Lightning + Mast = ????

[Witzend]

There is NO full time, safe solution to a direct lightning strike. The current is going to ground as quickly as possible, and there is NO predictable path. You may comfort yourself with these actions, as well as those of the U FL expert...at greater cost, but they will do nothing to guarantee the path and how it exits the boat.[/quote]


While I would generally agree with you position, lighting strikes are not all created equal, and for the less potent strike, proper measure may make a difference.

 

[Maine Sail]

There is NO full time, safe solution to a direct lightning strike. The current is going to ground as quickly as possible, and there is NO predictable path. You may comfort yourself with these actions, as well as those of the U FL expert...at greater cost, but they will do nothing to guarantee the path and how it exits the boat.

While I would generally agree with you position, lighting strikes are not all created equal, and for the less potent strike, proper measure may make a difference.

Minimizing danger to humans is the main focus of ABYC TE-4 and the insurance industry tends to support this. Last summer I was called to bond a keel stepped mast to a keel bolt before the insurance company would issue coverage so some companies actually expect this. There were other items too but this one stuck out to me.

I called them on behalf of the customer, and explained that ABYC TE-4 is a suggestion not a standard. After about a half hour of being bounced around trying to get a solid answer I was told. "Our data shows lightning ground systems save us money and pose less risk to occupants."

In short they did not care whether it was an ABYC requirement or not because their data is what they base stuff on. This was a tough boat to bond due to access and ran the customer about 4.5 hours of labor.. There is also data out there that suggests bonded/grounded boats get hit less then un-bonded / un-grounded boats.

I had two customers boats hit by lightning in September. One has been fixed and the other still has work to be done, a J-42. Both boats are newer and both boats were bonded/grounded to ABYC TE-4 primary / secondary lightning bonding. Both took bad strikes and neither suffered any hull damage. The bonding wires from mast to keel survived just fine as did most of the wiring on the boats. The primary bond on one boat was 1GA and on the other appears to be 1/0.

All electronics on one boat were toasted and some of the electronics on the other boat were, but not all. Was just doing the dance with the insurance adjuster last week about replacing items still "operable" but connected to a system, namely Sea Talk.. They won't replace them until they fail yet won't give the customer any idea of time frame as to what an "acceptable" after strike time frame is for a failure deemed to be cause by the strike.. Adjuster understands my arguments but the insurance company won't replace items still "turning on"..

Both boats have Marelon seacocks so the thru-hulls are not bonded. Both boats had crazing on the keels and blown off chunks of barrier coat where the lightning found ground through the lead keels. One boat appears to have had some of the strike pass through the engine ground as evidenced by a dry PSS after the strike (non-vented version).

No two lightning strikes are the same but the only thing I see some consensus on, as far as trying to minimize human danger and hull damage, is primary secondary lightning bonding.

There is NO system out there that will prevent a strike and no way to prevent one. Lightning hits what it wants. If there was even an ounce of evidence suggesting a system did "prevent" strikes the insurance companies would be offering discounts for having those systems installed. All you can really do is to try your best to "minimize" damage. Lightning bonding / grounding is the only thing I have seen that has support of the insurance companies and evidence to support that it can have a beneficial effect....

Many, if not most, new boat builders wire to ABYC TE-4, at least for primary bonding, and many also do the secondary bonding.

Lightning bonding on a new boat:

 

[All U Get]

Was the VHF antenna in #28 above the dissipator. Since my VHF antennas are 8-10 inches above the disipator I don't expect more than a bird deterrent from it. I'd have to raise it on a whip base to get under the 65 footers on the AICW. Lightning is just gonna hit where it wants. I watched St. Elmos fire once, that's wierd.

All U Get

 

[RichH]

Question for MaineSail, or those with High frequency / electronics experience ...... .

Are there any recommendations / discussions / recommendations via ABYC for RF 'chokes' as regards to the attempt at electronics protection for lightning strikes that are 'radio frequency - RF' events?
... other than physical disconnection (both pos AND negative side feed) and isolation of the equipment during thunderstorms ?

There was some intense 'debate' on another forum site of such attempt of selection of high and ultra frequency chokes for such attempt at lightning RF protection a long time ago ... and its been 'quiet' since then. Any info, references, etc?

... and yes indeed with Seatalk and other multiplexing common electronic systems ... when hit with an RF event, your lose the 'whole' system.

Thanx


Coronal effect (St. Elmo's fire) .... the 'last' time I got hit I was anchored next to a boat on which I noticed vivid St. Elmo's Fire in the top of his rigging AND on his 'fuzzy' mast top dissipator.... 1 micro-second later, I lost ALL my electronics, he had zero damage, We both had a 'cross strike' go above us; my boat sent up a visible 'leader' which met the 'cross strike' --- worst lightning storm I ever witnessed in my entire life with multiple lightning per minute. Boats were quite similar in design, only difference was he had a 'fuzzy' mast top dissipator.

 

[Bill Roosa]

hey MS.
Your point is well taken. if you don't provide a path to the water surface then it can exit anywhere. The lightning still follows the least resistance path to ground though. The insurance companies have been doing research lately and they found that (don't quote me the memory is failing more often these days) something like 80% of the 'exit' holes from lightning where at or near the water line. This was also coralated with a metal item being both tied to the lightning grounding system and that item being near the water line.
SO
provide a low resistance path to the water surface on the outside and you can encourage the lightning to leave you alone. This has been done for commercial buildings for years and it ALWAYS looks like a lightning rod at the highest point, a large low resistance cable along the outside that is totally dedicated to carrying the lightning current and a well buried grounding rod of at least 5 ft in length
With sail boats you have to make some adjustments as you already have the cables running from the highest point....... Perhaps it would be easier to think about it as discouraging the lightning from entering the mast and cabin/crew.

 

[Bill Roosa]

The frequency of a lightning strike is in the hundreds of kHz to the single digit mHz range. Ask any ham radio guy where to tune to hear all the lightning strikes on earth and he will always go to the 40, 80, or 160 meter bands (the latter being very noisy)
Trying to make a choke for a mast size system at those frequencies and VOLTAGES/currents would not be a good idea. the choke works by converting the current to magnetic field. the power used to create the field cannot be applied faster than the time constant of the coil so if you have (what amounts to) unlimited voltage and a coil on that path the voltage just builds up on the inlet and then jumps around the coil.
now if you had a low resistance path to ground and put the coil on the other paths that you are trying to protect that could certainly work. You would need to balance the max current the circuit components can handle (wire size) and the choke time constant (anybody know how long the average lightning strike lasts?) and provide a capacitive "short" to ground before the choke for those frequencies to keep the devices from preforming that function.
the components are not that hard to fabricate/buy and of reasonable size (the Admiral my have an opinion though as the coils are kinda large)
Given all the "stuff" that is going on in and around the mast base this would be an electrical engineering nightmare however as all those chokes/caps would no doubt interact both during a strike and under normal operation (read magnetic coupling between the chokes making the circuits appear to be connected when AC signals are present) An easier option is a low resistance path to ground down the shrouds and some quick disconnect plugs with grounding plugs at the mast base. When away from the boat or during a lightning storm just disconnect the mast base and plug the wires into the ground (which goes outside the boat also) plug.

 

[walt]

For RichH question about protecting electronics.

I’ve been involved in the design of consumer electronics including stuff that operated in the 1 to 2 GHz RF range which also involved a long cable. Manufactures lose money on equipment that is damaged by a lightning strike so they do put in some lightning protection on the RF inputs and the amount is usually based on some acceptable field return rate (which for a good manufacture will be very low). What is done is at the point where the signal comes into the box, there is a circuit called a "bias T" that basically taps off the DC coming in on the RF signal line while maintaining the RF impedance (i.e., 50 or 75 ohms). On the output of the bias T that has the low frequency and DC signal, there is a fairly high power "transorb" that basically clamps and dissipates any energy over what is supposed to come in. The transorbs are similar to a zener diode - they just turn into a low impedance past some breakdown voltage. The bias T must be designed so that it can handle all of the lightning energy that is passed through it to the transorb. This can all be tested in a lab with the proper equipment.

Ferrite chokes on the RF lines? Hmm... this is often done to control RF emissions from the cables but I suspect would have little effect on controlling damage from lightning. Also consider the very broad frequency spectrum of lightning and that a big portion of the energy is at lower frequency where the choke may not even do anything. My opinion is that you absolutely can protect RF input/outputs but you need to do it at the circuit design stage.

For things like serial data lines (NMEA or Seatalk), you should be able to place transorbs directly on the signal lines close to where the input of the device is. The transorbs look like a high impedance for the normal operating voltages of the data transmission but if there is a voltage spike on the line, the transorb will turn on and clamp the spike.

For DC power carrying wires, a transorb can also clamp and dissipate transients. Also, a simple capacitor will also limit damaging transients.

 

[Bill Roosa]

A question to the group:
where does the current come from that feeds the bottle brush lightning rod.
Presumably from the difference between the cloud induced charge in the brush and (same cloud) induced charge at the water surface.
Given a 50' mast and air as a dielectric that could be several thousands of volts. Sounds like it could work to me.
thoughts?

 

[walt]

Corona current explains what the wire brush dissipaters do, it explains why you get shocked on shrouds, also explains the buzzing noise you hear on a saiboat and also explains the repeated "pop pop pop pop" sometimes heard on a sailboat during a lightning storm when there are high electric fields present.

And of course also explains Saint Elmos fire.

I wrote this a while ago. http://zenpole.com/Corona_current_rev_0.pdf

 

[Bill Roosa]

An electrical picture that may help
imagine the cloud as one plate of a capacitor and the sea surface as the other.
now drill a hole in the middle of the bottom plate. that is the "hole in the water that is your boat hull.
take a length of straight wire and stick it up through the center of the hole so that most of it is between the plates and only a small length is below the lower plate. That is the mast keel circuit.
Now turn up the voltage and imagine what happens. Either the lower tip of the wire discharges the spark to the lower plate or it jumps the gap at the level of the lower plate (at the waterline).
An ideal case where there are no wires running from the mast and then along the deck to the hull and no large metal objects located between the mast and hull...... all which would encourage a spark from the mast keel circuit to the metal object to the lower plate

But wait, is not sea water very conductive and would let the current go from the keel to the water surface? yes leaving through the keel/hull is possible (and it does happen in real life) but only when the air gap between the wire and lower plate is of higher resistance than that of trying to push the voltage down past the lower plate and then up to the lower plate through a low resistance path. It really has nothing to do with the resistance of the path it has all to do with trying to push the electrons past the lower plate into a region outside of the capacitor plates. Another though experiment. What happens when i connect the lower end of the wire (keel) to the edge of the hole in the lower plate with a wire? The spark will follow the path of least resistance in all cases but there is no induced voltage on the part of the keel/mast circuit that is below the lower plate (water surface) so there is no tendency for the current to go that way. Unless the air gap between the keel/mast circuit at the lower plate level is greater (the hole diameter is larger) than the voltage needed to drive the electrons "out of the capacitor and then back up to the plate.
thoughts?

 

[walt]

FYI, there a couple papers referenced in the last link that used to be free on the internet - but went away. I scanned a printed out version I had and put it here

http://analogengineering.com/lightning/lightning_rod_study_1.pdf

This one is particularly interesting..

 

[Freedom77]

Had Freedom on an end tie at Lake Mead when a lightning bolt hit the mast. Or should I say the mast mounted radio antena. Turned it into a piece of meltled pasta.

 

[Bill Roosa]

hey walt
When I was in college we though that if you had a parallel plate cap (horizontal plates for this example) and put a wire between them vertically but not touching the wire would develop a voltage across it due to one end being more positive (the electrons gather there) and the other end being more negative (the electrons leave making it positive.
if you ground the bottom end guess what happens? the electric field still induces a voltage across it and the charge still gathers/leaves the end that is not attached
so I'm not buying your assertion that the mast is all at the same potential as the electric field is still there. i would note that you can't get a current without a voltage difference so if there is a discharge going on it has to be because there is a voltage difference between the mast top and bottom
Think of the mast as a flaw in the capacitor that lowers the max operating potential of the cap.

 

[Freedom77]

hey walt
When I was in college we though that if you had a parallel plate cap (horizontal plates for this example) and put a wire between them vertically but not touching the wire would develop a voltage across it due to one end being more positive (the electrons gather there) and the other end being more negative (the electrons leave making it positive.
if you ground the bottom end guess what happens? the electric field still induces a voltage across it and the charge still gathers/leaves the end that is not attached
so I'm not buying your assertion that the mast is all at the same potential as the electric field is still there. i would note that you can't get a current without a voltage difference so if there is a discharge going on it has to be because there is a voltage difference between the mast top and bottom
Think of the mast as a flaw in the capacitor that lowers the max operating potential of the cap.

Thank you Dr. Tesla.

 

[walt]

the wire would develop a voltage across it due to one end being more positive (the electrons gather there) and the other end being more negative (the electrons leave making it positive.
if you ground the bottom end guess what happens? the electric field still induces a voltage across it and the charge still gathers/leaves the end that is not attached

Before we discuss this, you should consider that you said a wire that is not connected to anything in an electric field will develop a voltage across it. Well.. what happens when you apply a voltage across a very conductive wire (hint - ohms law) - current flows. Is current flowing in your model and if so, where exactly is it flowing to.

FYI, charges do develop on either end the wire affecting the local electric fields and since no charge was added to the wire, charges did move in the wire for an infinitely short period of time. But without considering corona current, there isn’t any current flow in the wire and effectively no voltage across the wire..

 

[Bill Roosa]

Walt
an interesting read. Certainly makes the case against trying to avoid lightning. Not to be the Blue Falcon but I'm thinking that having a really pointy and lots of them lightning rod when most have nothing or are sorta blunt (normal mast without a rod) would be the best way to encourage lightning into the "other guy's boat" and not mine.
Does give some great data on the frequencies of lightning that another poster was looking for to build chokes too.

 

[Bill Roosa]

totally agree with you Walt
All i'm saying is yes there is a capacitive element and that causes there to be nan electric field from the top to the bottom of the mast and that would necessarily mean that the mast was not
all at the same potential
FWIW, I do agree with your paper in general as the outcomes are rational.

On a related note and a question to the group
if the wind blows away this "charge cloud" and causes a electric cycling "thingy" to go on, does that mean that wind can increase my safety in a thunderstorm?
I'd be interested in hearing from those effected as to what the winds where when the strike hit.

 

[Bill Roosa]

You are most welcome Freedom77
For my next dissertation..... lets talk ABYC lightning concopts
The ABYC is interested in protecting people not equipment so why do they recommend running the lightning into the cabin from mast base to keel or worse (IMHO) to the mast base then around the cabin outsides then back to the keel forcing people to sit in the middle??????
this makes no sense to me. you could not get a building to pass code inspection if the lightning down conductor ran inside the building.

 

[walt]

A quick note on the blunt vs. sharp rod paper I referenced a couple posts back.. These guys put a bunch of grounded almost the same lightning rods on a mountain top and observed what happened over a number of years. The difference was in the diameter of the rods and also some rods had a very sharp tip (Frankin) and some had a rounded blunt tip. They observed lighting strikes to the blunt rods(i.e., rounded at the top) but NEVER any strikes to the sharp lightning rods. Sharp "Franklin" rods of course do work but when put in competition with the rounded rods, the rounded rods got struck more often.

The sharper the rod, the better it concentrates electric field and creates higher corona current at a lower field. The duller rod was better at creating a high electric field over a longer distance.

The completely crazy and possibly very inaccurate conclusion to this would be that if your in a marina with a bunch of other boats, you would want a single sharp tip at the top of the mast and you would also want the mast grounded (or at least another conductor at the water surface – doesn’t need to actually be conducting to the water) as that will maximize the corona current.

If corona current is in fact important... what does happen with wind is that it blows away the positive ions faster (they are very massive compared to electrons so the electric field only moves them slowly). Since they move faster, the frequency of the pulsing will increase with wind as the electric field can build up faster.. I have actually heard this in a lab situation. There is probably higher corona current also with wind as the positive charge being removed faster allows the whole process to generate more current. How does this affect a lightning strike, I have no idea..

 

[RichH]

For things like serial data lines (NMEA or Seatalk), you should be able to place transorbs directly on the signal lines close to where the input of the device is. The transorbs look like a high impedance for the normal operating voltages of the data transmission but if there is a voltage spike on the line, the transorb will turn on and clamp the spike.
For DC power carrying wires, a transorb can also clamp and dissipate transients. Also, a simple capacitor will also limit damaging transients.

Bingo! "transorbs" ..... other names for such devices? any specific tech info you can steer me to?

Thanx for the great reply. My Boat Insurance company will profoundly thank you.