Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 09-07-2019, 06:43   #61
cat herder, extreme blacksheep

Join Date: Jul 2008
Location: furycame alley , tropics, mexico for now
Boat: 1976 FORMOSA yankee clipper 41
Posts: 18,967
Images: 56
Re: Lightning Protection, pros and cons

and then there is the clearwater ct 41 moon song with lightning protection that was burned by lightning..... just when you htink you are protected and 90 percent completed with the project..... bam. restart mandatory or quit boat. he is rebuilding, btw...his forward hatch acted as a chimney for the flames. see the horrifying pix in his facebook page. scary had he been home, baked donny.
so preach about lightning protection. this is not the first allegedly protected boat i know of that experienced issues due to that protection.
i suggested next time only use jumper cables into water from shrouds.
the mess was spectacular.
zeehag is offline   Reply With Quote
Old 09-07-2019, 06:59   #62
Registered User

Join Date: Mar 2019
Location: Punta Gorda
Boat: Aloha 32
Posts: 70
Re: Lightning Protection, pros and cons

I'll share my experience with installing lightning protection and working with higher voltages. Take from it what you wish when applying it to boat installations.

The first time I worked on what we called high voltage - 12.8 kV - (which the power companies refer to as medium voltage) we were installing a system in a 31 story building. It wasn't something electricians in my local did very often. One of the guys on my crew had a lot of experience so I tapped his knowledge during the installation.

Each leg of the 3 phase system was 7200 volts. That's what was carried through each cable and fitting. While installing the cable, the POCO rep and our resident expert both cautioned the installers not to make any sharp bends with the cable. Too sharp a bend and the current can blow out the bend.

If you've ever read stories about people struck by lightning you may have read about severe burns on their knees and elbows. Think of these as exit wounds. This is what happens when the "pressure" of high voltage encounters a sharp bend. Voltage is to electricity what water pressure is to plumbing.

When it came to "splices", where three or more cables had to be connected, we used these specially made elbows, designed to contain the the voltage. This was the only time a sharp bend was allowed. The elbows were connected to fittings on a rack.

Lightning protection cables I've seen on boats often have sharp bends in them. And we often read about stray current from a lightning strike reeking havoc on everything in the boat. I did two other 12.6 kV installations during my career and sharp bends were firmly an absolute no-no.

The cable we used to carry the 7200 volts was a 3/0 aluminum conductor with 3 layers of insulation. The first was a thick nylon jacket followed by a thinner rubber-type insulation and covered with a plastic jacket. Over that was a concentric aluminum flat strap, which spiraled over the cable and acted as a drain for stray voltage. This cable has a the plastic jacket over the concentric.

All this for only 7200 volts per phase. Nothing compared to lightning.

The diameter of the cross section of the cable is determined by the amperage required. Voltage determines insulation requirements, just like PSI determines the type and thickness of the pipe carrying the pressurized water. As you might glean from above, the cable we installed for that 12.8 kV system was over twice the diameter of the same conductor size for 600v rated insulation. And it was very stiff, comparatively.

Only once did I work on a installing lightning protection. Usually the electrical contractors hired a specialist contractor (Harger). I installed copper spikes on the top of a high rise. These rods came to a very sharp point, installed vertically. They were only about 18" tall. I was told by Harger reps the sharp point was necessary for the system to work properly. They were dangerously sharp.


All the copper spikes were connected with bare copper (I think it was 2/0), creating a continuous loop around the perimeter of the rooftop. Sharp bends were not permitted. The bare copper ran to the base of the building. The only time it was in conduit was through PVC sleeves between floors. It was cad welded to building steel at certain locations. I don't recall seeing the bare copper cable contained inside any junction boxes.

When it came to installing lightning protection on my boat, I will admit I'm on the fence. Taking what I have learned during my 35 years in the field, and specifically from what is mentioned above, I can't see how I could accomplish that same level of standards on a boat.
  • High voltage insulation on the cable
  • No sharp bends
  • High voltage rated connections
  • A sharp copper spike higher than the top of the VHF antenna
  • Dissipating the current where I want it to go (into the water)
And that last one leads me to proper grounding techniques.

Throughout my career, I've been involved in countless discussions regarding grounding. It was a never-ending debate. One of the issues is the fact when current isn't contained, predicting where it will go is just hocus pocus. Once you remove the containment, like insulation, you lose control of the path, and it will go where it wants to go. We knew how to control the path above ground, but once that ground rod or copper water pipe was connected to, it was anybody's guess.

What we never disagreed on was electrons follow the path of least resistance. The unknown was always what path offered the least resistance?

I am NOT recommending anything here. Just offering some tidbits of what I learned over the years. For me, the idea of neutralizing the positive and negative electrons in the air by providing a path to ground is good enough. As for controlling the path of a direct hit from a lightning strike at the top of the mast, through the mast and down into the water without it going anywhere else? Well, let's just say I'm a bit skeptical of how effective that would be.
Jules_M is offline   Reply With Quote
Old 09-07-2019, 07:22   #63
Registered User
 
CaptRory's Avatar

Join Date: Sep 2016
Location: SW Florida
Boat: Island Packet 32
Posts: 159
Re: Lightning Protection, pros and cons

As many opinions as sailors. Google Ewen Thompson, he is a UF professor and the pre-eminent expert on lightening and sailboats in the US. Also there is this...a really good primer on the subject: https://www.practical-sailor.com/blo...s=p_Blog070419
CaptRory is offline   Reply With Quote
Old 09-07-2019, 07:25   #64
Registered User

Join Date: Sep 2015
Location: Out of Norfolk Va
Boat: Tartan 37
Posts: 687
Re: Lightning Protection, pros and cons

Our boat been hit twice sitting by itself in a marina. I was personaly hit while working on a boat on the hard, high and dry nothing plugged in or grounded. The boat on the hard was the only sailboat out of the water, sitting next two a huge metal dry storage shed. I'm an electrical engineer and when you guys figure it out let me know. But I currently like be tied up next to a lot of other sailboats with bigger sticks.
puffcard is offline   Reply With Quote
Old 09-07-2019, 07:45   #65
Registered User

Join Date: Apr 2014
Posts: 23
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by Wotname View Post
Thanks Gord and I understand how lightning generates EMR at RF but I don't see any claim the discharge current (in the arc) is resonating at an RF rate.
In the same manner, a capacitor discharge spark is simply a pulse of DC and not moving back and forth at an RF rate. The same spark generates EMR in the RF spectrum
I think I get where you're not on the same page. "back and forth" is the wrong idea. It's not about current moving back and forth. It's about acceleration. "back and forth" is AC. we are not talking about AC (And AC doesn't generate EMR because there is no net acceleration of current, since AC flows in balanced conductors (2 phase, 3 phase, whatever, the net current flow in common mode (one particular direction or the other) is zero.)

Electromagnetic radiation is generated perpendicular to the acceleration of electric and magnetic fields (or electrons in general, because they posess both when moving) Once those fields stop accelerating, no electromagnetic radiation is emitted. Since lightning (and a capacitor spark discharge) is a common mode event (Not balanced by a equal flow of current in the opposite direction) and electron flow accelerates during the rise, then decelerates ( in other words, accelerates in the other direction ) on the fall of the pulse, and never achieves a steady state, it emits EMR --- It is also doing so at radio frequency. (Read: effectively at a frequency that can emit EMR if it is in an unbalanced conductor) It is subject to all of the skin effects of any other RF current (So Faraday cages work, be thankful of that the next time you're flying in an airplane) Admitedly, the higher the frequency, the more pronounced skin effect is, but lightning has a pretty broad frequency distribution due to the changing rate of acceleration during the fast rise and the slowing decay speed. An observation of the distribution of radiated EMR across frequency will clue you into the frequency spread (and relative energy at that particular frequency) in the strike.

If net current amplitude in the common mode (single direction) wasn't rising and falling at radio frequency, it would not emit EMR. At no point during a lightning strike (or a capacitor spark discharge) does a steady, zero-acceleration state occur until the strike ends.

Back and forth is not a thing. It's acceleration that's a thing.

Sean
WK7R
Texlan is offline   Reply With Quote
Old 09-07-2019, 07:56   #66
Registered User

Join Date: May 2019
Location: Longboat Key, FL
Boat: 42' Chung Wua Trawler
Posts: 80
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by puffcard View Post
Our boat been hit twice sitting by itself in a marina. I was personaly hit while working on a boat on the hard, high and dry nothing plugged in or grounded. The boat on the hard was the only sailboat out of the water, sitting next two a huge metal dry storage shed. I'm an electrical engineer and when you guys figure it out let me know. But I currently like be tied up next to a lot of other sailboats with bigger sticks.
In am also an EE. As was stated earlier lightning likes pointy things. Like masts. They concentrate the static charge which initiates the strike. When you see pointy lightening rods on buildings they are actually trying to get the lightening to hit that point instead of something else. If you are trying to not get hit then you really want a rounded top. That is my understanding from reading literature on the subject.
cpisz is offline   Reply With Quote
Old 09-07-2019, 08:10   #67
Moderator Emeritus
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
Lightning Protection, pros and cons

Quote:
Originally Posted by puffcard View Post
Our boat been hit twice sitting by itself in a marina. I was personaly hit while working on a boat on the hard, high and dry nothing plugged in or grounded. The boat on the hard was the only sailboat out of the water, sitting next two a huge metal dry storage shed. I'm an electrical engineer and when you guys figure it out let me know. But I currently like be tied up next to a lot of other sailboats with bigger sticks.


We were sitting in a little place to eat in Carrabelle Fl a couple of years ago waiting for the storm to pass so we could dinghy back out to the boat behind Dog Island.
Anyway we were beside the local baseball field, that of course like nearly all baseball fields was circled by a chain link fence, the backstop was a much higher chain link construction and the field was circled by light poles with of course lights on them.
Lightning struck near the pitchers mound, ignoring all that grounded steel and light poles.
I have no idea why, apparently the leader coming from the ground completed the circuit first.
I think maybe that is what we are missing, that there are many, many leaders coming from many sources and the first guy to connect gets the strike, and it’s not always where we would expect?
a64pilot is offline   Reply With Quote
Old 09-07-2019, 08:28   #68
Registered User

Join Date: Apr 2014
Posts: 23
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by a64pilot View Post
I think maybe that is what we are missing, that there are many, many leaders coming from many sources and the first guy to connect gets the strike, and it’s not always where we would expect?
Exactly..

I think sound engineering has always been to focus on how to safely deal with the massive electrical currents rather than speculation on how to avoid them in the first place.

And even if there was a magical round or fuzzy device you could put at your masthead that kept your boat from being hit directly, the boat next to you gets hit and now what do you do with the massive currents flowing through your mast and boat by magnetic induction and voltage gradient over the seawater's surface and through shore power(if applicable)? If you can engineer all of your boat's "effective conductors" to rise and fall together in with the earth potential, you're in a better place than if you hadn't at least tried to prepare for it.
Texlan is offline   Reply With Quote
Old 09-07-2019, 09:03   #69
Registered User
 
Group9's Avatar

Join Date: Sep 2010
Posts: 2,909
Images: 10
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by Wotname View Post
Ahh, no... Aircraft are very affected by lightning. Bits and pieces of the fuselage go missing after been struck and a full inspection has to be carried out - it was part of my previous occupation to do such inspections. It is true their electronics are rarely affected but this is due to the design and installation methods that are employed.

Normally a definite entry and exit point can be identified!
A friend of mine had a brand new airplane (a jet) struck by lighting while parked in Mobile, Alabama several years ago. I don't remember everything that was affected, but I remember it being so bad that the insurance company totaled it. Maybe he sold it, but I know he never flew it again.
__________________
Founding member of the controversial Calypso rock band, Guns & Anchors!
Group9 is offline   Reply With Quote
Old 09-07-2019, 09:05   #70
Registered User

Join Date: May 2019
Location: Longboat Key, FL
Boat: 42' Chung Wua Trawler
Posts: 80
Re: Lightning Protection, pros and cons

Yup. We can only reduce the chances and try to survive the strike. We can improve the odds but we will never eliminate the chance.
cpisz is offline   Reply With Quote
Old 09-07-2019, 09:16   #71
Moderator Emeritus
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Jacksonville/ out cruising
Boat: Island Packet 38
Posts: 31,351
Lightning Protection, pros and cons

Quote:
Originally Posted by Group9 View Post
A friend of mine had a brand new airplane (a jet) struck by lighting while parked in Mobile, Alabama several years ago. I don't remember everything that was affected, but I remember it being so bad that the insurance company totaled it. Maybe he sold it, but I know he never flew it again.


That was on the ground, we had a helicopter hit on the ground in Germany and the Army refused to “total” it, which as the Maintenance officer I was against, I believed it should have gone back to Depot at least, every piece of steel in that aircraft was magnetized.

If they are hit when airborne, they seem to suffer little damage.

The helicopter was chained to the ground, four chains right in front of the tail wheel and two on the main landing gear. The lightning struck the FM antenna on the tail. I assume the lightning would have gone to ground through those four 5/16” chains by the tail and I’m sure a lot of it did, but when inspecting the aircraft, I found that both pitot covers had holes burned in them where the lightning obviously exited the pitot tubes, which were on the wings, well forward of those chains.
Interestingly all the electronics worked, even I believe the FM radio that was connected to the antenna that was struck.
a64pilot is offline   Reply With Quote
Old 09-07-2019, 09:36   #72
Registered User

Join Date: Sep 2015
Location: Out of Norfolk Va
Boat: Tartan 37
Posts: 687
Re: Lightning Protection, pros and cons

The OP video reminded me of a lightning strike in St Michael, about 45 years ago. We were eating crabs on the dock at the Crab Claw, waiting for a storm to pass. When a 38ft sailboat anchor out got hit. The boat sank in less than 3 seconds. This guy yells "That my boat! My dog is out there on it." So we rally up the dinghy and headed out. Found the poor dog, the boat was in 6ft of water and you could see that the boat split in half, stem to stern. It seemed like the boat was built in two halves.
puffcard is offline   Reply With Quote
Old 09-07-2019, 10:04   #73
cruiser

Join Date: Feb 2012
Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
Posts: 1,111
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by GordMay View Post
Electricity will take ALL paths to ground, in approximately inverse proportion to the impedance of each path.
Yes, according to Kirchhoff's circuit laws. But there's a twist with lightning: the current is flowing through a channel of plasma (the "4th state of matter") surrounded by an otherwise non-conductive medium (air). So the current in air remains confined within the plasma channel -- not counting the currents electromagnetically induced in nearby conductors.

Kirchhoff's laws apply once the lightning current is flowing through conductors, but not while flowing through the air.
Cpt Pat is offline   Reply With Quote
Old 09-07-2019, 10:17   #74
cruiser

Join Date: Feb 2012
Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
Posts: 1,111
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by Wotname View Post
I'm not sure why you think that airplanes are almost never struck by lightning.

I have personally inspected maybe 10 in the last 25 years. There must be hundreds of thousands of other aviation engineers/mechanics in the world. Even if only 1% have seen as many as I have, that means tens of thousands of hits but likely it is many more.
That's why I said "almost never." Here are nine accidents, over many years, that were attributed to lightning: http://lightningsafety.com/nlsi_lls/avaition_losses.html

Many times, the lightning doesn't strike the aircraft - the aircraft instead flies into the superheated plasma channel from lightning passing around and ahead of the aircraft. In these cases, damage is confined to the leading edges of the airframe.

When you consider how many aircraft are in the air at any given time worldwide, flying around thunderstorms, and how few are struck; a metallic-framed aircraft is a relatively safe place to be. Now that composites are being increasingly used, I'm not sure that safety record will continue. And lightning protection is a known engineering challenge with aircraft containing composites.
Cpt Pat is offline   Reply With Quote
Old 09-07-2019, 10:21   #75
cruiser

Join Date: Feb 2012
Location: Half Moon Bay, CA, USA
Boat: 1963 Pearson Ariel, Hull 75
Posts: 1,111
Re: Lightning Protection, pros and cons

Quote:
Originally Posted by Group9 View Post
A friend of mine had a brand new airplane (a jet) struck by lighting while parked in Mobile, Alabama several years ago. I don't remember everything that was affected, but I remember it being so bad that the insurance company totaled it. Maybe he sold it, but I know he never flew it again.
Were the aircraft tie-downs made of chain? Was the plane refueling, with the ground strap connected? Was the plane connected to an external power source? Was the boarding ramp down touching the ground? Were airstairs up against the airframe?


The Faraday Effect only applies to insulated containers. Electrically connected to ground, there's no Faraday Effect protection.
Cpt Pat is offline   Reply With Quote
Reply

Tags
lightning, rot

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pros and Cons of a Saildrive? Being There Monohull Sailboats 13 07-12-2020 16:38
Pros and cons of leading halyard and reef lines to cockpit? Davidhoy Deck hardware: Rigging, Sails & Hoisting 138 28-09-2016 02:25
Pros and Cons and Various Modern Cruising Sail Plans Hugh Walker Deck hardware: Rigging, Sails & Hoisting 1 16-02-2012 05:05
Pros and Cons Between a New and Old Catamaran guysnell Multihull Sailboats 38 01-01-2012 12:54
Dock ownership. Pros and cons? bmiller Monohull Sailboats 19 14-06-2006 14:36

Advertise Here


All times are GMT -7. The time now is 22:59.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.