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Old 10-12-2004, 13:45   #1
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LIGHTNING - Some new data.

I received the following from a Brit friend and, though aimed at the aviation industry, I thought it of great interest to any kind of cruising.

I watched a riveting TV programme last night that might have been of interest to you, about the latest research into lightning and how it can affect both aircraft and space flight. I hadn't realised how much new information there was on what's such a common phenomenon, things like sprites, which are blue and red coloured lightning that comes down in a funnel shape to clouds from around 80km up in the atmosphere, then turn into a normal looking lightning bolt to the ground, but it's positively charged and can hold about 10 times as much energy, and last up to 10 times as long, as a 'normal' negative bolt. There are also jets, which fire upwards for about 15km from the top of clouds, but hardly anything is known about these. They're now almost certain it was a self-generated lightning bolt that brought down the space shuttle last year, the one that disintegrated on re-entry over California. Ironically one of its crew's missions was to film and study lightning from space and some of the video they took showed sprites and positive lightning being triggered when a meteor shower entered the high atmosphere; the thinking, supported by a previously unseen amateur video of the re-entry and break-up, was that it was the shuttle itself that triggered such a lightning bolt which destroyed it
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Old 11-12-2004, 00:10   #2
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Lightening is certainly a mysteriuose phenomena and only a fraction of it understood.
I have a freind that is working in the feild of the ceramics on the shuttle. They have done extensive testing and have pretty much proved that the piece of foam that broke off the main tank was the cause of the Shuttle disaster. They have been able to identify its size, speed, path and the exact tile it struck, where and at what angle. The impact had either shattered the tile, punched right through it or lifted it enough to cause a problem. All those scenareo's had been reproduced in experiments. From that they were able to recreate how the rest of the event unfolded.
Lightening often hits spacecraft. It is a frighteningly common experiance. Aircraft as well can be hit and frequently are. But modern air and space craft are now designed to handle most of such events.
Not quite so the Sea going vessel. It tends to be on the thick end of a major current flow to a very massive earth sink called Mother Earth. The difference is that lightening in the air stricking air/space craft is usually because of two reasons. The craft is charged or it just happens to be in the path of the bolt. Although the events around the craft may be creating the events that lead to the discharge. i.e. the massive amounts of air being drawn down around the space craft at lift off due to the exhast gasses being blown away. Or an Aircraft being charged by air moving over its surface. With a Boat, it is because it just happens to get the massive current sink called Earth closer to the charged atmosphere that has been wanting to leap the distance but hasn't quite made it yet. So the boat tends to be in the middle of a very high current/voltage feild with devastating consequences.
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Old 11-12-2004, 03:41   #3
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Talking This gets me thinking !

Just what exactly has anyone come up with lately on diminishing the effects of a lightening strike ? How about tying a chain to the mast and dropping the other end overboard? Hmmm. Bet'cha ol' Gord would know. Heyyyyyy Gord, ya out there ?
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Old 11-12-2004, 05:30   #4
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I hesitate to offer any lightning amelioration advice - due to the complexity of the subject. No matter how much one says, there is always more to the issue, and it becomes a daunting task to present exhaustive advise, that adequately addresses the many important issues involved. In 1999/2000, I wrote over 20,000 words (about 3-4 major consecutive magazine articles) on the subject, and (through a disastrous string of events) I lost all my composition and research. I’ve never had the energy to undertake the task since.

Understand that the following offers a very stripped-down opinion, and should not be relied upon as (anywhere near) complete.

Caveat emptor !!!

Anchor Chains, Booster Cables, and the like, provide INEFFECTIVE & dangerous lightning grounds plates !!!

Minimum ABYC standard design criteria for a Lightning Ground Plate are:

• Minimum area – one square foot totally submerged for salt water (more for fresh water)

• Thickness – minimum of 3/16"

• Width – minimum of 3/4" (for a grounding strip)

• Materials – copper, copper alloy, stainless steel or aluminum.

Other important guidelines relative to designing the external ground plate are:

(1) The ground plate should be located as close to directly under the down conductor (mast) as possible.

(2) The edges must be sharp and exposed, and not caulked or faired into the adjoining hull surface.

(3) The grounding strip, if used, should extend from directly below the mast towards the stern and be electrically connected to the aft end of the engine (a minimum strip length of 48" is recommended, with an appropriate width to yield at least 1 square foot of area).

(4) A pair of thru-bolts should be installed at each end of the strip to prevent it from twisting. Intermediate bolts may be used as necessary.

(5a) I (personally) do NOT recommend the use of “Sintered” ground plates (designed for RF grounding), such as the “Dynaplate”, for LPS systems. It is suggested that the water trapped in the many small pores could boil & explode during a ground strike.
(5b) Chain does NOT meet (any of) the above criteria, and should not be used (except as a poor emergency substitute).

STRIKESHIELD offers a Temporary Mast to Ground Plate attachment system (It reads interesting - but I’ve never used it - so perhaps someone who is familiar /w the product might comment further):
http://www.strikeshield.com/product.html

Respectfully,
Gord
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Old 11-12-2004, 08:55   #5
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The case for steel as a hull material

This has always been one of my reasons for not dismissing a steel vessel. Once down below, given a deck-stepped mast, you are in a fairly decent Faraday cage. This has always appealed to me in some ways.
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Old 12-12-2004, 03:06   #6
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Quote:
The ground plate should be located as close to directly under the down conductor (mast) as possible.
So how do you do that in a catamaran?
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Old 12-12-2004, 04:30   #7
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LPS for Cats ?

I have no professional experience in designing/installing a practical LPS for Catamarans. What follows is merely theoretical musing.

LIGHTNING PROTECTION for CATAMARANS:

The design of a lightning protective system for a catamaran is obviously problematic.

Excepting metal-hulled cats, the question is how to complete the vertical Down-Conductor from Mast to the immersed Ground Plate. A (more or horizontal) down conductor segment connecting the Mast Step with a ground plate on each hull would, most likely, have too much of a horizontal run to prevent the strike from jumping off the wire in its quest for a more direct path to the water.

Considering the metal mast as the primary down conductor, the lightning circuit to the water can be temporarily completed (when anchored or docked) with a detachable submersible ground plate connected to the mast down connector with a heavy clamping device.
Ie: see “Strikeshield”
http://www.strikeshield.com/ -&- http://www.strikeshield.com/catassembly.html

To provide a catamaran with reasonable lightning protection under sail, a design scheme emphasizing Parallel Lightning Paths might be considered.

This would consist of carefully grounding the cap shrouds to make them the preferred electrical path of least resistance. Lower shrouds on a metal mast should also be included, but only after providing good grounding of the cap shrouds.

If using Shrouds for Lightning Down Conductors, they must have assured minimum electrical resistance at all joints through which the lightning current is expected to flow. This may require placing copper jumper wires around the mast tang-to-shroud wires as well as around turnbuckles to assure good conductivity.

Each of the parallel lightning paths from the common air terminal to their ground plates should be designed as the equivalent of a single-path installation. Lightning, with its capricious nature, is not likely to arbitrarily split its charge between routes, which may have different electrical resistance. A safer assumption would be that the lightning strike will take the (undeterminable) route of lesser resistance, which will then have to carry the full discharge load (one or the other shrouds will “take the hit”).

You should also appreciate that when the catamaran is underway (perhaps with a hull lifting), there may be momentary lapses in the electrical contact between that hull’s ground plate and the water. I don’t believe that this is likely, in a Cruising Cat’.

FWIW
Gord
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Old 14-12-2004, 07:08   #8
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In regards to steel boats, I'm reminded of the time I was helping fellow cruisers through the Panama Canal. As we were nearing the locks, following a large ship, the ship was struck by lightning as I happened to be looking at it through binoculars. The ship's antennae were spectacularly vaporized and they had to resort to hand-held VHF's to speak with the lock workers.

At the time, I was on a 42' steel Colvin, a quarter mile away from the ship. One of the crew helping us that day was a doctor and we all told him to get below immediatly. He asked why and we told him that he would likely be protected down below, but as we were entering the locks and had to be above, we wanted our medical specialist healthy in case one of us got zapped.

I have seen proof of the ineffectiveness off the "fuzzies" at the top of the mast. Twice in the past two months (and several other times as well), I saw first-hand that these boats were not helped in the least. In one case, the fuzziy was partially melted.

My feeling is that you can ameliorate your chances of a strike by maybe 20-30% by doing everything the ABYC and other experts advise. Their advice may or may not change the severity of strikes, though I think it has some effect.

Lightning just doesn't care sometimes, regardless of what we do.
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Old 14-12-2004, 08:29   #9
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Quote:
tenknots once whispered in the wind:
In regards to steel boats, I'm reminded of the time I was helping fellow cruisers through the Panama Canal. As we were nearing the locks, following a large ship, the ship was struck by lightning as I happened to be looking at it through binoculars. The ship's antennae were spectacularly vaporized and they had to resort to hand-held VHF's to speak with the lock workers.

At the time, I was on a 42' steel Colvin, a quarter mile away from the ship. One of the crew helping us that day was a doctor and we all told him to get below immediatly. He asked why and we told him that he would likely be protected down below, but as we were entering the locks and had to be above, we wanted our medical specialist healthy in case one of us got zapped.

I have seen proof of the ineffectiveness off the "fuzzies" at the top of the mast. Twice in the past two months (and several other times as well), I saw first-hand that these boats were not helped in the least. In one case, the fuzziy was partially melted.

My feeling is that you can ameliorate your chances of a strike by maybe 20-30% by doing everything the ABYC and other experts advise. Their advice may or may not change the severity of strikes, though I think it has some effect.

Lightning just doesn't care sometimes, regardless of what we do.
First, I love your signature! Hillarious!

Did you feel that the steel hull was indeed a good protector? It is my feeling, having come from a Physics background originally. Lighting, while highly unpredictable, certainly follows one rule, like all electricty: It follows the path of least resistance to ground.

The steel hull should be as safe as a car in an electrical storm, since in both, you are surrounded by metal which will conduct the electricity and direct it toward ground, through the path of least resistance (the metal hull/body)

However, it would seem that there are certain issues that come up in a boat rather than a car.

1) When the electricity exits the hull into the water, does it overheat the steel, causing any breeches or damage to the steel hull?

2) Are there any other "short resistance" paths for the electricity to follow through the cabin, rather than sticking to the outside hull structure? (ie: a metal support for a deck-stepped mast?)

3) Can you actually go below, or will you have to be out on deck, as in the canal example above?

This certainly is an interesting thread, especially since I am currently back to the drawing board on which boat to purchase this fall.
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Old 15-12-2004, 12:05   #10
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Just a few notes.
Yes it is true that the current will follow the path of least resisitance. But only if the conductor is big enough to carry all of it to ground. Thus you have to worry about anything else that can conduct, As a charge will follow any and all conducting materials on its path to ground. That includes a person.
The strike on the ship was most likely because the radio was transmitting at the time. No one (as far as I know yet) understands why a strike seems to go to a transmitting antennae. But it is a reminder to all, in a storm, DO NOT transmit unless you absolutely have to and if you can, disconect your radio from both its antennae and the power supply.

No the steel will not over heat. The water will disapate the heat and the surface area is very large. If the surface area is small and water is trapped in it, i.e sintered bronze plate, the varporizing water could cause the plate to shatter.

I don't believe there are any "Best" materials or "Worst" materials to have as a boat. Steel may sink the current to ground. But it may also be a better attracter of the strike in the first place. Glass may be a better insulator. It tends to look worse off after a hit, because the current has had to leap distances to conductors on it's jorney to ground. Wood is no different. I am not sure what will happen with Ferrocement. I know of one that lost some plaster in a strike, but it may have had other problems to allow moisture into the plaster.
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Old 15-12-2004, 16:45   #11
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Just to add to the "lightning is not fully understood" mantra ... there is now concrete proof (high speed photography) that in at least some cases, there is a component of lightning that emanates from the Earth upwards! At this point in time, it is not understood at all. Whether this could happen to a vessel or not, I have no idea ... but ... how wierd is that?

L S/V Eva Luna

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Old 15-12-2004, 16:53   #12
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Just to add to the "lightning is not fully understood" mantra ... there is now concrete proof (high speed photography) that in at least some cases, there is a component of lightning that emanates from the Earth upwards! At this point in time, it is not understood at all. Whether this could happen to a vessel or not, I have no idea ... but ... how wierd is that?

L S/V Eva Luna

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Old 15-12-2004, 19:09   #13
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Lightning

The part that goes up has been known for some time and photographed. To me lightning is similar to the riddle "where does an elephant sit in a bar" anywhere it wants. I have had the rigging humming very loud and lightning struck land a few hundred yards away. Michael
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Old 16-12-2004, 00:08   #14
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Ground strike lightening is the best understood. The thing that goes up into the air is called a "Leader". It is not understood why and what it is exactly, but it is this "leader" that the strike follows back down to earth. The comment I made earlier about a transmitting radio being a likely target for a strike is because the transmision effect has the same affect as the Leader does. This is called a "Triggered" strike. A storm usually produces negative going strikes to ground, but a disappating storm often produces less common positive strikes toward the rear of the storm.
There are aproxamately 1 to 2 thousand lightning storms around the Earth at any given time. About 100 strikes are taking place every second. Most of those strikes are Cloud to Cloud and are the least understood. There are things happening above the storm head as well. Red Sprites and Blue Sprites, elves and one other I can't remember. No one understands why and what they really are. But one guy has a theory that seems to be sound. As a result, research is now underway with satillites being placed in orbit, fitted with speacial equipment to try and detail what is happening. One thing that is understood, is that a continuose current of about 1 amp and around 200 to 500 thousand volts is being feed into our upper atmosphere. Exactly what affect this has and what it's real importance is, is still not clearly understood. But I don't think anyone should turn the switch off just yet.
And finally, just to really confirm my nerdish nature, a lightening strike produces vast quantities of Ozone, which of course ends up in our upper atmosphere and protects us all from radiation and UV. The thunder is cause by the strike super heating the air to around 20,000 degrees. That is 6 times hotter than the Sun's surface. The air is "blown away" and the compression wave radiates away becoming a sonic shock wave.
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Old 16-12-2004, 02:32   #15
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[QUOTE]Alan Wheeler once whispered in the wind:
" A storm usually produces negative going strikes to ground, but a disappating storm often produces less common positive strikes toward the rear of the storm."

These "positive" ground strikes (ground to cloud) are generally much higher energy, and more damaging than the more common "negative" strike (cloud to ground). About 10% of all ground strikes are thought to be positive .
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