Lightning Protection, pros and cons

[Wotname]

Originally Posted by kivanc

Bonding all metal parts is critically important. It lets lightning current run through a path.

However, in case of a vessel, salt is the major conducting element which attachs on everything and makes the whole boat a conducting surface. So in fact, you can't create a path to lightning current on a boat because everything is conductive and lightning current seeks the shortest way to reach to water.

For a random tower on the mountain for instance, you can partly predict where the current will leave the structure. On a boat, the path is not predictable, just like the potential damage in equipment.

Regards,
KK

OK, lets put a couple of facts into the above.

Salt (NaCl) does not conduct electricity unless it is a solution (usually water) or molten. The conductivity of seawater varies but 5 S/m is a common number. As a comparison, the conductivity of copper is around 60,000,000 S/m and aluminium is around 35,000,000 S/m. Both of which is a little bigger than 5.

The current path of the lightning is simple- it takes all available parallel conducting paths at an inverse proportion to the impedance i.e. lower impedance, higher current.

However induced voltage potentials created from various current paths does make predicting other current paths quite difficult.

[Cpt Pat]

Originally Posted by a64pilot

I believe everything on my IP is bonded, I have been told that was to help protect it from lightning damage.
However I am to put it mildly, very suspicious as it would seem logical that the bonding would have to be very large diameter cabling to carry that kind of amps, and it’s not.
So I’m thinking that even though every piece of metal is bonded, it’s not going to make much difference as it’s all bonded with what looks like 10ga wire.
Mast, all the chain plates, the metal tanks, the thru hulls of course and engine.

When in comes to bonding wires: bigger is better. But, while the transient currents in lightning can be mega-amps, the duration is on the order of milliseconds. The amperage rating of wires are based on steady-state currents - not very short duration pulses. In broadcast installations, we frequently used 8 or 10 AWG uninsulated wire.

Nearly all the current flows only in the outer millimeter of the wire due to skin effect. Heavier wire provides a larger outer surface area, which is good, but nearly none of the current flows down the interior cross sectional area of the wire. If you ever inspect a conductor that has taken a serious lightning hit, you'll see the outer surface is melted a bit, while the interior is undamaged. We used uninsulated wire so we could visually identify damage during routine inspections. I wouldn't recommend uninsulated copper wire in a sea water environment because the insulation offers some corrosion protection.

You'll get a larger lightning-current-carrying surface area and lower inductance with flat strap instead of round wire. I use braided stainless steel strap. American Grounding Systems sells that type of strap. (http://www.ags.bz/)

[mako]

So Capt Pat, drawing a conclusion from what you said, ideally one would use copper tubing as a conductor instead of wire or strap?

[Cpt Pat]

Originally Posted by Mr B

When you get hit with one of these,
Will your counter measures work or not,

(See photo - post #161: http://www.cruisersforum.com/forums/...ml#post2948030)

My countermeasures will work better than no countermeasures at all. Actually, that looks like the hits my 1,000 foot tower (the highest object in a 300 mile radius) took in the Nebraska plains about once a month in the summer.

Come on sailors! Since when do we take a: "we're doomed - there's no point in even trying," attitude about any of the challenges from Mother Nature?

[Cpt Pat]

Originally Posted by crazyoldboatguy

And, of course, if there are any bends, curves or corners in those cables reduces their effectiveness - or do I’m told. How do you do that on a sailboat?

You do the best you can. "Strive for improvement - not perfection."

"Perfect" should not be the enemy of "good."

[Cpt Pat]

Originally Posted by makobuilders

So Capt Pat, drawing a conclusion from what you said, ideally one would use copper tubing as a conductor instead of wire or strap?

Tubing would be very hard to work with, and you wouldn't gain anything over solid wire unless your only goal was to save on weight and materials. In fact, in broadcast transmitters, even down in the AM broadcast range, the RF conductors frequently are hollow copper tubes, and waveguide conductors to the antenna for VHF/UHF service are also hollow copper tubes plated with a thin layer of silver. All the RF current passes through that thin sliver layer. (Silver is the best conductor.) Nothing would be gained by using solid conductors.

When you're running a thousand feet of waveguide up in the air inside a tower, weight savings is a real consideration. In a waveguide (or coax), you are trying to contain the RF energy within a specific characteristic impedance (usually 50 ohms) so it all radiates at the antenna - not from standing waves on the waveguide leading to the antenna (expressed as the Standing Wave Ratio - less is better). Flat conductors can't perform that containment function. But with lightning, you aren't concerned with characteristic impedance.

For lightning, flat strap has lower inductance - and a larger conductive surface area than round wire, using the same amount of conductive materials.

[Exile]

Originally Posted by kivanc

The lightning protection triad:

1. Bonding: prevent side-strikes by assuring a low impedance path between all conductive paths. Connect all bonded systems to a single "common ground" point to prevent AC/RF ground loops.

2. Grounding: provide a low impedance path to earth.

3. Suppression: provide an arc-path to ground that will conduct destructive voltages from developing on un-grounded signal paths and AC mains supply entering the facility:

* * *

Of the three items in the triad, bonding is most important. If lightning hits a system (vessel) and raises its potential a million volts above ground, and that entire system is so well bonded that no differences in potential (voltages) are created between system elements: nothing happens to that system. Thermal damage potential is then limited to strike point and the discharge-to-ground point on the system.

Cpt Pat (and/or others) -- Do you also agree, when it comes to our boats that is, that bonding is the most important factor in lightning protection? I ask because my boat is set-up like a64's IP, namely all metal thoroughly bonded together (as far as I can tell), but no other grounding equipment. After first buying my boat 12 years ago, I read Nigel Calder's thoughts on the topic and I recall him being ambivalent. As I recall, he cited two (opposing) schools of thought on the subject, namely (1) that it's a good idea for dissipation purposes in accord with kivanc's comments above, and (2) it's a bad idea because it can direct a strike to thru-hulls and maybe other critical components.

I've simply left mine alone because it's apparently a good idea for protection against corrosion, but figured the jury was still out on its utility for lightning protection. I've sailed through and been exposed to plenty of lightning storms but have never been hit, but of course that doesn't mean much.

Comments?

[Cpt Pat]

Originally Posted by Exile

Cpt Pat (and/or others) -- Do you also agree, when it comes to our boats that is, that bonding is the most important factor in lightning protection? I ask because my boat is set-up like a64's IP, namely all metal thoroughly bonded together (as far as I can tell), but no other grounding equipment. After first buying my boat 12 years ago, I read Nigel Calder's thoughts on the topic and I recall him being ambivalent. As I recall, he cited two (opposing) schools of thought on the subject, namely (1) that it's a good idea for dissipation purposes in accord with kivanc's comments above, and (2) it's a bad idea because it can direct a strike to thru-hulls and maybe other critical components.

I've simply left mine alone because it's apparently a good idea for protection against corrosion, but figured the jury was still out on its utility for lightning protection. I've sailed through and been exposed to plenty of lightning storms but have never been hit, but of course that doesn't mean much.

Comments?

I too am ambivalent when it comes to thru-hull fittings. Mine (two) are bonded, but I've made sure I have a dissipating surface that is much larger to take more of the current, and on a much more direct path from the masthead to the water.

In my case, I chose a 4 square foot zinc plate (not bronze - I have an aluminum propeller to protect from galvanic corrosion). I suspend the plate astern when lightning is an issue (not often in California), and leave it suspended when at the dock. Underway, it just skims along a few inches beneath the surface without much drag (based on the small amount of tension it produces in the tether lines). I believe this may be the cheapest solution to providing a large surface area dissipation surface - and it isn't attached to the hull where it could blast a hole in the hull. The plate cost me, as I recall, about $40. I have two Dacron 3/8 diameter tethers attached to the forward corners of the plate that I tie to the stern cleats, and a 2 inch wide flat stainless braided line that attaches to forward center of the plate and the backstay chainplate. I set the length of the tether to keep the stainless braid connection to the plate out of the water at the dock (to protect propeller from the aluminum to stainless galvanic couple).

BTW, though most of this discussion has been about direct hits by lightning. your vertical mast can also receive substantial currents induced by vertical strikes at some distance away. The distant strike acts like the primary in a transformer, and your mast becomes the secondary. Tesla tried using this effect to transmit bulk current. It's good it didn't catch on - or we may not have a useable radio spectrum. The point is: your vessel may have already survived a good number of induced strikes, the risk of which is many times higher than direct hits. Or maybe it didn't, producing seemingly random failures in delicate electronics: especially the receiving sections of radios and LEDs. We had a rash of those failures at my harbor after a thunderstorm last spring. Whatever protection you put in place for direct hits - even if not fully adequate - will give you significant protection from these more likely indirect hits.

[Exile]

Originally Posted by Cpt Pat

I too am ambivalent when it comes to thru-hull fittings. Mine (two) are bonded, but I've made sure I have a dissipating surface that is much larger to take more of the current, and on a much more direct path from the masthead to the water.

In my case, I chose a 4 square foot zinc plate (not bronze - I have an aluminum propeller to protect from galvanic corrosion). I suspend the plate astern when lightning is an issue (not often in California), and leave it suspended when at the dock. Underway, it just skims along a few inches beneath the surface without much drag (based on the small amount of tension it produces in the tether lines). I believe this may be the cheapest solution to providing a large surface area dissipation surface - and it isn't attached to the hull where it could blast a hole in the hull. The plate cost me, as I recall, about $40. I have two Dacron 3/8 diameter tethers attached to the forward corners of the plate that I tie to the stern cleats, and a 2 inch wide flat stainless braided line that attaches to forward center of the plate and the backstay chainplate. I set the length of the tether to keep the stainless braid connection to the plate out of the water at the dock (to protect propeller from the aluminum to stainless galvanic couple).

BTW, though most of this discussion has been about direct hits by lightning. your vertical mast can also receive substantial currents induced by vertical strikes at some distance away. The distant strike acts like the primary in a transformer, and your mast becomes the secondary. Tesla tried using this effect to transmit bulk current. It's good it didn't catch on - or we may not have a useable radio spectrum. The point is: your vessel may have already survived a good number of induced strikes, the risk of which is many times higher than direct hits. Or maybe it didn't, producing seemingly random failures in delicate electronics: especially the receiving sections of radios and LEDs. We had a rash of those failures at my harbor after a thunderstorm last spring. Whatever protection you put in place for direct hits - even if not fully adequate - will give you significant protection from these more likely indirect hits.

Interesting & informative comments thanks, here and elsewhere throughout the thread. I've noticed boats tethering zinc anodes to prevent stray current corrosion at marinas, but had never heard of trailing a zinc plate while underway.

Good point about my boat having already survived a number of secondary or induced strikes. Chances are it likely has, and may explain some consistent albeit temporary electronics failures since owning the boat. Could also explain why some electronics have long lives while others don't, seemingly without explanation.

Not sure if this qualifies as one of the induced strikes you describe, but I once heard about an anchored boat that took a direct hit to the mast but suffered no damage whatsoever. Instead, the strike traveled down the mast, through the keel, and out into the water. It then reportedly took out an alternator on a boat anchored nearby! In hindsight, perhaps the alternator was the result of an induced strike or maybe a different one altogether, but if nothing else impressed upon me the randomness of it all.

[Brezent]

Originally Posted by Cpt Pat

I too am ambivalent when it comes to thru-hull fittings. Mine (two) are bonded, but I've made sure I have a dissipating surface that is much larger to take more of the current, and on a much more direct path from the masthead to the water.

In my case, I chose a 4 square foot zinc plate (not bronze - I have an aluminum propeller to protect from galvanic corrosion). I suspend the plate astern when lightning is an issue (not often in California), and leave it suspended when at the dock. Underway, it just skims along a few inches beneath the surface without much drag (based on the small amount of tension it produces in the tether lines). I believe this may be the cheapest solution to providing a large surface area dissipation surface - and it isn't attached to the hull where it could blast a hole in the hull. The plate cost me, as I recall, about $40. I have two Dacron 3/8 diameter tethers attached to the forward corners of the plate that I tie to the stern cleats, and a 2 inch wide flat stainless braided line that attaches to forward center of the plate and the backstay chainplate. I set the length of the tether to keep the stainless braid connection to the plate out of the water at the dock (to protect propeller from the aluminum to stainless galvanic couple).

Really interested in your dissipating plate attached to the backstay. I have an SSB antennae in my backstay, so guessing this would not work for my boat?

[the dude abides]

I suffered a direct hit 2019. I had a lighting dissipater on top. I have a mono hull and there was a cat behind me, we were the only two boats there on a remote island in Southern Thailand. Lighting storm came up. There was lightning all around. Direct hit which also shocked me. Took out everything. When you are in a storm like the one I experienced, nothing is going to help. At 2:30 am when i got struck, it woke me up as I was as my whole body got shocked with it and was jerking around like a puppet on a string. Once that was over I rushed out to the cockpit and another bolt hit the water just behind me. It was everywhere. No one will convince me that they could mitigate that lightning storm. It was like being shelled

[mako]

Very interesting story. What damage did your boat suffer?

[Cyrus Safdari]

Originally Posted by Cyrus Safdari

There is no such thing as lightning protection. Nothing will dissuade or prevent it. Nothing will minimize damage. Much of the claimed methods will actually make things worse. Bronze plate on hull? Great until it gets superhot and blows a hole in your keel. The bolts holding it will alone cook surrounding fiberglass. Chain or wire thrown over side? Lighting jumps around. There is no accounting for it. There is just too much energy. It will fuse engine bearings.

Lightning myth is that it follows path of least resistance. Sure but only after trying out all other paths.

Anecdotal claims are many none are reliable. Best thing to do is not get hit. That's all.

I hereby retract all the above. Sorry I should have read more before opining