Lightning Protection for Electronics

[Emmalina]

Originally Posted by Michael Cobbe

Put everything electric in the oven it acts as a Faraday cage.

Mmm and how long do you think it will take to remove all your instruments/autopilot chargers etc !!

[stull61]

Originally Posted by Dave_S

If you ground your mast to the water aren't you increasing the likelihood of being hit with an unquantifiable possible decrease damage ?

From what's the experts are saying, this is not the case.

[StoneCrab]

My understanding is that the hardest part of a lightning protection system in a FRP boat is how to ground it. Lightning is a surface effect due to the high voltages. I don't think sticking a copper rod into the water would be very effective if you were to actually get a strike. There wouldn't be enough surface area on the rod... and depth doesn't help.

Boats that are holed through typically have burn holes at the water-line.

If you had an internal Faraday cage and it was conductive to the mast, I would think it would act like one of those Leyden Jar capacitors getting charged up until the dielectric resistance of the hull is exceeded and an explosive spark burns through to the collector ground / water surface.

https://www.youtube.com/watch?v=xjW-isgOijs

Lightning rods on a house try to protect the house by dissipating the electron build up through the multiple pointed tips so that the voltage differential doesn't get high enough for the big spark to jump the gap between the heavens and the earth. The lightning rods try to balance the charge forces by giving the electrons an easy path to follow. St Elmo's fire can be seen glowing at the tips during lightning storms when there is a high possibility of a lightning strike.

Those mast top brushes serve a similar purpose on a sailboat and do quite well on metal hulled boats. The weakness in these systems for wood and composite hulls lies in the lack of a good grounding surface leading to a charge build up on the rigging, chainplates, and electrical system. The damage occurs as the electrons seek a discharge path. With today's electronics, it doesn't have to be a lightning strike to take out the low voltage circuits in your radio, gps, TV, computer, MFD etc.

Another post mentioned that the equipment that was not turned on, didn't become damaged. I am confident that the little switches protected the electronics because mains voltage remained below 1000 volts without an actual strike. As parts fry, new paths are required, so the high voltage wanders around the circuit boards seeking an outlet. The gap in the switch may have been enough for the electrons to look elsewhere on the active boards. When the voltage gets high enough though, a straight path through composite material is possible. Switches and hulls don't make much of a difference at that point.

It makes me wonder about how carbon fiber composite fare under these circumstances.

[Dave_S]

Originally Posted by stull61

From what's the experts are saying, this is not the case.

It doesn't seem to make sense. If you are providing a path of less resistance it must be more attractive.

This is above my pay grade so I'm just applying my version of logic. Happy to be wrong.

[Glasshopper]

A few years back whilst a storm was brewing and clouds getting purpler, I disconnected my VHF coax at the base of the mast, thinking I was soooo clever, then subsequently heard a 'clicking' noise every few seconds -well before any visible lightning. The clicking turned out to be sparking from the coax to the aluminium compression pole (I can only conclude high atmospheric static as the storm was brewing and, energy accumulating in the coax, perhaps dielectric only, but in any event the outer sheath was also live. I know this because trying to grab it to reconnect it was a very Homer Simpson experience. The voltages I was measuring with the Fluke23 multimeter were 80V, then 240V and the following day, the meter which was rated for 1000V RMS was well and truly dead.
What I learnt was that disconnecting WITHOUT EARTHING was a mistake, because my 12V distribution panel (a transistorized circuit board, in the Bavaria cruiser) was thereafter buggered, eg; press 1 button and 4 different circuits get energized. I have since replaced the panel with a very Russian looking Blue Sea 8068 because I fancy that World Circuit Breakers will have a better survivability and certainly better for DIY individual replacement. I'm also ruminating over a longer term plan to relocate all masthead instruments and anchor light. Maybe to the top spreader, the bimini, or even abandon completely. Certainly my recent AIS installation has a totally separate antenna mounted on the bimini.
Regards, Rob.

[mitiempo]

.....replaced the panel with a very Russian looking Blue Sea 8068....


Russian looking?

[Groathill]

My lead keel is encapsulated in GRP and thereby hopefully not electrically connected to the sea water - and not suitable for grounding protection.


I plan to fix a copper plate larger than a square foot (as recommended minimum area) to the outside of the keel.


Does anyone have a good reliable and lasting way to attach/connect a thick copper wire to the grounding plate?



I intend to feed the wire through the hull encapsulated with epoxy - and connect to the internal lead keel, mast, engine and internal ground network.

[NPCampbell]

Originally Posted by StoneCrab

My understanding is that the hardest part of a lightning protection system in a FRP boat is how to ground it. Lightning is a surface effect due to the high voltages. I don't think sticking a copper rod into the water would be very effective if you were to actually get a strike. There wouldn't be enough surface area on the rod... and depth doesn't help.

All electricity travels on the outside of a conductor ... except lightning. I am guessing that even though the copper rod can't carry the current, it might provide an initial low resistance path to ground. When the incredible current of the lightning starts flowing down that path it will simply create an additional low resistance ionized air plasma path as it did for over a mile to get down to the boat in the first place.

[Frankly]

Originally Posted by Groathill

fix a copper plate larger than a square foot (as recommended minimum area) to the outside of the keel.

Keep in mind the charge build up is between the clouds and the water surface.

Locating the plate deeper is probably not an optimal arrangement.

I suspect this is the reason Dr Thomson's side arc sytem is located around the waterline.


Frankly

[BigBeakie]

Originally Posted by NPCampbell

All electricity travels on the outside of a conductor ... except lightning. I am guessing that even though the copper rod can't carry the current, it might provide an initial low resistance path to ground. When the incredible current of the lightning starts flowing down that path it will simply create an additional low resistance ionized air plasma path as it did for over a mile to get down to the boat in the first place.

Yes, that's exactly right. It is quite counter-intuitive that providing an excellent charge dissipation path actually prevents charge buildup, but that's apparently how it works. The charge equalisation happens in a microsecond, as I understand it, and the stepped leader from the cloud negative charge is "looking" for a charge "cloud" to connect with. By providing as direct a path as possible to the sea surface where the charge is accumulated, the charge differential between negative and positive ( or positive and negative in the case of the more uncommon positive bolt) is equalised much more easily and rapidly. You might think, as I used to, that this would encourage a strike, but that's not what Dr. Ewens research has shown.

NB: If I have mis-interpreted any of the information, be aware I have no qualifications whatsoever in this field!! Consult Dr. Ewen directly would be my sincere advice.

So in short, use a lightning rod with a spherical surface, not a pointy tip.
Put ultra low resistance Seidarc conductors at the water level, not below the surface.
Use high surface area low resistance cable to connect the sea surface conductors as per the pattern in the instructions, and without tight radius turns.
Electrically bond into the conductor path a top rail on the stanchions if you have one.

See details at Marine Lightning Protection Inc.

[Rorzech]

[QUOTE=BigBeakie;3271871]Stull,

Nice to hear of another user of Dr. Thomson's system on the forum! I had fairly extensive communications with him before we purchased the system, and have incorporated our ideas into the build. I have not installed the Seidarcs yet, and will not do that until the boat is launched and I'm confident of exactly where the waterline will be.

Here are my thoughts so far:

1. The down conductor from the mast is crucially important. It should go straight down to the water surface. I'm using 95mm2 cable connected from the mast base exterior, runs beside our Stainless compression post (but inside an electrically insulating cover) to a 20mm diameter copper rod electrode that can be dropped down through a conduit to the water surface under the bridgedeck when at anchor. It's pulled up out of the way when sailing so it's not damaged from floating debris, or wave pressure.

2. All electrical wires and aerial cables have quick disconnect fitting at the top of our mast compression post in the saloon. All wires to electronic instruments & displays have quick disconnect fittings at the navigation station. Same with all wires to instruments at helm. The disconnect fittings are multipin, so several items can be disconnected just by pulling the fitting apart, like a trailer to car connector. I have three to pull apart as fast as I can when lightning threatens. I just wasn't confident enough in surge protectors.

I think that this system will be good for most strikes, but there are lightning super-bolts that are so huge that they would over power any cleverness we may think we can come up with. But buildings are well protected by the principles of this type of system whereby there are large conductors that run down the corners of the building connecting earth to lightning rods at the corners, and they work.

I used to keep a light dog chain hooked to the rear chain plate and when lightning was threatening , I would throw it in the water and it dangled about 5 ft in the water and lightning would crash around me as close as 600 feet. I couldn't believe we didn't get whacked. Since then I learned that lightning does not like to go around corners, 2 lightning travels from the ground to sky not the other way around.3 if you put razor sharp needle spikes, better yet knives at the top of your mast they will absorb the stray ions and electrons and drain them to the water ground and protect you in a cone shape umbrella so the lightning can't see you. I've never been hit and I had no electronics to loose but next year I could loose thousands if I get hit. I'll also do like you using the quick disconnect method. Use every method you can come up with. No one really knows what really works.

[ArmyDaveNY]

Would a wooden mast, with non-metal rigging reduce the likelihood of a strike? Although it probably wouldn't eliminate the possibility of a lightening strike, would it make it less attractive to lightening, especially when in a marina, mooring field, or anchorage?

[Rorzech]

WOODEN mast ? Aren't trees made of wood ? Doesn't lightning hit trees millions of times every day on the planet ?

[ArmyDaveNY]

Originally Posted by Rorzech

WOODEN mast ? Aren't trees made of wood ? Doesn't lightning hit trees millions of times every day on the planet ?

Indeed they are, which is why I asked if it would REDUCE the likelihood of a strike.

Is a wooden mast more conductive than an aluminum mast or less conductive? I was under the impression that they are less conductive, but not being an expert, I have no idea if this is so and if so, how much less conductive.

[NPCampbell]

Originally Posted by Rorzech

WOODEN mast ? Aren't trees made of wood ? Doesn't lightning hit trees millions of times every day on the planet ?

So why do witches burn?