy into the volume stays in the volume because of the short time frame (ie, none of the heat generated exits the volume)
The total equation for temperature change is then:
delta Temp = I**2 * R * delta time / ( mass * C )
Mass = density * volume = density * area * length
For copper, density = 8.8e3 kg/m**3
C = 287 J/Kg*C = specific heat of copper
Delta time assumed is 7e-4 seconds (summation of a bunch of 2 usec pulses over a much longer time frame)
For a "typical" 30KA peak current lightning strike, the temperature rise in one meter of wire is
gauge / resistance / mass / temperature rise in C
----------------------------------------------------------------------
10 / 3.3e-3 / 4.63e-2 / 158 C
8 / 2.1e-3 / 7.35e-2 / 99.6 C
6 / 1.32e-3 / 1.16e-1 / 25.0 C
4 / 8.31e-4 / 1.85e-1 / 9.84 C
2 / 5.22e-4 / 2.94e-1 / 3.90 C
The last column "delta T in C" is the temperature change in Celsius due to the power deposited in the wire.
For much stronger strike of 100 K amps,
gauge / resistance / mass / temperature rise in C
----------------------------------------------------------------------
10 / 3.3e-3 / 4.63e-2 / 1750 C
8 / 2.1e-3 / 7.35e-2 / 1110 C
6 / 1.32e-3 / 1.16e-1 / 278 C
4 / 8.31e-4 / 1.85e-1 / 109 C
2 / 5.22e-4 / 2.94e-1 / 43.3 C
Note that the temperature rise in the wire does not depend on the lenght. Longer wire will have larger volume/mass so you end up with the same temp rise no matter what lenght.
If you believe the numbers (I have no reason not to)... for a 30KA lightning current, the temperature rise in even 10 gauge wire is only 158 C. Copper melts at 1084.6 C.. so no problem.
For the much stronger 100KA lightning current, you can see that 8 gauge wire has increased temp by 1110 C - ie, its melted. But 4 gauge wire has only increased in temp by 109 C - not much at all.
Other than digging through text books, here is the only place I can find a reference on the method used.
http://www.eng-tips.com/viewthread.cfm?qid=253435&page=1
The time of 7e-4 seconds comes from an assumption that there are about 350 pulses over 35 msec and each pulse lasts 2 usec. 350 pulse * 2 usec = 7e-4 second (from some reference I will find is someone REALLY wants to know).
I think that a "typical" lightning strike is much like the "average" man, great for statistics but awfully hard to find in life.
I believe that most people who have lived to tell about their experience with a lightning strike were, A. very lucky and B. exposed to a minor strike. Two years ago the top ten feet of a utility pole was blown into kindling wood by a strike but the telephone cables survived.
I believe that most people who have lived to tell about their experience with a lightning strike were, A. very lucky and B. exposed to a minor strike. Two years ago the top ten feet of a utility pole was blown into kindling wood by a strike but the telephone cables survived.
lightning calculation correction
Thanks Walt. After reading your post I realized that I was assuming the time. In this case a strike lasting 1 second. A pretty massive lightning strike. you are of course correct.
Thanks Walt. After reading your post I realized that I was assuming the time. In this case a strike lasting 1 second. A pretty massive lightning strike.
you are of course correct.- Status