Lighting Protection - From Mast or From Butt Plate ?

[ShipShape]

Originally Posted by arjand

How did you isolate your forestay?

The SS lifelines and aluminum toe rails were the main potential conductors aft and I've removed those, and have no large metal items for well over 6' aft of all metal associated with the bow. For the nav lights and windlass wires I've put tight loops in them positioned where I estimate any side flashes from those points cannot get to any other conductors. The forestay chain plate is external so only the backing plate can be grounded, which is useless. In a few months I'll pull off the forestay chain plate and pushpit to inspect them for crevice corrosion, when I remount them I *might* ground the pushpit ...

[ShipShape]

Originally Posted by Ram

Great Job Shipshape! I have a cat and wondering if I run a few 2/0 wire like you have in the photo dropped straight in the water below the mast ,how effective would that be?

Howdy Ram,

The only thing more effective would be to have your mast extending into the water! Lightning will take the easiest path to ground, and by having conductors straight in the water there's no fuss with changing directions and materials to get it through a hull and onto a ground plate. The problem with wires in the water is (drumroll): Corrosion. Electrons travel on and near the surface of conductors, and corrosion changes the properties of the surface of the wires so they no longer conduct easily, and if some other path to ground is easier then that's the way it will go.

Not having to go through a hull is rather convenient so I thought about what I would do if I had a cat. I would do exactly as you suggested, but use a less corrosion-prone conductor. I DID NO RESEARCH - I'll leave that up to you! - but stainless steel wire rope is the best option that came to mind. I seem to remember that 18-8 conducts better than 316, and it is cheaper too. There's info out there - pick the cheapest, most readily available, most corrosion resistant best conducting wire rope you can find - that way you won't procrastinate every time you have to renew it.

Below I copied part of another post I made a few weeks ago - now is a good time to read that so you understand why wire rope is the best thing to use. You want to use wire with the smallest strands possible - they will corrode quicker so you will have to renew them more often, but they can conduct a lot more per surface area than larger diameter strands. There's an acceptable balance for you somewhere!

Now connect the wire rope to your mast somehow - doesn't matter how but don't swage them to anything, and it needs to be cheap and cheerful or you won't be diligent about renewing them every time the wire corrodes. Use an anti-corrosion conductive paste at all connections. You want the maximum area possible between your mast, the connectors and the wire strands - remember all the electrons on their way to ground have to come together at the connectors and they really don't want to do that - they want to stay as far from each other as possible, that's why I used two conductors 180 degrees from each other, and grounded my mast step bolts to provide that option too.

Make the wire rope long enough so it is always in the water, and I would fray the end to give the electrons more room to jump off. Find a way to store the rope(s) on deck so no one gets stabbed, drop them in the water during storms, rinse them off with fresh water just like the rest of your rigging, and you should get some decent life out of them. Corrosion is a killer - inspect the rope and connections regularly.

Even though you are not going through a hull the other "rules" still apply - bend radius, changing direction, potential for side flashes, etc. You'll still need to pay attention to your shrouds, all metal items within six feet, the wiring ... And I have no idea if any of this works for fresh water.

Hope this helps - it was fun to think about!

[ShipShape]

This is a general explanation - no need to explain things correctly at the subatomic level.

Electrons repel each other like crazy, so their behavior is rather predictable. For standard DC current electrons get bumped from atom to atom, and good conductors are those that make it easy for this to happen - like copper and aluminum. Free electrons, such as those from lightning, travel on the outside of conductors because that is where it is easiest for them to move and they can get the furthest away from each other. For round conductors, the smaller diameter the conductor the more electrons that can fit per surface area.

To illustrate this to yourself, draw two circles, one with a circumference of one inch and one with a circumference of two inches. Now get a bunch of dots from your paper hole puncher and set them around the outside of the circles just touching each other, and just touching the line of the circles. Does the larger circle have exactly twice as many dots as the smaller circle? No, it has fewer per inch. And if you repeat the experiment putting dots on the line Inside the circle you will see that many fewer fit inside the same size circle than did outside.

Lightning ground FYI: Copper braid is not permitted for lightning ground systems - the electrons must make many direction changes, and copper ribbon is not permitted because so few electrons can fit on the surface as compared to the same amount of stranded wire. Also, both are prone to surface corrosion, which causes massive resistance. If you ground your shrouds be sure to ground the CHAIN PLATE and not the backing plate - grounding the backing plate does not work because the current must make two 90 degree turns through the bolt at two very inadequate connections.

[onestepcsy37]

i was struck by lightning last summer in the abacos. my boat, a 37 foot fiberglass cutter, is not grounded in any way. nothing. not because i don't know about it but because i'm not so sure it does any good.

we were sailing in the sea of abaco when a big thunderstorm caught up with us. i decided to drop sails and drop anchor to sit it out. these storms pass quickly and the sea of abaco is only about ten feet deep. i managed to get the boat set up just as the storm struck. lots of wind and rain. i was standing in the companionway, under the bimini, using my handheld gps to watch for signs i might be drifting.

there was a loud bang - sounded like a 155 going off over my head - and i saw a blue light come down the mast. it was over so quickly there was no time to be afraid. i looked around the deck and everything seemed to be in place so i went down below to check for leaks or other damage. nothing. my wife had been sitting down below and wasn't sure what had happened until i explained it to her. since it was getting late and growing dark i decided to just stay anchored until morning. the storm passed and we had no further problems. in the morning, and over the next few days, i discovered the extent of the damage.

the alternator was fried. fortunately i had a spare alternator.
some of the engine instruments - ammeter and water temp, were not working.
some of the interior light bulbs, but not all, were burnt out. one of them actually exploded. they are all automobile type bulbs.
the vhf radio was fried.
the depth sounder was fried.
the navtex was not working. i later discovered that it not only contained a fuse on the positive wire but also on the negative wire. the negative fuse was blown, and when i replaced it the navtex worked again.
i should mention at this point that the vhf, depth, and navtex are all wired through the breaker panel.
the autopilot, fridge, and solar panel were not harmed. these are all hard wired to the battery bank with fuses/breakers in line.
all the nav lights were blown.

that's about it. maybe $500 worth of damage. was i just lucky? would a 'proper' grounding system have saved me from any damage? damned if i know....

[Ram]

Originally Posted by ShipShape

Howdy Ram,

The only thing more effective would be to have your mast extending into the water! Lightning will take the easiest path to ground, and by having conductors straight in the water there's no fuss with changing directions and materials to get it through a hull and onto a ground plate. The problem with wires in the water is (drumroll): Corrosion. Electrons travel on and near the surface of conductors, and corrosion changes the properties of the surface of the wires so they no longer conduct easily, and if some other path to ground is easier then that's the way it will go.

Not having to go through a hull is rather convenient so I thought about what I would do if I had a cat. I would do exactly as you suggested, but use a less corrosion-prone conductor. I DID NO RESEARCH - I'll leave that up to you! - but stainless steel wire rope is the best option that came to mind. I seem to remember that 18-8 conducts better than 316, and it is cheaper too. There's info out there - pick the cheapest, most readily available, most corrosion resistant best conducting wire rope you can find - that way you won't procrastinate every time you have to renew it.

Below I copied part of another post I made a few weeks ago - now is a good time to read that so you understand why wire rope is the best thing to use. You want to use wire with the smallest strands possible - they will corrode quicker so you will have to renew them more often, but they can conduct a lot more per surface area than larger diameter strands. There's an acceptable balance for you somewhere!

Now connect the wire rope to your mast somehow - doesn't matter how but don't swage them to anything, and it needs to be cheap and cheerful or you won't be diligent about renewing them every time the wire corrodes. Use an anti-corrosion conductive paste at all connections. You want the maximum area possible between your mast, the connectors and the wire strands - remember all the electrons on their way to ground have to come together at the connectors and they really don't want to do that - they want to stay as far from each other as possible, that's why I used two conductors 180 degrees from each other, and grounded my mast step bolts to provide that option too.

Make the wire rope long enough so it is always in the water, and I would fray the end to give the electrons more room to jump off. Find a way to store the rope(s) on deck so no one gets stabbed, drop them in the water during storms, rinse them off with fresh water just like the rest of your rigging, and you should get some decent life out of them. Corrosion is a killer - inspect the rope and connections regularly.

Even though you are not going through a hull the other "rules" still apply - bend radius, changing direction, potential for side flashes, etc. You'll still need to pay attention to your shrouds, all metal items within six feet, the wiring ... And I have no idea if any of this works for fresh water.

Hope this helps - it was fun to think about!

Some very good ideas here-i never worred much about it before because I was in the Med and we have very little lighting compared to South Florida where I will be sailing next year-

[Cheechako]

"Lightning will take the easiest path to ground, and ..."

really?

[ShipShape]

Originally Posted by Cheechako

"Lightning will take the easiest path to ground, and ..."

really?

Nice picture, but unrelated to both this thread and my quote you chose. This thread is not about lightning, it is about grounding the mast on a sailboat. Hope that answers your question / clears things up for you.

[Cheechako]

Sorry, I could have sworn the OP said: "I have an alu mast on a BIG alu butt plate. I am replacing the wire of the lighting protection." Unquote...
Guess I must need new glasses....

[rebel heart]

Wooden mast. Good article here: Lightning Ground Systems

Put a lighting rod up, use heavy gauge wire to run it to the top of the track, then heavy wire to a plate. I think I'm supposed to bond all the chainplates but I never did that.

[IslandHopper]

I want whatever these guys have....



When i called the "Big Rig" (Technical call sign for big crane..lol) up to see how he fared after the strike, he replied "meh, if i had a hundred dollars for every time that happened i would be a richer man"........no lights went out, and apparently only one or two breakers tripped....

FYI, the construction barge is called the DB30 and we are working in Bass Strait, thats my boat rafted up at the top of the below pic....

DB30...

[Wotname]

FWIW, lightning actually follows all known rules of electrical theory however due to the large charges and currents involved, some the more obscure laws become important and we forget that.

For instance, force a couple of amps down a wire with a tight bend in it and nothing happens but magnify that up to hundreds or thousands of amps and the forces that make the current want to travel on the outside of the bend become very significant.

Lightning does not take the easiest path to ground. It travels between areas of greatest potential difference (within a given distance) to equalize the charged areas (basic electrical theory). Of course the surface of the water (or ground) may be one of the areas of charge that the strike travels to but it isn't the only one.

In order for current (the strike) to flow between the charged areas, the charge has to be great enough to ionize a path in the air which reduces the resistance of the air considerably and thus allows very high currents to flow along the ionized path. This very high current then creates its own problems, mainly heat and electro-magnetic fields.

The biggest fallacy is that the current only flows along the easiest path. It doesn't, it flows along all parallel paths between the charged areas in inverse proportion to the resistance. So while the difference between say a path of 1 ohm compared to say 50 ohms seems big, one fiftieth of say 5,000 amps is still 100 amps flowing along this "high resistance of path" of 50 ohms.

All this really shows is how important it is to provide a very very low resistance high current capacity path from your mast to the surface of the sea in the straightest line as possible.

[rebel heart]

Can someone explain to me how a 4 gauge wire is supposed to transfer 30,000 amps?

[sabray]

guess maybe it has to do with voltages in the millions.

[Wotname]

Originally Posted by rebel heart

Can someone explain to me how a 4 gauge wire is supposed to transfer 30,000 amps?

Hmm... try keeping it very cold and the duration of the current flow very short. Having the wire made from a very good conductor helps too.

Seriously - I don't recall the "fusing" rating of 4 gauge wire but it is dependent on ambient temperature and the duration of flow plus any "high resistance" connections involved. I would guess that even at room temperature, it would carry 30,000 amps for microseconds and perhaps milliseconds.

EDIT. Rethinking the subject and given the melting point of copper, I would speculate that it might carry 30,000 amps for seconds

[Wotname]

Originally Posted by sabray

guess maybe it has to do with voltages in the millions.

While the voltage between the charged areas may start of being huge, the potential difference across say a 4 gauge wire used for connecting the bottom of the mast to the seawater ground plate will be quite small in comparison - possibly only hundreds of volts. Really depends on the other resistances in the circuit, i.e. ionized air path and mast. The resistance of the ionized air path varies greatly and is very dependent on length. Really the mast and its grounding are only small factors in the overall circuit.

Of course, these are the only one we can control and they the only ones that matter to the sailor in the event of a lightning strike! Getting them wrong does have serious consequences!!!