At the risk of sounding like a newbie, which of course I am. I would like to know what the toilet brush on the top of my mast is for
And this is?
- Thread starter Zom-B-Land
- Start date
It’s a lightning protection device. There’s some controversy about whether they’re actually effective.
www.practical-sailor.com
Lightning Protection: The Truth About Dissipators - Practical Sailor
Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.
www.practical-sailor.com
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,037
Or it could be a real industrial toilet brush for cleaning the commode at a truck stop. 
You be the judge.
You be the judge.
Stored up there, you'll always be able to find it.Or it could be a real industrial toilet brush for cleaning the commode at a truck stop.
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The article in post 3 is interesting because it discusses the futility of this type of device in dissipating charge. The idea being that if you can dissipate the charge in a particular location, lighting wont strike there. Lets say you could dissipate charge with the wire brush twice as fast as the ground could supply it. Fairly soon the charge would drop to a low level. But.. this is not at all the case and the paper put some numbers on this. In that paper, salt water can actually supply charge 200 thousand times faster than the wire brush can dissipate charge. Ie, this mechanism of protection is completely futile.
Good discussion on lightning get complex as you really need to understand electric fields. A couple papers at the bottom of this post discuss lightning rod improvement studies. Interesting because if you are in a marina, you want your neighbors sailboat mast to be a slightly more effective lightning rod than yours. The guys in the papers did lightning studies where they had a bunch of (I believe) 6m tall lightning rods on a mountain top in New Mexico. They varied diameter and blunt vs sharp. Its interesting that in this field of competing lightning rods, the sharp tipped rods never got struck while the blunt rods had numerous strikes.
If you buy a lighting terminal now, it will be blunt shaped. Many years ago, it would have been sharp tipped. While trying to dissipate charge is a futile effort, the papers discuss how electric fields and corona currents affect leader generation. They attempt to model why the sharp tipped rods were less competitive at receiving lighting strikes.
http://lumma.org/microwave/Lightning...entStudies.pdf
https://journals.ametsoc.org/view/jo...l_2.0.co_2.xml
Good discussion on lightning get complex as you really need to understand electric fields. A couple papers at the bottom of this post discuss lightning rod improvement studies. Interesting because if you are in a marina, you want your neighbors sailboat mast to be a slightly more effective lightning rod than yours. The guys in the papers did lightning studies where they had a bunch of (I believe) 6m tall lightning rods on a mountain top in New Mexico. They varied diameter and blunt vs sharp. Its interesting that in this field of competing lightning rods, the sharp tipped rods never got struck while the blunt rods had numerous strikes.
If you buy a lighting terminal now, it will be blunt shaped. Many years ago, it would have been sharp tipped. While trying to dissipate charge is a futile effort, the papers discuss how electric fields and corona currents affect leader generation. They attempt to model why the sharp tipped rods were less competitive at receiving lighting strikes.
http://lumma.org/microwave/Lightning...entStudies.pdf
https://journals.ametsoc.org/view/jo...l_2.0.co_2.xml
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While it may not be proven to be effective, it can't hurt to leave it there. My boat had one, and, for almost 20 years, never received a lightning strike.
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I always thought those things were to dissipate any static electricity from standing rigging and spars, St. Elmos fire and such. Long ago I was going surfing and there was a very dark thunderstorm offshore, on the beach where it was not raining the humidity was oddly very low. When knee deep a lightning strike couple miles offshore made a tingle below water level and my hair stand up above. Paddled out on my knees so when I sat up at the line up I was still dry above the waist, another strike resulted in tingle of the legs and my hair standing up again. After the first wave and my body was wet I couldn't feel the strikes anymore, grounded I guess. No science just a once in a lifetime weird demonstration on electricity and water that left me a little unnerved.
FYI, the wire brush will enhance corona current. There is a good description of how this works in one of those papers (I will dig it up and post it if anyone is interested) but the high electric field at the top of the mast will pull an electron from an air molecule leaving behind a positive charged ion. The ion floats away driven by wind and the field of the charged cloud. The electron goes into the mast where it will either charge the mast like a capacitor or flow to ground.
So the wire brush things dont discharge.. in fact they do the opposite. But.. that is also OK.
I would not buy one new.. but also would just leave it there. Who knows.. maybe it does some sort of very complex electric field modification that makes upwards streamer creating less likely similar to the pointy lightning rod. Who knows..Im pretty sure the wire brush doesnt do anything bad.
So the wire brush things dont discharge.. in fact they do the opposite. But.. that is also OK.
I would not buy one new.. but also would just leave it there. Who knows.. maybe it does some sort of very complex electric field modification that makes upwards streamer creating less likely similar to the pointy lightning rod. Who knows..Im pretty sure the wire brush doesnt do anything bad.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 23,037
What? I was hoping it was a key to the Bermuda Triangle. Now that would be cool.
Thanks to all who have contributed. Some funny ones but also some really interesting and hood links. Lightning is one if those things to keep in mind as I have come across two boats so far that had lightning strikes. Much thanks to all. Zom-B out
Like always bear hunting with an overweight friend, you only need to outrun your friend not the bear.
My masthead is crammed with stuff, the guy across from me has a freestanding mast with large open masthead that serves as a feeding platform for the local osprey. I appreciate him taking the hit for all of us to enjoy nature on his boat.
I've never had lightning protection in 40 years and have never been hit by lightning.
Here's an interesting assessment of the lightning protection issue.
Lightning Is Huge Factor in Rising Insurance Costs. Why Won't ABYC Help?
Only They Can Get Us Out of This Mess, Loose Cannon Argues
Hair stands up because the follicles hold onto electrons and electrons repel each other, so they stand up as a way of getting the farthest away from each other as possible. By getting wet in salt water, you may have created a liquid Faraday cage that meant the electrons traveling through the conductive water over your skin couldn't move towards the inside of that saltwater shell that coated your body.
I don't know, nor have read much about lightning protection on boats, but it always baffled me as to why you would run the conductor down the mast and to the keel through the center of the boat. Wouldn't it make more sense to bond the keel plate to the outer shrouds and stays so a masthead lightning strike would more likely encourage the electrons to stay outside the interior of the boat? Wouldn't the conductive stays create a Faraday cage around the sensitive equipment and lives inside?
-Will
I think the idea is that carrying the current down in a straight line is the best. That much current doesn’t like to make turns. You also don’t want to build a configuration where the current is running on the perimeter and then tries to jump to the keel or mast across the interior.
We had a boat with one of the tallest masts in the harbor for 24 years and never received a lightning strike. We didn't have a "dissipator". Banging pots with spoons is supposed to keep bears away. Worked in our apartment in New York for as long as we lived there.
Well, yeah, that was my point about the Faraday cage approach. The problem, I see, with bringing the charge to the interior, is it may decide to pull from multiple points, like the engine and battery grounding to relieve the potential that a single heavy ground wire can't do. There's a LOT of wattage in a lightning strike and even if it went straight to the keel, it could still burn a hole through the interior along its way. The Skin Effect uses that potential to keep the charge out of the interior.
In my high school experience, most people seem to believe that the safest place during a lightning storm when driving is in your car because of the insulating value of rubber tires from ground. It was even taught by some uneducated teachers. But cars are safe because of the skin effect. When you consider that thousands of feet of air isn't enough insulation from ground, to keep lightning from the few inches a car's chassis is above the ground won't stop it.
I have no idea how many boats that do get struck by lightning, suffer little or no damage. Has anyone heard of a direct strike on a sailboat that didn't cause damage?
My previous boat was struck twice. In both cases, no major fiberglass damage (one burn mark on deck next to an upper shroud chain plate) BUT extensive electrical damage. Not really a pattern but random stuff stopped working, some melted power wires etc. Mast was bonded to a Dynaplate under the boat.
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