Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 25-05-2015, 11:42   #46
Registered User

Join Date: Aug 2013
Location: Saint Lucie county FLa
Boat: 35' Pearson sloop
Posts: 383
Re: Lightning Dissipator -- Any Good?

I understand all the negatives about dissipators however I also notice the large numbers of them around big commercial airports, military instalations and even around ammo. Storage dumps. Why? As to the comment about repairing more boats with them than without them, I think is just coincidence. How about a chain from the backstay to the water? My mast is a bit like a giant lighting rod!
__________________

__________________
lesterbutch is offline   Reply With Quote
Old 25-05-2015, 12:21   #47
Registered User

Join Date: May 2009
Location: Vancouver, Wash.
Boat: no longer on my Cabo Rico 38 Sanderling
Posts: 1,794
Send a message via MSN to John A
Re: Lightning Dissipator -- Any Good?

If there is the remotest possibility that they'll work, why not install one?

We all carry spare anchors, lite rafts, eprib, life jackets, life belts, etc, in anticipation that something could happen and just maybe our purchase will be needed. r
__________________

__________________
John A is offline   Reply With Quote
Old 25-05-2015, 13:18   #48
Registered User
 
sanibel sailor's Avatar

Join Date: Feb 2013
Location: Sanibel FL
Boat: 1979 Bristol 35.5 CB
Posts: 977
Re: Lightning Dissipator -- Any Good?

That lightning bolt just came thru a gap of several thousand feet of air space. I think it cares little about conductive paths/insulators or even bottle brushes. It is random and kinda does what it feels like. I don't think our common concepts about electrical behavior are all that applicable.
__________________
John Churchill Sanibel FL
NURDLE, 1979 Bristol 35.5 CB
sanibel sailor is offline   Reply With Quote
Old 25-05-2015, 13:19   #49
Registered User
 
sanibel sailor's Avatar

Join Date: Feb 2013
Location: Sanibel FL
Boat: 1979 Bristol 35.5 CB
Posts: 977
Re: Lightning Dissipator -- Any Good?

Quote:
Originally Posted by Nicholson58 View Post
We have a similar device. In the last two strikes, it managed to save itself but nothing else. Total wipe-out of VHS AIS STERIO 60 amp main breaker, 20 glass tube BUSS fuses, many LED lights etc. Also melted and exploded was the Windex next to the undamaged lightning preventor.
I guess it worked then... survival of the fittest.
__________________
John Churchill Sanibel FL
NURDLE, 1979 Bristol 35.5 CB
sanibel sailor is offline   Reply With Quote
Old 25-05-2015, 18:04   #50
Registered User
 
Nicholson58's Avatar

Join Date: Jan 2011
Location: Live aboard
Boat: Camper & Nicholson58 Ketch - ROXY Traverse City, Michigan No.668283
Posts: 3,466
Images: 83
Re: Lightning Dissipator -- Any Good?

Quote:
Originally Posted by lesterbutch View Post
I understand all the negatives about dissipators however I also notice the large numbers of them around big commercial airports, military instalations and even around ammo. Storage dumps. Why? As to the comment about repairing more boats with them than without them, I think is just coincidence. How about a chain from the backstay to the water? My mast is a bit like a giant lighting rod!
"Step on a crack & break your mother's back"

"Lightning never strikes twice" HMMMMMmmmmmm We seem to get it right in the lighting dissipater about every 1.5 years.

The generally accepted practice is to make the boat, rigging, hull approximate a faraday cage. The metal rigging permits the electrons to get as far from one-another as possible. There should be conductors along the hull surrounding the cabin space like a large bird cage so the electrons can continue to avoid each other. The cage is bonded to a ground plane. Chains over the side attached to the rigging provides yet another path to ground. We have all of this - but no matter. Perhaps it will be better in salt water.

Photo is in Marquette harbor at Cinder Park. The basin is surrounded south & west by high bluffs & commercial buildings with flag poles & towers. The structure you see is to the east. It is the historic ore dock where ships used to load up. We were awakened to rolling thunder about 5:30 AM. This followed our last electric attack by about two weeks & 2500 bucks. We franticly unplugged everything. I watched as the ore dock was struck three times in 10 minutes. Glad to not be at the yacht club.
Attached Thumbnails
Click image for larger version

Name:	DSCF7600.jpg
Views:	78
Size:	407.2 KB
ID:	102703  
__________________
Nicholson58 is offline   Reply With Quote
Old 26-05-2015, 05:34   #51
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Re: Lightning Dissipator -- Any Good?

Always good to see an old thread resurrected .

I'm pretty sure but can't prove that these dissipators don't dissipate any static electric field.

I do know they are no way similar aircraft static wicks and any argument that they work in a similar fashion is false.

Let me explain why aircraft are fitted with static wicks and how they work and you will be able to see why the argument is erroneous.

The aircraft skin builds up a static electric field during flight, especially when travelling though moist air. This charge migrates to the pointy parts of the trailing edges and will build up to tens and tens of thousands of volts. Left unaided, it will finally arc off in big sparks. Just like a small lightning flash really. The corresponding RF noise emitted during the discharge can be strong enough to shut down legacy nav aids (ADF) and VHF coms (remembering the coms are AM, not FM). Also causes errosion of the aircraft skin - not good.

The static wick is well bonded to the aircraft skin at one end and the other end has a couple of fine sharp metal points. In between is a high resistance path, some hundreds of thousands of ohms.

The static field still builds up and still arcs off but now it arcs off at the ends of the sharp points. The sharp point also allows the voltage to arc off at a longer valve than just the aircraft skin however it is still many thousands of volts. The real difference is the high resistance path the discharge occurs though. This limits the discharge current dramatically and thus limits the amount of RF interference as the size of the RF interference is proportional to the current flow. The actual circuit is high volts
on skin, high value resistance in the static wick and low resistance of ionized air (ie spark path).

This in no way resembles what one is trying to do on a boat with a dissipator
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 26-05-2015, 05:55   #52
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,577
Images: 240
Re: Lightning Dissipator -- Any Good?

Quote:
Originally Posted by lesterbutch View Post
I understand all the negatives about dissipators however I also notice the large numbers of them around big commercial airports, military instalations and even around ammo. Storage dumps. Why? ...
Generally speaking airports & munitions dumps don’t use Charge Transfer Systems (ESE Dissipators), but do use Traditional Lightning Protection Systems (Franklin) , per NFPA Standard 780 (2014).

See l para 6.2.d ➥ http://www.faa.gov/documentLibrary/m...0-5340-30H.pdf

And ➥ https://www.wbdg.org/ccb/DOD/UFC/ufc_3_575_01.pdf

And ➥ Scientists Cite Failure of Non-Standard Lightning Rods in Death of Adventure Island... -- TAMPA, Fla., April 17, 2012 /PRNewswire-USNewswire/ --

And ➥ http://www.ecle.biz/wp-content/uploa...etter02.08.pdf

NFPA 780 (2004) ➥ http://www.uscg.mil/petaluma/TPF/ET_...s/NFPA_780.pdf
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 26-05-2015, 06:44   #53
Registered User
 
transmitterdan's Avatar

Join Date: Oct 2011
Boat: Valiant 42
Posts: 4,019
Re: Lightning Dissipator -- Any Good?

For many years I have worked with television and radio towers around the world. I have probably worked on as many tall towers (over 300 meters) as anyone. I don't climb towers but design stuff that hangs off them. About 20 or so years ago the bottle brush "static dissipator" fad came along. At first it seemed like they might change the probability of lightning striking tall towers. But after a few years it was pretty clear that strikes were random and the dissipator idea wasn't doing anything statistically useful.

It's obvious that nothing can change the odds of getting a lightning hit. The reason is the source of the electric field (ion charged water particles) is huge compared to the things man can build. And the breakdown of the air path in between is also subject to random motion of molecules. Thus the path lightning chooses to take is random. Statistically, taller (many meters) objects are struck more often than shorter ones which makes sense. But for a given height object there is nothing that can reduce its odds of taking a lightning strike. This is so in spite of the strong desire to change that equation. But height is only statistically significant when the ratio of height to separation is large. If the separation between two tall objects is the same as the height of the tallest (ratio of 1) then that statistical advantage goes away. So boats in an anchorage are all just about equally likely to be struck and it depends on the randomness of the storm itself whether your boat gets hit or not. The odds are really high that you will not be struck.

What you can do on plastic or wood boats is create a low inductance, low resistance path from the mast to the water. Not an iron chain or battery jumper cables but a real metal strap (aluminum works as does copper) as wide and short as possible from the mast to a few keel bolts for metal keels (not encapsulated) or a bronze plate bolted to the outside of the hull. Two straps are better than one. Corrosion treat the strap(s) and connections and then inspect monthly. This can reduce the damage to equipment and the hull. But a really large strike can damage pretty much anything no matter what.

So it helps to have good insurance because you simoly can't prevent damage from a really big direct hit.
__________________
transmitterdan is offline   Reply With Quote
Old 26-05-2015, 12:31   #54
Do… or do not
 
s/v Jedi's Avatar

Cruisers Forum Supporter

Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 9,198
Re: Lightning Dissipator -- Any Good?

Here we go again

- The dissipators do not prevent lightning strikes: true and proven beyond doubt.

- The dissipator is a bad lightning rod: not just true because you should never use a dissipator in the role of a lighting rod. For sailboats, the mast itself works as a lightning rod.

- The dissipator does not dissipate: not true but like everything, they must be installed correctly (which is bonded to ground)

Below is Wotname's post and he accurately describes how the static wick works on an aircraft. A correctly installed dissipator works in the exact same way. Boats build up the static charge due to both the wind molecules and weather systems just like on airplanes. This means you also get uncontrolled arcs if left unaided: we call this St Elmo's fire dancing in the rigging and it has done so for ages, here is a nice drawing from Wikipedia:


So the use of the dissipator is to dissipate the static charge. This will not prevent a lightning strike but it may prevent or at least delay a leader forming (before the lightning strike, a leader forms as a possible path for the strike) which may land the strike elsewhere. This is key: the strike still occurs but may hit something else. The dissipator acts like a camouflage.

Before investing in a dissipator, one should invest in a bonding system that has a bronze plate under the hull right next to the mast, with a big cable connecting it to the mast. This cable should be short and straight, no bends because lightning wants to go straight and will blow holes in fiberglass if left unaided. Also, all the chainplates should be connected to the bronze plate. I have a ketch and was hit in the mizzen with the main mast untouched. It means a ketch needs two bronze plates.

Last but not least, the dissipator only works when it too is bonded to the plate. You can use the aluminium mast as conductor but a wooden mast needs a cable or stay for this.

Another important thing is the SSB antenna. If you use an isolated backstay then you must have a jumper or switch to ground it and disconnect it from the tuner. I have seen lightning hits on the insulated backstay so this is not theoretical.

cheers,
Nick.
Quote:
Originally Posted by Wotname View Post
Always good to see an old thread resurrected .

I'm pretty sure but can't prove that these dissipators don't dissipate any static electric field.

I do know they are no way similar aircraft static wicks and any argument that they work in a similar fashion is false.

Let me explain why aircraft are fitted with static wicks and how they work and you will be able to see why the argument is erroneous.

The aircraft skin builds up a static electric field during flight, especially when travelling though moist air. This charge migrates to the pointy parts of the trailing edges and will build up to tens and tens of thousands of volts. Left unaided, it will finally arc off in big sparks. Just like a small lightning flash really. The corresponding RF noise emitted during the discharge can be strong enough to shut down legacy nav aids (ADF) and VHF coms (remembering the coms are AM, not FM). Also causes errosion of the aircraft skin - not good.

The static wick is well bonded to the aircraft skin at one end and the other end has a couple of fine sharp metal points. In between is a high resistance path, some hundreds of thousands of ohms.

The static field still builds up and still arcs off but now it arcs off at the ends of the sharp points. The sharp point also allows the voltage to arc off at a longer valve than just the aircraft skin however it is still many thousands of volts. The real difference is the high resistance path the discharge occurs though. This limits the discharge current dramatically and thus limits the amount of RF interference as the size of the RF interference is proportional to the current flow. The actual circuit is high volts
on skin, high value resistance in the static wick and low resistance of ionized air (ie spark path).

This in no way resembles what one is trying to do on a boat with a dissipator
__________________

__________________
s/v Jedi is offline   Reply With Quote
Reply

Tags
lightning

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 13:08.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.