Lightning ground

[Isla-Mae]

On the starboard side of the keel on my O'Day 25 is a steel plate with the inscription "Do not paint". It has two bolts that appear to go through to the forward section of the bilge. Assuming this is a lightning ground, what would be the most effective way to make a connection to the mast?

The mast step is stainless with four bolts going through the the cabin to secure it. I also plan to rest the mast foot on a small block of Marine Tex (flexible polymer), and there will be a static dissipator bolted to the mast head. I am located in the lightning Capitol of the world, Central Florida.

 

[Pat]

On our 272, the mast and nearly everything that can be grounded by a manufacturer was grounded thru to the keel, with the caveat not to rely on lightening ground systems noted many times in the manual by O'day.. I'm certain the mast or mast plate would have been included in the system. Our boat does not have a steel plate on the exterior however, so your system may be different. Pat

 

[Joe11688]

I've often wondered whether it would be more effective to just connect a long chain to one of your stays and drop it over the side into the water if you happen to be caught on board during a lightning storm. This way you get that cone protection in the event of a hit.
As a former lineman for a power company, I was always told that it's that second point of contact that kills you. In other words, electricity follows a path and it tries to seek a ground. If a person is standing on something grounded, the electric charge goes right through that person which is known as the first point of contact, and burns a path to ground which is the second point of contact. If you're sitting in the cabin during an electric storm with the mast grounded to the keel through the cabin, the chances may be greater of getting hit by lightning because of your close proximity to the ground. The lightning bolt is going to follow that path to ground, burning everything in it's path.

There are exceptions to this rule of a second point of contact. For instance; an energized high voltage wire breaks off the top of a pole and lands on the ground still burning. A person walks over to it and as he gets closer with one foot on the energized earth, a difference of potential between both of his feet on the ground can cause death by electrocution.

I don't know a lot about grounding a sailboat but I'd want some kind of cone type protection where the charge goes to ground on the outside of the boat. A ground must require a good solid connection to work or else it will blow right off on an initial hit.

Perhaps a 10' length of #2 stranded copper wire with a neoprene jacket would work. A ground plate could be connected to the end that goes into the water.

Will it work? I don't know, but some type of grounding system that can divert the charge around the boat is better than no protection at all if your boat ever gets hit when you're on board.

 

[Forrest15112]

If the manufacturer went through the trouble of installing a plate for surge protection, it would seem that they would have attached the mast to it already. Anyway, if that's what it is, you can bolt a heavy wire to it from the mast. I work on commercial communications systems and, although land-based, I never see lightning dissipators in use anymore. If your connection is in the bilge area, regular stranded wire may not work out so well if it gets wet. On buried and other weather exposed grounds, we use unshielded solid, tinned #2 wire. This is very durable and can handle large surge currents. The main thing is to provide a low impedance path to ground. Some folks recommend jumper cables from the water to the rigging, or the chain mentioned above, etc. The problem with all of those types of remedies, is the poor connection between the mast, the stays, and the jumper cables or chains. My standing rigging is attached to the mast with T-hooks. While this will conduct some electricity, it will not likely handle the current of a direct strike, especially when there is a massive hunk of aluminum mast that goes straight down.

 

[RichH]

The "lightning guru" from FSU is now in independent practice and now recommends an entirely different schema for lightning protection ... side arc electrodes: http://www.marinelightning.com

The use of a chain for grounding protection would seem 'pointless' as all the links would be be in 'point to point' contact .... a really 'rotten' method of 'conductivity', especially for 'radio frequency' lightning events, lightning can be either an amperage event or a RF event, or a combination of the two. The alligator clips on jumper cables would also yield 'poor' connectivity for extremely high amperage events. Apparently 'todays' thinking is that the best protection is the grounding/dissipation of lightning AT or TO the SURFACE of the water.



Here's some summary info from the marinelightning.com website:
http://www.marinelightning.com/Siedarc.htm
Providing exit terminals around the perimeter of the hull is the key to an effective system design since, in addition to dispersing the current more uniformly around the boat, it also enables the lightning down conductors to be routed externally to all wiring and conducting fittings. This is illustrated for a sailboat on the right. The lightning conductor from mast base connects to both the chainplate and the loop before passing down to a daisy-chain SiedarcTM electrode just above the waterline, and from there via an immersed HStripTM to a keelbolt (and base of a keel-stepped mast). SiedarcTM electrodes at bow and stern provide more exit terminals from the loop to the water. This geometry is mirrored on the port side, as indicated by the dashed lines. That is, there is a total of two HStrips and six SiedarcTM electrodes. Thus a conducting grid covers the interior of the boat and a total of eight exit terminals are distributed over the hull near the waterline. For a keel-stepped mast, make another connection from the mast base to both the keelbolt and the HStrips.

Guiding the current on the outside rather than through the middle of the boat minimizes shock risk and emi. In addition, a bonding loop around the boat at about deck level equalizes potentials, provides additional paths for current flow, and can be used for bonding conducting fittings. In a major departure from the status quo, NFPA (the National Fire Protection Association) has recently revised their watercraft standard (NFPA 780 Ch.8) to include the concepts of a loop conductor, external down conductors, and perimeter grounding electrodes. See our Standards page for details. With this new system the conductor layout more closely mirrors that found on the typical lightning protection system on a building. We call this system of external lightning conductors and peripheral exit terminals the ExoTerminalTM protection system. In the photo below, we have shown where additional (internal) lightning conductors, grounding terminals, and air terminals were installed to fabricate this type of system

 

[Joe11688]

That makes sense.

 

[Isla-Mae]

Your responses were well received, even those that were quite technical. Thanks!
On closer ex inaction of the "Iron" plate showed it was actually solid brass, approx. 8"x3"x1", with two 3/16 brass bolts going through to the bilge. I bought a length of #6 marine cable that I plan to attach one end to the mast step bolts that come through the cabin and the other to the two bolts in the bilge. At the top if the mast I will moving the static dissipator. The mast will have a solid connection to the step, hopefully adequately grounding the system and supporting the excremental static dispersal. Having two lengths of chain that can be easily hooked to the chain plates and dropped overboard in threatening conditions is my advanced plan. Does anyone care to score this idea on a 1 - 10 scale, with comments?

 

[anchorclanker]

I must say, my opinion on the subject has changed 180 degrees since joining this forum. Between what has been discussed, links to various sites discussing the research findings, its been quite a learning curve. Ive gone from believing in no bonding/grounding, to being fully bonded.

On another note, this "tossing a chain" over the side thing keeps coming up, and perhaps a thread dedicated specifically to the subject of lightning protection should be created, before someone gets themselves killed.

 

[Joe11688]

Myself, I've been though numerous lightning storms on my boat since I've owned it. I don't ground anything on it. I just find a protected cove and anchor out in it.

I only mention the chain just to have something to throw out there on this subject. Would is use a chain or a wire for lightning protection on my boat? probably not.

There is anywhere of up it or more than a million volts in a lightning bolt so I was told by an OSHA safety man we had years ago who used to come to our plant and teach pole rescue, and CPR. Would a properly grounded boat sustain this potential strike? I don't know and I don't want to find out.
One of the guys on the other forums had mentioned that he and his wife anchors their Mac 26 and paddles to shore when there's an impending lightning storm coming their way. Maybe that's the answer, but you can get hit by lightning just as easy on shore as you can on your boat. Myself, I prefer to stay on my boat. In fact I've been known to sleep right though it while on the hook.

 

[Pat]

In addition to the great posts on the subject, I've wondered what happens when I (owner) install some new piece of equipment, say a stereo, and don't ground it to the
grounding system installed by O'day? Or a VHF raido...Doesn't that nullify the purpose of the grounding system.... We had friends who moved to Florida from Wichita and took their Catalina 42 down to Florida and promptly were struck by lightening two separate times in the Gulf of Mexico and I believe this happened twice and this ruined nearly every piece of elec. equipment on the boat...according to what I remember, it was a rather slow demise of virtually all electric circuits/ equipment...by that I mean the
current continued to destroy the boat's systems...is that possible....the Erickson 32 next to my boat was hit by lightening 3 years ago at the slip and again, nearly every peice of electrical equipment on the boat had to be replaced....Our 272 was next to his
boat but we did not sustain any damage that I'm aware of and I think I would certainly know by now...i guess my question; is there a residual current that could cause the damage to occur over time rather than instantly? Maybe a dumb question....Pat
equipment on the boat....

 

[Forrest15112]

In addition to the great posts on the subject, I've wondered what happens when I (owner) install some new piece of equipment, say a stereo, and don't ground it to the
grounding system installed by O'day? Or a VHF raido...Doesn't that nullify the purpose of the grounding system.... We had friends who moved to Florida from Wichita and took their Catalina 42 down to Florida and promptly were struck by lightening two separate times in the Gulf of Mexico and I believe this happened twice and this ruined nearly every piece of elec. equipment on the boat...according to what I remember, it was a rather slow demise of virtually all electric circuits/ equipment...by that I mean the
current continued to destroy the boat's systems...is that possible....the Erickson 32 next to my boat was hit by lightening 3 years ago at the slip and again, nearly every peice of electrical equipment on the boat had to be replaced....Our 272 was next to his
boat but we did not sustain any damage that I'm aware of and I think I would certainly know by now...i guess my question; is there a residual current that could cause the damage to occur over time rather than instantly? Maybe a dumb question....Pat
equipment on the boat....

It wouldn't necessarily nullify the safety measures already in place, but it presents another path to ground through that device. By another path, I don't mean that every device that's grounded offers a path through it for a surge. What it means is that there is a path through that stereo, vhf, etc that is at a different potential than other devices that are bonded to the ground system. Ideally, every device and significant piece of metal would be bonded to the grounding system. The grounding system should have a single point to earth ground. During the surge, all grounds would be at the same potential and a direct path to that single point would be the path of least resistance. It doesn't mean that your electronics won't get destroyed, but it could prevent arcing inside your boat, through you, or through the hull where there is no plate that can sustain the high currents. In other words, it will save you and your boat.

In your friend's boat where things failed over time after a direct hit, it was likely due to induced currents on the wiring or even some of those devices not grounded properly and some of the surge current making it's way to earth through those devices. When lightning strikes, a magnetic field is generated in the immediate area that will produce a voltage on any conductor that is in the field. This is induced current and explains how devices in the boat next door might be damaged. It just depends how much voltage is induced as to how much damage there will be. This is also the type of surge that your power strip/surge protector at home is designed for. There are devices for antenna connections at your radio, AC power protectors, telephone, cable TV, etc. These are all more common sources of surges than direct hits and where we are really likely to see damage to electronics. EVERY protection device requires a good ground to route the current to. I have seen people who spend good money on surge protectors for their antennas only to not ground them. The current is going to go to earth one way or another.

Your chances of a direct hit are slim, but there should be a direct low resistance path to earth that will handle the majority of the current and not blow holes in your boat.

 

[Joe11688]

I think that your electronic equipment has a better chance at surviving a direct hit if it's completely disconnected from any grounding devices. Just unplug it till the storm is over.
One of the guys in our club lost all his electronics from a direct hit to his Baha Cruiser one year while on the mooring behind our club. I never think to unplug my VHF when I leave my boat on the mooring but I always take my Autohelm autopilot with me when I leave the boat.

 

[anchorclanker]

From all I have read:

An unprotected (unbonded/ungrounded) boat, presents as much or greater potential to a strike.

The unprotected boat could be holed as electrical charge discharges into the surrounding water at or about the water line. Various pictures online are testimony to the effect. Chain plates can be burned out, rudder gudgeons burned off, almost anything you can imagine. Lightning can be weak, or it can also be so powerful its almost immeasurable. There is nothing that is non conductive, only materials of low conductivity. Given enough potential, lightning can go through (or around) virtually anything.

By protecting the boat, your not necessarily trying to reduce its potential to a strike, but attempting to reduce the damage to the boat and/or equipment should a powerful strike occur.

Several years ago as my daughter and I were coming back to the dock, I noticed her hair stood up. At the same time I saw hers, she saw mine. We were in an aluminum fishing boat and I knew a strike was imminent, but I didnt know exactly what to do. Should we jump? That didnt seem right. I had her get down on the floor and I gassed the sucker while getting as low as possible. We were only 100 feet from shore, so I just drove it up on the beach and we bailed out and headed for the camper.

In contrast, I feel much safer on our sailboat, even with a 30 foot lightning rod in the air. Its not bonded yet, but it will be.

I am not sure what a chain would do over the side, but given a choice I will just stay in the cabin rather than try finding out.

 

[Pat]

I think you are correct in stating, "By protecting the boat, your not necessarily trying to reduce it's potential to a strike, but attempting to reduce the damage to the boat and or equipment should a powerful strike occur. And when I stated above that some of the
equipment we have added is not connected to the installed bonding equipment, the equipment I've added is bonded by it's connection to a battery where thru the 12 volt
system or the AC......is that a true statement or am I just totally off base? The Wichita Public Schools made us take shop classes in Middle School, but the fact that I could get a bulb to glow with a proper battery and switch was not very impressive. pat

 

[anchorclanker]

It is my understanding that a powerful lightning strike to a structure (boat,car, etc..), can create an electrical field often coined EMP, or electro magnetic pulse. Think of it as a cloud of high electrical energy or charged atmosphere, separate from the actual bolt itself. This EMP can invade electronic devices, and whether plugged in or not, they can be destroyed as the energy finds its way into delicate circuitry such as transistors IC's, and microprocessors.

Further, it is my understanding that gounding these devices internal chassis grounds to the bonded and grounded structure, will either help to disipate the EMP energy away from the devices, or not allow the EMP energy to build in the first place.

In aviation, aircraft are struck by lightning almost every day, and often multiple aircraft every day. Consider that these aircraft are primarily aluminum structures and highly conductive. Consider also, that all electrical systems and equipment aboard are thoroughly grounded to the chassis, and all parts of the chassis are bonded electrically to each other. The aircraft's body, or fuselage, becomes a faraday cage, and as long as all electrical grounds are connected to that chassis, the energy stays outside.

In a strike, the voltage passes over the outside of the aircraft, and most often without any physical damage whatsoever. It should be of interest, that the Apollo 12 spacecraft was struck not once, but possibly multiple times, during liftoff, when the exhaust plume created a pathway for energy of nearby storms during launch. It knocked their computers offline but they were able to reboot them and continue on to the moon without trouble. I can assure everyone, that the ships entire structure and electrical components and systems were completely bonded and grounded.

Our boats are wood and fiberglass and not highly conductive. By bonding all conductive metallic hardware together and installing ground plates below the water line, we are recreating the aircraft chassis. It is my understanding, that electrical systems not directly connected to the bonded and grounded structure, create a potential source of increasing the EMP energy, and a pathway that could potentially pull the EMP energy "inside" the cage.

From what I have garnered, it is advisable to either bond and ground all it fully, or do nothing at all. But dont do it halfway. You may invite far more damage than either process.

 

[Joe11688]

A plane in the air is like a bird sitting on a high voltage wire. The potential is even. It's that difference in potential that can kill the bird. For instance, the bird sitting on the wire comes in contact with an opposite phase or sticks his beak on a grounded
transformer cover or wet cross arm. This is where that second point of contact comes in.
A lot of times a crane operator can jump clear of the crane after his boom comes in contact with a high voltage aerial cable and can survive. It's only when he walks back to the energized vehicle and comes in contact with it that he gets electrocuted.

 

[anchorclanker]

A plane in the air is like a bird sitting on a high voltage wire. The potential is even. It's that difference in potential that can kill the bird. For instance, the bird sitting on the wire comes in contact with an opposite phase or sticks his beak on a grounded
transformer cover or wet cross arm.

While I did say most aircraft come through a strike undamaged, not all do. Occasionally it will burn holes through wing, control, and fuselage surfaces. It is not the same as a bird on a wire. The bird as you say, has no potential sitting on a wire, unless he gets near one of the other wires. The airplane, and in the case of this discussion, a sailboat, can pass through an area of very high potential, and the energy will pass through (hopefully over) the structure.

The crane operator is generally safe as long as he stays in the machine. Its when he leaves the cab that he places himself in grave danger, as you say, he places himself between two potentials. The ideal way to leave a vehicle with power-lines across it, is to just stay put and wait for the power crew. Just stepping onto the ground could likely be your last mortal move. However if the car is burning, you may have to try. Without touching any metal on the car, you have to put both feet down on the ground, together/simultaneously, with them tightly together/touching, and then "hop" out of the field area, again with both feet leaving the ground, and contacting it simultaneously. If one foot steps out of the energy field while the other remains, your probably going to be smoked.

There was a guy jumped out of a skid loader after striking overhead wires, but hung onto the cab handle as he hit the ground. Blew off his hand and both feet but amazingly he survived.

 

[Joe11688]

I think we're just splitting hairs on this topic. Most sailors are only interested in finding out the best way to protect their boat and their lives during lightning storms. Myself, I'm not going to worry about it. I won't be out there this year because of health issues.