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Ground plate / earth bonding

Ground plate earth bonding

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#1 Mogle

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Posted 24 June 2013 - 05:22 PM

We replaced the batteries and changing system on-board. When the job was done I was told by the company that did the job that my earth bonding / ground plate needs to be replaced.

 

I have seen that the connector pin is very rusty with a possible minor leak risk. The ground plate, looks well covered with anti-folding paint from the previous owner. The plate needs replacing.  It is one inch wide and 4 inches long, just left of the keel. It looks well fitted to the hull. From the inside I got two connector pins. I asked my two local chandler if they had a “Ground Plate”. No help there. A quick look at Nigel Calder’s _Boat owners Mechanical and Electrical Manual_ got my eyes to pop. Page 224 “Minimum area of 1 square foot is ISO requirements.” You must be kidding! More reading – for fiberglass boat and external keel or metal centre board will do.

 

My earth is not my iron keel. It is a 1x4 inch well anti-folded external metal plate! And recommended size is 1 square foot!

 

Nigle goes on and recommends a 1 inch by 12 feet ground plate to protect for lightning strikes. Walking on the yard at winter time I have never a yacht with that on her button! Any advice? My yacht is 42”.



#2 jerryj2me

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Posted 24 June 2013 - 08:44 PM

The path to the water needs to be:

 

straight

short

high amperage - low resistance

 

Other than those three items it's an exercise in common sense.

 

In a prior life I dealt with lightning strikes on antenna towers,

the metal towers at the bases generally were concrete base which you don't have here,

but the lightning strikes would come straight down the tower to ground, and generally not travel very far from that path.

 

Mast and shrouds need to have a path to the water, as close to the base of the mast as you can get.

 

Even if that conductor is encapsulated at the "near water" point, I suspect the lightning will arc from that point to the water, toasting whatever is in between the two.

 

For your particular problem, I would suggest having a similar plate to what you had

custom made, do not know if there is something off the shelf available.

 

http://www.marinesur... protection.pdf

 

The guidelines in the above are pretty good. - they use the 1 sq ft as well, but make mention of using th eprop, shaft and transmission as part of that path.

 

my 2 cents!



#3 Oxygen Mask

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Posted 26 June 2013 - 01:45 AM

Random thoughts-

 

A 4" strip for a 42" boat is about right.  ;-)

 

Seems like the plate should not be coated with antifoul for best results?

 

Calder's thinking was state of the art old school - more is better.  Today, we know that all that metal may or may not help prevent strikes, and may or may not help channel the strike safely to water, and may or may not blow the bottom right out the hull if it does.  One thing that science and insurance companies have proven beyond all doubt, is no method or system can be proven to prevent strikes or prevent damage from a strike, and using nothing at all is statistically the same odds.  Do what makes you feel safer.

 

Personally, I feel that bonding the keel to the elect system can easily lead to its rapid corrosion, so I won't do it.  Others disagree. 



#4 amro

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Posted 26 June 2013 - 01:57 AM

http://www.marinco.c...ndard-dynaplate

 

Used them on some big yacht builds. They have a rough/pitted surface which creates more surface area.



#5 jerryj2me

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Posted 26 June 2013 - 05:01 PM

Random thoughts-

 

A 4" strip for a 42" boat is about right.  ;-)

 

Seems like the plate should not be coated with antifoul for best results?

 

Really don't think paint is gonna affect things much. Not sure if there's any science out there and not just speculation, or this is how its always been done. There's stuff on antenna towers, but thats a different game.

 

Sounds like a study for Practical Sailor!



#6 jerryj2me

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Posted 26 June 2013 - 05:32 PM

quick search:

 

http://www.marinelig...com/science.htm

 

some real research:

http://edis.ifas.ufl.edu/sg071

 

Bunch of good research links at the bottom of this page:

http://www.frugal-ma..._your_boat.html

 

This looks useful:

http://nsgl.gso.uri....u/mdug80001.pdf

 

Similar:

http://nsgl.gso.uri....u/ncug95004.pdf



#7 Frogwatch

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Posted 26 June 2013 - 07:41 PM

You want the Dynaplate for your VHF and other normal grounding needs.  These sintered plates have high internal surface area and are good for dissipating small currents.  They are NOT good lightning grounds because they cannot dissipate high currents due to the high fields involved.  The fields make the Dynaplate act like it has only its external surface area when trying to pass the thousands of amps from a lightning strike.

 

You could build in a lightning ground by fastening strips of Cu to your hull.  Although I am probably the ultimate experimenter do it myselfer, even I thought this was absurd on my cruising boat due to the risk of the strip coming off. 

 

So, the better solution to a lightning ground is to use a deployable one.  My first was made from 2' x 2' copper flashing joined by soldering and bolting to a lug to #4 tinned Ancor battery cable with a big battery clamp on the boat end.  The copper flashing has a 3/8" poly bridle attached so ti can be dropped overboard and tied to the boat.

When you see a T-storm approaching, you drop it overboard and clamp it to your mast.  Unfortunately you cannot use it underway and it is a pain to stow.  BTW, DO NOT use normal battery cable because it will corrode at once to green jelly as the salt water wicks all the way up the insulation.

 

My latest, shown in the attached pics is made from stainless steel cloth (actually nice stuff) with rigid stainless rods at top and bottom.  It also has the #4 Ancor battery cable but has a large welding clamp on the boat end so you can twist it on the mast connection to get a good low resistance connection.  Lower it overboard, make sure the cable has no significant bends and attach it to the mast up reasonably high.  Attach the 3/8" poly line to a cleat, rail or similar so you don't lose all.  Depth in the water does not matter much but it should all hang vertically.  You see the stainless cloth has large surface area (4 sq ft) and lots of "edge".

It can also be used while underway if deployed from the stern with floats on the stainless rods and cable as shown.  It can be towed at up to 10 kts.

On a sailboat, it is intended to be attached to ones mast and there is also an additional length of cable and connection to also attach to something else too, like your shrouds.  BTW, I also disconnect my masthead VHF antenna at the base of the mast and short the antenna coax there with a shorting plug to make the antenna and mast at the same potential.This way, a strike thet hits the antenna goes thru the mast and not down the coax and into the cabin.

The bag it all stows in is made from silver coated ripstop nylon so you can put your VHF and other sensitive electronics in it to prevent EMP damage from a strike.  During a storm, I put a GPS, the main 25 watt VHF and cell phones in the bag and use an old handheld GPS and 5 watt handheld VHF.

The attached pics were mde this past weekend in deployment and towing tests from my powerboat in N. Florida.  This weekend, I intend to do deployment  and towing tests from a Hunter 23.

Is it practical?  I dunno yet but it does partially alleviate my deathly fear (justified) of lightning and allows me to use my inherent geekiness to make stuff.

Attached Files



#8 jerryj2me

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Posted 27 June 2013 - 04:00 PM

(facepalm)

 

A lightning strike is not going to nicely travel that one pretty path and travel out to your stern float toy.

 

A lightning strike at the masthead will cause current down any and all paths to the water, not just the one you think is the most favorable.

(look up "current division in parallel resistances")



#9 SloopJonB

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Posted 27 June 2013 - 04:27 PM

Random thoughts-

 

A 4" strip for a 42" boat is about right.  ;-)

 

Seems like the plate should not be coated with antifoul for best results?

 

Really don't think paint is gonna affect things much. Not sure if there's any science out there and not just speculation, or this is how its always been done. There's stuff on antenna towers, but thats a different game.

 

Sounds like a study for Practical Sailor!

 

Most bottom paint is full of copper or tin so I doubt it will act as an electrical block. If you want a fully grounded system, why not simply run some big ass cable to the keel? It'll take an awful long time for a keel to wear away from galvanics - that big lump ain't exactly a zinc anode. The owners a couple of generations down the road can worry about it.



#10 Soley

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Posted 27 June 2013 - 04:56 PM

The 80ft sail boat I ran had the masts grounded to the keel bolts with 0 gauge wire, as approved by ABYC. All ends were covered in dielectric grease. As it was a cruising boat we had pretty hefty anodes on the keel.

 

The electrical system was grounded to a designated anode. I never ground to the prop, shaft or p bracket on a cruising boat, although they are protected with anodes.



#11 Frogwatch

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Posted 27 June 2013 - 06:17 PM

As JeryJ points out, the current will indeed divide and follow various paths.  However, your mast is almost certainly the highest conductivity so it will carry most of the current.  From the mast, you do not want your thru hulls to carry most of the current because they will be destroyed.  The function of my floating ground system is to provide the best path to ground so most current will go that way.

One of the peculiarities of a lightning pulse relative to straight DC is its high frequency components causing it to follow surfaces easier than than following a bulk conductor.  This is why my cable has numerous small individually tinned wires and why the use of a large area ground is good and why the ground having lots of "edge" works well.

Does an externally ballasted keel work as a lightning ground?  YES.  Does it work well?  Maybe  After a lightning strike, keels and other painted metal surface are often seen to be covered with many tiny pinholes in the paint where the current exited.  Aside from the damage to the paint, this seems to me to indicate a source of resistance to dissipation that might lead to side strikes from one metal piece to another on the boat.  I'd prefer a dedicated lightning ground.

Will your prop act as a lightning ground?  Yes, but do you want it to?  With all the sharp bends the current would have to take, you almost guarantee side strikes.

While I don't think people should freak out over lightning, I see a lot of complacency and the attitude that it acts randomely.  No, lightning acts in well understood ways and we can do things to mitigate damage.  Preventing and predicting strikes is a bit more difficult and if you happen to be in the wrong place................Although I have a background in HV discharges and know how to try to avoid lightning, I have still almost been hit 3X so am strongly motivated to deal with an eventual strike.



#12 jerryj2me

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Posted 27 June 2013 - 07:19 PM

the earlier links with research and the ABYC guideline for boat surveyors I think is a good guideline.

 

Almost being hit doesn't count in my opinion, a long trailing wire behind the boat will exhibit a lot of inductance leaving it out of high transient current path largely. 

 

Keep it short, straight and thick.



#13 Frogwatch

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Posted 27 June 2013 - 08:48 PM

Do long lightning rod conductors work ?  Obviously they do but they are uninsulated most of the time.  However, they still work when afixed to a surface that stays dry and unconducting (relatively).  Yes, there is some inductance but with a short cable run (20') it will not be enough to reduce its efficacy much.

However, when that big voltage pulse hits the cable, the thin insulation will likely break down eliminating any inductance.  The Low freq stuff will have no prob and by then the insulation would break down for the HF stuff.

One could replace the cable with uninsulated cable but I think the change in inductance would be minimal.

I may find a way to actually test it.  I know of some ancient posts (not aids to nav or serving any purpose now)  out in the water from which I could attach a long metal pole and my ground.



#14 BalticBandit

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Posted 28 June 2013 - 12:18 PM

you might consider putting the instruments into the microwave (if you have it) or the oven (next best thing) as those act like farraday cages (the former being designed to be one).

 

Note that its not just the straight strike that causes problems.  A strike also causes a localized EMP.

 

Have you considered running a balloon from your floating plate?  something like a weather Balloon covered in a light wire mesh with wire running down as the tether that is net net taller than your mast?   This would serve both as a charge bleed (reducing the likelihood of a strike) as well as a sacrificial strike point



#15 jerryj2me

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Posted 28 June 2013 - 04:15 PM

That wire out the back is essentially an open circuit for this purpose.

The inductance and group delay of that 20' of wire is huge.

 

"the thin insulation will likely break down eliminating any inductance"

 

That is total nonsense.

If this was not a matter of safety, I would roll my eyes and just ignore it.

 

The ABYC guidelines I posted before is a good guideline, otherwise Darwin is going to get you.

 

If you want to drop something in the water, make it a heft chunk of metal and cable, connect it directly to the base of the shrouds and drop it straight overboard, with ***straight*** being the important word.

 

As for "light wire mesh on a weather balloon"  - heres an idea instead of that - go get in the middle of an anchorage with a lot of taller masts all around you.

 

Do long lightning rod conductors work ?  Obviously they do but they are uninsulated most of the time.  However, they still work when afixed to a surface that stays dry and unconducting (relatively).  Yes, there is some inductance but with a short cable run (20') it will not be enough to reduce its efficacy much.

However, when that big voltage pulse hits the cable, the thin insulation will likely break down eliminating any inductance.  The Low freq stuff will have no prob and by then the insulation would break down for the HF stuff.

One could replace the cable with uninsulated cable but I think the change in inductance would be minimal.

I may find a way to actually test it.  I know of some ancient posts (not aids to nav or serving any purpose now)  out in the water from which I could attach a long metal pole and my ground.



#16 Frogwatch

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Posted 28 June 2013 - 04:37 PM

Having considerable experience with HV discharges MIGHT give me some credibility here.  The 200 V rated insulation of the cable will not last on exposure to a million volts with the water at ground potential only a few thousandths of an inch away.  No, it is not an open circuit at all and I defy JerJ to provide any calculations to show it is..  Even better, experience trumps theory because lightning conductors DO WORK otherwise nobody would ground lightning rods with the conductors they use,  These conductors are often a hundred feet long or more.  The conductor I use has about 5X the surface area/length of the typical lightning ground conductor for lightning rods.

His talk of "hefty chunk of metal" conductors is pure nonsense as the HF components of lightning are well known to mostly travel on the surface of even good conductors. (BTW, that is why even 60 HZ power lines are stranded).  Yes, a 'straight" conductor is best but if you are under power that may not be feasible and a gradual curve of the conductor from your mast to the water over a distance of 20' is nothing when people who ground towers reccomend no bends greater than 8" radius of curvature. I've also seen this 8" number used for lightning conductors on boats too.  Compare it to the 20' of mine.

 

My personal experience based on:

 

MSEE, MS Physics, 30 yrs experience with very high voltage discharges, patents, work with pulsed power weapon systems



#17 Frogwatch

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Posted 28 June 2013 - 05:37 PM

I will now provide the answers to how much inductance my conductors provide.  Use these sites as references:

www.dtic.mil/dtic/tr/fulltext/u2/a234306.pdf‎

http://chemandy.com/...-calculator.htm

www.sonnetsoftware.com/pdf/cst/lightning-strike.pdf‎

 

A lightning pulse has frequency components mostly in the KhZ region based on the first and 3rd references.  Using the second reference we can then calculate the total impedance of my 20' conductor to be 2.5 ohms.  Seems like a lot.  However, consider the impedance of your mast  using the same calculator and you get about 5 ohms or a shroud  and you get nearly 9 ohms.

SO, the impedance of my conductor is considerably less than that of your mast or shrouds and is less than ANYTHING else but a straight short connection from mast to water which may not be feasible when underway.  So, if you must be underway to maintain control or get to safety, my towed ground provides the least impedance path (if you do not have a lightning ground affixed to your boat or use your keel/hull as a ground).

My ground does have a short cable to be used to simply hang the ground over the side from the mast when you are stationary.  The towing is to be used only if you need to maintain steerage.



#18 jerryj2me

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Posted 28 June 2013 - 09:11 PM

For anyone doing this, I strongly suggest this:

 

http://www.marinesur... protection.pdf

 

That's a pretty well developed reference on the subject, and its industry recognized ABYC practices on the subject.

 

Frogwatch? If you are such an electronics wizard, then you need to go sit at the base of your mast during a lightning storm. Benjamin Franklin would be proud of you, and Darwin can display you as an example. Let us know how your learning experience works out.



#19 Frogwatch

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Posted 28 June 2013 - 09:57 PM

JerryJ:

 

Thank You as you have proven my system is in accord with the ABYC in every reespect but 1.  Mine is not as thick as they like but mine has 4X the surface area.  This must be where i saw the 8" radii of curvature thing and the radius of curv of my trailing conductor is probably measured in tens of feet.  Oddly, a system approved by JerrYJ would seem to have braid as the conductor and I would agree with him on that but ABYC says not to use braid.  I am not sure why they say not to use braid.

My system is considerably better than their minimum specs.

Now, as for sitting at the base of the mast during storms.  Remember that in minimizing electric fields, distance is everything, so even with a very good system, one should be as far as possible from something at millions of volts with no conducting path between you and it.  However, at millions of volts, every surface conducts making distance even more critical (why HV insulators on HV transmission lines are convulated).

JerryJ, any idea why the ABYC doesnt like braid?  #4 braid has the same X section as the #4 conductor they like but more surface area.



#20 sailSAK

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Posted 28 June 2013 - 10:48 PM

My guess is ABYC is stuck on the idea that solid wire will crack and work harden.  Seem to see that a lot in their literature and their proponents ramblings.  While they do have some pretty good standards they are not the end-all for many arguments.  For a lightening ground/bond you can forget about insulation (no value) and use a heavy/beefy conductor as you can.  A metal bar would be good.  If lightening does flow through a wire you can be damn sure the wire will get hot enough to melt any insulation it has and probably start a fire.   The idea isn't to channel all the current through one path-its to provide a better path than *you* or your hull to reduce the odds you get killed.  Thats it. 



#21 Oxygen Mask

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Posted 28 June 2013 - 11:06 PM

It's LIGHTNING.

 

Lightening is what happens when you throw stuff overboard.



#22 Frogwatch

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Posted 28 June 2013 - 11:09 PM

"Braid"  is not solid.  It is made from lots of small wires braided together in a sort of flat conductor that si generally bare with no insulation.  It is exactly what I'd expect would be best .  So, why doesn't ABYC like it?



#23 jerryj2me

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Posted 29 June 2013 - 12:56 AM

It's LIGHTNING.

 

Lightening is what happens when you throw stuff overboard.

Like tossing Froggywatch in the drink?

 

Oh, and Frogwatch - your system is neither vertical or straight as explicitly spelled out in the ABYC document. So save the bullshit for those that did not read the document and hopefully they will buy it. Meanwhile go sit under that mast if you want to keep insisting that you are right.

 

SailSak - you do want the conductor to be insulated, but not for the readily apparent reason. I do agree it needs to be stranded wire as per the document, that has to do with work flexing, I agree. It is a similar thinking for wiring in airplanes as well. The reason you want the conductor insulated is for a different reason:

 

Corrorsion

 

Nautical grade wire is plated and not raw copper, and even as a ground wire, you want it insulated to minimize corrosion. I had a lightning ground strap in the bilge in my last boat that rotted in half due to corrosion. The insulated ones were fine, and the bare wires at the crimp connectors rotted through. The new ones were sealed at the ends so the bilge water ingress was minimized.



#24 BalticBandit

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Posted 30 June 2013 - 06:03 PM

I suspect that the reason ABYC doesn't want braiding is that for a given surface area, it tends to have more impedance as the actual distance travelled is longer for each braided wire bit than the straight line of the conductor.  Aslo the tinning on braid will eventually wear off as you work the braid



#25 Maine Sail

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Posted 01 July 2013 - 01:57 PM

And my personal experience is that I have seen piles of boats hit by lignthing, I am a marine electrician the guy called in to fix the strike damage. Only in a few cases, where the main grounding conductor was severely corroded at teh mst base, was the wire insulation melted. It was usually very small too, on the order of 8GA..

 

Our own boat was hit and is wired to better than ABYC standards when it comes to wire gauge.. No melted down conductor, no melted secondary conductors and no holes in the hull. The system worked as I had hoped it would.. We lost all electronics, as I would expectbut the vessel suffered zero hull and wiring damage. I am still working on a J-Boat that was hit and also wired to ABYC standards. No holes in hull, no melted down conductor though some smaller 24GA NEMA wire was damaged..

 

I worked on a boat last summer not wired to the ABYC guidelines, no lightning bonding. The hit followed the VHF cable and blew numerous holes in the hull along where the cable laid on or near the hull. Boat was totaled.

 

There is one common denominator I see over and over in strikes and that is a boat with a mast ground installed usually suffers less hull damage than one without, when hit. Right now, in my own "n" group of strikes, boats without any lightning bonding have been hit more than boats with, and boats with proper down conductors and lightning bonds survive better structurally. No boat fairs well when it comes to electronics...

 

 

Having considerable experience with HV discharges MIGHT give me some credibility here.  The 200 V rated insulation of the cable will not last on exposure to a million volts with the water at ground potential only a few thousandths of an inch away.  No, it is not an open circuit at all and I defy JerJ to provide any calculations to show it is..  Even better, experience trumps theory because lightning conductors DO WORK otherwise nobody would ground lightning rods with the conductors they use,  These conductors are often a hundred feet long or more.  The conductor I use has about 5X the surface area/length of the typical lightning ground conductor for lightning rods.

His talk of "hefty chunk of metal" conductors is pure nonsense as the HF components of lightning are well known to mostly travel on the surface of even good conductors. (BTW, that is why even 60 HZ power lines are stranded).  Yes, a 'straight" conductor is best but if you are under power that may not be feasible and a gradual curve of the conductor from your mast to the water over a distance of 20' is nothing when people who ground towers reccomend no bends greater than 8" radius of curvature. I've also seen this 8" number used for lightning conductors on boats too.  Compare it to the 20' of mine.

 

My personal experience based on:

 

MSEE, MS Physics, 30 yrs experience with very high voltage discharges, patents, work with pulsed power weapon systems



#26 Frogwatch

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Posted 01 July 2013 - 05:39 PM

Maine Sail:

 

Your experience is just what we need to hear about, what works and what does not.

Any ideas on how to protect electronics?  Would disconnecting the electronics from the boats help?



#27 Maine Sail

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Posted 01 July 2013 - 08:52 PM

Maine Sail:


Any ideas on how to protect electronics? 

Yep, INSURANCE !!!



#28 Maine Sail

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Posted 01 July 2013 - 08:55 PM

Maine Sail:

 Would disconnecting the electronics from the boats help?

No, not in all strikes.

 

My own strike too out:

 

iPod - not plugged in or connected to anything

Laptop - not connected to anything and in its case

EPIRB - These are wireless

3 Hand held GPS units one wrapped in tin foil and in my ditch box. None were plugged in

1 Hand Held VHF not plugged into anything

 

Oh and my compass was blown 12-18 degrees out of whack so that old axiom....... (wink)

 

The good news is that electronics are easily replaceable. A sunk boat is a totaled boat..... Our hull survuved with zero damage.



#29 Frogwatch

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Posted 01 July 2013 - 10:05 PM

The wrapped in foil one got zapped too?  That surprises me.



#30 jerryj2me

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Posted 02 July 2013 - 12:30 AM

High current transients create EMP pulses which include magnetic fields.

 

Magnetic fields go right through aluminum.

(low magnetic permeability)

 

Magnetic fields induce currents in other conductors.

 

Currents in conductors create voltages, depending on the impedance.

 

Poof!

 

It only takes a little to go overvoltage on a semiconductor and the gate oxides of the transistors get fried.

(5V on old CMOS silicon, 0.8V on the newest stuff)

 

You will do better with this stuff in the oven on the boat, due to it being steel, although stainless steel has crappy permeability as well. How about an old fashioned steel lunchbox?

 

Froggy - one thing you seem to be missing is that the lightning does not travel within the conductor in many cases. Instead that conductor serves as a path for initial conduction, and a lot of the discharge bulk is in the ionized air around the conductor.  Also, your earlier statement about the frequency content of the lightning strike (based upon the Sonnet link you provided) is not relevant. The example uses a Navy ship with an all steel hull and an all steel topside, which is not the case with most sailboats. Remember - time constants are determined by the discharge path.



#31 Frogwatch

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Posted 02 July 2013 - 03:24 AM

Static mag fields go right thru Al, a very rapidly changing field not so much as it induces current in the Al and then the skin effect causes that current to be mostly on the surface and produce a B field to oppose the changing mag field.  Various places on the net sell weird collapsed conductive things produced by intense very raopidly changing mag fields.  For example, you can buy "shrunken quarters" that are smaller than a normal quarter but all the features are still there but the quarter is also thicker. This efect is also used for an "ultra-fast closing valve" for nuke effects testing; an aluminum tube is pulsed at the same time as the nuke thingy goes off causing the Al tube to collapse in a few tens of nanoseconds.  The resulting tube looks very weird, tubular at the ends but suddenly becoming a tiny solid piece.  Here at the Nat High Mag Field Lab, they make big magnets they pulse with very high currents very rapidly.  They have to make the coil super strong to resist collapse from this.  This is why I find the non-blocking of the field from the lightning to be surprising.  I'd expect the Al foil to produce a current that opposes the changing B field.  Further, when I consider the emp shielding I have seen(yes, I've seen a lot), It is mostly copper or Al.  it is Al on the walls with copper seals on the Aluminum doors around the edges, no steel at all.

 

A lightning pulse travels on the surface of most things and not in the air around them.  In almost all cases, including something like Boron Nitride (one of the highest dielectric constants), the breakdown strength of the surface is less than the breakdown strength of air (except at the dip in the Paschen curve, breakdown strength as function of gas pressure).  So, the bulk of the current flows on the surface or very close to the surface.  Yes, you do get corona discharge at corners and edges but not on smooth surfaces.

 

I checked several references for the freq content of lightning (check the one on EMP of lightning compared to EMP from nukes) and you will see that they all give roughly the same numbers.  Once you hit breakdown, there is very little resistance to give a time constant of the boat acting as a capacitor or inductor. Imagine shorting a capacitor or inductor with essentially zero resistance.  The electrons in that discharge are "free electrons".  Do you really want a dissertation on the physics of HV discharges in solids and gasses?  I can give you one.

 

Now, you can buy mag shielding foil (mu metal foil) but I do not think you should need it.



#32 Maine Sail

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Posted 02 July 2013 - 12:17 PM

All I can tell you is that the aluminum foil did squat at protecting my hand held GPS. It was wrapped tightly in foil then inserted into a freezer bag with a dessicant pack and stored in my plastic waterproof ditch box, which is now an Army ammunition box made of steel.

 

I had literally just replaced the batteries in the GPS about three weeks before the strike. I try to use lithium batteries in all my emergency gear, personal strobes, lights, GPS etc. etc. and I had just done my yearly replacement. The GPS booted and worked perfectly after the battery change and lfound the satellites in about 10 seconds from re-boot, even from isnide the cabin..

 

When the insurance surveyor was actually on-site I pulled it out of the foil fully expecting it to work, as I had read that it "could" work. I fired it up and the screen just went "BLIP" and it promptly died, TOAST......... Surveyor checked that one off the list too....

 

Lightning is very unpredictable. Oh and not a single fuse on our boat was blown but everything electrical/electronic was fried. I see this quite often actually...



#33 jerryj2me

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Posted 02 July 2013 - 01:40 PM

Lightning is very unpredictable. Oh and not a single fuse on our boat was blown but everything electrical/electronic was fried. I see this quite often actually...

 

Fuses have such long time constants that they won't do much for you in these types of situations.

Ditto for circuit breakers. There are some specialty protection shutdown circuits that will respond, but they are outside the scope of what you would use on a boat.

 

I think the guidelines in the ABYC document about short straight and vertical discharge  paths are about the best you are going to do. Unpredictable sounds about right, some fo the research links I posted earlier have some insights that are useful here.

 

 

Do you really want a dissertation on the physics of HV discharges in solids and gasses?  I can give you one.

 

Not really, in your mind you are the divine source of all wisdom so please lecture yourself.

 

While you are doing so, go put the tin foil hat on and sit under your mast.

Eddy currents induced in the  tin foil should protect you from the lightning strikes.

 

Skin effect on a piece of aluminum foil (rolls eyes) good god...



#34 Mogle

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Posted 02 July 2013 - 02:11 PM

I got my Dynaplate Amazon today - will fit it next time I am down at the yacht. And yes she is out of the water.

 

Interesting read this lightning stuff. When asking about ground / earth plate I was not thinking of lighting.

 

The best protection is most likely your insurance - and a spare GPS unit or two.   



#35 Soho

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Posted 02 July 2013 - 05:40 PM

Interesting thread - lots of knowledge there.    So riddle me this,  my keel is an encapsulated lead one,  no keel bolts to bond the mast to.   What then is best method of installing some protection against a strike -  previously, not now, the chainplates were all connected back to the electrical system ground which is attached to the prop strut.  

 

We don't get a lot of lightening where I am moored.  but still I do worry. 



#36 Frogwatch

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Posted 02 July 2013 - 05:48 PM

Soho. my keel is also encapsulated which is waht drove me to this lightning ground thing.



#37 jerryj2me

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Posted 02 July 2013 - 06:57 PM

Interesting thread - lots of knowledge there.    So riddle me this,  my keel is an encapsulated lead one,  no keel bolts to bond the mast to.   What then is best method of installing some protection against a strike -  previously, not now, the chainplates were all connected back to the electrical system ground which is attached to the prop strut.  

 

We don't get a lot of lightening where I am moored.  but still I do worry. 

Whats wrong with putting it back to the prop strut as the original manufacturer had done? (I presume)

 

As for the enclosed keels, maybe you can drill thru the bottom of the boat and get a conducting rod into the metal keel by that path, or if the top of the metal keel is available in the bilge, drill the top out for a threaded connection-insert.



#38 Maine Sail

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Posted 02 July 2013 - 07:23 PM

my keel is an encapsulated lead one,  no keel bolts to bond the mast to.   What then is best method of installing some protection against a strike -  previously, not now, the chainplates were all connected back to the electrical system ground which is attached to the prop strut.  

Something like this as close to the centerline as possible. The problem with Dyna plates as they have the potential to literally explode when hit. Seeing as they are drilled into the hull probably not something you want to be taking the brunt of a direct strike.

 

120656553.jpg



#39 Soho

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Posted 03 July 2013 - 08:41 PM

I could go back to the prop strut,  but I was skeptical of that path as it has several connections and turns, before getting to the strut.   Was not convinced it was a good path to take.  

 

Drilling into the keel from inside is potentially possible,  had not really thought of that one,  presume in the case of a strike at some place it just blows the covering of the keel off. 

 

Maine Sail,   I race the boat and having something like that on the hull is just too hard to swallow at this time.  






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