built in lightning protector in a new wooden mast construction

[Cecil Borel]

I am building a wooden mast for my Mark Smaalders Kahuna 32. The mast is a hollow "box" construction, and I plan to run conduit up the mast to wires for mast head light and antenae.

I would like to add lightning protection to the boat.

Would it be good to run some sort of conductor up the inside of the mast? The conductor would be grounded to the bronze bolts-lead keel.

How about using copper pipe as the conduit,and ground it to the keel?

Any thoughts, references, opinions would be helpful.

[Woxbox]

I suspect that somewhere in this extensive site you'll find some relevant information. It sounds like a good idea in some respects, the weight of the copper maybe being the worst part. And then the internal lines will almost certainly get fried if you do get a hit unless you go to some lengths to isolate them from the pipe.

[seo]

That sounds like a good idea.
Here are some links and quotes from the all-time bestselling page-turner "National Fire Protective Association "NFPA 780 Standard for the Installation of Lightning Protection Systems 2004 Edition"
which can be accessed through this link:
http://www.atmo.arizona.edu/students...A_780_2004.pdf
Chapter eight, "Protection of Watercraft," includes these standards:
8.2.2.2 The use of conducting materials that are part of the structure of the watercraft, such as
aluminum, shall be permitted.
8.2.2.3 All copper conductors shall be the grade ordinarily required for commercial electrical work,
which generally is designated as providing 98 percent conductivity where annealed.
8.2.3* Copper Conductors.
8.2.3.1 Copper cable conductors shall be of a diameter not less than 4 AWG for the main down
conductor, not less than 6 AWG for two parallel paths, or 8 AWG for more than two paths (such as
those to shrouds and stay connections on sailboats).
8.2.3.2 The thickness of any copper ribbon or strip (except for grounding plates and strips as discussed
in 8.5.4) shall be not less than 20 AWG.

8.3.4 Nonmetallic Masts. A nonmetallic mast not within the zone of protection of a strike termination
device shall be provided with an air terminal as described in Section 4.6.
8.3.4.1 The air terminal shall extend a minimum of 152 mm (6 in.) above the mast.
8.3.4.2 The air terminal shall be provided with a copper conductor or strip securely fastened to the
mast.
8.3.4.3 The down conductor shall have a conductivity equivalent to a 4 AWG copper conductor.
8.3.4.4 A grounding system meeting the requirements of Section 8.5 also shall be provided.
8.3.5 Radio Antennas. A solid metal vertical radio antenna shall be permitted to serve as a strike
termination device for small nonmetallic watercraft, provided a provision is made to ground the metal
antenna with a conductor equivalent to a 4 AWG copper conductor.

8.3.5.1 The conductor shall be routed vertically to the maximum extent practical (minimizing bends,
etc.) to the lightning grounding plate, the lightning grounding strip under the watercraft, or to an
equalization bus.

8.4.4.1 An interconnecting conductor, equivalent to 8 AWG copper conductor, shall be provided at all
locations where sideflashes are likely to occur.

8.4.6.1 Shrouds and stays shall be permitted as part of the path to ground from the mast (strike
termination device) to the lightning grounding plate or strip.

8.6.2* Seacocks and Through-Hull Fittings. Seacocks and through-hull fittings shall not be
connected to the main down conductor but shall be permitted to be connected to the underwater
grounding strip, the lightning grounding plate, or the equalization bus.
8.6.3 Metal Masses. Metal masses such as engines, generators, metallic tanks, steering systems
located inside the vessel, and metal life rails shall be connected to the lightning grounding plate,
grounding strip, or equalization bus as directly as possible.
8.6.4 Engine Grounding. To minimize the flow of the lightning discharge currents through the engine
bearings, the engine block shall be permitted to be grounded directly to the lightning grounding plate
or lightning grounding strip rather than to an intermediate point in the system.

8.7.1.1.5 Metallic keels or centerboards shall be connected directly to the lightning grounding plate or
strip or shall be permitted to serve as the lightning grounding means if they provide the 0.09 m2 (1 ft2)
area required to be in contact with the water.
8.7.1.1.6 If a centerboard is used as the lightning grounding means, a warning sign shall be provided
that clearly states that the centerboard shall be in the down position in order to function as a lightning
ground.
8.7.1.2 Cruising Sailboats.
8.7.1.2.1 All shrouds, stays, sail tracks, and metallic masts shall be connected to the lightning
grounding system, since it is assumed that occupants of the boat will be in proximity of forestays,
backstays, and shrouds during the operation of the boat.
8.7.1.2.2 Grounding of all metallic masses on the boat shall be in accordance with all applicable
sections of this standard.

And there's more!!!

My general comment is that NFPA rules for everything from NFPA 1 life safety in schools and public buildings to NFPA 302, small commercial vessels, to this one are the basis for ABYC, USCG, American Bureau of Ships, and most local and state fire codes. The committees that draft the rules are guys who really do know their stuff. I'm often amazed by the witless opinions, based on no training, education, or apparently any rational thought, that are stated as fact in magazines and on the internet.

Assuming that you're going to use an external metal sail track, you could use that as one of the two down conductors, and use a 6 AWG wire inside the mast. Otherwise (gaff rig), I'd use a single #4AWG.
Personally, I would use the bare copper stranded conductor. The code does allow use of copper strip, but I don't see anything about tube. Would it work? dunno. I think I'd be inclined to run my mast wiring through a plastic conduit.
Where I WOULD use copper tube (or solid bronze rod) is at the upper "air terminal" otherwise known as the lightning rod. If this sticks straight out of the top of the mast it can be used to mount a wind telltale, or maybe a flag halyard.
At the lower end, I'd certainly go straight to a keel bolt, but I wouldn't clamp it under a keel bolt nut. Instead I'd drill and tap into the top of one bolt (hopefully one that's standing an inch or so above the keel) and connect the down cable to the keel bolt with a terminal fitting attached by a bolt in the tapped hole in the top of the bolt. This keeps the connection out of the bilge water and salt, and promotes a better connection.
I'd use the same attaching point to connect #8 AWG copper wires running along the hull to connect to the chain plates. If they're inside mounted, attach right to the plate. If they're outside, go to one of the nuts on the through-plank bolts that attach the chainplates.
If you have deadeyes and lanyards you'll have to rig jumper cables to connect the shrouds to the chainplates.
At the top of the shrouds, it would be good if the mounting tang attaching bolts made a good connection to the internal down conductor.
The backstay is sort of a problem, because it requires a long horizontal lead to get to a ballast keel bolt. On my boat, which has a backstay and an overhanging counter stern, I have a jumper cable that goes from the backstay to the rudder shaft, which is solid bronze, and sits in a cast bronze foot bearing. I have thought about putting a 1 square foot copper ground plate below the waterline aft, so that the cockpit winches, backstay, and steering gear could be connected to it, but have not done that.
Hope this is helpful.
One final comment. I once rebuilt the hollow rectangular mast of an H28 ketch, and while I had the mast apart I took some heavy aluminum foil, coated it with plastic spray, and put it inside the top ten feet of the mast. The foil was intentionally folded and crumpled a bit. This made my boat really light up on other boats' radar sets. Even brighter than an aluminum mast, I guess because of the irregular shape of the foil.

[Ian McColgin]

I don't like the idea of direecting the flow inside the mast as the heat build-up in a confined structure like that is likely to cause damaging air compression. AKA blow up the mast. Aluminum masts are themselves terrific carriers and, rather like a gauss cage, protect what's inside.

I've seen masts that use the heavy bronze of the sail track carried down below the gooseneck by either cable or flat strap. It seems that you'd run the risk of ignighting the sail along the luff, but I've no reports of such. I just don't know. On Goblin, the stays and chainplates were bonded to the keel so they made an effective gauss cage anyway. On Marmalade, the nearly verticle head stay is bonded to a bow strap down and under to a steel shoe over the whole bottom.

Lightening protection is interesting in that there's a lot of vigorously asserted dogma which later tests show was wrong but is still advocated.

Add to that that almost anything works at least once and nothing works all the time.

G'luck

[seo]

Ian,
I don't think that a very high voltage current creates much heat when flowing through a low resistance conductor like a copper grounding cable. Which is, I guess, why current running through a sail track doesn't ignite the sails.

[paladin]

Bad idea......Ian's on the right track. I assume you will use standing rigging of some sort. Tie all the stays together at the top of the mast with a short piece of flexible SS cable and let the rigging carry it to the chainplates, and then tie all the chainplates together inside the hull to the keel bolts if you so like. You still run the risk of blowing a hole in the boat. Without getting into a long detailed discussion there's enough energy in a lightning bolt to light up a small town for a week or three and a few bolts and a lead keel ain't agonna be much deterrant.

[seo]

In 1973 I was working for a newspaper, and did an interview with a professor of Electrical Engineering at the University of Minnesota who had a grant from some federal agency (NACA? NASA? don't remember) to study the effects of lighting strikes on aircraft. In his lab he had: A military surplus WW2 B25 bomber, for a target. Something similar to a Tesla coil for generating lightning. He also had access to all of the government's records on aircraft lightning strikes, which included about thirty feet of bookshelf full of incident investigation reports.
From this interview I learned a couple of interesting things:
1) He had been doing research in the field of lightning strike for almost twenty years.
2) Doing research for NFPA was very productive, because they are in large part an insurance-industry supported group, and can get access to the companies' records. Insurance companies know when buildings and vessels get hit by lightning because they get the damage claims, and the investigation reports from surveyors and adjusters.
3) Lightning kills a lot of people and livestock.
4) If you're in a house during a lightning storm, close the windows. Glass is a very good insulator, and lightning generally won't penetrate a single pane of glass, even though there's a great deal of energy in a lightning strike. But lightning might come in through an open window on its way to a path to ground, which might be the copper plumbing in your house. And if you're touching a faucet at that moment, the lightning might pass through you, because your salty-liquid body is a better conductor than air. If that happens you might be unscathed, injured, or blown to smithereens.

To get some idea of the amount of research being done on lightning, I'd suggest googling "lightning research university of minnesota." or Florida, MIT, Michigan, CalTech, etc.
This website:
http://www.jasperthompsonlightning.com/industrial.htm
belongs to a company based in Minnesota that I used to go by on my way to high school. They're a well-established company in terrestial lightning protection, and their homepage includes brief articles on "lightning facts" and "lightning science" that are informative.


The main point that I took away was that lightning was going to get to ground, and at each moment along its path to ground it would change course to pass through an area of lower resistance. Think of water trying to flow downhill. It will follow the path of least resistance, even if that results in a zig-zag course. The difference being that "downhill" is a pretty easy concept to grasp, and water flows slowly enough so that anyone (even Bob Dylan) can "just sit down on this bank of sand and watch the river flow." Lightning, on the other hand, moves very fast, and responds to changes in resistance, not elevation.

The following material comes from this website:
http://metals.about.com/gi/dynamic/o...fMaterials.php

The table below shows the electrical conductivity of materials as a percentage of the conductivity of copper. Below that is a quote that comments on the differences.
Silver 105%
Copper 100%
Gold 70%
Aluminum 61%
Nickel 22 %
Zinc 27%
Brass 28%
Iron 17%
Tin 15%
Phosphor Bronze 15%
Lead 7%
Nickel Alum. Bronze 7%
Steel 3 to 15%
"Perhaps the most interesting fact revealed by this chart is how low most copper alloy materials rank in relative conductivity. One might easily assume that alloys such as the brasses and bronzes, because they are mainly copper, are nearly as conductive as copper. This is not the case. The small percentages of tin, aluminum, nickel, zinc and phosphorus that make up these alloys degrade the electrical performance of the resulting alloy to a far greater percentage than their compositional percentage in the alloy."

This chart explains the weakness I can see with the common practice of using shrouds and stays as ground conductors. Stainless steel (with a chromium content of 12-20%, nickel content of 14-18%) is only 8-12% as conductive as copper. In addition, you have lots of connectors where you can have an area of corrosion and high resistance, which can cause a side flash as a charge of lightning suddenly decides that the path of least resistance isn't going down the jumper wire inside the hull that leads from the bottom of the chain plates to the ground bolt. Instead, it might leap across the cabin to a bronze centerboard trunk, or a copper fuel tank.
For that reason, I think that using a single continuous copper conductor going straight from the lightning rod at the top to the ground at the bottom is the best approach. Would it be better to drill a hole out through the hull? Maybe down through the ballast keel below the mast step, with a solid copper bolt that would clamp to the conductor at the top end, and to a copper ground plate outside the hull? Maybe.

As noted in post #3 above, I would connect the shroud-mounting tangs on the mast to the copper conductor, and install the jumpers from chain plates to grounding bolt. I don't know if there's a problem with the copper wire being inside the hollow mast. Would a lightning strike cause the copper wire to heat up like the heating element in a toaster, boiling the moisture vapor in the air inside the mast so that it causes a steam explosion that blows the mast apart? That seems improbable, but I'm not an expert. I do remember going to the Boston Science Museum, which has a really remarkable exhibit in their "Theater of Electricity." They have Tesla coils and an enormous Van de Graaf generator (must be fifty feet high). Here are some pictures from that:
http://www.mos.org/sln/toe/cage.html
Directly after that display, which is the finale in their show, not more than a minute later, my son and I went up and talked to the operator while he was still inside the cage. The metal of the cage wasn't hot. My son, who was a rather impressionable fifth grader, is now majoring in Physics.

I think the trick to avoiding heat is to use a good conductor, which means big enough, and made of the right material (copper). The thing that would argue most strongly in my mind against the risk of a steam explosion is that the air inside the mast ought to be at ambient humidity, maybe even a little lower. Even on a foggy rainy day, when arc-welding right inside the open door of my shop, I don't see any indication of steam being formed out of the air. In fact, I think that's kind of unlikely from a physics point of view because the water entrained in the air is in the vapor state already. Heating it won't turn it into vapor, with the attendant expansion because it already is vapor.
Contrast that to when I drop a red-hot steel workpiece into a water bucket outside my shop. Now THERE you see some serious steam generation. If you dropped a lid on the bucket, the generated steam would push it right off. If you dogged the lid down, something would give, possibly explosively.
So, if your mast has water inside it, you might have a steam explosion. Otherwise, IF the ground wire got hot the air would expand somewhat, the way air does when you heat it.
I hope that makes sense. I'm not the physics guy in the family, and he has fled to northern climes and foreign lands.

In any event, I don't think that lightning protection is either: a) a black art or b) particularly susceptible to seat-of-the-pants innovation. The incidence of lightning strike is pretty rare, somewhat random, and the "forensic" evidence left in the aftermath of a strike suggest the ineluctable power of a a vengeful god more than the working of a natural system.

[Woxbox]

I will disagree that strikes on boats are rare - at least in areas with frequent thunderstorm activity. I know our boat has been hit twice, and probably three times. The arrestor was burned right off after the last strike. But no other damage was done. The incidence of strikes on boats in south Florida, thunderstorm capital of the world, is very high. But most don't result in sinkings or fires or even destroyed electric systems. The main thing the studies show is that it is very unpredictable, but that boats protected properly always fare better and may not be damaged at all.

[mike hanyi]

I seen it done on a S&S design from the mid 70's on a wooden mast, but the cable size was massive like 3/4" and added a hell of a lot of weight.
If Olin designed it in, it cant be bad thinking, but the cost is the weight

[seo]

This from the NFPA rules
8.2.3.1 Copper cable conductors shall be of a diameter not less than 4 AWG for the main down
conductor, not less than 6 AWG for two parallel paths, or 8 AWG for more than two paths (such as
those to shrouds and stay connections on sailboats).
#4 AWG bare copper ground wire is available from these guys
http://www.gacopper.com/CopperWire.html
at $1.35/ft for cut lengths
shown as weighting 126 Lbs/1000', which works out to .126 lbs/foot. So 50 feet of it would weight 6.3 Lbs. The diameter is shown as being .201 inches.
It would be interesting to see the plans for the boat mentioned in #9 above. From what I know of it, Olin Stephens himself was not deeply involved in things like designing the systems on cruising boats. Rod Stephens was more involved in rigging and construction. I would hazard the guess that if this mast had a very heavy ground wire in it that this was the owner's idead.
The weight of double zero or 2/0 cable is .4 Lbs/foot, diameter is about half and inch (depending on insulation). This is very heavy cable, usually seen only in the battery cables leads of boats with big engines.

[Cecil Borel]

Great replies and discussion! Thanks vey much. I had been planning to use spectra dyneema for standing rigging, so I may have to run some kind of conductor down the rigging to the chainplate. I was posing my question now because I have to close up the mast soon and anything not inside once it is closed will have to find another path!

Thanks again

[seo]

Oh, no.
I am not familiar with the electrical properties of Spectra. I'd used it in towing, where a Spectra barge bridle can be handled by one guy, easily, as opposed to two guys and a powered capstan to handle a steel cable bridle.
BUT. I think I know that spectra has very different conductivity properties from steel, and that there may have been some rig failures to do with that and lightning. It's not a field I know about.
My suggestion would be that you find someone who's really knowledgeble about this BEFORE you close the mast up. There's an intuitive logical guess as to the right approach, but I wouldn't hang my own hat on that, and so won't express it. Good luck, and please let me/us know what you come up with. This is new technology, and the store of knowledge is evolving very quickly.

[seo]

Woxbox:
You're right that lightning strikes aren't rare. I've read that earth is struck by lightning something like 100,000 times per minute. Or is it second? Anyway.
I guess what I meant is that it's rare enough that an individual boat owner won't learn a lot from their own experience with lightning strikes because a) it doesn't happen very often, and b) it's not easily susceptible to intuitive understanding.

For example, I know what to do when I capsize a Laser, because I've done it so many times. And I know what to do if someone falls overboard, because I've been trained, and done the drills, and have trained other people.

Even though I've been on board a ship, underway, when it was struck by lightning, I can't say I learned much from the event. Given the fact that at the time we were blowing tanks that had last carried gasoline, so that the decks were flooded with gasoline vapor, the main thing I learned was that God was on somebody's side that day.

Which doesn't mean that I think the only way of dealing with lightning threat is fingering your St. Christopher medal.

However,
I'm very curious about your comment that the "arrester was burned off." What kind of arrester, and where was it, and any other details you can think of would be very interesting.

[Woxbox]

We had one of those standard bottle-brush type arresters bolted to an aluminum bracket on the masthead. There was also a radio antenna and a standard nav/anchor light up there.

If I recall the series of events correctly, the first sign of a strike was that the arrester was crooked and scorched looking one day and the plastic lenses in the light were just plain gone. No sign of them. But nothing else was amiss. The bulbs even worked.

The second sign of a strike -- a full year or so later -- was that the arrester was totally gone. When a mate went up to try to unbolt the stub to put in new one, he found it was basically a welded mess that wasn't going to come loose. It had been inspected between the two events and seemed to be solid and functional despite it's appearance.

In both of those instances, the boat was tied up at the dock and no one was on board.

In the maybe instance, I was on board anchored behind Plantation Key in Florida. A fairly intense storm passed over with frequent strikes in all directions. Then one hit that sounded totally different from the rest. It was from all sides at once, and a single "whap" -- no echo or resonance in it at all. I took this to be a direct strike on the mast. There were no other boats in the vicinity. But no sign of damage. I didn't see it -- I was cowering below in my bunk, keeping a healthy distance from all things metallic.

That's all I know of it. Beyond that it's all conjecture.

[seo]

Was it a wooden mast?
Was the arrester connected to a ground system?

[Woxbox]

Aluminum mast. This is a 35' production catamaran. The owner's manual doesn't detail the ground system and I haven't traced it out. As best as I can figure, the two saildrives are used as grounds. There's no metal in the keels, of course, and no separate ground plate. The mast seems to take the electric load, since there's no indication of grounds to the chainplates.

[bertho]

Hi guys,
nice interresting thread..!
I have on my new boat not only dyneema standing rigging, but also two 55 ft stick of carbon on her ! ... and still wondering what to do about lightning protection.. to many input for my small computer !
I'm sailing on equator level +-10 deg, and I pass already through some crazy tunderstorm where lightning was like on a nightclub a saturday night !,, just make me scarry but nothing happen so far..
seriously what to do ??
mast for the time being is almost isolated from the ground..how connecting what where ?? or doing nothing !
best regards
Bertho

[seo]

Catalina, the big California manufacturer, does not install lightning ground systems, but then in the owner's manual they reprint the NFPA pages on lightning grounding. I guess their lawyers tell them that they're better off if they put it on the owners to install their own systems. Kind of strange.
Regarding spectra line, I haven't seen any information about its conductivity. For carbon fiber (CF) masts, they are more or less conductive, depending on how they're built. I have read about them suffering complete failure upon being hit by lightning. I do not know what the current state of the art is for these rigs. I would not be surprised to find that it is equal parts of legalese and engineering mumbo jumbo.
When dealing with any object that sticks up high in the air (sailboat mast), my thought is that it's safer with a straight, low resistance path to ground built in. Copper lightning rod at the top, copper 4 AWG cable runnning straight down to a 1 square foot copper ground plate. But I might be very wrong.
The basis of my thinking is that any material is somewhat conductive, particularly when wet, as things often get during thunderstorms. Given the almost infinite amount of voltage in a lightning strike, it is logical (to me, at least) that any mast that's more conductive than the ambient air surrounding the mast will become the preferred path to ground of a lighting strike. Once the lightning has entered the mast, it seems logical that you have two problems: 1) side flashes to more conductive parts of the boat, and 2) failure because the resistance is high in the conducting mast, and it becomes a resistance heater. Based on that, it makes sense to follow the conventional rules and provide a low-resistance path to ground, on the idea that this will be likely to prevent: a) side flashes and b) Your mast exploding.
Let me say that this is ONLY an exercise in logic. I DO NOT KNOW what the current state of the art it. I assume that somebody, somwhere has researched it to some extent, but don't know who, or where their conclusions are published.

[Woxbox]

One extensive study of sailboats in particular found that the probability of a strike is not affected by the presence of good grounding. But boats that have protection suffer far less damage, if any at all, than do boats with no protection. Even if you just clip a jumper cable onto a chainplate and toss the other end overboard, that's better than nothing. (And I have seen that done.)

[seo]

Well, that comment above was pretty lightweight. Here's what I've come up with in the last little while:
This weblink is to a company that makes CF masts:
http://www.gmtcomposites.com/files/C...AINTENANCE.pdf
The final maintenance item they mention is: "Check the lightning protection system to insure adequate path to ground."

This link is to a Florida company in the business of installing marine lightning protection. There articles contain what sounds like a certain amount of technobabble, but it IS a technical subject. They also develop, market, and install proprietary lightning protection devices, so their commentary isn't completely arms-length. But it seems pretty credible.

This is the link to another company in the business:
http://www.strikeshield.com/faqs/str...-technical-faq
In their comments there's the following on CF masts:
"Q: Will the Strikeshield work on a carbon fiber mast?
A: The Strikeshield CSS system can work on a carbon fiber mast, however, the system requires the installation of a high capacity copper conductor inside the carbon fiber mast to connect the air terminal to the contact plate at the base of the mast. SEYLA Marine will specify and build the necessary components for such an installation.

Q: What would happen to the carbon fiber mast if it did not have this copper conductor?
A: When you run a large electrical current through a resistive material like carbon fiber it will cause heat to be generated because of the electrical resistance in the material. Sort of the same thing as what happens when you turn on a stove element. The immediate heat generated can cause the de-lamination of the carbon fiber sandwich or cause the humidity contained in the binding resins (epoxy) to heat up and explode."

Q:Should the sailboat be bonded?
A" ABYC and other such entities recommend that stanchions, chain plates, and large metal equipment such as stainless water tanks be bonded to the lightning ground. Decisions to bond or not to bond and what to bond are largely personal decisions. We do not subscribe to the grounding of chain plates through-hulls or the bonding of any metal object on the sailboat to the lightning grounding circuit. If you are interested in this subject, we strongly recommend reading:
"The marine electrical and electronics bible" by John C. Payne.

So, it's difference of opinion that makes a fistfight. Or something like that....

I've sent an email to one of the companies cited here, asking about special considerations for spectra standing rigging, and if there's a response I'll put it at this thread.


http://www.marinelightning.com/Infor...ndingGuide.htm

[seo]

This is the question that I asked, and the response from Ewen Thomson, PhD, the president of:
marinelightning.com
Hello,
Do you have any information on how the use of spectra shrouds and stays would effect the design of a lightning protection system on a sailboat?
Thanks very much.
SEO
Hello SEO
Spectra and Dyneema are very poor electrical conductors. That is until they get wet or absorb moisture from a salty atmosphere when their conductivity may become high enough for them to become attractive to a lightning strike. This (the risk of a lightning attachment) is really only a concern for a tall rig (height > ~ 100'). Since to my knowledge no experiments have been conducted on the effects of spark or lightning attachment to wet non-conducting fibers, the consequence is unknown: it could be a catastrophic destruction of the fiber or it could be a relatively benign surface flash phenomenon similar to that observed over water . In either event, the design of a lightning protection system is the same, with an air terminal at the masthead, a main-sized conductor down the mast, a conducting grid of conductors external to the hull, and multiple grounding terminals around the waterline. See NFPA780-2011 for details and an article I wrote for Exchange for the explanations.


I just got finished reading the article, here:

http://www.marinelightning.com/EXCHANGEOct2007Final.pdf

I don't have the expertise to pass judgement on Thomson's article, but it is clear, concise, and comprehensible. I recommend it to anyone interested in this question.

[bertho]

Seo
thanks for the link, very interresting pragmatic view, but still don't give the ..light ! , it's sure a carbon mast is a mixt between carbon fiber, and thermoplastic resin, as epoxy, if you execed some temp, you will "unglue" and definitvely ruin the composite !
Have my fore stay in inox..will ground this one by outside bronze protection directly to the water.. will be one already..
rgds
bertho

[Phil Y]

My mizzen (50'ketch) has a strip of flat copper, about 20mm by 5mm, inside the mast, down to a keel bolt.
Phil

[seo]

My mizzen (50'ketch) has a strip of flat copper, about 20mm by 5mm, inside the mast, down to a keel bolt.
Phil

Your ballast keel runs all the way aft under your mizzen? That a long hunk o' ballast...
In the NFPA rules above there's mention of flat copper as being an acceptable conductor.

[Phil Y]

No-Balia has twin keels, so the central keel timber is just that. To be honest I'm not sure what mechanism actually conducts the charge into the water, as she is sheathed (from new) and there is no obvious copper plate or the like on the outside.

[seo]

Cool boat! Where do you sail with her? Who designed/built/owned her?
It might be a good idea to check the electrical continuity/resitance between the ground strap at the mast and the hull sheathing. It might be a reasonable guess that the builder used the sheathing as the ground plate, and over the years corrosion might have worked it's way in there.
which gets to a part of the article by E. Thomson in #21, where he refers to "air gaps" in grounding circuits as a way (I think) of providing ground bonding to things like through hull fittings, while not contributing to galvanic corrosion. I think the idea is that if there's a narrow gap between (say, for example) the ground cable and a through hull fitting, then in all normal service there'd be no current flow through that circuit. But in a lightning strike, with very high voltage, the current would jump the gap, and current would flow.
That's just as I understand it. Better explanations would be welcome.

[Sailor]

I read an article recently and I know it won't help but I can't remember anything that will help find it, Author title, magazine. It was a powercruising mag though. Talked about lighting protection from a guy who did alot of that. Developed a system as it were. Seems the keel isn't the best place to ground to. Most strikes that do damage tend to blow out the side even with traditional lighting protection. His system seems to involve several square "pads" placed around the hull around the water line rather than down low where we typically see them. I got the mag at the halifax boat show this summer if anyone else was there and read it they may be able to chime in. I think I may have posted in a similar lighting thread once I saw the mag. You might find it in my previous posts search thingy if you look.

[Woxbox]

One interesting phenomena is that if the ground wire runs against the inside of a thin hull on its way down to the keel, the current can take a short cut through the hull to the water instead of making the trip all the way to the keel. I believe this is seen in glass hulls, which have little thickness or insulation to them. Anyhow, the damage is not great - often no more than a small hole is left behind, just enough damage that the boat slowly sinks. Maybe this is why the guy mentioned by Sailor preferred putting the grounds near the waterline?

[seo]

It sounds like the company that I mentioned in #21 above, with a link to an article about that. One of the points he mentions is that as lightning passes through an FRP hull it leaves behind a trail of carbon in the laminate, which is quite low resistance, and will attract side flashes in the future.

[Lucky Luke]

Thank you Soe for looking around the web (and other sources) for us on this worrying matter (at times: VERY worrying!). I know what your name, S.O.E, stands for, now: "Search Engine Optimization" .Saves others a lot of time

I am no expert at all in that and am happy to have never had my boats hit by lightning, but I do not like both the ideas of "attracting" a bolt of lightning, which ALL the "protectors" do, but even less conducting it inside the boat! Alas the fact IS that boats do get hit by lightnings, not too often happily, and that it feels better having some kind of "protection" than none...although I have never got any! All what I have ever done was to disconnect the radio antennas from the radio, and "ground" them through bronze plates (actually an agglomerate of small bronze balls), that were fitted on the hull for this purpose.

The classic bits of chain running from the shrouds and dipped in the water do not seem to be very efficient, referring to expert studies.

In Bertho's case (hi, mate!) his rigging is almost non conductive, at the exception of the forestay. Carbon fiber masts are poor conductors, but example exists of carbon fiber masts that have been "fried". There was a big stick in Port Canto (French Riviera), standing tall above other, that was destroyed by a lightning. I do not know if any kind of "protection" was fitted to this boat...??!?

So, I think that we have to consider two things: do we want to attract lightnings by a system that will divert the bolt down into the water (hopefully) without destructive side flashes, and in this case what is the way to do, or do we want to have minimum chances to get hit by being as isolated as possible?

My idea is that, if our rigging is such that it may be prone to attract lightning anyway, we better have efficient protection but which has to be entirely outside of the boat, and "divert as directly as possible" the bolt to the sea. As steel, and even more stainless steel, are not very good conductors compared to copper, and therefore would no make a "tempting" path for a bolt of lighting, a thick tinned copper wire should be installed running along one or more shrouds, that would be connected to immersed copper plates during storms. In order to have the "attachment" of this copper wire protected against chafing (it is often just a few rounds of tape!!!), it should not run along the top shrouds but along the mast and then to lower shrouds. With an alloy mast, this wire ( pure aluminium wire) could be connected to the mast itself at the level of the lower shrouds too.

With aluminum stick and aluminum hull, there is so much conductive metal there that the boat is already a system by itself. With a steel hull,, the epoxy coating are very efficient insulators and they would behave similar to FRP or wooden boat.

When a boat is in a marina, unless having the tallest stick around, there are usually other things around that would get hit first: buildings, mountains, pylons...., but when alone in a bay, these copper plates could be there permanently, or almost.

At sea however, having copper plates dancing around the boat is not desirable, and a more stable installation would be preferred. Ideally, that would be come copper flat bar(s) fixed to the outside and connected to plates fixed to the hull. If I quite like the idea on a "not too yachtie" wooden boat, it is more difficult for others. So, in these cases, the bolt of lightning could be "temporarily" directed inside the boat, and the conductor(s) used for that purpose (rigged up at sea only) connected to underwater plate(s). Question remains if all metallic fittings leading to the outsides should also be connected to this conductor...??? I feel reluctant, but the specialists may have a different opinion...?

The other option is to offer a bolt of lightning as little as possible for him to want to hit you: no "attractive" path. Ideally this would mean no conductors outside, not even stanchions or deck gear, but this is practically impossible. A wooden mast without metallic sail-track, with only textile standing rigging - or none! - and no antennas or other conductors going up there would have very little chance of being hit and then better has no "protection" system at all...but are we going to design/ build boat with this as a first priority???.

What do more knowledgeable people than I about this subject say?

[Lucky Luke]

Have my fore stay in inox..will ground this one by outside bronze protection directly to the water.. will be one already..

A conductor that could nicely lead a lighting down to the water from your stainless steel forestay would be a bronze bande molle (I do not know what it is in English: that strip of metal that protects the bow) running all the way down to your lead ballast?
Got the feeling that your polyurethane painted masts should be less attractive to a lightning than your forestay connected to the water this way, no?

[floatingkiwi]

What a lightning rod does is form a connection between the earth or sea, and the sky, via your boat, and is continually dissipating the flow of electrons into the air above you, reducing or eliminating a buildup which results in lightning.
If there is no lightning rod, the blast could go from the ballast, across the gap to the chainplates, for example, and blow a hole in your hull and anything else closeby.
Lightning rods do not attract lightning, they pass it slowly and harmlessly.
Prevention is better than cure.

[Lucky Luke]

Lightning doesn't actually strike a boat or anything for that matter. It is a buildup of negative ions, or positive for the human race to understand easier,in the earth or sea that suddenly shoots UP into the positively charged or neutral clouds.
What a lightning rod does is form a connection between the earth or sea, and the sky, via your boat, and is continually dissipating the flow of electrons into the air above you, reducing or eliminating a buildup which results in lightning.
If there is no lightning rod, the blast could go from the ballast, across the gap to the chainplates, for example, and blow a hole in your hull and anything else closeby.
Lightning rods do not attract lightning, they pass it slowly and harmlessly.
Prevention is better than cure.

Seems you only read the first page of the book, Kerry! As I said, I am no expert, but your "pass slowly and harmlessly" is nothing short on a nonsense. Sorry.

Yes, we know that, there is a a path that is created going UP by ions, but then, once this path is created, it is the difference of potential that causes this enormous discharge of energy, and although the "human race" (what are you?) has "decided" that electricity "goes" from positive to negative, it happens to be the other way in fact as far as information is transmitted between electrons, but all in all it does not matter: electricity does not have any significant "direction" but for the magnetic field it creates.

Clouds themselves have various charges, positives or negatives, higher or lower, and lightnings occur not only from surface to sky but in the sky and moreover "above" the clouds. Lightnings an happen without clouds, too, although far less destructive than in a storm.

This "....reducing or eliminating a buildup which results in lightning" is nonsense! It is the charge above that creates a difference of potential and ionized air. After that, it only will take the less resistive path, which ions have built up, but do you think this difference of potential miraculously "dissipates" into the atmosphere "up" through the lightning rod?

You obviously haven't seen how repeatedly a church fitted with a lightning rod and thick copper flat bars DOES attract bolts of lightning (therefore protecting the buildings around), and how the copper get HOT: it looks like it has been flamed!

[floatingkiwi]

There is ongoing debate about the energy around us and different schools of thought on what goes on when these electrical occurences do all kinds of interesting things to objects. Like"foo fighters" and other "St Elmos Fire" explained, ball lightning etc, fail to be described in a concrete manner, there are certain ways to think that may all result in something that works.
Yes, I believe , in some situations that the earth is negatively charged and the buildup can be bled into the air , balancing, or at least lessening, the dangerously extreme opposites that the sky and earth have , due to certain meteorological event.
I too am not a fulminologist , but am intrigued by all such stuff.
I removed to first part of what I wrote , but not before it was read by some, in case it triggered some adverse response.

All great minds were at one time doubted or condemned .Has anyone conclusively explained everything that puzzles.

[seo]

I think that the idea of "not attracting lightning," makes as much sense as the proverbial Ostrich with its head in the sand, or my dear departed father's comment on the subject of seat belts that "if I thought I was going to get in a car crash, I wouldn't drive." Logical in a way, but ultimately dumb. Logical, and smart, is to adopt the point of view that it's not a question of "if", but "when."
Having grown up in an area (farmland Minnesota) where there was lots of lightning, and we the owners of the tallest barn around, I got many opportunities to watch lightning strike things. Trees, barbed wire fences, a horse (which exploded) a next door neighbor (who didn't explode, but had headaches for years afterwards.) And I once actually saw lightning hit the lightning rod on the roof of the barn.
Around the water, I've been on board a ship when it got struck by lightning. The only damage was to the radio operator's low frequency aerial, which hung in a two-hundred foot long swoop from the wheelhouse atop the midships house, aft over the tank deck to terminate on the front of the stack on the aft house. What an exciting moment that was.
Over the years I've installed a half-dozen lightning systems, either on new-builds or retrofits, and often felt that I was flying blind more than I liked. So I've read about it some. Which doesn't make me an expert, and I'm not sure even qualifies me to have an opinion.
I do know, however, that in the forty-some years that I've been reading about lightning that the current of thought on the THEORY of lightning has shifted back and forth. I remember when the most latest new knowledge was that lightning struck UP from the earth, not DOWN from the sky. I don't think the scientists think that anymore, but maybe some do. But from what little I know, the empirical knowledge of how to protect against lightning damage has been pretty consistent.
A while ago I read an article written by a sailor who had sailed all the seven seas, there and back and beyond, yar, me hearties, and one day while becalmed in the Bay of Bengal (or somewhere equally romantic) he was beset by tempests, lightning, thunder, waterspouts, etc. Probably mermaids worked their way in by the end, but along the way he was near-paralyzed with panic at the prospect of being struck by lightning, and suddenly (moment of epiphany here) realized that it was CRAZY to have a lightning ground on his mast, and so he laid hold of his cable cutters, tumbled on deck and cut the treacherous cables away. And his brave barkie WAS NOT HIT BY LIGHTNING. Which proved his point. To himself, anyway.

[floatingkiwi]

You say,"So I've read about it some. Which doesn't make me an expert, and I'm not sure even qualifies me to have an opinion. " Yet your pages of information you furnish here would,( although very modest and an enjoyable read), indicate otherwise, in my opinion.
And you claim that someone with a positive opinion on a matter you say you are not an expert in the field of," makes as much sense as the proverbial Ostrich with its head in the sand", and you find it," Logical in a way, but ultimately dumb. Logical, and smart, is to adopt the point of view that it's not a question of "if", but "when."
I believe that if there is a possible means of prevention to a potential problem that makes sense to me, I am not going to condemn it but accept it as something seriously worth considering. If some other dude before my time has gone to great lengths to compile what he believes may help someone in the future, I think he deserves the right to at least be heard, as everyone with a brain in their swede that is capable of rational thought and educational guess is entitled to an opinion.
I do agree with, not if but be certainly prepared for when, approach.
At the end of the day, I think we at least agree on the same "fix", on this matter, which is ultimately what is important here, yes?
And another thing. Does anyone here really believe that the immeasureable amount of power that is passed from one medium to another in the form of a lightning bolt, can actually pass through a little wire and a strap of copper without much more than melting it? I find that unbelieveable. It defies physical realism. As far as I am concerned, there is more here than meets the eye. Like Woxs burned bottlebrush and the tips of cows horns glowing blue, along with the countless accounts of hovering globes of light dancing about the rigging and on it goes.I don't trust my eyes alone to comprehend the forces at play on our magical planet, the planet that we know so much of, yet so much more we do not. Sometimes if we close our eyes and our mouths, the smell can be deafening.

[Phil Y]

Seo she was designed by Arthur Robb, sister ship to Bluebird of Thorne. I keep her in Tasmania, Australia.
Phil

[floatingkiwi]

Here is something on your bottle brush dissapator woxbox.

[seo]

I apologize if the "Ostrich with head i sand" comment wasn't polite. What I was thinking about was that ignoring a hazard did not make it go away, and that ultimately every vessel will be in that point on the globe where it's the short path to ground for a lightning bolt. Which to me makes it logical to follow best engineering practice in terms of leading the bolt to ground without devestating excursions through the hull shell, or through one of the people on board.

[floatingkiwi]

You actually saw a horse...... aah..... explode? Man that musta been something.

[kbowen]

The incidence of lightning strike is pretty rare, somewhat random, and the "forensic" evidence left in the aftermath of a strike suggest the ineluctable power of a a vengeful god more than the working of a natural system.

Our camp on a freshwater lake in Maine was hit recently when we weren't there and looking around the damage, one could find no comprehensible pattern: around the structure, random nails had the wood blown off from around them but one could see no line of damage between one nail and the next nor any reason one nail was affected and another not. A couple fishing rods on horizontal display on the walls were destroyed with deep burn marks on the wall where they used to be, but again, there was no apparent connection between areas of damage. The house has no electrical system or plumbing, and I don't know if that saved it from burning or caused the damage we saw.

[floatingkiwi]

So as the interest in this dissipating of charge into the atmosphere suggestion of mine, is under rigorous debate with never before seen exchanges of information that would make a library feel inadequate, I thought I might point out that the bottlebrush that Wox had on his mast was indeed, disintegrated through it releasing a buttload of charge into the air, causing heat and possibly some crackling and maybe a bluish globe somewhere, and resulted in the avoidance of an actual bolt of lightning.
That is what I reckon was what went on there, and I am stickin with it.

[Woxbox]

There are two arguments about lightning rods/arresters. One is that they attract lightning, the other is that they dissipate the charge and prevent it. Maybe both can occur, and maybe the two potential effects average each other out. I don't know. But the only study I've ever seen that attempted to figure it out concluded that boats with lightning protection get hit just as often as those without any. But the boats without protection can be sure to see more serious damage. But as Seo says, a person has to be crazy to leave his boat unprotected. I've been on board through any number of thunderstorms, and even knowing that I've got a good ground system, I'm still on tender hooks when the strikes are close by.

[seo]

The bottlebrush things seem to be in use by utility companies to protect their transmission lines. Which suggests that they work.

[Lucky Luke]

I think that the idea of "not attracting lightning," makes as much sense as the proverbial Ostrich with its head in the sand

Maybe...?
Maybe also that, if a boat offers no "obvious" conductor from "up there" to "down there", a lightning will "most likely" hit something else....?!?? I think that maybe valid in a marina, and that surrounding boats with lightning rods high up will get it and you would be safe.
Of course, that looses all validity in the open sea, where that boat will be not only alone but where spray and humidity will have made it conductive, hence most likely to be hit. The thing is that boats, on the average, spend much more time in a marina than in the open sea. That does not mean, however, that I defend this practice but just cite it as the other option taken by some. It is just a fact.

It is also a fact that very few boats would be concerned, most having at least a metallic rigging, or in the case of motorboats multiple antennas and other metallic structures.

So we are back to basic discussion on the best way to protect a boat, as much as possible.

I repeat: I really feel that there is basically something wrong in directing a lightning inside the boat by a conductor running (from the outside) along the mast or other parts of the rigging, and entering through deck to later go out again through hull! Instead, something similar - but more performing - to the old method of having a chain or lengths of chain relating all the chainplates and dipping in the water, this all outside the boat, seems much more satisfying, just that it is impractical at sea and might not prevent frying all the onboard electronics! Then, if the lightning rod itself is a well known thing, if running one or more heavy gauge copper wire down is no problem (inside a wooden mast: I am very reluctant too!), all the problem is the grounding.

As you know, we are building this wooden schooner, with wooden masts, and lightning protection to the last of what we know is better forethought than regretting later not to have given it due consideration.

Questions would then be:
- lightning rod to the main mast or to both?
- one or how many conductors down from the lightning rod(s)?
- conductor in a groove in the mast or running along a shroud?
- If along the mast: how to get to (which?) grounding besides entering the deck?
- If entering the deck, and even if continuing as directly as possible to one (or more?) lead ballast bolts, how to make sure a bolt of lightning will not, "while it is in there", find some side path to some "interesting" engine of tank, plumbing or else....and eventually right through someone?
- In this case too, should all tanks, engine, seacocks, batteries negative terminal, electronics, etc...be all connected and grounded with the lightning conductor to the ballast, all that together?
- If going down along some shroud(s), meaning then to the chainplates (outside planking on this boat), should there be an (external) conductor continuing farther down to the water to some grounding "item"? I would feel inclined to something in this line, for sure!
- Would not, even in this scenario, be the danger of some sideflashes entering the boat through the chainplates bolts, and finding some "interesting" paths inside the boat, just the same as above, and then eventually to the keel bolts in the end, but having perhaps killed someone "on the way"?
- Since all external conductor(s) down to (what sort of?) grounding is not that easy anyway on a sheathed hull where one does not want to do multiple screw holes, and the fact that the through hull chainplates bolts exist anyway - with the danger mentioned here-above - shouldn't it then just enter the hull through these bolts and go down to the ballast?
- should there be a "ring" all round the boat that connect all theses "lightning terminals", including the forestay> bobstay? Could lifelines be used for this purpose or should there be a separate conductor for that purpose? (I have never seen such thing which seems advocated by the experts!).
- etc....etc....

?????????????????????????

[floatingkiwi]

Theoretical protected zone is height of mast , the same distance as the radius of a circle at waterline, around the vessel. Like an inverted cone with a 90 degree point.
Lightning rod should terminate in a sharp point and be 6 inches above anything else.
Aluminum mast is acceptable as main down to ground. A wooden mast needs a 4 AWG in a direct a path as possible to ground. Metal hull is good and an external keel or centreboard will do well. Otherwise a ground plate will need to be fitted.
All fittings should be, obviously, heavy duty, to first class standards with protection from corrosion.
In addition, all parallel paths should have their own seperate 6 AWG from chainplates and any other parallel paths,directly to ground. (as opposed to a grounding strip horizontally , then to ground) . Lightning doesn't like turning corners so directly as possible is the best and this way has the added advantage of running perpendicular to other boat wiring which is generally horizontal.
An external Grounding strip , (instead of grounding plate or hull ,if steel) can also be fitted, below waterline, at all heel angles and above bilgewater and another run inside with the two through fastened. This way the forestay at the fore end the b'stay and engine at the rear and various other grounding cables tied to it around the length of the thing.
To minimize side flashes, any bends if needed, in grounding cables should not form an arc greater than 90 degrees and have a minimum radius of 8 inches.
Additional security , substantial metal objects within 6 feet of any paths to ground , should be tied into the grounding system with 6 AWG.
Metal through hulls are probably better left excluded.
This is what I am doing on my boat anyway. It is a wooden hull and mast with no engine and basic wiring so excuse me if it is not as detailed as other setups may require.
Apart from that, insulate and isolate yourself from any water or metal . Except for a cold beer in an aluminum can.
BTW I thought I had better add that any info here, (other than my opinion and how I see things),
is directly out of Nigel Calders, Boatowners Mechanical and Electrical Manual, How to maintain, repair and improve your Boats essential systems.
Thanks Rick for the recommendation, this is an excellent Bible for any boat and if anybody wants I can photograph the important stuff on lightning protection ,(i.e. specs on grounding plates/ strips etc), as long as it does not encroach on any legal infringement.

[floatingkiwi]

There are two arguments about lightning rods/arresters. One is that they attract lightning, the other is that they dissipate the charge and prevent it. Maybe both can occur, and maybe the two potential effects average each other out. I don't know. But the only study I've ever seen that attempted to figure it out concluded that boats with lightning protection get hit just as often as those without any. But the boats without protection can be sure to see more serious damage. But as Seo says, a person has to be crazy to leave his boat unprotected. I've been on board through any number of thunderstorms, and even knowing that I've got a good ground system, I'm still on tender hooks when the strikes are close by.

I picture it thus. Disregarding the direction in which lightning travels, if one could take a giant cord and plug one end into the earth and the other end into the clouds, a charge buildup could not occur as any opposit charges caused by meteorological activity would instantly be balanced through your cord, right?
Seeing that we cannot carry a thing like this to connect the two mediums, we can make do with the best we can. A clean and direct route through our vessel with highly conductive connection to earth, through a hull or grounding plate at one end , and a pointed, copper, preferrably kept as clean and sharp as possible terminal at the other end.
The better we make this connection between the earth and clouds, the better it will emulate the big cord, and balance charges to a safe level, before they build up to the point where a sudden discharge will occur.
The bottom end is easy as it is in direct contact with earth,(or water), and the top has only air to connect to at the other end. Air, not being a very good conductor , it would make sense to me to have as many fingers of the system, probing it as possible.
The giant cord I could keep tight and small and solid to connect with ground and the top end I would unravel and spread out and seperate every little strand of copper and spread them out and as far reaching as I could to maximise its joining with the swirling and ungrabbable clouds and more importantly, the invisible charges at work amongst them.
That is why I am considering a multi pointed terminal for the top end of my connection to the sky, with the ballast as the other..
An arrestor is a device inserted in the line between the coax and antenna at the antennas base which, with debatable effectiveness, shorts lightning through a normally nonconductive to ground bypassing the coax, or something like that, used usually in powerboats without the height of a mast, using a metal antenna as part of their lightning prtection.

[kbowen]

I tend to be a fatalist on this topic: I have been on Lake Michigan with our 30' aluminum mast poking up as the tallest thing within 10 miles, with waterspounts and lightning all around us and the air glowing green, and have not gotten hit. It defies logic! The Icelander in me puts it all in the hands of Thor, my BA in Physics is useless, and my (age-increasing) ADD can't reconcile the conflicting data: drag some jumper cables in the water off the backstay, and after that, what will be, will be.......

[seo]

Kbowen,
Your problem is quite obviously that you got a BA in physics. If it had been a BS in Physics, things would be very different. Or not...
SEO

[seo]

Lucky Luke:
You might be interested in this lightning ground gizmo.

http://www.strikeshield.com/Lightnin...cts/dissipater

The strikeshield company claims to have expertise with carbon fiber and spectra rigs, and multihulls.

Also, in this article:
http://www.marinelightning.com/EXCHANGEOct2007Final.pdf
the author talks about the idea that the best place to run lightning ground cables is on the outside of the vessel, creating a "cage of protection" around the vessel and its crew. In keeping with your comment wondering whether running a gazillion volts of electricity right through the main cabin was such a great idea.
He also talks about placing the grounding plate at or just above the WL:
Quoting from the article:
Third, the multiple lightning conductors coming down the outside need to be terminated
in multiple grounding terminals, preferably close to the waterline. Distributing the down
conductors and grounding terminals uniformly around the hull promotes current flow
away from the boat. This minimizes voltage differences in the water below the boat and
hence considerably reduces the risk of sideflashes from conducting fittings, even those
that are close to the water.

However this poses several practical problems if the only allowable type of grounding
terminal is a one square foot immersed ground plate or strip. It is difficult enough to
convince someone to bore holes through the hull below the waterline for installing even
one immersed ground plate, let alone many. Doing this would appear to increase the
risk of sinking after a lightning strike rather than decreasing it. In particular, if there has
been any water leakage through these holes a steam-boiler type explosion is distinctly
possible. So, if one is a problem, “multiple” compounds this to the point of infeasibility.
And what about the old requirement that the ground plate should always be immersed?
If a sailboat heels or powerboat comes to a plane the ground plate can become airborne.

So when the new standard mandates multiple grounding electrodes this could cause
serious implementation problems. Note that “grounding electrode” is NFPA’s new term
for a grounding terminal in that it is a conductor through which current is passing at the
interface between the lightning protection system and the grounding medium (water
here). Fortunately, the damage we showed earlier indicates that lightning does not
necessarily share this preference for immersed grounding conductors. In fact, the
corners of water tanks, plumbing fixtures, metallic fittings and anchor chains seem to
work just as well, and frequently much better. The same is true for immersed
conductors such as metallic through hulls and propeller shafts that may have contact
areas much less than one square foot. The waterline is a very popular target for
sideflashes, and multiple exit points is the norm, especially in fresh water.
5
Recognizing that onboard fittings frequently act as inadvertent grounding electrodes, we
have introduced the idea of a supplemental grounding electrode, one that has a contact
area of less than one square foot, including zero. The standard still requires at least one
main grounding conductor with an immersed area of at least one square foot, but now
smaller additional grounding terminals are also allowed. This makes it feasible to install
multiple grounding terminals using existing metallic fittings such as through-hulls,
propeller struts, and rudder posts even those with contact areas less than one square
foot. Alternatively, smaller fittings specifically designed to act as grounding electrodes
can be added, as we have done for John Henry below. Note that ABYC TE-4 also
allows that "Rudders, external ballast keels, or any metallic fitting with at least one
external face can be used for supplemental grounding so long as they meet other
requirements in this bulletin…".

This site shows installation and layout of these "Seidarc" ground terminals.
http://www.marinelightning.com/Siedarc.htm
This makes sense to me, but that doesn't mean it works.