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Bene, as I understand it the lightning rod does not "grab" static from the sky, but rather it allows the GROUND CHARGE to bleed off UP into the sky. When there is a trike, normally the ground charge goes UP creating a path of ionized air, and then the cloud strike comes DOWN that same (more of less) path, creating the damage.

A pointed rod apparently can discharge ions better than a rounded or blunt rod, which is why some makers were using "bottle brush" designs with many fine wires at the tip, since each fine pointed wire end allows another point where ions can bleed off.

If someone on a sailboat had a blunt lightning rod--it wasn't for performance reasons.
This is CORRECT. Lightning isn't attracted to the points, per se (though they certainly can be hit)... but static dissipation is the point (no pun intended) here.

As a charged area in the sky, a cloud usually or an area of clouds, moves past, it DRAGS ALONG BEHIND it an opposite charge looking for a place to go. In a static discharge (which lightning is that exactly) the ground charge will pull up a "grounded system" and the points on several lightning rods will force a static discharge, slower than a direct lightning discharge into the space around it.

This is why lightning rod systems on buildings include many, many points, all connected electrically together, and then tied to a ground path.

In a very powerful build up of static, many hundreds of thousands of coulombs of energy can be ready to discharge. Sometimes, even a lightning rod system can't stop it from happening!

I've had, over the course of about 19 years, about 6 or 7 very close strikes. I have a 20 foot tower, plus another 10 or so feet of antenna above the house. I've had wooden fences hit, trees next door and even the house down the hill from me (about 30 feet lower in altitude) - but my tower hasn't been hit (knock wood).

I usually keep my antenna systems grounded through a switch when not in use.

But you never know!

I was present at a friend's house many years ago when his CB antenna was stuck. Fiberglass antenna. It was pretty much vaporized, the coax cable melted and the radio was thrown across the room. His desk, the curtains and nearby electrical outlets caught fire. The breakers in the house and several neighboring homes were tripped. The phone system was pretty much obliterated in the neighborhood as well.

I've been "involved" in two near misses myself, both of which hurt like hell. Lightning hits what it wants to hit, when it feels like it, and the rest of the time it will spare you and your equipment.

Even with protection - you can still be struck. BUT, remember this, protection is BEST used to protect your equipment and persons than ignoring it.
 

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His CB antenna was probably not grounded.
Ummm... no, his equipment was properly set up.

A DIRECT STRIKE will pretty much demolish anything hit by it (in 99% of the cases).

I've seen a lot of direct strike damage, and properly grounded or NOT isn't relevant.

While being "properly grounded" will help, remember that on antennas - especially those that are fed with coaxial cable, there is NO grounding system on the antenna elements, as they are fed RF energy, which comes through a center conductor on the coax.

A direct strike on the antenna simply conducted the energy through the center conductor to the radio itself. The radio was indeed grounded internally, and thus, completed the path and blew the radio to bits.
 

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The brush like lightning dissapators don't make much sense on a boat, since they require a fairly decent ground connection, which most boats lack.

There are basically two schools of thought on lightning protection on sailboats.

1) Ground the boat, and bond all the major metal structures to the lightning grounding system. This will give lightning a path to the water in the case of a strike and also act to protect the occupants as much as possible. However, grounding the boat as such will increase the chance of getting struck slightly.

2) Don't ground anything on the boat. This reduces the chances of you actually getting struck. However, if you do get struck, the chances for catastrophic damage go way up, as sideflashes may occur and there is greater risk to the occupants of said boat.
Brushes are wire brushes... they contain a LOT of "points" to dissipate static and are by virtue of the amount of AREA better than a single point.

School of thought #1 above is correct....

School of thought #2 above is incorrect....

Salt water is VERY conductive. Fresh water is almost NON-Conductive, but will still kill you if you're in it and lightning hits near by (near by meaning within up to 10 MILES).

It amazes me to see some of the stuff that people put on the internet in this forums that they "believe is true" because "they have seen it".

I've read a dozen or so things about radios and antennas in this forum and on Cruisers forums that are just plain wrong, and sometimes dumb.

Lightning, if there is a DIRECT STRIKE can and will KILL you, and destroy every piece of electronic gear on your boat. Period. REGARDLESS of any and ALL protective measures you take.

Lightning is a non-discriminatory function of electrical energy and will seek the path of least resistance to ground (or in the case of the boat to water). It can and probably WILL be through your electrical system. It most LIKELY WILL destroy everything connected to the battery/electrical systems.

At the extreme amperage ratings of a bolt of lightning, and the unpredictability of what it can (and WILL) do you have to assume the worst is possible, take every precaution and then if the boat is hit, hope it paths to the water over the surface of the wet deck, and not through you, your electrical system and other people.

But, NOT taking ANY precautions at all will ensure that whatever is highest (your mast) will conduct the next bolt through your mast, to the hull, where it will leap to the electrical system (lighting on the mast) into your electrical system.

Placing a lightning rod on the highest points of the boat and surge arrestors on equipment will reduce the damage, but not completely mitigate it.

It takes approximate 600 volts to jump across one mil (1/1000th of an inch)... A lightning bolt typically A lightning strike can be from 300kv to 600kv, and can push as much as 15000 - 20000 AMPERES (current, the stuff that will kill you). It takes 10 milliamperes to stop your heart.

Remember the 600 volts and 1/1000th of an inch? Lightning can travel many MILES...

Don't play around in it, and don't play with it. Put protection up on the boat, and stay under cover if you can in a storm. (Obviously you might not be able to do this caught IN one at sea, but don't make yourself a target either).
 

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Is there anyway we could get some physics professors on this? Or maybe the mythbuster guys? They did that episode in the giant room that simulated lightening. They could us a Fred-sized boat and measure the effect of lightning protection.
I'm not a "Professor", but I certainly have a pretty in-depth physics background. lol. I taught electronics and physics for several years. I'm also a trained "weather spotter" - and an "amateur meteorologist" - I've got several years of working with the National Weather Service under my belt and get training every year from them.

I've been a Radio/Electronics guy for about 40 years.

I pretty much know what I'm talking about - but certainly if you can find a "Professor" get them in here.

I like the mythbusters too..... but suffice it to say, they do short lived experiments on things. I've seen real-time, actual evidence, and cleaned up the messes at transmitter sites, after lightning strikes. I've also seen people hit, and have been taken down twice by near misses.

Damage to electronics not plugged into a surge protection device have been handed to me many times... the strike was miles away, but took out modems and mother boards because they were plugged in.
 
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