Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 29-04-2021, 16:06   #46
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

But ..... even if all of this "science" about the alleged buildup of charges, etc., radio towers with elaborate ground systems are frequently the target of lightning. So it’s safe to say that no grounding system can prevent a lightning strike. It might reduce the frequency of the strikes, maybe but there’s not a lot of good studies that prove that.

Once you actually get hit, your only hope is to divert as much of the strike away from, or around, sensitive equipment. But that’s almost always a case of sometimes it works and sometimes it doesn’t. Luck plays a big part.

The Army study referenced earlier is a good example of confirmation bias. If one believes that a grounding system will help, it tells you how you might build one. But it starts with the assumption that grounding is a good idea. It offers no proof to that.

Once you admit that no system is guaranteed to prevent a strike, or to always protect the target from damage, it becomes a nebulous trade off between how much time and money one is going to spend up front against the potential frequency and resulting damage of a strike. There’s no perfect system and no right answer.
Bycrick is offline   Reply With Quote
Old 29-04-2021, 18:17   #47
Registered User

Join Date: Jan 2016
Location: San Diego, CA
Boat: Beneteau 40.7
Posts: 298
Re: So my boat lacks a lightning ground.

For those of you looking for a wire size that will handle most lightning strikes, the consensus is #6AWG, 0.162 in. D in solid copper. I suggest #4AWG, 0.2043 D.
Of course this does not solve the key problem of delivering the strike at the mast head to the water but at least whatever strike current gets to the wire will not destroy it.
Understand that the wire cannot handle the strike current very long, just long enough that the lightning pulse will not melt the wire.
thunderhoof is offline   Reply With Quote
Old 01-05-2021, 07:26   #48
Registered User

Join Date: Dec 2018
Location: Wichita/Pensacola
Boat: Lagoon TPI 37'
Posts: 416
Re: So my boat lacks a lightning ground.

Thinking about this topic for several years has created alot of worry. It is the one thing that worries me offshore. With the capability to fry all GPS, electronics, and EPIRB with a dead house bank and dead engines while blowing holes in the boat. Causing us to go back to compass and paper charts. One benefit of diesel, if you keep them running during lightning, chances are they may still be running if fuel flow hasn't stopped.

My plan good or bad is to throw all GPS devices (MFD and hand helds), extra EPIRB, and portable VHF into the oven with go bag next to oven. Drop anchor 15-20' into the water on bridle. Then wrap chain around the base of mast with zip ties.

Don't know if this makes it worse or better.
sailingchiro is offline   Reply With Quote
Old 01-05-2021, 07:57   #49
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

"Don't know if this makes it worse or better."

And quite honestly, neither does anyone else. Providing conductive paths to ground may help. On the other hand, that particular lighting strike may find its own path regardless of what you do.

Even a perfect faraday cage doesn’t always protect completely. Studies have shown the the current flowing on the outside surface of the cage can sometimes induce destructive currents on the inside surface of the cage. And that assumes that the cage itself is perfect, which is certainly NOT the case with a microwave or regular oven.

Do what makes you comfortable, but don’t think it’s based on "good science."
Bycrick is offline   Reply With Quote
Old 01-05-2021, 09:15   #50
Registered User
 
Cyrus Safdari's Avatar

Join Date: Jul 2009
Location: St Augustine, Fla
Boat: 1967 Pearson 35
Posts: 364
Re: So my boat lacks a lightning ground.

Ah the old myth of oven as a Faraday Cage...

Put a cellphone inside the oven, then call it. If it receives calls, then it presumably isn't an effective Faraday Cage which really shouldn't have any holes or penetrations.
They do sell soft-lined and hardbox lightning resistant bags and boxes. Some are also water resistant. A simple tin box, with plastic drawer liner inside, can work too if the lid forms a continuous connection. But the cellphone test is an easy one. The idea isn't that thecellphone replicates lightning, rather the idea is that if the box doesn't block cellphones then it probably can't block the emp ofa lightning strike. (Military grade rubber seals incorporate little bits of metal)

Better than just hoping for the best. Anyway, lightning is unpredictable but it isn't voodoo and we've been dealing with it and similar electrical issues in planes, boats, buildings, rockets, trucks etc for generations and we've learned a few things, one of which is probably: doing something is better than nothing


Note: some people get upset when cherished myths are challenged, and the oven as Faraday Cage is one of them.

Anyway screw the electronics, id be concerned about how for example the bolt can crack up the prop shift log on its way out. Try getting down there in a rush to block a leak.

I'm surprised by people who wouldn't stand under a tree during a lightning storm, as every golf course in the US warns about, and yet are dismissive of waving a 50ft aluminum stick around (height, not material, is associated with lightning strike frequency, so this applies to wooden masts btw) But thats how we misperceive risk. Honestly among my friends much of the groaning about the requirement of lightning protection come from the same folks who don't really want to change cutlass bearings or other PITA standard maintenance, because it is a PITA really not because they have any rational grounds to oppose lightning protection
Cyrus Safdari is offline   Reply With Quote
Old 01-05-2021, 10:28   #51
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

An oven or a microwave is simply a metal box. If it were solid metal it would be a good faraday cage. The minute you put holes in it, some radiation can pass through the holes, the frequency is dependent on the size of the holes. If one cuts a hole in the box, then you have to block radiation passing between the cover itself and the box. There are two basic ways of doing this.

The most obvious is some kind of conductive gasket compressed between the cover/door and the box. With enough compression and clean surfaces, this works. But my propane over has a silicone gasket, so it’s worthless at EMI protection. If the conducive gasket isn’t compressed all the way around the opening, it won’t work either.

Another, often simpler mechanically easier way, is to NOT make an electrical seal around the opening, but rather to design the cover and box in such a way as to form a "choke joint." Look it up,on Wikipedia. It’s simple, effective but only works at certain frequencies. So it might be wonderful it keeping the microwaves in at a single frequency, but be awful at keeping a broad band pulse (like lightning) from getting in.

So the cell phone test is essentially worthless.
Bycrick is offline   Reply With Quote
Old 01-05-2021, 20:55   #52
Registered User

Join Date: Feb 2014
Location: Niagara Falls
Boat: Westsail 32
Posts: 596
Re: So my boat lacks a lightning ground.

On my Westsail 32, on the top of the mast a brush type lightning protector is installed. The mast and rigging electrically float free, they are not grounded.

In 2003 I was on a singlehanded voyage on the Atlantic from the BVI to Charleston SC. On about the ninth day, in a light breeze, a thunderstorm appeared in the distance. I peered at it, trying to decide which side to pass it on, and decided it was moving to my right, so I should head toward its left side. Well, Wrong Way Seymore, that's what they call me. A light rain started, the ocean was perfectly flat and the Westsail was an outstanding tall thing on it.

I happened to be looking off the starboard side when a stroke of lightning hit, about 250 feet to the side of the boat, on that calm sea, in that light drizzle!! D'you know, when lightning hits water, it makes a dent about the size of a bathtub??

A month later I posted that on a bulletin board and someone who was knowledgeable replied. As I remember, he said that lightning rods work on buildings on land because of the resistivity of the soil, and they don't work on boats on the ocean because ocean water has no resistance, so all the electrons rush right in to the lightning rod, which discharges. Something like that.... He said some other relevant things too, but I don't remember them.

Five years later, my boat was on a dock at Hinckley's in Savannah GA and there was a violent thunderstorm. I was away from the boat, and the office staff told me that, as they warched, lightning struck the boat beside mine, on the other side of the dock! They said a strong bolt of lightning came about four times. I was dispooped and checked all my electronics, and they were all OK.

I SAW all of these things, THEY ACTUALLY HAPPENED as I've described.

Make whatever you want from this.

----------

I think, the bottom line is, it's the luck of the draw.
Seymore is offline   Reply With Quote
Old 02-05-2021, 01:14   #53
Registered User

Join Date: Jul 2005
Location: Bellingham
Boat: Outbound 44
Posts: 8,837
Re: So my boat lacks a lightning ground.

Faraday cages are usually made of mesh, there is no requirement to be solid metal.
Paul L is online now   Reply With Quote
Old 02-05-2021, 13:44   #54
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

Some faraday cages are made of mesh. But the holes will in fact allow energy to pass through depending on the relation of the size of the holes to the wavelength of the energy. Since lightning has a frequency range of essentially DC to several hundred MHz, the holes have to be pretty small to block all the energy. A solid box with a good conductive gasket on all contact surfaces is as good as you can get.

A metal oven, with a metal gasket, and firm compression on a clean surface works. But for example, my oven gasket is silicone, so the oven is useless as a faraday cage. You can’t just assume that an oven will protect anything.

A microwave oven is designed to keep energy at 2450 MHz from getting out. That says absolutely nothing about letting energy from DC to 1000mHz from getting in.
Bycrick is offline   Reply With Quote
Old 02-05-2021, 19:54   #55
Registered User

Join Date: Jul 2005
Location: Bellingham
Boat: Outbound 44
Posts: 8,837
Re: So my boat lacks a lightning ground.

Quote:
Originally Posted by Bycrick View Post
Some faraday cages are made of mesh. But the holes will in fact allow energy to pass through depending on the relation of the size of the holes to the wavelength of the energy. Since lightning has a frequency range of essentially DC to several hundred MHz, the holes have to be pretty small to block all the energy. A solid box with a good conductive gasket on all contact surfaces is as good as you can get.

A metal oven, with a metal gasket, and firm compression on a clean surface works. But for example, my oven gasket is silicone, so the oven is useless as a faraday cage. You canít just assume that an oven will protect anything.

A microwave oven is designed to keep energy at 2450 MHz from getting out. That says absolutely nothing about letting energy from DC to 1000mHz from getting in.
The goal on a cruising boat is not to block all the energy. You are only trying to block a reasonable amount of the damaging strike energy to protect your backup electronics. There is no evidence that lightning has significant, damaging power at the gigahertz ranges for a cruising boat application. Putting your backup electronics into a microwave or oven is an easy, reasonable step that is likely to be protective in many cases. Don't let perfect be the enemy of good.
Paul L is online now   Reply With Quote
Old 03-05-2021, 06:50   #56
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

" There is no evidence that lightning has significant, damaging power at the gigahertz ranges."

Absolutely true. The energy in lightning ranges from (almost) DC to 300-500 MHz.

Thus it seems reasonable to think that a choke joint, carefully designed to block 2450 MHz (the specific frequency of a microwave oven) is likely to be of NO USE at all in stopping lightning energy.

An oven which uses a silicone gasket to retain heat is also not going to be very effective as a faraday cage.

Some ovens (microwave or otherwise) have a conductive gasket and can be quite effective as a faraday cage. But many other, for example the ones that I just happen to have, do not.

So, it’s not always a good idea to just put things in the oven to protect them from lightning. In some cases, it’s no better than leaving them on the galley counter.

One has to follow the science, not just do what makes them feel good.
Bycrick is offline   Reply With Quote
Old 03-05-2021, 06:54   #57
Registered User

Join Date: Jan 2014
Location: Panama City FL
Boat: Island Packet 32 Keel/CB
Posts: 791
Re: So my boat lacks a lightning ground.

"Don't let perfect be the enemy of good"

Amen,

Frankly
Frankly is offline   Reply With Quote
Old 03-05-2021, 07:23   #58
Registered User
 
cadmus's Avatar

Join Date: May 2011
Boat: 1984 Nor'Sea27
Posts: 121
Re: So my boat lacks a lightning ground.

cadmus is offline   Reply With Quote
Old 03-05-2021, 07:29   #59
Marine Service Provider
 
pbmaise's Avatar

Join Date: Jan 2007
Location: Langkawi, Malaysia
Boat: Jay Kantola - Trimaran 65 ft by 40 ft beam
Posts: 874
Re: So my boat lacks a lightning ground.

Lightning has struck at least 4 times around my vessel. Several of those times I was holding the helm and felt a jolt. The jolt was great enough to cause the fluorescent lights in my pilot house to glow. The "jolt" I felt was from a feeler. None of my electronics were ever damaged despite these jolts. BTW I always kept a backup cell phone with a complete set of charts and Open CPN in the stainless steel oven.

The "strike" is called the return stroke that travels up from the ground into the sky.

See: https://cambridge.dlconsulting.com/?...xt-txIN-------


IMHO you don't want the least path of resistance to be your vessel.

Therefore, I think my vessel was protected from harm for several reasons despite the fact it had a tall aluminum mast.

#1 - No chain plates were grounded and the hull wasn't steel.
#2 - The mast was decked stepped onto a deck that wasn't steel.
#3 - All wiring up the mast was insulated and devices mounted up the mast were well sealed.

Therefore, the least path of resistance for a lightning strike was not to include my vessel in the path. It was to come directly from the water and travel to the sky.

If you rig a vessel with a mast grounded directly to the water...then YES...you likely will create the exact situation that would encourage the bolt to travel from the water, into your boat, and then out the top of your mast. The very close proximity of the bolt strike and extremely high current running to the ground in your boat will in turn create EMP that will fry your electronics.

EMP dissipation rate is a square rooted. So the farther away you can get that burst to occur the better for your electronics and it need not be very far. Having a giant jolt run up your mast where you have a radar dome mounted isn't going to end well.
pbmaise is offline   Reply With Quote
Old 03-05-2021, 07:31   #60
Registered User

Join Date: Nov 2018
Posts: 730
Re: So my boat lacks a lightning ground.

Argument by aphorism, as usual, isn’t very effective. While doing something, anything, might be better than doing nothing, that isn’t always the case. Sometimes just doing something makes me feel better, without necessarily actually changing the course of the universe.

Some ovens can be quite effective as a faraday shield. Others are virtually useless. Putting your GPS in either might make you feel better. Is that the "good" that we should accept over the "perfect?"
Bycrick is offline   Reply With Quote
Reply

Tags
boat, lightning

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Activecaptain on Android Cell lacks much detail Capn Jimbo Marine Electronics 0 25-08-2018 17:10
Prospective boat lacks a few systems jimp1234 Monohull Sailboats 28 08-01-2017 08:53
Mounting Lightning Ground Strip? Beausoleil Electrical: Batteries, Generators & Solar 2 28-09-2012 12:21
DIY Copper Lightning Ground Plate - How Thick ? sv.Crake Construction, Maintenance & Refit 4 13-07-2011 14:46
No Keel Bolts - How to Ground for Lightning ? sabray Construction, Maintenance & Refit 19 25-08-2010 11:12

Advertise Here


All times are GMT -7. The time now is 00:32.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.