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Old 03-01-2016, 16:06   #31
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Re: Should mast be grounded or not?

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Originally Posted by kas_1611 View Post
Can't recall where I read it but there is a gizmo available much like a bottle brush that you can fix to the top of the mast which dissipates the static charge, dramatically reducing it and therefore your "visibility" to lightening.

If you can find this and are going up the mast to fix the VHF then it might be worth fitting one. No guarantee it will prevent you being struck but anything that can reduce the odds has to be worthy of a try.

As for protecting your electronics do what we do in a storm. If it can be unplugged and moved put it in the oven or microwave. Both of these are very effective Faraday cages, especially the microwave. Just remember to unplug the microwave and ensure the gas is isolated. If you are on shore power then you should be grounded through the cable but again no guarantee.

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Read my #14 above. The only mast top item not destroyed was this bottle brush POS. Only the stalk for the wind cups and its instrument remained (but not working). Aqua Signal tower remained - LED's blown, Windex and antennas were melted. All we found were bits of SS on deck.

Unplug & hide in the oven/microwave is probably the best option. Most stuff is too big or too difficult to uninstall. I installed 2-pole switches to air gap isolate both + and - leads. This was successful on several devices. Unplug antennas, unplug the entire mast.
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Old 03-01-2016, 16:10   #32
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Re: Should mast be grounded or not?

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Originally Posted by kas_1611 View Post
Can't recall where I read it but there is a gizmo available much like a bottle brush that you can fix to the top of the mast which dissipates the static charge, dramatically reducing it and therefore your "visibility" to lightening.

If you can find this and are going up the mast to fix the VHF then it might be worth fitting one. No guarantee it will prevent you being struck but anything that can reduce the odds has to be worthy of a try.

As for protecting your electronics do what we do in a storm. If it can be unplugged and moved put it in the oven or microwave. Both of these are very effective Faraday cages, especially the microwave. Just remember to unplug the microwave and ensure the gas is isolated. If you are on shore power then you should be grounded through the cable but again no guarantee.

Keiron
Understanding Lightning Protection

Forespar Lightning Master Static Dissipator
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Old 03-01-2016, 17:08   #33
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Re: Should mast be grounded or not?

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My understanding is that it is not a good idea to use an SSB grounding hull plate for lightning ground because it's a metal sponge. All the water filled cavities in the "sponge" can explode from the instant steam when lightning runs through it. YMMV
Sorry, but this yet another myth.

When asked on another CF thread no one had seen, or talked to someone who had seen, a lightning damaged grounding plate.
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Old 03-01-2016, 18:34   #34
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Re: Should mast be grounded or not?

Those lightning diffusers are a total waste. Have hauled a number of boats at our marina here on Long Island NY where the diffusers aren't even touched or melted and all of the electronics on the boats were smoked. Don't waste your money.
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Old 03-01-2016, 20:39   #35
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Re: Should mast be grounded or not?

Hi all, Very interesting reading here...I don't want to sound like a dummy here but what is an air gap double pole switch? If these will protect electrics I would install one before each item on the boat...
Thanks a lot
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Old 03-01-2016, 23:16   #36
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Re: Should mast be grounded or not?

I have dealt with this problem professionally for some years and my take is this:
The highest and most pointy item will likely be struck even if it is an insulated item (nice and wet from a storm), A mast top antenna is the most likely target. A gas discharge lightning arrestor typically has a breakdown voltage of about 50 volts or more so the input to which it is connected must stand this transient voltage. Disconnecting the antenna cables is the only real protection. Make sure any mast mounted equipment such as a radar has a ground lead from the antenna frame. Of course ground the mast, shrouds and stanchions to the keel or a conductive hull plate. The industry standard is #6 AWG copper wire for lightning grounds, crimped or clamped, not soft soldered at any joints. I prefer routing this wiring at least 4 inches from any other wiring. Physically open any power connections at the main points, don't depend on little glass fuses for any protection.
One last thought. A carbon or wood mast requires a separate copper ground wire from the masthead to avoid destruction from a strike.
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Old 04-01-2016, 06:52   #37
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Re: Should mast be grounded or not?

Greetings and welcome aboard the CF, Pole, & thunderhoof.
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Old 04-01-2016, 07:05   #38
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Thanks Gordmay... I've been skulking in the background watchin' and learnin'... wealth of knowledge here. Thanks guys
PS. I keep my yacht in Simons Town which is situated on the south peninsula in Cape Town. Anyone need any info about this part of the world please feel free
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Old 04-01-2016, 07:43   #39
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Re: Should mast be grounded or not?

Quote:
Originally Posted by Viking Sailor View Post

>>>
Originally Posted by Mycroft
My understanding is that it is not a good idea to use an SSB grounding hull plate for lightning ground because it's a metal sponge. All the water filled cavities in the "sponge" can explode from the instant steam when lightning runs through it. YMMV
>>>

Sorry, but this yet another myth.

When asked on another CF thread no one had seen, or talked to someone who had seen, a lightning damaged grounding plate.
What's a myth?

Why will anybody lead their lightning strike ground to the same ground that a pretty expensive piece of radio equipment is connected?

In none of the boats I have sailed (some of which were pretty biggish maxi class yachts), the SSB ground and the mast ground were tied at any point. And my job on these boats was to take stock of, and suggest corrections and amendments to, their electronic equipment. So I did dig into what is connected to what and why.

I have never seen mast ground tied to SSB ground in those boats. Perhaps this is common in smaller boats where installations are made by owners.

b.
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Old 04-01-2016, 09:12   #40
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Re: Should mast be grounded or not?

If I understand what you're referring to, our mast does have a little bottle brush looking thing up there. The lightning defintely hit the 3ft. steel whip mast VHF antenna, and made a quick trip through the boat on it's merry way back to earth. Two electrical fires as a result, with burning wire insulation to put out. One of the fires was the power leads to the ( now deceased) VHF and the other fire was in one of the engine compartments. That one was a plastic Radio Shack type hobby project case that PO had put some meters on for a battery monitoring system. I'm not even going to try to list all the stuff that got fried in this strike, but it was a lot. Most of our DC connected systems. Batteries didn't last long after that, either.

Wife and I were sitting at the galley table when the bolt hit, and we both got mild shocks. Mine was a tingling to my hand resting on the galley table, She got a shock to her foot and one of her ears rang for about 24 hours. It was like the whole world got whacked with a bat there for a heartbeat. Only nice thing about lightning is that if you realized what just happened, it's mostly over. Except for the fires and damage. We were sitting about two feet or so from a metal compression strut, that the mast is bolted to. It's wondering where the bottom of this strut is connected, if at all, or if it should be grounded that started this thread.

I'll take some photos of the mast head damage when I go up there, hopefully later this week. I'm waiting on a 60 ft. LMR400 cable I ordered for the Wilson.

So I plan to have two antenna sticking up higher than the mast, the VHF whip and the Wilson marine. Both will be grounded to brackets bolted to the mast aluminum, and of course they both use coax.
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Old 04-01-2016, 09:14   #41
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Re: Should mast be grounded or not?

Lightening protection, as with many other boat subjects, attracts many differing points of view. I therefore, often go with advice which seems to make sense to me. One such piece of advice I received was in relation to grounding the stay from the inside of the chain plate to a grounding plate on the outside of the hull. The question as to whether this will afford adequate protection in the event of a strike is discussed at length elsewhere. The other reason for grounding the mast is that this allows the mast and rigging to assume the same ground potential as the sea. If the mast is not carrying a different potential then hopefully the lightening is just as happy striking the sea.
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Old 04-01-2016, 09:29   #42
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Re: Should mast be grounded or not?

I never said these things work nor do I have any personal experience of them, touch wood I won't need to either.

Nicholson, correct me if I am wrong but isn't your bottlebrush lower than the wind gauge and antenae? If so then surely that would negate the purpose of it as there is something higher. Bit like having your lightening conductor at home lower than the TV aerial. Just an observation and I freely admit I could be wrong on this.

Idylles, again how were these fitted and were they the highest item on the mast?

A good analogy would be a church steeple with a bronze cross on the top. If the lightening conductor is not fixed the the cross or is not higher than said metallic item then the cross will be struck every time.

I know these bottle tops are supposed to diffuse the static rather than conduct any strikes but if you have something pointy sticking up above that diffused "umbrella" then it defeats the purpose.

Or am I missing something?

Of course another way to minimise your risk of being struck is make sure there is a boat nearby with a bigger mast than you
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Old 04-01-2016, 10:15   #43
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Re: Should mast be grounded or not?

One thing I haven't figured out is grounding the rigging and then sticking an antenna on top of it like an old barn with a lightening rod? Can anyone speak on using a spark gap device on an antenna coax.
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Old 04-01-2016, 10:35   #44
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Re: Should mast be grounded or not?

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... Can anyone speak on using a spark gap device on an antenna coax.
BTW: The CF has several members that are highly expert in all things radio: btrayfors , ka4wja, transmitterdan (to name a few that come to mind). If we don’t hear from (one/some of) them, you might send your query, as a PM.


According to Nautel
Air Spark Gap:
The most important lightning protection device is a properly adjusted air spark gap, that is located at the base of the antenna and is connected to the lowest possible ground impedance. This air spark gap must be considered as the first line of defence against lightning. Its principle function is to shunt the majority of lightning currents to a low impedance ground at the base of the antenna. When properly adjusted, it will minimize the transients flowing towards the transmitter through the coaxial RF feeder
http://www.nautel.com/wp-content/upl...s-Sep-2004.pdf

http://www.nsarc.ca/tech_archive/art..._30sep2013.pdf



The NEC requires an antenna discharge unit for shore based installations
http://www.reeve.com/Documents/Artic...ents_Reeve.pdf
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Old 04-01-2016, 10:41   #45
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Re: Should mast be grounded or not?

Cadence-
If a spark gap arrestor is installed on the coax, normally your radio sees "nothing" there. But if the voltage on the coax exceeds the breakdown voltage, then it can jump a physical gap directly to a ground lead. This is very much the same way that spark plugs in a car work. The air gap prevents the circuit from completing until the voltage reaches a certain point, typically ~30,000 volts in a car, but spark plugs were and still are actually used as home-made "air gap" protectors. The commercial ones use an inert gas for stability and are pretty much "well of course we use them" on commercial antennas.
Now, if the breakdown is 50 volts, you can still see 50v on your coax (49.99?) from a static charge building up. But even though your radio is powered from "12" volts, an improperly matched antenna can reflect back substantially higher voltage when transmitting (an SWR higher than 1:1) and typically modern radios will withstand at least a 1:3 SWR, which I think means 36 volts, without damage. I don't know the specifics but expect they will vary a bit with the make and model of radio, so you'd need to contact the maker and ask them to be sure.


A friend of mine used to be a broadcast engineer for WCBS, when all the major carriers were on the Empire State Building and transitioning to the WTC. The ESB gets something like 500? 1000? lightning strikes every year, they are routine. And despite all the antennas, we used to joke that they hardly ever had to hold up the "Please stand by..." sign. Between good grounding and good protective devices, commercial carriers operate through lightning every day. He did have to replace power transistors, sometimes, because no protection is perfect. Just not often.


Does protection work all the time? Well, as they say at Planned Parenthood, no, not all the time. Just most of the time, and that can certainly make a difference. (G)
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