Getting A Handle On Lightning

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In a past life (And still part of the current one!) I was a communication engineer deploying radio/microwave systems on towers and tops of very high buildings where it was not a question of if you would get hit by lightning... Just WHEN it was going to happen. So planning and installing a new radio system was allot of  "did you think of every possible point where lightning may find a weak spot?" It got to be a game however, if wrong or failed to consider all aspects, would result in downtime of a large radio system or police department which had a really dim view of their radios not working... Needless to say I got really good at it and factory certified by key companies related to lightning protection. One of  the police departments radio system I reworked services the area where I live so in order not to get tickets or dirty looks... Enough said!!!

Here are some of my experiences with lightning and food for thought only.... You CANNOT STOP LIGHTNING STRIKES... just try to direct it where it will not do damage and THAT is the whole trick. Getting there has been open to interpretation and too many theories but bottom line is you want to make the electronic equipment look very undesirable as a path while providing something to give lightning a hand wave and tell it "come and get me! I'm yours!" How's that for an opener?

Don't get caught up in the fact that you may have a fiberglass hull and put that aside for now. Picture a "mast" with a lightning rod on top at some elevation that, floats above ground (Boats don't have masts that go directly to the waterline) which also includes mast top antennas (Any kind) plus wiring for lighting that we want to isolate from all this and should be treated as a separate issue. The big trick is providing the most direct path to the base of the mast then coupling it to the water... salt or freshwater (in the presents of high voltage fresh lake water conducts).

What I wouldn't do... Rely on any ONE technology to do the job... Only combinations work. Dynaplates were specifically designed to provide RF  (Radio Frequency) coupling to the water... Not ultra high current/voltage lightning discharges due to it's construction (beads of metal soldered together) on a fairly small bronze plate. Add high voltage/current and it "could" blow apart if completely relied on. I have long been an advocate of a large solid bronze plates to act as the lightning ground and Dynaplates to be used for what they were intended for... Not someone's interpretation.

Bottle brushes or Sweeps on a mast top help... multiple spiked rods help... Anything to help discharge a charge buildup. As long as you give them a solid path to ground for discharging what they have collected and a core rod to handle a direct hit. There has been criticism of this technology but bet they don't have a 300 foot, a 200 foot tower in one location and a 200 foot and 100 foot tower in another, to watch sparks fly when lightning is discharging.  Too many times I have seen boats with a brush or some kind of mast top protection added without any effective discharge path... Again the bottom line of giving lightning or, in this case, the buildup of a charge somewhere to go via heavy conductors to ground.

One method I have used in the past is to take a 3 inch strap with a 4 gauge stranded copper wire tacked down the middle of it starting from the base of the mast and two runs...one port and the other starboard around the cabin (No sharp bends!) and hull down to a pair of bronze plates 3 feet by 2 feet and tie off the strap to them via all mounting through-bolts plus tying the plates to each other... Sort of a circle from mast base down to plates with few sharp turns. I don't know if these plates are commercially available in your area but we were able to get them made locally. I would think that some keel coolers isolated by their rubber hoses would offer the same surface areas and thickness to handle lightning duty. Again, food for thought. Here are some diagrams of possible solutions to ponder..

It is important to de-couple coaxial cable wiring that is simpler than you may think... Typical VHF mast head installations use a fiberglass whip which is grounded at the mount base however no decoupling is done at the base so if lightning were to hit this arrangement the path would be to blow up the antenna, travel down the coax into the cabin, through the radio and finally arriving at the negative side of the DC buss bar taking out everything around it too. Lightning does not like to travel in circles at all... When you coil up coaxial cables they appear as very high impedance chokes to the path (time delayed) where if lightning were given a more direct discharge path simultaneously, would take it. On my installation jobs where I am putting antennas on a mast, I will ground the coaxial cable shield to the mast at the top and again at the bottom (Shown In Diagram) where is comes out I then coil up 7 to 10 turns 6 inches in diameter (RG-8X. For RG-214 8" dia. Coil) then run the cable to a grounded lightning protector (Grounded to our main ground) to provide path delay and not to clobber the protector with high current so it can survive for another day.

DC wiring is handled a little different but the same rules apply. One trick I love (started by the phone company like 100 years ago) is to spiral the positive/negative together and run it where ever.. (See Picture). Several reasons for doing this... Reduces electronic impulse noise to/from the cable, keeps it neat and will not radiate or act as an antenna (Important to your SSB Radio) After prepping the wiring like this down the mast, make a coil it like the coax and ground it to the protector plate as the coax. There are DC protectors available too if you really want to get into it! Mast mounted radar should also be coiled up at the mast base for a degree of isolation too. By doing all of this you choke off any unrestricted paths from the mast into the innards of the boat minimizing damage and protecting sensitive electronics and you!!!

 Lightning Hit Another Boat But Damage Done To Others

That always bugged me as to how could it happen... In an article I once read described "surface propagation" of lightning as it travels along the ground or water... The example they used was a cow standing under a tree... The tree takes a direct strike but kills the cow that did not take the direct hit. What killed the cow? The noise? What they pointed out was, as the lightning traveled along the ground a difference in potential between the cows legs did him in where the rise of voltage/current closest to the tree for a matter of microseconds was substantially higher than the legs farthest away from the tree. So for a moment the path was up the "near" legs and down the "far" ones... Power crews, working on 500 KV lines use static suits coupled directly to the line they are working on to keep all their body parts at the same potential.

I had a similar experience where I was driving along in my car talking on a VHF ham rig (using a magnet mount antenna, ungrounded case) with the mobile mic in my hand in a hell of a storm with tons of lightning dropping all around me... Really bad. The next thing I remember was talking then getting one hell of a jolt that shook me up bad enough to pull over and a buddy picked me up. We figured the grounded mic hang-up button the back of the mic in one hand and the wet steering wheel in the other did the trick... Won't forget that one!

In a situation where you have several water contacts used for grounding SSB rigs another for bonding in a fiberglass hull, they may not be exactly all tied together quite the same way (Ground/bonding wire lengths/paths/distance, prop and shaft) so for an instance there may be enough difference between "sets" of water contacts that the voltage potential would go through the roof for a moment. People forget "time propagation" in lightning equations and that's really important.

How about the Lead Keel? Most of them are encapsulated in fiberglass or epoxy paint (Isolates it from water) so they offer no direct water contact at all. Nonsense of capacitive coupling is wrong and if used for lightning protection or discharging, will result in some type of keel damage.

Hope this helps fuel good ideas.

John

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