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Old 25-07-2016, 06:03   #1
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Chart table faraday cage?

My recent lightning strike has gotten me thinking about future protection of portable electronics like EPIRBs, handheld GPS/VHFs, laptops, etc. I've seen threads discussing putting these items inside your oven, but this seems like something you can do if a thunderstorm is imminent and you're on the boat, but what if you're not there. So what to do to protect your gear in a convenient way, even when you're not onboard?

I like to keep stuff like this either in the chart table or in drawers/storage nearby. So how about lining the inside of some of these spaces with fine copper mesh to form a faraday cage inside which your equipment will be better protected? Is it feasible to have a reasonably good faraday cage with material like this? Would it need to be grounded to the boat's bonding system? Would copper mesh be the best material for this?

The PO of my boat had removed the nav station to add more storage and counter space across from the galley - might be OK for coastal cruising, but a blue water boat needs a nav station so I intend to rip out what he did and build a new chart table, etc in its place. As I design and build this it would be great to include lightning protection. Of course nothing can fully protect your equipment from lightning, but does this idea have any merit at all?

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Old 25-07-2016, 06:14   #2
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Re: Chart table faraday cage?

Which handheld items were damaged during your lightning strike? What were they doing when damaged?

A Faraday cage is just an enclosure of metal. It does not have to be grounded to anything to perform its function. But it has to be fully closed on all sides. If it has an opening then the opening has to have some kind of good low resistance metal/metal seal when closed.
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Old 25-07-2016, 06:22   #3
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Re: Chart table faraday cage?

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Which handheld items were damaged during your lightning strike? What were they doing when damaged?

A Faraday cage is just an enclosure of metal. It does not have to be grounded to anything to perform its function. But it has to be fully closed on all sides. If it has an opening then the opening has to have some kind of good low resistance metal/metal seal when closed.
Actually I had no handheld equipment onboard during the strike, as I'd literally just bought the boat. A lot of the built-in electronics and other electrics are damaged, and I just got off the phone with the insurance company to start the claims process. I was more thinking proactively about *future* protection, and building that in to the new nav station I'm going to install in the next year or two.
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Old 25-07-2016, 06:32   #4
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Re: Chart table faraday cage?

I have never actually talked to anyone experiencing failure of handheld equipment due to a lightning strike. So I was curious that you might be the first.

One obvious answer is to get a metal box with a lid that fastens with screws (no hinges). Thin steel is a good choice of material. The screws should be about 4 inches (10 cm) apart. When leaving the boat put all the handheld stuff in the box and put the screws in the lid.

A fancier box can be made if the lid seals with electrical contact strips sometimes called finger stock. This eliminates the need for lots of screws.

In my experience failure of powered off handheld equipment due to lightning is mostly the stuff of Internet legends.
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Old 25-07-2016, 06:38   #5
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Re: Chart table faraday cage?

Microwave ovens will work. A regular oven will not because the window and the gap at the door. Try non conductive grounding or anti static bags like what delicate computer parts are shipped in.

They are made from a metalized plastic and have a zip lock closure and are made specifically to protect electronics. I found ones on eBay that I can fit my laptop in.
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Old 25-07-2016, 06:50   #6
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Re: Chart table faraday cage?

We keep our satphone in an old cookie tin at the nav station. The portable GPS and handheld VHF have their own tin. We also have a large ammo box where the laptops, instrument displays, tablets, phones etc. go when there is lightning about. When we left our boat in Borneo for a few months we removed all electronics, including the radome, and stored them ashore.
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Old 25-07-2016, 06:50   #7
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Re: Chart table faraday cage?

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Microwave ovens will work. A regular oven will not because the window and the gap at the door. Try non conductive grounding or anti static bags like what delicate computer parts are shipped in.

They are made from a metalized plastic and have a zip lock closure and are made specifically to protect electronics. I found ones on eBay that I can fit my laptop in.
Trying to avoid things like ovens and microwaves, and build the protection in to the nav station itself, if possible. The anti-static bags are a good idea in addition to the faraday cage as they would provide extra electrical protection, and also protection against moisture with the aid of some silica gel packets.
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Old 25-07-2016, 08:41   #8
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Re: Chart table faraday cage?

Quote:
Originally Posted by Delancey View Post
Microwave ovens will work. A regular oven will not because the window and the gap at the door. Try non conductive grounding or anti static bags like what delicate computer parts are shipped in.

They are made from a metalized plastic and have a zip lock closure and are made specifically to protect electronics. I found ones on eBay that I can fit my laptop in.
When I read this I questioned our plan to use our Dickinson diesel stove as a cage. It has no window and the oven handle actually locks down forming a seal. Does that meet the requirement as you know them? Hoping not to rethink this. Sorry for kidnapping the thread.
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Old 25-07-2016, 08:53   #9
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Re: Chart table faraday cage?

The likelihood of a hand-held item being affected by a lightening strike is slim to none unless it is in your hand and being used at the time of the strike. The lightening will typically strike the highest point of the boat and the current travels down cables, wires, rigging etcetera to reach the ground provided by the water you are floating on. This applies an enormous voltage to the conductors, and anything attached to the conductors therefore is at risk of being damaged because radios, plotters et. al, are all connected to the ground circuit in the boat. That's why your electronics get fried.

It's also why so often lightening strike on a sailboat punches a hole in the hull as the current goes down the rigging and flashes down the wet hull to the ocean.

So if something isn't connected to the boat wiring, which hand-held gear typically isn't, then the likelihood of damage is virtually nonexistent. This is the same as you being safer inside the boat during a lightening event than on the deck!
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Old 25-07-2016, 09:48   #10
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Re: Chart table faraday cage?

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Originally Posted by rodgoult View Post
-----
So if something isn't connected to the boat wiring, which hand-held gear typically isn't, then the likelihood of damage is virtually nonexistent. This is the same as you being safer inside the boat during a lightening event than on the deck!
Then there's the idea that lightning is basically unpredictable. A friend was standing in his galley near the companionway when his boat was struck by lightning. The lightning jumped from his vhf to his shoulder, then exited from his ankle to the foot pump lever. He wasn't touching anything at the time, with the exception of his feet on the cabin sole.

He was fine, except for two fifty cent sized patches of burned skin.
Lightning is strange stuff.
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Old 25-07-2016, 10:00   #11
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Re: Chart table faraday cage?

https://weather.com/health/news/catc...rikes-20140114
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Old 25-07-2016, 11:11   #12
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Re: Chart table faraday cage?

Now I am somewhat more confused than usual, or at least uncertain: Will a Faraday Cage protect a wired device located inside the cage? I'd always thought a Faraday Cage was effective against loose electrical charges (EMP, lighting, etc. looking for a route) but not that which was carried by wire into the Faraday Cage. Can someone with both actual and theoretical knowledge please answer, rather than those folks like me speculating based upon experience, intuition, and /or partial information.
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Old 25-07-2016, 11:11   #13
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Re: Chart table faraday cage?

Just the science of it suggests you'll need to surround your protectables with a solid or mess conductive surround... and all those surfaces need to be soldered or bonded together. In practice I suppose just the top cover could be hinged at the back to allow easier in/ out access of your electronics. If it's not easy you'll not use it! If you hinge it just make sure there is a flexible wire grounding the lid to the 'box' so your not relying on an iffy metal hinge for grounding/ bonding. I have a bigger sailboat/ more bigger stuff than would fit in a drawer... done mounted to bulkhead. My 'what if' plan is that I have small handheld radios, GPS,... in a 'bread box' just in case. In 40 yrs of sailing in Chesapeake Bay and Caribbean... both with their fair share of lightning, never had a strike.


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Old 25-07-2016, 11:21   #14
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Re: Chart table faraday cage?

Quote:
Originally Posted by rodgoult View Post
The likelihood of a hand-held item being affected by a lightening strike is slim to none unless it is in your hand and being used at the time of the strike. The lightening will typically strike the highest point of the boat and the current travels down cables, wires, rigging etcetera to reach the ground provided by the water you are floating on. This applies an enormous voltage to the conductors, and anything attached to the conductors therefore is at risk of being damaged because radios, plotters et. al, are all connected to the ground circuit in the boat. That's why your electronics get fried.

It's also why so often lightening strike on a sailboat punches a hole in the hull as the current goes down the rigging and flashes down the wet hull to the ocean.

So if something isn't connected to the boat wiring, which hand-held gear typically isn't, then the likelihood of damage is virtually nonexistent. This is the same as you being safer inside the boat during a lightening event than on the deck!
You might want to update your ideas. Grounded or not grounded, a lightening strike can destroy anything in the boat. The "cone" of protection is more myth than reality. Grounding does allow lightening a quick path to earth, but its no guarantee. But better that option than having it blast through the hull. Whether an appliance is grounded or not has little bearing on the massive electrical disturbance caused by lightening once inside a boat. Even our epirb, sealed in a plastic tube, got fried.
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Old 25-07-2016, 11:22   #15
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Re: Chart table faraday cage?

Quote:
Originally Posted by rodgoult View Post
The likelihood of a hand-held item being affected by a lightening strike is slim to none unless it is in your hand and being used at the time of the strike. The lightening will typically strike the highest point of the boat and the current travels down cables, wires, rigging etcetera to reach the ground provided by the water you are floating on. This applies an enormous voltage to the conductors, and anything attached to the conductors therefore is at risk of being damaged because radios, plotters et. al, are all connected to the ground circuit in the boat. That's why your electronics get fried.

It's also why so often lightening strike on a sailboat punches a hole in the hull as the current goes down the rigging and flashes down the wet hull to the ocean.

So if something isn't connected to the boat wiring, which hand-held gear typically isn't, then the likelihood of damage is virtually nonexistent. This is the same as you being safer inside the boat during a lightening event than on the deck!
Wrong.

The magnetic fields from a lightning strike are so high and ramp up so quickly they can induce currents in in the wiring of items not attached to the electrical system of the boat in anyway.

Not being attached improves the items' odds and probably decreases the severity of the damage but in no way garuntees protection.



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