Lightning Strike

[Forrest15112]

Each link in the old man's chain connection is a small electrical connection that will rapidly increase in impedance as more current is applied, such as in a direct strike. Same is true for shrouds and stays, turnbuckles and hooks will conduct electricity, but will not efficiently pass the surge. An example is to take a look at the guy wires supporting a radio tower. They tension those cables with turnbuckles, but usually attach a wire across the turnbuckle to more efficiently conduct the surge. If you look inside the radio hut, they typically do the same across metal electrical conduit junctions, outlet boxes, and switch boxes. This is because the regular attachment is not suitable for high current, or lower current in many cases even.

High current surge energy does not want to make turns as it travels toward earth. Sharp bends in wires are common places that get blown out and surge arcs to something else - possibly a person nearby. This is the reason for grounding. The jumper cables and chain are not ideal and the chances of it working effectively are not too good. Ideal would be a direct straight path to ground with no 90 degree turns on the main absorber. Any necessary turns should be gradual, but a metal keel in the water with a #2 wire bonded to the mast is much more likely to be efficient and safer.

Electronics can be reasonably protected from induced current caused by nearby strikes or delivered via shore services. Surge suppressors are designed for this type of protection, not direct hits. Real surge suppressors, not power strips with a single MOV across the leads, are effective. Companies like Raycap make very good "whole house" suppressors that could be incorporated to the AC supply provided there's a good path to ground. Coaxial RF suppressors, ethernet, telephone, & cable TV are other entry points that should be protected with a suppression device. All require good ground connections to work.

 

[wmcminn]

Great ideas, thanks! Keep them coming. Frustrating process. Odyssey now hauled with hull being looked at again. Event July 8, this is taking way too long.

 

[Chief RA]

If the chain directs the current around my boat rather than through the hull to ground: I'm for that! Lighning won't even try to follow the link curvatures of the chain! It will just blast right through any developing impedence whatever it is! It will tend to travel down the least resistive path and I sure hope it is the chain if I am in the boat! What makes you think the internal ground strapping is going to survive any better than the shroud lines, chain, cable, etc would? I think the intent was, if it might help; do it! Chief

 

[Chief RA]

wmcminn: I sure hope they finally get this thing done right for you! It is a healthy discussion you have generated on this subject, and you have gotten some good feedback assistance as well. If any of this keeps one of us from getting hurt or his boat messed up it would be a "good thing".
Best of luck, Chief

 

[SeaTR]

Good discussion people ! Secondary (induced) current IS serious...essentially all of the "non-direct circuits" in the boat are involved in the lightning strike as if they are a secondary winding of a transformer. And, as such, when the voltage is high, as in a lightning strike, the current / voltage that is produced in these secondary circuits is directly proportional, but the amount of induced current / voltage drops off exponentially as the distance away from the lightning travel path increases.

Now, granted this induced current / voltage is produced from a DC spike and acts like a PULSE to the secondary circuits on the boat, but nonetheless, all those electronic gizmos contain printed circuit boards, IC chips..etc, and WILL be affected. They are not designed for the "higher VOLTS" range, but rather MILLI-volts or less. They will certainly get flashover arcing, to various degrees, on the circuit boards / chips / wiring...thus frying various parts, and good luck trying to repair individual circuit components these days !!

It boils down to "black box" replacement of the entire affected unit(s) (VHF, GPS, bilge pump..) because gone are the days of diodes, resistors, capacitors, inductors and transistors.

I had suffered a lightning strike 3-4 yrs ago as well. It vaporized my VHF antenna, the pressure wave blew apart my Windex wind indicator, fried my VHF radio and 2 bilge pumps, and shot a couple of fuses / fuse holders across the cabin from the power panel.

Yes, I did have a grounding cable attached to the mast...a #6 awg crimped with large spade lugs to ensure good electrical continuity at both ends (mast foot and the keel bolt). No, I did not take an installed resistance check from mast to keel bolt, but periodic visual inspections yielded no corrosion / high resistance connections, and my PM is to dismantle, clean as necessary, and replace as necessary, then reinstall yearly.

Once again, good discussion...!
I applaud your inputs and perspectives...!

 

[reworb]

Great ideas, thanks! Keep them coming. Frustrating process. Odyssey now hauled with hull being looked at again. Event July 8, this is taking way too long.

My boat suffered a direct hit in very early August ... still in the yard.

Make sure they take the rig down and replace all the wiring, mine was burnt in several places and while it showed continuity then, it probably would have broken in several months ... on my dime. One of my shrouds also was also damaged and had to be replaced, that wasn't visible until the rig was on the ground, even tho a rigger had gone up and inspected the rig.

Don't rush the process, yards are very familiar with lightening strikes down here (southwest Florida) all say the same thing stuff that woks one day suddenly mysteriously quits working inspect everything slowly and methodically. If the boat was in the water when it was hit check the glass around the thru-hull even if the thru-hull is ok the glass around it may be damaged make sure they use a pressure washer around those areas.

Finally don't let the insurance company push you around, you have certain rights under the policy make sure you understand those rights. Sometimes insurance companies like to make it appear that they are doing you favor by paying your claim, they are not, its what they owe you. You bought and paid for a product from them and now its time for them to deliver that product.

 

[Forrest15112]

If the chain directs the current around my boat rather than through the hull to ground: I'm for that! Lighning won't even try to follow the link curvatures of the chain! It will just blast right through any developing impedence whatever it is! It will tend to travel down the least resistive path and I sure hope it is the chain if I am in the boat! What makes you think the internal ground strapping is going to survive any better than the shroud lines, chain, cable, etc would? I think the intent was, if it might help; do it! Chief

Lightning is an electrical surge and is subject to the laws of physics. During a direct hit, it will take EVERY path to ground. The lower impedance paths will take the brunt of it. The surge doesn't make turns well, especially through high impedance paths like a chain with hundreds of poor interconnections. The internal ground strapping typically is sufficient to provide a low impedance path directly to ground, not around the side, or through multiple terminals, etc. This wire or strapping will rise in current, but will deliver the surge to earth before the wire is destroyed because of the low impedance bonds. This is why it will usually survive and perform it's function. As I understand your statement, you think the surge will just blast through the high impedance junctions on every link and route the majority or a large part of the surge to the sea over the side. That might get someone killed as the surge is very likely to arc to something else. It's not a good idea to have multiple grounds at different potentials either, for the same safety reasons. The chain, or the jumper cable isn't a good idea as a primary ground or adjunct to a properly bonded boat.

 

[Chief RA]

Forrest: Of course it will seek multiple paths! Some of the strapping I have seen in these boats only 'theoretically" will withstand the current. Multiple grounds would not seem to be a problem to me as long as it helps shunt the strike! Who said the chain or cable was the "primary ground"? Grounds at different potentials, you have an active imagination!
You need to read the post "zincs corroding too fast". It will give you an indication of how poorly many of these boats are cross strapped to ground!

Chief, FCC lic.#1890, EE,IE,ET

 

[Forrest15112]

Chief, my reply was based upon the notion that a chain tossed over the side is somehow a good addition to a safety ground system. I tried to explain why it isn't. Whether some boats have poor grounding or no grounding makes no difference. A chain is a poor conductor and could make matters worse. A chain in the water is at a different potential than the keel. That invites more dangerous possibilities. I'm not specifying any particular installation, just in general, the chain is a poor substitute.

 

[walt]

A chain in the water is at a different potential than the keel. That invites more dangerous possibilities. I'm not specifying any particular installation, just in general, the chain is a poor substitute.

How could a chain over the side make anything worse? You can get complicated if needed, I think a lot of folks here will follow.

Is it because during the process of installing the chain, you would be more vulnerable? Or that the presence of the chain led you to think you were completely safe sitting right under the mast?

I would agree on these, dont really understand any other reason??

 

[Chief RA]

Forrest: You do not make much sense! I know you tried to explain why the chain would not really help with the grounding but I don't agree with you! Your theoretical approach indicates you must have limited education in electronics and trying to force your opinion does not work with me. Grounds that function properly have only one potential; 0 volts, or it is not truly grounded! Nobody is trying to tell you the chain is the answer to all lightening problems: just that every little bit of added assurance COULD help! Chief

 

[walt]

Actually Forest is a very good resource for lightning etc.. just happen to not agree with him this one time.

What you always need to consiider with lighting is that air is a very good insulator - until it gets ionized and then its a good conductor. And, since lightning just used air to travel a long ways, once it gets near the water surface, it has no problem using either metal or ionized air to get to where it wants to go. In metal conductors, there are parameters such as inductance or skin effect that limit current flow for fast changing current (like lightning).

Keep in mind also that as a bolt of lightning is comming down from the sky, all that charge creates an electric field. While the bolt travels "fast", the electric field travels at the speed of light and creates positive charge at the water surface before the charge gets there. To some extent its the same way that current flows in a capacitor even through there is no phisical connection between the plates. Its the water surface where induced current has flown, not down underwater at the keel.

If that charge coming down were to happen to be near your mast, the mast is a potential short cut to ground so it gets used. At the bottom of the mast, if anything is limiting that charge getting to ground, electric potential builds up again and if it gets to some level, it will use ionized air - from the bottom of the mast to the water surface. Any sort of conductor from the bottom of the mast to the water - be it a bonded keel or even a chain hanging over the side helps to get the charge to the water surface. If the conductors can do a good enough job, they win out over ionized air. If they are inadequate, ionized air steps in and gets the charge to the water surface.

Its somewhat of a competition between trying to use a known conductor and path to get the charge to the water vs. air. And air is very good in this competition.

Now the chain is not a very good conductor - both too high of resistance and also too high of inductance. So the chain likely wont compete well with air and the chain doesnt stop a flash over. But I dont see any way it could make things worse - unless it gave you a false sense of security. I think someone may have a model where they think a chain would increase the chance of a flashoever - I dont think this is a good model.

 

[Forrest15112]

How could a chain over the side make anything worse? You can get complicated if needed, I think a lot of folks here will follow. Is it because during the process of installing the chain, you would be more vulnerable? Or that the presence of the chain led you to think you were completely safe sitting right under the mast? I would agree on these, dont really understand any other reason??

Initially, the chain may have a low impedance to ground, but that is only at lower current flow. As the current rises, the impedance across all those links will rise dramatically possibly causing the surge to arc from the chain to something else. Here's an analogy of why i think it could make things worse: Would you toss a 20 gauge wire over the side in the same fashion? No, because at higher current, that wire becomes a resistor and will vaporize. The surge that vaporized the wire may arc to whatever is nearby. Each link in the chain is similar to a very thin wire.

The chain is likely galvanized, zinc coated steel, stainless, etc which are not good conductors compared to copper wire. This presents a difference of potential to ground when compared to the primary ground. Sea water may be an ideal earth ground, but the placement of the chain, including it's depth adds to that difference of potential when compared to the keel. This last part is probably mostly insignificant on a small boat in saltwater.

Poor placement of chain (wrapped around the mast and not bonded) + hundreds of poor conducting links + poor conducting chain material + at least two 90 degree bends + difference in electrical potential with respect to ground = poor choice for protection.

 

[Forrest15112]

Forrest: You do not make much sense! I know you tried to explain why the chain would not really help with the grounding but I don't agree with you! Your theoretical approach indicates you must have limited education in electronics and trying to force your opinion does not work with me. Grounds that function properly have only one potential; 0 volts, or it is not truly grounded! Nobody is trying to tell you the chain is the answer to all lightening problems: just that every little bit of added assurance COULD help! Chief

You asked for what others thought. I gave you my "limited education" opinion and explained why. I read my other posts and don't see where I was forcing my opinion or personally insulting anyone, except for possibly the 'old salt' who recommended this to you. If I offended you personally, it was not my intention.

Grounds that function properly are the result of proper installation and adhering to common practices that are proven effective. The chain over the side doesn't meet several of the proven and common practices. In opinion, it offers little more than false assurance for the reasons i listed in other posts.

 

[walt]

Ground potential differences are important in a "system" where electrical instruments are interconnected to prevent damage. But in the case of sailboat "ground to a chain in the water" to ground of the keel - not even slightly important. It’s the water surface that has all the positive charged ions just waiting for the electrons - for both salt and fresh water.

A long time ago I actually measured the inductance of a chain - really poor. I completely agree that it is worthless in a lightning system whose purpose is to prevent a side flash (i.e., ionized air). However, charge follows electric field and easily jumps between metal and ionized air. In the case of the chain, I think it probably looks like a bunch of smaller inductors connected together in series and in the way we normally look at conductors, wouldn’t conduct well. But in the case of lightning, each time the charge encountered an inductance link, the potential would build and ionized air would step in to continue the flow. If the best electric field path was still down the length of the chain (which is likely unless the chain took a small radius turn), the charge would likely follow the chain - arcing over each time it needed to..

We are all guessing here, I’m pretty sure no one has ever wasted the money to actually test a chain for this application since it’s clearly NOT even close to the best choice. I just don’t believe that the chain would make anything worse however.

FYI, I don’t like analogies... they can be easily used to mislead..