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Old 03-01-2016, 11:01   #16
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Re: Should mast be grounded or not?

My mast is deck stepped with a heavy wire straight down to a Dynaplate. Right or wrong, his is the way the boat was equipped when I purchased it.

My main reason for posting is because of the masthead mounted VHF and Bullet M2.

Good electrical has always stated the boat should only have ONE negative ground point, so I insulated both of the above units from the mast to eliminate that using sheets of 3/16" vinyl.
Both units work just fine, and there are no other ground points in the system besides the big one just outside the battery box.
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Old 03-01-2016, 11:25   #17
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Re: Should mast be grounded or not?

Quote:
Originally Posted by AnglaisInHull View Post
There was discussion of grounding and lightning strikes in this thread, but no clear conclusions:

Offshore Sailing in Thunderstorm far from land
It is beating a dead horse!
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Old 03-01-2016, 11:43   #18
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Re: Should mast be grounded or not?

I have a 38ft steel boat... Deck stepped mast. Will the lightning fry my electronics or, being steel, will the charge travel through the hull and out the easiest path? I'm thinking the inside of the boat is kind-of a faraday cage because of the pathetic cellphone signal when I'm down below.
Does steel hull make a difference? I'm assuming most of the posters here are referring to Glass Fibre boats?
Keen to know if anyone has an insight or an experience...
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Old 03-01-2016, 11:54   #19
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Re: Should mast be grounded or not?

Quote:
Originally Posted by Pole View Post
I have a 38ft steel boat... Deck stepped mast. Will the lightning fry my electronics or, being steel, will the charge travel through the hull and out the easiest path? I'm thinking the inside of the boat is kind-of a faraday cage because of the pathetic cellphone signal when I'm down below.
Does steel hull make a difference? I'm assuming most of the posters here are referring to Glass Fibre boats?
Keen to know if anyone has an insight or an experience...
I believe the steel hull will behave as a Faraday cage. You are probably less likely to have troubles. No guarantees. I think there are statistics kept by insurance underwriters that include this. I recall seeing them once.
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Old 03-01-2016, 12:13   #20
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Re: Should mast be grounded or not?

s
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Originally Posted by hellosailor View Post
But there are also lightning protectors from companies like PolyPhaser that will help divert a direct strike from the antenna to a ground path, instead of down the antenna cable (which you presumably also need to replace) and the electronics.


Polyphaser has been a leader in lightning protection for over 45 years (that I know about) and probably has more commercial government, and military communications installs than all the rest of the other companies combined. I've serviced repeater sites where the antenna took a hit, blew it to bits and blew the Polyphaser off the common point copper plate, but the repeater still worked.

Now that doesn't always mean you are 100% safe from freaky lightning by using any lightning protection device. Nothing can give you 100% protection from lightning. What I am saying here is you're much better off protecting your equipment with Polyphaser units than not.

The reason I said "equipment" is because they make devices to protect landline coms including CO's and PBX systems, service entrance points, EMP protection (nukes), etc. So they are not just a company that protects RF equipment.

Look at it this way. They make a coax unit that will help protect your VHF radio for about $60.00 (GSA price, don't know what the street price is). Seems a small price to pay for what is considered by many Coms professionals (including radio AM/FM stations, military, cell sites, Amateur Radio Operators, etc.) as the go to device for protection.

BTW: I have never worked for them nor sold their equipment, but I wish I had a dollar bill for every one of their units I installed.

You may also want to read this PDF. While not dedicated to marine installs, the basic theory is applicable, especially coommon point grounding of your Coms equipment. Page 79, et seq is a real eyeopener to the uninitiated!
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Old 03-01-2016, 12:48   #21
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Re: Should mast be grounded or not?

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
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Old 03-01-2016, 13:07   #22
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Re: Should mast be grounded or not?

Thank you everyone for posting here.

OKay. We live with metal lightning rods on our boat. These are called masts. There is no effective way to develop a grounding strategy even though salt water is the most effective ground.

A lightning strike can be nearly a million volts. You cannot get this directly to the salt water no matter the method. The best method is to disconnect EVERYTHING. Turn everything off.

All while the storm continues. Connecting the mast to the water is a good measure to take. But it is no guarantee.

There is no Faraday shield solution. Except put the boat in a tunnel. Or even under power lines.

I do not know of an overvoltage solution for lightning.

P
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Old 03-01-2016, 13:13   #23
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Re: Should mast be grounded or not?

Pretty good and helpful read
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Old 03-01-2016, 13:55   #24
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Re: Should mast be grounded or not?

I suspect one of the problems here is 'what is a lightening strike'. It may be that some protection works in some cases, eg you get hit by a small side branch or a 'week bolt' and it runs down a 'safe' path. When you think about the potential energy in a big strike it is hard to imagine anything surviving it. Here in NW Canada it is common to see tree stumps several feet in diameter the have bee ltterally blow apart by lightening. I have always thought that if one of those hit the mast it would probably melt the mast and blow the boat apart! I wonder how many ''disappeared without trace' are down to lightening. Personally I do nothing and hope that lightening dose not see my wooden hull as a potential ground path plus avoid thunder storms.
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Old 03-01-2016, 14:14   #25
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Re: Should mast be grounded or not?

Tree stumps are a bad comparison. Depending on how much moisture is in the tree (species, time of year, sap flow, recent rainy weather) the lightning strike normally will superheat the moisture, resulting in a steam explosion inside the tree. So a weak strike in a damp tree, and there's just shrapnel left. A stronger strike in a thinner dry tree? And it might just char the trunk.
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Old 03-01-2016, 14:32   #26
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Re: Should mast be grounded or not?

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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Old 03-01-2016, 14:33   #27
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Re: Should mast be grounded or not?

I carry CHAINS that I attach to the rigging that reach into the water, never had to use them, so don't know how well they would work.
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Old 03-01-2016, 15:18   #28
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Re: Should mast be grounded or not?

Chains are probably the worse way of accomplishing a path to ground. There is very little contact area between the links and what there is is often corroded. You would be better off using wire or strapping.

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Old 03-01-2016, 15:25   #29
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Re: Should mast be grounded or not?

It's a crap shoot. We lived in a house that it came in the kitchen window several times. Had a truck hit driving down the highway, wiped out the electronics. Had boats grounded and not, never got hit with lighting all over the place. So I guess it is happenstance.
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Old 03-01-2016, 15:36   #30
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Re: Should mast be grounded or not?

Bottle brush; Yes, some municipalities in Florida have them installed on every traffic camera at every intersection, and some company sold them "guaranteed!" to mariners for a number of years. Dunno how the municipalities feel, but there is at least one thread a number of years old remarking on the many sailors who couldn't collect a cent from that Guarantee.


FWIW.
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