MacGregorSailors.com

I use a CQ "Porcupine" static charge dissipater #8741 pictured at the bottom of this link http://thewireman.com/prodpix4.html - just bolted to the side of the top of the mast. I used something similar on my last boat for 18 years and thru many thunderstorms with no hits or damage, a lot of the time being the tallest mast around and spending most of those years in Florida and the Caribbean where lightning is frequent.

Mark

Lightening produces in or about........ 5000 to more than than 10,000 Amps at any where from 1,000,000 to 100,000,000 Volts
though it only last from .2 to less than .5 of a second. However your conductor, Must be able to carry this load to ground none the less.
All the while without vaporizing or disintegrating or even getting to red hot as to be the cause of a fire...
The discharge or static electricity to the surrounding atmosphere by use of a wire mast broom, is questionable at best.
Here a report of a hit note how small the boat was that was hit and surrounding by bigger taller boats........
http://www.smh.com.au/news/national/bla ... 56094.html
in 17 year's at Winthrop Harbor with anywhere from 300 to 500 sailboats in attendance not one strike and Chicago is known as well for having lots of Lightening.
Your best deterrent is just having good insurance
Some facts and figures in less than 10 minutes of reading time........http://hyperphysics.phy-astr.gsu.edu/hb ... ning2.html

There seem to be two alternatives when it comes to preparing for lightning:

Provide a dedicated grounding route or do nothing and provide the poorest channel (ie hide from lightning aas best possible)

I have chosen the latter and its also the cheapest

Personally, I don't think the latter option (hide) even exists. Dive's post above testifies to that. Lightning as often as not chooses a lesser target, from that of the highest, most grounded one. When it arcs across a mile (or miles) of air-insulation, it couldn't care less about the last few feet (IMHO) :-S

For the most part I agree (the exceptions are lightning rods that work)

So if there is little difference, I choose to spend the money on a bigger engine and not lightning protection. 10 days till my new, second hand 90 HP Yamaha. (not relevant to this thread, I'm just stoked about it)

Trouts Dream wrote:For the most part I agree (the exceptions are lightning rods that work)

Note too, that we always use no less than 2/0 braided copper cable
If you have a system installed by a Licenced, Bonded, Trained and Educated, Certified Installer.........your entitled to his Insurance Plan as your secondary insurer Work your hardest do your VERY BEST and Lightening is still beyond predictability.

It seems to me that although theories concerning lightning are plentiful, there is no definitive theory that you can take to the bank. Lightning protection on a sailboat therefore seems akin to wearing a necklace of garlic to keep werewolves away. There is no absolute knowledge that it works, but it probably cannot hurt. And, if it makes you feel more secure, then why not?

Bransher wrote:It seems to me that although theories concerning lightning are plentiful, there is no definitive theory that you can take to the bank. Lightning protection on a sailboat therefore seems akin to wearing a necklace of garlic to keep werewolves away. There is no absolute knowledge that it works, but it probably cannot hurt. And, if it makes you feel more secure, then why not?

Because you might cause the opposite effect .....?

I dont worry about the volts.....

The amps will kill and do the damage.

and most of the current is carried in the rapid oscillation of charge and its direciton during the entire bolt. The ionized air carries most of the current. Our wires are suggestions for formation of the ionized channel location. I figure the 2 to 4/0 is a better suggestion than my 5 or 7/64 steel stays....

Kind of like "dont worry about drowning......the fall will probably kill ya)"

Divecoz wrote:The discharge or static electricity to the surrounding atmosphere by use of a wire mast broom, is questionable at best.

Just curious as to why you say this Dive. Aircraft use the same principle to wick the static charge from the airframe, while in flight. Although they do not use this for lightning protection. Lightning strikes on planes in flight occur because the airframe itself provides a path for the lightning on it's journey to an opposite charge.

I use the same principle to drain the charge from my truck while traveling at highway speeds. I know that it works, because I carry very sensitive ham radio equipment and without the dissipator, the static level (depending upon humidity levels) is about 35 micro volts. When using the dissipator, the floor level is less than 1 micro volt. Usable received signal strength is about .25 micro volts. This is a significant difference.

As far as what lightning will strike. Generally the so called "cone of protection" can be used to figure your protection from taller objects near you. This can be determined by using a 45º angle from the top of higher objects near you. In other words: If you have a mast that is 35 feet above the water level, you would have to be within 35 feet of an object that is 70 feet tall to be within it's "cone of protection". The boat in Dive's picture was on a mooring and not within a cone of protection.

Even though this is generally true, lightning does not travel in straight lines and make steps of about 150 ft./step. It can change it's angle of travel by almost 90º at times. This means that it can be below the 50% level of a tall object and change direction, then strike within the "cone of protection", or even part way down the tall object.

There is no sure way to avoid a lightning strike. You can mitigate the damage with proper bonding and grounding, but the cost for a Mac is prohibitive and when done improperly, is worse than no protection at all.

~Rich

Hamin' X wrote:

Divecoz wrote:The discharge or static electricity to the surrounding atmosphere by use of a wire mast broom, is questionable at best.

There is no sure way to avoid a lightning strike. You can mitigate the damage with proper bonding and grounding, but the cost for a Mac is prohibitive and when done improperly, is worse than no protection at all.

~Rich

You answered most of it right there. No sure way and mitigate IMHO you might have added the word most in there after the word mitigate as well. Now allow me ask you? Doesn't movement of your vessel...improve the effects of that dissipator?
Lightening hit a 30 foot tree less than 30 feet from my 48 foot tall 55 x 55 foot house with its two chimneys above that.... right in and among that cone was a power service aerial cable running the property line for over 100 lineal feet with bare 2/0 neutral carrier and my 15 foot 2" Rigid IMC service head grounded with 2/0 braided copper cable that is cad-welded to a 10 foot ground rod... go figure...BTW I am glad it took the tree and not mine and or my neighbors electrical systems....... and maybe our homes as well.

waternwaves wrote:I dont worry about the volts.....

The amps will kill and do the damage.

and most of the current is carried in the rapid oscillation of charge and its direciton during the entire bolt. The ionized air carries most of the current. Our wires are suggestions for formation of the ionized channel location. I figure the 2 to 4/0 is a better suggestion than my 5 or 7/64 steel stays....

Kind of like "dont worry about drowning......the fall will probably kill ya)"

I've never played or ever even worked with a million volts. that would smart....
But I suggest you not be standing too close behind me, if I take a hit off the spark plug from my Bike....or even the dang lawnmower

As far a the vessel having to move, it does not have to, as the ions circulate independent of air movement. My radio towers do not move and it is the movement of my truck and aircraft that creates the charge.

Glad your home wasn't damaged. The mistake that we make when considering lightning, is thinking of it as coming down from the sky in a straight line. Whatever path the bolt was taking at the time, the tree was obviously the closest it had to earth. As you know, it will always take the path of least resistance.

I am glad that you mentioned cad-welding, as this is the only bond that will take lightning strikes over the years and is used in all commercial grounding systems. All others lack corrosion resistance, or mechanical strength. This is why I was saying that the cost would be prohibitive for a Mac.


~Rich

Rich do you use the brooms on towers??? I have never seen or installed those on towers. I have run miles , hundreds of miles of 500 MCM copper cable over the years in some very elaborate ground rod configurations though. My understanding and maybe memory.... is the broom allows for the build-up, to release ( discharge so to speak) its release capability is enhanced , as the vessel ( that's building up the charge) moves through the ions/atmosphere.......( ? )
That Bare service neutral cable runs right thru that tree so to speak... that tree is on the lot line with the service.. Its coming down Friday...It didn't do well. All Those Good Paths to ground and it........ chose a Wet Box Elder Tree instead...go figure but dont try and out figure lightening....

Ask A Scientist
General Science Archive

Lightning Strikes

Author: john blaylock
Text: Does lightning strike from the ground up or from the clouds down?

Response #: 1 of 1
Author: Robert Topper
Text: A Most Excellent Question! I actually did not know the answer to
this right away, but I have done a little reading up on the subject. Lightning
happens when a cloud builds up a separation of charge. The bottom of the cloud
(facing the earth) has a negative charge (extra electrons) while the top of
the cloud expels positive charges up and out into the upper atmosphere. So
the cloud has all this extra electrical energy on the side facing the earth,
and eventually it dumps the energy down towards the earth, which tends to have
a positive charge (for complex reasons) compared to the cloud's underbelly.
When the stroke begins, a series of little pulses of electricity come down
from the cloud towards the earth at really high speeds (about 1/6 the speed of
light!). These pulses are called steps, and the trail they pulse down along
is called the step leader. (not ladder). The air gets ionized along the step
leader and so this column of air becomes a good conductor of electricity. So
when the step leader (which is so faint that it is practically invisible) hits
the earth, a "conducting wire" of air is set up from the cloud to the earth.
Now charge can flow, but the first charges to move are the ones at the bottom
of the wire (near the earth). So, the stroke (which is now visible) starts at
the bottom (the earth) and runs UPWARDS from the ground! This return stroke
produces the bright light and a lot of heat, which causes the air to expand
suddenly, which causes a thunderclap. This sequence often repeats, with the
charge going up and down the leader. -Thanks to Feynman. There is a really
neat article in National Geographic on this subject! Check it out! http://news.nationalgeographic.com/news ... facts.html