lightning strikes/ avoiding them?

[GordMay]

Wheels:
So, how does one "isolate" (insulate) the boat against all those millions of watts of lightning power?
Gord

[CaptainK]

There might be another version to what I was saying earlier?

You could have a lightning rod at the top of the mast. And from there, run a small chain down the mast. And run it all the way down, like a rigging cable. And into the water?

Then a small insulated pole holds the chain away from the boats hull, and the rest of the mast. That chain. Running from the lightning rod away from the mast & hull held out on a insulated pole. Would isolate that current. And keep it away from the boat itself. While the chain continues its path to the water. That pole, would have to be really insulated. To hold all the amps being pushed through that chain!!

In a storm. The lightning would hit the rod. And continue to travel down the chain. Uninterupted, into the water. This is as good as it gets!!

After a major strike. You'd more than likely will have to replace certain key componants. More likely the insulation on that pole, that holds the chain away from the boat, and into the water.

[CaptainK]

Electrical equipment insulation.

http://www.practical-sailor.com/news...arts/912ac.pdf

http://products3.3m.com/catalog/us/e...er/output_html

http://www.sdplastics.com/phenolic.html

http://www.islandnet.com/robb/marine.html

http://www.fishingandboats.com/light...rotection.html

http://www.ul.com/

[CaptainK]

Understanding Lightning Protection


3 articles for your consideration...
Credit to the writer is provided. These articles were sent to us from unknown sources and we provide them simply for there informative value and in the interest of promoting safety.

Over the past couple of hundred years, as science has learned more about the nature of nature, lots of folks have tried to find ways to protect their homes and businesses against damage from lightning. But even after Ben Franklin's famous kite proved that lightning is an electrical force, and discoveries by such famous scientists as Volta, Ampere, Ohm, and others, lightning still remains something of a mystery. And we are still looking for ways to minimize damage.

Several years ago, while preparing an article on "Lightning Protection Systems"( Practical Sailor, December 1993), I interviewed one of the engineers responsible for preventing lightning damage to the U.S.'s largest power utility, the Tennessee Valley Authority, plus others at firms making lightning damage prevention systems for high-risk operations such as petroleum refineries and tank farms. The conclusions reached were fairly simple, and within a short time after the article was published, advertisements began to appear for devices called ion dissipators, like those previously offered only in high-tech industrial systems. These are stainless steel wire brushes, typically about two inches in diameter and about eight inches long. You can buy a similar brush for a few dollars from a supplier of dairy cleaning equipment; the ions probably can't tell the difference, but you will have to build your own mount.

Although there remains some controversy about how well the Lightning Protection Systems (LPS) function, there is little or no argument about the fundamentals of good lightning protection:
(1) It is better to avoid being struck in the first place, but
(2) if your boat does get hit, you will suffer less damage if the strike is grounded as directly as possible. With these basics in mind, let's review and reiterate some general science that every boat owner can and should understand so that he or she can make the best use of the devices that are being sold. Armed with a few facts, you can better analyze your boat's lightning risk and make the best LPS installation or improve your present protection.
FACT: It is better to avoid being struck so you do not want to "attract" a strike to any part of your boat. The power of a direct strike is likely to heavily damage anything in its path and nearby electronics will suffer corollary damage from a side-effect of the strike, the magnetic pulse. Therefore, I suggest that the primary goal of an LPS must be to allow the accumulating "ground charge" (the buildup of energy in the earth or sea below a thunderstorm) to drain away at a low voltage level and to prevent the initiation of a strike. This is what the "ion discharge" or "dissipator" air terminals are designed to do. For these to be effective, however, they must be part of a well-designed system.

FACT: No LPS is any better than it worst component. Although the most obvious part of an LPS is the air terminal (or dissipator) mounted atop the rigging, it actually starts with the water beneath the boat. What is needed is the best possible ground so that the charge building up in the water can get to the air terminal. You can guarantee the best ground by having a bare metal hull.

Oh well, so much for the best. What's second best?

Second best is to have many square feet of metal wetted by the water. If this is still a problem, it is possible that connecting all underwater metal through-hull fittings to the LPS may be helpful, but you run the substantial risk of having a fitting blown apart in a strike, leaving a big hole in the hull of your boat.

In practical terms, it comes down to this: If I were a boater in Florida's "lightning alley", I'd make sure the boat was well grounded. One way to do this is make a grounding plate from 1-1/2" to 2" wide bare copper grounding strap, as long as can be fitted below the waterline, epoxied to the hull exterior. As an alternative, make a "buss bar" using 1-1/2" - 2" copper strip under the boat running from the base of the mast to the engine or, another alternative, several square feet of copper sheet epoxied to the hull, with a substantial grounding lug extending into the bilges directly below the main LPS cable (which, in turn, leads straight to the air terminal). If it were not feasible to run this cable - 4 AWG is a good conductor - straight down the masthead to the bilge, I'd make up a jumper cable long enough to reach from the overhead to the bilge, to be clipped in place when a storm threatened. This means that access must be provided to the cable, where it enters the cabin overhead, and to the ground lug with sturdy (bare!) connection points to which you can clamp the jumper. Do you think that this is too much trouble? Ask someone whose boat has been struck.

FACT: Lightning strikes are radio frequency (RF) events. It is true that the build-up of energy is a direct current (DC) phenomenon, and the current flowing during a strike is unidirectional, but as each spark starts and stops, a great deal of high frequency RF power is generated. This is why you can hear distant lightning storms on your AM radio-and when a strike does hit your boat, everything in the path of the strike becomes part of a wildly varying, enormously complex network of tuned RF elements. What you may find hard to believe is that a length of solid metal conductor is a perfect insulator at certain RF wavelengths. This may cause very high voltages to appear between two points (perhaps several feet apart) on a mast, a wire, or a length of metal trim. These voltages are the source of a sometimes deadly effect called "side flashes" that flicker between various parts of a boat - and its occupants.

To avoid becoming part of a side flash, you should understand the second purpose of the LPS; martyrdom (self-sacrifice).

When the LPS fails to prevent a strike, it must sacrifice itself in such a manner as to best prevent damage to the boat and its occupants. You encourage this vital role of the LPS by visualizing the path(s) that a lightning strike might take, then make the LPS conductor the one path that is as short, as straight and as low in resistance as possible. Then, during any lightning threat, you and your crew should stay as far away from this "favored" path as you can.

If you've done a good job on these basics, from ground plate to conductor to air terminal, and if you keep as far from the primary protection conductor as possible, then you've taken practical steps to guard against one of nature's mightiest forces.

Only one more suggestion: monitor weather reports and avoid being caught out in a thunderstorm!

Copper straps, bars, and plates designed for lightning protection are available from Thompson Lightning Protection, (612)455-7661.

Bill Laudeman spent more than 30 years working as an industrial technologist and engineering project manager before becoming a marine surveyor. He has published his first book, Sailboat Wiring.

Disclaimer Warning
Overboard Designs/Overboard Boating is in no way responsible for any damage or injury which may be caused from acting upon the content of this page.

[CaptainK]

Cone of Protection from Lightning - Faraday's Cage

This spring seems to have brought the most extreme weather in history. With heavy thunderstorms you will often find lightning. Lightning on the water can bring life-threatening circumstances. For your safety and the safety of others boating with you we have updated and are republishing this article on Lightning Protection.


Even though the odds are in your favor that your boat may never be hit by lightning, if it happens it can have devastating effects. Don't take a chance, protect yourself. If you are in a small boat and close to shore when a thunderstorm approaches, get in and off the water immediately. Better yet, don't go out if thunderstorms are predicted. But what if you are miles offshore and a storm pops up? Hopefully, you have prepared in advance.

The voltages involved in lightning are so high that even materials that would normally be considered non-conductive become conductors, including the human body. The voltages are so massive that if they start to travel through a boat's structure - say through its mast - then meet with high resistance (for instance, the hull skin) the current discharge, in its attempt to reach ground, may simply blow a hole in the non-conductive barrier. The safety conscious Captain should make sure that his vessel is properly protected. Reference should be made in detail to the standards for lightning protection as set forth by the American Boat and Yacht Council (ABYC) and the job should be performed by a licensed marine electrician.

In theory, a lightning protection system is used to create what is know as a "Faraday's cage," so called after the late nineteenth-century scientist Michael Faraday. The principle of a Faraday's cage is to provide a surrounding, well-grounded, metal structure, in which all of parts are bonded together and carry the same electrical potential. Such a "cage" attracts and carries any lightning strike to ground much like lightning rods on buildings. In other words, you need to provide an unobstructed way for the lightning to dissipate its energy to ground (the water surrounding you). Faraday himself risked his own life to prove this theory. The additional benefit of a lightning protection system is that it tends to bleed off any charge build-up in the general vicinity, possibly averting a lightning strike in the first place.

So how does a lightning protection system work? In a boat, the "cage" is formed by bonding together, with heavy conductors, the vessel's mast and all other major metal masses. A marine electrician must tie in the engines, stoves, air conditioning compressors, railings, arches etc. with a low resistance wire which would ultimately provide a conductive path to ground (the water) usually via the engine and propeller shaft, keel bolts, or better yet, a separate external ground plate at least 1 square foot in dimension. It is important that you ensure that your crew fall within the protection of the "cage," something not always feasible when the vessel is not built of steel or aluminum. On fiberglass or wooden boats it is advantageous to have a mast or other conductive metal protrusion extending well above the vessel, creating what is known as a "cone" or zone of protection.

It is generally accepted that this cone of protection extends 45 degrees, all around, from the tip of the metal protrusion. This means that if the aluminum mast of the average sailing vessel is properly bonded to the vessel's other major metal masses and is given a direct, low-resistance conductive path to ground, the entire boat should fall within the protected zone. If the vessel has a wooden or composite mast, a marine electrician can achieve the same effect by installing a 6 to 12 inch metal spike at the top and running a heavy conductor down the mast and as directly as possible to ground, usually through the engine and propeller shaft.

Again, refer to the ABYC standards and have a professional marine electrician install your lightning protection. This is not a do-it-yourself project.

John Payne, on Lightning protection...

Lightning has long been a problem for mariners. As far back as the early 1800's boat builders were installing lightning protection systems to minimize the catastrophic effects of strikes. These methods were essentially the grounding of spars and rigging. More than one vessel lost mizzens and masts along with compass problems as a result. Bonding systems were also evolved as a response to dissipation of strike energy. In the late 20th century, nearly 200 years on, the same measures are still valid. It is a fact that virtually all classification societies and national marine authorities lay down recommendations for protection of vessels from lightning strikes, but very few cruisers bother to adhere to the them. From my own experience the figure is around 5%. Of more importance is the startling statistic uncovered during research that nearly 10% of fatalities on cruising yachts are the result of lightning strikes, out of the 100 killed in the US through lightning strikes yearly. Lightning causes along with death and injury an enormous amount of damage in shore installations, in particular in the telecommunications and electrical power distribution industries. For these simple economic cost considerations many measures are taken to design systems that minimize the effects of strikes. The main effects are high energy, high voltage transients that result in flashover and damage. They can be either resulting from direct strikes or induction into power or signal cables, or induced, either through capacitive or inductive coupling.

Lightning Physics

What causes lightning? Within the cloud formation, strong updrafts and downdrafts generate high electrical charges. When the voltage reaches a sufficiently high level both cloud to cloud and ground discharges occur. Strikes occur when the ground is at positive polarity and the cloud negative region attempts to equalize with ground. Alternatively strikes can occur when the positively charged cloud top equalizes with the negative ground, or when the positive charged ground equalizes with the negative charge cloud or the negatively charged ground equalizes with the positive charged cloud top.

Lightning consists of a number of components, which form a multidirectional flow of charges. Peak currents can exceed 200,000 amperes (200kA) at over 30,000°C for a matter of milliseconds (25-100 ms). The positively charged ions rise to the cloud top, and the negative ions migrate to the cloud base. Regions of positive charged ions also form at the cloud base. Eventually the cloud charge levels have sufficient potential difference between ground and another cloud to discharge. The processes are as follows:

* Leader. The leader consists is a negative stream of electrons consisting of many small forks or fingers that follow and break down the air paths offering the least resistance. The charge follows the fork finding the easiest path as each successive layer is broken down and charged to the same polarity as the cloud charge.

* Upward Positive Leader. This is a positive charge that rises some 50 meters above the ground. (Sometimes from your mast head)

* Channel. When the two meet a channel is formed.

* Return Stroke. This path is generally much brighter and more powerful than the leader and travels upwards to the cloud partially equalizing the potential difference between ground and cloud. (Often directly through your vessel)

* Dart Leader. In a matter of milliseconds after the return stroke, another downwards charge takes place following the same path as the stepped leader and return stroke, sometimes followed by multiple return strokes (multi-pulse surges).

· Multi-pulse Surges. These occur in over 70% of strikes. This phenomenon is where up to 20 re-strikes follow the initial strike at intervals of around 10-200 milliseconds apart. In addition continuing currents of 200-500 amps with durations of up to 1-2 seconds may also occur. The movements happen so fast that it appears to be a single event. This sequence can continue until the differential between cloud and ground has been equalized.

Protection Systems

Protection can never be achieved using a single method, and a number of measures should be used to minimize the risks. The main objectives of any systems are:



· Capture of the strike at a nominated point, ie mast head

· Conduction of the strike current to ground safely using a well installed down conductor that reduces side flashes

· Dissipation of the strike energy to ground, through a low impedance ground system so that rises in ground potential are minimized

· Equipotential ground bonding of all relevant systems and components

· Protection of power supplies from high voltage transients and surges that may damage equipment

· Protection of conductors both power and signal from induced surges that may damage equipment



As a reference to official guidelines the measures are in accordance with NFPA 302 Fire Protection Standard for Pleasure and Commercial Motor Craft

Lightning Protection Zone. The most reliable protection system is one that grounds any strike directly and the principles are as follows:

* Grounding. The primary purpose of a grounding system is to divert the lightning strike discharge directly to ground through a low resistance circuit suitably rated to carry the momentary current values. This has the effect of reducing the strike period to a minimum, and reducing or eliminating the problem of side strikes as the charge attempts to go to ground. As electricity follows the path of least resistance to ground, little goes down the stays.

* Cone of Protection. The tip of the mast, or more correctly a turned spike clear of all masthead equipment gives a cone of protection below it. The cone base is the same as the mast height. This protective cone prevents strikes to adjacent areas and metalwork, which in a yacht can mean stays, rails or other items lower than the masthead.

Lightning Protection Systems. Most classification societies, American Boat and Yacht Council and other advisory bodies generally recommend lightning protection in the form of a directly grounded mast and spike. Other devices have come onto the market, and effectiveness of most has yet to be conclusively confirmed.

The Great Myth. Lightning rods and grounding actually attract lightning strikes! The presence of a properly installed lightning protection system will give a number of advantages:

* It will safely ground the strike energy

* It will in most cases limit the damaging effects of heat and reduce the current levels flowing, as well possibly the length of time the strike takes (this is in milliseconds). This reduces damage to equipment and crew

* In GRP vessels, in particular multihulls, under certain weather conditions, a static charge builds up on the deck. It is my contention that ungrounded vessels actually promote strikes to the vessel due to this condition. Additionally grounding the mast dissipates this charge, and in the process removes a common cause of radio (RFI) noise that occurs as small arc occurs as the static charge goes to ground.

Mast. Lightning will generally strike the highest point, and take the path offering the lowest resistance to ground. The mast is usually the strike point. Note that a stainless steel VHF whip does not constitute any protection.

Mast Spike. The mast spike ideally should be a copper rod with pointed end. To avoid metal interaction, stainless rods are commonly used but should be of a thicker section than the more conductive and lower resistance copper. The spike should be at least six inches higher than any other masthead equipment, including VHF aerials. Many commercial units (Dynarod and Seaground) have an offset in the rod, which although not being the required straight section would be satisfactory. The purpose of the point being sharp is that it facilitates what is called point discharge. Ions dissipate from the ground and effectively cause a reduction in potential between the cloud and the sea. In many cases the strike may be of lower intensity or not occur at all.



Dissipation Systems

Lightning Protection Device (LPD). This was an Italian development of some 10 years ago, and consists of a high performance varistor. The device is designed to interact with the electrical charges of the initial stepped leader where current values are relatively low and avoid the return strokes. Charges accumulate on the atmospheric electrode and varistor poles. The varistor conducts and the charge condition on the electrode alters. These charges leave when some streamers form to meet the leader.

No Strike Charge Dissipater. This is based somewhat on the pinted spike only that there are many points in a brush arrangement. This is to stop development of a stepped leader forming and minimize the strength of any that do occur,

Mast Cable. Much of the damage in a strike results from heat, as the large current flow into a resistive cable acts as a heater. It is essential that cable cross sectional area is sufficient, typically 35mm² or greater. Under no circumstances use soldered joints alone, as they will melt during a strike causing further havoc. Always crimp connections and ensure that all bonded connections are clean and tight. All connections must be bolted.

Grounding. A good ground requires direct and permanent immersion in seawater. It must also have sufficient area to adequately dissipate the strike energy. Through hull fittings must never be used as a primary ground point unless you want to sink the vessel. The bonding cable from the mast base to the ground plate should be as straight as practicable without sharp corners as side discharges occur and this is called corona discharge. Similar side discharges can occur from boat to boat in crowded marinas. Normally I enclose the cable in high quality electrical conduit to reduce the possibility of side strikes on the cable, as electrical insulation will frequently break down under high voltage conditions.

Steel/Alloy Vessels. Connection of the mast base with a large, low resistance bonding strap to the hull or as more practical the mast step is sufficient.

GRP Vessels. A keel acts as a good ground and is sufficient. Bridge out with a stainless link at least two keel bolts to spread the contact area. On multihulls you have to install a large separate ground plate, such as a radio ground (Dynaplate, Wonderbar or Seaground). This will ensure that there is a large and efficient ground area. Do not use the radio RF ground plate as the lightning ground. Never bond the lightning system to the corrosion system bonding, machinery or electrical system negatives or grounds. Never bond the lightning system to bronze through hull fittings (unless you want to sink the vessel!).

Wooden Vessels. Wooden vessels normally have a metal mast track. The track should be properly grounded. If possible a copper strap can also be run, although this is not always practical. Direct bonding to a ground plate or the keel should use the same grounding method as GRP.

Emergency Ground. A heavy gauge copper cable can be clamped to a stay over a half-meter section. The other end should be clamped to a ground plate, and hung over the side. Do not use chains and anchors (another great myth), as they are ineffective as a ground.

Electromagnetic Pulse. A vessel can have damaged equipment from a strike within a few hundred meters. Insurance companies don't like to accept claims on damage unless you can show total damage to masthead systems. A strike sends out a very large electromagnetic pulse, which is a strong magnetic field. This field is induced into wiring and systems as a high voltage spike, doing just as much damage. If you suspect damage from an induced electromagnetic pulse from a localized lightning strike, check with all vessels adjacent to yours, and get statements to support the contention. Generally all the electronics will be out if this is the case as the mast and any wiring acts as a large aerial.

Sidestrikes. It is common in very closely moored vessels and crowded marinas to have lightning strikes literally jump from vessel to vessel as it attempts to find ground on ungrounded vessels. Usually the strike exits from stays, chainplates and spreaders. In many cases the strike will go to water from the chainplates causing serious damage to hull and fittings. In many cases the rig may topple.

St.Elmo's Fire (Brush Discharge). This phenomenon is more common on steel vessels and when it occurs usually precedes a strike, although the effect does not occur all the time. The vessel in effect becomes a large ground mass. Ionized clouds and balls of white or green flashing light that polarizes at vessel extremities characterize the discharge. The discharge of negative ions reduces the potential intensity of a strike. Damage to electrical systems is usually induced into mast wiring, as the steel hull itself acts as a large Faraday cage.

Corrosion Factors. Considerable care must be taken when bonding various items of equipment into a lightning protection bonding system. On steel and alloy vessels the hulls are the one ground plane for all equipment and all grounds are held at the same potential. In GRP and timber vessels it can be more complicated, but problems may arise where indiscriminate bonding of through hull fittings and other items is carried out. It is easy to create differences of potential between various items creating a corrosion nightmare. After connecting up a lightning system, it is prudent to monitor the corrosion rate of anodes, and observe any underwater bonded items.

Bonding. Most authorities recommend that all stanchions, chainplates, and large metallic equipment such as stainless water tanks should be bonded to the lightning ground. Failure to bond can result in side flashes as these can offer an alternative path. The bonding should be made at the point closest to the main conductor. I prefer not to bond the stays and chainplates as often recommended. My reasoning behind this is that if a good low resistance path is made from mast to keel or groundplate the strike energy will be directed that way. Grounding stays offers alternative high resistance paths, encouraging side strike activity. Current flows can also cause crystallization and permanent damage to stainless stays and fittings in a severe strike (try and get that past the insurance company!). Bonding must be undertaken with care. Dissimilar metals such as the aluminum mast copper strap, and steel must be interconnected to ensure no galvanic corrosion can occur. More importantly interconnection of various grounding systems must be undertaken with great care. It is only necessary to bond internal metallic equipment within six feet of the mast. In practice this is rarely water tanks under bunks etc, but should include tankage under the cabin sole.

Lightning Safety. In an electrical storm, the following precautions should be taken to avoid any shock or something more serious.

* Stay below decks at all times.

* Stay well away from mast, boom shrouds, chainplates and the mast compression post or mast if below deck.

* Take a position and plot it prior to shutting down, or in case of all electronics equipment being blown.

* Turn off all electronic gear and isolate circuit breakers if at all practical. Disconnect aerials also if practicable.

* Do not operate radios until after the storm unless in an extreme emergency.

* After a lightning strike, be aware that the compass may be incorrect.

* Check all running rigging and fittings after a strike as damage can occur that may seriously affect vessel capacity to sail.

* Check all through hull fittings for damage, if you have decided to risk bonding them.

Contact us here!

Call, Sales/Management -1-800-YACHT20 (922-4820) or 410-263-2311


http://www.bayacht.com/aaa/nl-artic/...g/lightart.htm

[claire]

I don't think we took a direct hit, more probably
some "secondary" effect. We "only" lost our wind indicator which happens to be the most expensive of the indicators in the tridata instrument suite!

Even then, we lost the wind data, but there is no visible damage to the mast top unit.

All our mast antennas were disconnected.

Since then, we decided to stop bothering about grounding the mast.

Cheers

[NoTies]

Ouch cap'nK, my eyeballs are bleeding

[Alan Wheeler]

Gord, that is the crux of what I am trying to say really. Their is "NO" true wayof protecting a boat or any item from a strike, when out in the open. It has been proven that the tallest item does not mean it will recieve a direct hit. So making yourself small does not solve a problem. It is proven that well insulated won't always protect you. It is proven that well bonded won't always protect you.
NO ONE KNOWS, just why a "leader" does exactly what it does. So I then am far from an Authority on the subject. But I do believe it is the leader that is the important "trigger" in the whole thing. If you can isolate yourself from a leader forming, you have a better chance of insulating yourself as a target. The leader is some form of charge from ground up. It's like rubbing a ballon over someones long hair and then holding it immedioately above their head. the hair all stands up. The hair represents the leaders. But NO, this is NOT what a leader actually is. It is just an explanation of what happens over the storm area.
Here is another point to consider, a direct hit is not actually common. It also seems there is a big difference with damage between a direct hit and a side hit. A direct hit seems to do more heat type damage. Probably result of high currents. A side strike seems to do a lot of damage by high voltage and magnetic inductance. It is the side strikes that tend to do the weird things. A direct hit can have tremendouse heat and tends to just blow wiring. But sometimes it can actually be safer for electronics that are not connected.

I haven't read CptK's post yet. Maybe some answers are within some links. But I need some time.HAve to go to work now.

[GordMay]

I’ve written over 10,000 words on the mechanics (physics) of Lightning as applied to sailboats - and have not answered the fundamental questions to my satisfaction. Hence, I try to avoid detailed offerings on Lightning Theory, which leaves me (more or less) speechless on the subject of Lightning Mitigation* for Boats.
Lightning Protection would be a misleading term.

Notwithstanding the former, and my current bout of severe arthritic pain, I cannot remain totally silent.

Wheels has, more or less, put the point to the question.
Since you cannot isolate yourself from the voltage gradient (cloud vs gnd water), nor dissipate charge accumulation - you cannot protect yourself from the likelihood of receiving a strike.
All you can do is mitigate the effects of that strike. This is done through a Lightning Grounding System, of about 1 Ohm DC resistance (not 10), and low RF impedance (per Rick’s excellent treatise).

The purpose of lightning rods is often misunderstood, and many people (mistakenly) believe that lightning rods "attract" lightning. In fact, lightning rods (and their associated downconductors & grounding electrodes) provide a relatively low-resistance path to ground, that can be used to conduct the enormous electrical currents when lightning strikes occur. BTW: “Blunt” (rounded) lightning rods are more effective air terminals than the oft-recommended “sharp” tipped rod.

‘Streamers’ don’t always originate at the boat, nor ‘Leaders’ from the cloud.

Negative Lightning accounts for about 90-95% of all lightning “strikes”.The lightning bolt usually begins when an invisible negatively charged stepped leader stroke is sent out from the cloud. As it does so, a positively charged streamer is sent out from the positively charged ground or cloud. When the leader and streamer meet, the electrical discharge takes place up the streamer into the cloud. This return stroke is the most luminous part of the strike, and the part that is really visible. An “average” bolt of negative lightning carries a current of 30 kiloamperes, transfers a charge of 5 coulombs, has a potential difference of about 100 megavolts, and lasts a few milliseconds.

Positive Lightning makes up less than 10% of all lightning. It occurs when the stepped leader forms at the positively charged cloud tops, with the consequence that a positively charged streamer issues from the ground. The overall effect is a discharge of positive charges to the ground. Positive lightning bolts are typically six to ten times more powerful than negative bolts, last around ten times longer, and can strike several miles distant from the clouds. An average bolt of positive lightning carries a current of 300,000 amperes, transfers a charge of up to 300 coulombs, has a potential difference up to 1 gigavolt (a thousand million volts), and lasts for tens or hundreds of milliseconds. During a positive lighting strike, huge quantities of ELF and VLF radio waves are generated.

FWLIW,
Gord

[CaptainK]

Sorry pwederell, that your eyes are bleeding?

Wheels. You better read my posts. It explains it all right there.

And Gord.

At least Gord seems to have read my posts? At least he posted a small part of his topic, inwhich I did not mention. Which is about positive & negative lightning!!

Read on Wheels. Read on?

[s/vAngel]

For anyone interested, the grounding plate I'd installed on the outside hull, below-the-waterline is called a "Dynaplate". Some say they're okay and other's say they're not. After talking with a boat captain who had one for six years on his ketch and was struck twice, I found that he appreciated his. The lightning did cause his masthead antenna to melt at the base and fall off and it also screwed with his electronics by turning on the entertainment system, but didn't "hurt" the hull fiberglass (like it did with my ungrounded hull when it made its own path and just blasted through.)
The Dynaplate is mounted as close to a keel stepped mast or compression post as possible with a heavy copper strap from the plate's bolts to the mast base. If I remember from those college electronics course days, lightning travels on the "outside" of the conductor so surface area matters. Two other vessels that were ungrounded like my ANGEL also suffered strange damage that I know of. One 25-ish foot sailboat had multiple pinpoints blown through the hull and had to immediately be hauled. Another looked like she had a bomb go off in her interior, but remained floating and the strike seemed to go out of the hull in multiple spots. My only guess is that the strike bounced (?) around in her interior and splintered wood in random spots as well as made the classic spiderweb cracks in the fiberglass. These cracks couldn't be seen until the bottom paint was removed.
A third sailboat that I'd just learned about by talking to other cruisers is that he was struck and had all his lights blown out but no hull damage that he could find. He was ungrounded also.
So far, I'm rooting for the Dynaplate. After the nasty stuff that happened to ANGEL, there couldn't be any worse, right?

[CaptainK]

I have read articles about "Dynaplate," in the past.

It seems that only the yachting community praises this device. But it does not reduce the chances of a lightning strike on your boat.

It will, however, reduce the possibility of severe hull damage and electrical shock potential. A proper bonding and grounding system using Dynaplate shoe(s) will help provide a direct, controlled high-capacity path for lightning dissipation.

Enhances Electronic Performance
SSB and AM radio transmitters rely upon a proper size ground to operate to their designed capacity. A dynaplate grounding shoe helps provide a large solid surface (the water surrounding your boat) to "push off" from. This is technically known as "counterpoise", and the other necessary half of your antenna system.

The bronze Dynaplate material also serves as the next sacrificial metal on the galvanic scale after your zincs, providing another buffer against corrosion of stainless steel parts.

[GordMay]

A couple of photo’ examples of Lightning “exit holes”, suggesting that Fibreglass is NOT an insulator (against lightning).
http://cruisersforum.com/photopost//...php?photo=1637

I'm not convinced of the efficacy of sintered bronze plates/shoes (Dynaplate) for Lightning Ground Electrodes (plates), and wouldn't recommend using them in lightning mitigation systems.

[s/vAngel]

Hi GordMay,
What do you recommend as opposed to the dynaplate? you know much more about this than I. I'm-was- a mechanical engineer, not electrical. This stuff is over my head and all I care about is, if this is possible, avoiding or reducing the damaging effects that lightning has done to my innocent little Bayfield cruiser.
What are your personal experiences with this Dynaplate critter? Someone just told me that they can explode when hit ?!!!, due to the trapped moisture deep in the surface area of the sintered bronze pieces that it's made of. Everyone has a different opinion and I'm happy to hear 'em all. I'm hauled out and doing a bottom job and have time to change things for the better in time for the next cruise.
Geeze, those photos were scary. Thanks for pointing those out.
rb

[Alan Wheeler]

Yeah OK I acknowledge I am being pedantic here, but... Fibreglass "IS" a good insulator. It's just wasn't a "thick" enough insulator. Back to the water system again, voltage pressure is kept withing the garden hose by the "hose". So the hose is acting as the insulation. But if the pressure is high enough, it will rupture the insulation and squirt out. An electrical insulator is any material that doesn't freely conduct elelctrons. But some materials are better than that than others. The really good ones can be thinner than a not so good one. Once the insulation can no longer withstand the electrical pressure, a spark will jump right through. With the fibreglass, two things would have happend, the pressure was so great it broke throught the insulation at what the pressure found as the "weakest" point. It may have been weak at that point due to several reasons. It was most likely thinnist at that point and possibly had high moisture content in a pocket. The "spark" would have caused sever localised heating. It would have vapourised any moisture and/or chemical in that imediate area and cuased the material to blow apart.

Angel, sheesh I hope you weren't struck by lightening and had a name change to Angel But anyway's, a dynaplate does carry a reputation of blowing apart with a direct hit. Many have suggested here in the past, that the plates ability to have a large conductive surface due to it's make up, is quickly made null as marine growth take residance within its structure. I think the general consensus is just a flate piece of plate is as good as a cintered one.