Faraday cage
- Thread starter Navicula
- Start date
- Status
Its a grounded metalliic cage (usually of copper mesh) that prevents radio waves from entering or exiting. Useful in the lab to test sensitive equipment without external interference.
A practical use would be to enclose a theater so those rat bastards can't use their cell phones while I'm trying to watch the movie!
A practical use would be to enclose a theater so those rat bastards can't use their cell phones while I'm trying to watch the movie!
Last edited:
Haaaha. Got that right w/ the phones. But the idea is, the oven IS the "faraday cage", as it is mostly metallic, and doing as the aforementioned shielding.
The seal on the door probably makes it a poor substitute for a faraday cage. The only electrical connection would be the hinges and possibly a door lock. And most do not ground the oven so you do not even get the basic protection.
I've read quite a few posts where folks put their stuff in the oven to protect it only to have it still get fried.
Probably best to just put it in a small metal box
I've read quite a few posts where folks put their stuff in the oven to protect it only to have it still get fried.
Probably best to just put it in a small metal box
some feel that by putting your small electronics in the microwave or oven, they can be protected from a destructive EMP if lightning strikes the boat.
Evidence suggests this is true, and the process that does so goes back centuries to the concept of a "faraday cage" invented by Michael Faraday in the early 1830's
It is also the lightning protection by bonding your mast to keel etc.
http://boatsafe.com/nauticalknowhow/lightning.htm
Protect your phone from lightning
Foolproof. Works every time.
Take cell phone, and clip on a jumper booster cable like the kind you keep in your car. Make sure it is very firmly attached. If the clip has little serrated teeth, this is even better.
Attach the other end to your cap shroud at deck level.
Note: cables must be about 12 feet long
Then, lower the phone into the water.
It will be fully protected by the earth potential of the water surface, and is 100% safe from lightning.
I have a foolproof method to protect cell phones from lightning while offshore.
Foolproof. Works every time.
Take cell phone, and clip on a jumper booster cable like the kind you keep in your car. Make sure it is very firmly attached. If the clip has little serrated teeth, this is even better.
Attach the other end to your cap shroud at deck level.
Note: cables must be about 12 feet long
Then, lower the phone into the water.
It will be fully protected by the earth potential of the water surface, and is 100% safe from lightning.
Are you sure 12 feet will work? I was thinking about bonding it with the anchor before deployment..
Foolproof method? Let's say a game of chance with the odds in our favor. Lightning follows the laws of physics but with so many variables involved it effectively seems to us that it may strike at random. It's power can vary from strong through awsome. Efforts to contain it, direct it or dissipate it can be rather useless. It will hit where it may independent of any of our efforts. The only conforting thought is that the probability of being hit is low and the probability of being hit while on board is even lower. I gave up on bonding and installing diffusers long time ago and now just focus on bettering my odds. It has been observed that boats near shore get hit with more frequency than boats a few miles out. I will delay approaching shore until the storm subsides which works well in conjuction with maintaining sea room to handle wind and waves. (That is if I get caught out as not going sailing on stormy weather will improve odds real good) It gather that a boat at the dock is more suceptible to getting hit and that is what insurance is for but making a point of not being aboard in stormy weather improves my odds. Inevitably you will get caught ashore and aboard and then you roll your dice but with the odds conveniently on your favor. Ground your mast and you may attract lightning or keep it ungrounded and suffer more damage, these are theories, your call. If it makes you feel better to store your electronics in the oven by all means go ahead but don't take anybody's word regarding wether it works or does not work.
Or as the claims adjuster so eloquently pointed out after lightening destroyed all our electronics, nothing is non-conductive. There are things with very low conductivity, but nothing is absolutely zero. Given enough potential even glass will conduct.
I have been doing my own research on all this bonding/grounding as it applies to sailboats. What I have concluded is bonding and grounding the mast to the keel will greatly increase your odds of a lightening strike (many times in fact), but will theoretically lower the damage one would otherwise receive should the boat be struck without grounding/bonding.
A good homemade faraday cage would be a cardboard box covered with aluminum foil, all seams closed. Put the electronics you wish to protect (battery removed) inside the box in packing material to keep it centered, and seal it. Then place that box within another larger box, also with packing, and also covered with foil.
From what ive read, a good EMP would still wipe them out unless your underground. I dont know what kind of EMP energy anyone sees on a boat during a lightening strike, or if a microwave will really save anything, but it would probably be a good idea to have good navigation skills using map, compass, and sextant, rather than rely on a GPS that may no longer function.
I have been doing my own research on all this bonding/grounding as it applies to sailboats. What I have concluded is bonding and grounding the mast to the keel will greatly increase your odds of a lightening strike (many times in fact), but will theoretically lower the damage one would otherwise receive should the boat be struck without grounding/bonding.
A good homemade faraday cage would be a cardboard box covered with aluminum foil, all seams closed. Put the electronics you wish to protect (battery removed) inside the box in packing material to keep it centered, and seal it. Then place that box within another larger box, also with packing, and also covered with foil.
From what ive read, a good EMP would still wipe them out unless your underground. I dont know what kind of EMP energy anyone sees on a boat during a lightening strike, or if a microwave will really save anything, but it would probably be a good idea to have good navigation skills using map, compass, and sextant, rather than rely on a GPS that may no longer function.
Actually there is both insurance company and Florida Sea Grant data that suggests grounding your mast both reduces the risk of damage to the boat in a strike strike is safer... Ungrounding your boat does not minimize the potential of a strike and ungrounded boats actually get hit at about the same rate..
I recently added primary bonding to a vessel that failed an insurance survey. The insurance company wanted to see the mast grounded as their own data shows it to be both safer and less costly to them.
Problem is "myths" get repeated on the net with no data to back it up. That is false as far as actual insurance and study data is concerned.
Nope I had a GPS wrapped in tin foil, inside a Pelican Case stored in a Ziplock bag with desicant and it still got fried. Tin foil has little resistance to EMP...
I don't have a microwave but now have a solid metal ammo box for electronics. We had multiple items not plugged in that were fried in our strike including the GPS in tin foil.
Our boat is lightning bonded to better than ABYC standards and we suffered ZERO hull damage. The same night we were hit, amongst 1100-1200 other spars, a teeny, tiny un-grouded Call 22 was hit. It was perhaps the shortest spar in the anchorage and un-grounded. Holes were blown in its hull and it almost sank before it was rescued.
According to some insurance companies the data does not support that ungrounded boats have less strikes, it is the opposite. The insurance companies have claims data and this is why they support ABYC TE-4 wiring.
According to a conversation I had recently with an underwriter it shows that grounded boats are hit slightly less often and sustain less severe hull damage when they are hit. Both types of boats are hit and both can sustain significant damage but grounded boats more often sustain less damage..
If the insurance industry saw ANY benefit to ANY system other than a boat wired to TE-4 standards then they would likely give a discount for having it installed. They see ALL systems hit but are more concerned about minimizing damage and claims pay outs hence the support for ABYC TE-4.
The customer mentioned above recently went through a survey and the surveyor "noted" that the boats spar was not wired to TE-4 (not grounded to the keel bolt). He called me because he knew TE-4 was not technically an ABYC "requirement" and how could the insurance company demand it? I called the insurance company on his behalf to try and argue the case that TE-4 was not a "mandatory" part of ABYC standards and was a "suggestion".
After three or four people I got someone who knew what they are talking about, or it seemed it, and basically told me that they don't care if it is mandatory or not, they go off claims data and boats not grounded suffer higher damage claims and are hit more often (his words not mine). They relented a little and gave him 30 days to ground his boat... I still disagree that they should have made him do this to keep coverage but they are the ones paying out if you are hit.
This data looked at 71 boats that underwent physical hits both with and without protection in both salt & fresh water. It measured the severity of damage. These are actual hits and the damage to boats with grounding systems and boats without.
As we can see boats with protection suffered less hull damage.
Level 0 = No damage and level 4 = Most Damage
Grounded boats edged out non protected in terms of the least damage in every level of protection from no damage to the worst damage.....
Boat US one of the largest insurers of sailboats has this to say:
[FONT=Verdana, Arial, Helvetica, sans-serif]"The amount of damage a boat sustains is determined in part by how the strike exits. In a properly bonded system that follows American Boat and Yacht Council standards, the strike should follow a low resistance path to a boat’s keel or an installed grounding plate[/FONT]"
Dr. Ewen Thompson the foremost authority on marine lightning strikes has this to say about grounded vs. not.
"There is no support for the argument presented by some sailors that they should not ground their sailboat since it will increase the chances of it being struck by lightning."
We know that grounded boats are safer in a strike and we know that boats that are not grounded get hit at similar or greater rates.
Having been hit, and having worked on numerous other boats that have been hit I would never not ground my vessel to ABYC TE-4 or better.....
I do not doubt that some insurance companies require that boats be bonded but the fact is that there are also reputable marine insurers that do not. If the data showing less strikes and less damage was so conclusive then I'm sure they would all be requiring it. To my knowledege the marine insurance industry has not commisioned a scientific study that conclusively has demostrated that bonding is the best course of action. In the absence of such a study the personal opinions of individual underwriters is just that opinions. Underwriters and some companies may feel it is their duty to support the ABYC guidelines to justify their actions to shareholders. As has been pointed out they really have no solid understanding of the lightning issue and only as it refers to property losses and the justifications for their actions.
Not sure what your saying. Wrapping the GPS in foil wont work, it cannot physically touch the foil. Pelican case wont work. Ziplock wont work. In some instances, nothing will work.
Supposedly, one test is to place your sell phone in something you think will protect it, and call it. If it rings it supposedly wont be of any protection.
As for lightening strikes and bonding, you been around it way more than me, im just relaying what ive read.
One could say that when you look at property loss claims paid out, and see less damage and less cost in claims associated with boats that are lightning bonded, that is a pretty good data set. Considering the insurance companies are the ones to pay in a strike they get to make their own rules.. When we were hit one of the first things on the insurance companies claim sheet was for the surveyor to inspect for a lightning bonding circuit.. I am sure they still would have paid, but then likely made me install one if none was there.
The hole in the; "I am not going to bond/ground my mast & rigging to minimize a strike" is that people forget that you have still placed Earth potential at the top of nearly every sailboat spar out there.
VHF, wind speed, tri-color, all round, masthead, windex light, TV antenna & spreader light are all connected to Earth on-board the vessel. The neg/ground of each of these appliances is directly connected to the boats DC system/battery and then off to the engine for the starter connection and then to the ocean for Earth potential. Heck half the keel stepped spars I see are sitting directly in bilge water right next to a keel bolt. In one strike the mast step bonding wire was missing and when the strike hit the water in the bilge was vaporized to the point that it blew the cabin sole cover boards off. Boat has massive pin holes in the hull, delam and was totaled.
So even without a large gauge wire to help pass at least some of that energy more easily to ground you have placed Earth potential 45'-80' above the surface of the water. IMHO I have yet to see an "isolated" sailboat, as it relates to lightning...
Even my neighbors 18' Hobie Cat was hit about 8 years ago. This boat has no electrics what so ever and no path to ground. Lightning hits what it wants to. You can only try to minimize damage, and we have data that shows a good lightning bond does so. No one, as of yet, has found a way to minimize the potential of a strike, not even Dr. Thompson..
As I previously mentioned, on the same night our boat was hit a little Cal 22 was also hit. The boat had no down conductor between the mast and the keel and no lightning system to speak of. It blew holes in the hull where the VHF cable had been run back to the radio where it was resting / laying on the hull behind the settee. The VHF cable is where the lightning apparently found the Earth it was looking for. It had no other "exit" point and the combination of a damp bilge and VHF wire resting on it likely gave it the path of least resistance even though the boat was not "lightning bonded" it was still hit hard..
Our boat, struck during the same exact storm. She suffered zero hull damage and uses the keel as the main down conductor lightning ground along with secondary bonding conductors.
Everything electric on-board was fried but she did not sink like the little Cal 22.. The lightning grounds also picks up chain plates, engine and other metal fittings as secondary conductors. We have plenty of wires in the boat near the waterline that the strike could have used to blow holes in the hull but I have to surmise the more direct path & LARGE wire to the keel, with less resistance, took the brunt of it.
When this strike happened there were over 1100 sailboats moored in Falmouth Foreside.
(Image Courtesy SkyPic.com)
The two boats hit that night could not have been more different. The Cal 22 had one of the shortest masts and according to the surveyor, no lightning system what so ever. It had holes blown in the hull from the VHF cable. So there goes the "taller masts will get hit first" urban myth.
Perhaps 97% of the boats in Falmouth have a taller mast than a Cal 22.... It still got blasted... It also blew the myth of "don't provide a path to ground and you won't get hit".. This boat had no low resistance path to ground from the mast to the keel or a lightning plate. It still got holes blasted clean through the hull....Our boat has a medium sized mast for the anchorage and is wired to ABYC standards with regards to lightning. She had ZERO hull damage, but still got hit. A few years ago I was feeling pretty smug when the boat directly behind us, about 20 yards away, got hit. He had just spent nearly 4k on the "latest and greatest" lightning system including a brand new fuzzy dissipator/lightning attractor.... His boat was hit no less than 3 weeks after spending 4k on this "latest & greatest" lightning system. His boat also did not sink or have holes blown in it, so maybe it worked, but his entire boats electronic systems were toast.
The Cal 22:
I've come to realize that if lightning wants your boat, it will get it, and there's not a darn thing you can do. Other than to try and minimize hull damage and minimize the potential for side flashes if you get hit your gear is likely toast or will be shortly there after..
If you do get hit get your own surveyor and be sure to write up EVERYTHING electronic on-board. We had a couple of items still "operable" after the strike and they died within a month or two. Lucky we had a good surveyor who wrote it up for 100% replacement of all electronic devices.
Just be glad your boat does not have a carbon fiber spar. My friend Kim & her husband were hit to the tune of nearly 6 figures because a carbon spar hit by lightning is quite often a total loss..... Their boat had $65,000 carbon rig as well as sails that had holes burned in them. The spar was bonded and the hull suffered zero lightning damage...
People can do what they want but I would urge anyone to at least bond the spar to an external plate or the keel to try and minimize the potential of a sinking or total loss of not jsut the electronics but the hull as well.
I don't have detailed knowledge of marine insurance practices, or ABYC standards, but I do have a better than average understanding of protecting against lightning damage in general. Everything Maine Sail has posted is in line with what I've been taught. Lightning isn't a magical force that has no predictability. It's been studied thoroughly and there are guidelines to protect and diminish the damage resulting from direct or nearby strikes. That isn't to say that lightning strikes can be prevented, but that once the strike occurs, the resulting surge can be controlled. I think some people confuse this and assume that since you can't thoroughly prevent or accurately predict when and where strikes will occur, that the resulting surge is also unpredictable. That's the part that is utterly predictable. Electrical surges do not defy the same laws of physics that govern the electricity from your battery bank.
The chances of taking a direct strike aren't any better if you're grounded to the earth, but your chances of severe damage and injury/death are much higher if not. I suspect lightning strikes boats near shore more often, because there are many more boats near shore. Insurance companies are driven by statistics and base their coverage requirements on that. For example, it's a known fact that fire suppression systems work, but residential houses aren't required to have them for fire coverage. You might get a discount from some companies if you have one though. I'd bet that some marine insurers will discount your premium if your boat is grounded/bonded. My point is marine insurance companies don't have to commission scientific studies of lightning because the data is out there. It's not a global warming consensus or other theoretical nonsense.
- Status