Eb asked me to start a new thread to "show us what you're doing to protect your new toys now" after replacing them due to lightning.
First, let me describe what happened. I was not aboard at the time, so this is reconstructed. My Freedom 30 was tied up in its slip on a Friday in early August in the Chesapeake and there was a typical August thunderstorm, along weith lightning. The marina owner later told me that there was a very close strike, so close his office lit up. The next day, I was aboard and began to notice that nothing electronic worked. (It later turned out that the depth sounder transducer and the electronic compass sensor did survive.) Since we could find no physical evidence of a strike, many folks told me that it was probably due to the electromagnetic pulse from a nearby strike. My son noticed that there was some scorching in the plugs connecting the VHF cable to the antenna cable running up the mast. A new VHF radio didn't work all that well, so I replaced the antenna. I took apart the old VHF and found that there was a very distinct burn mark inside the case where the antenna cable plugged in. So I'm assuming that in fact the strike hit the VHF antenna, traveled down the mast cable and fried everything connected to it in one way or the other. (This doesn't explain the loss of the 120v GFCI, however, or the electronic switch on the bilge pump.)
Sorry, too long an introduction. Ebb, as far as I can tell there's really very little that I can do to protect my new instruments. Everything appears to be grounded properly and I did not have side flashes trying to blow a hole in my hull to get out. From what I've read, and I read a lot, the only reasonably priced device is that sort of wire brush affair that you mount at the masthead, and there's no real consensus that it works. I'm told that real lighning protection probably could be provided at extraordinaily high cost and at a weight penalty that would sink the boat. Even disconnecting everything when you leave the boat doesn't protect you from the electromagnetic pulse. So, for better or worse, I've simply replaced everything and will keep my fingers crossed. I wish I could share an easy solution but there really doesn't appear to be one. I do recommend a good insurance policy.
Al
Thanks Al,
Have to be brief, on the run.
Have heard that the brush is bunk. Might have a hard copy so I look for it.
The extreme method I have to contemplate is a solid bronze plate of a certain dimension with SQUARE edges directly under the mast on the outside of the boat with oversized thru bolts with cable going up both sides of the hull - or the doorway in the case of the Ariel - with both directly connected to the mast. This without any bends or as straight as possible. Something like that.
I don't know if there are ANY PROVEN systems to protect a boat from lightning. Whos's to say that the jolt won't knock out a hole in your boat the same size as the plate? Who's to say?
In the Ariel you'ld have to have the plate on one side of the keel. One plate NOT faired in per specs and you would go slower on one tact. Put another on on the other side and go even slower.
Electronics are supposed to be protected if you unplug them and put them in a metal box.
r i g h t !!
(Did you share the strike with others there? Maybe in a marina you can get struck a second time? Remember on a thread here someone saying (Bill?) that clipping battery cables to the upper shrouds at the chainplates and tossing the ends in the water was as good protection as any.)
Found these, and they seem like interesting reading...
http://www.thomson.ece.ufl.edu/lightning/
http://www.marinelightning.com/
Sorry, forgot to add these.......
http://www.boatsafe.com/nauticalknowhow/lightning.htm
http://www.strikeshield.com/
One thought is that with regard to lighning, there is no an absolute and the rationale for whatever you do should not be thought of as a binary - it works or doesn't work.
The issue is whether whatever you do for lightning protection diminishes the liklihood of a destructive lightning strike. I think it is reasonably well recognized what can maximize the liklihood of a lightning strike - but that does not mean that all lightning will strike that target.
So looking at the opposite case - what decreases the liklihood - there are numerous alternatives - and many are based on black magic. Just because a boat gets hit doesn't mean that such and such doesn't work. It may have diminished the liklihood or the damage.
As for bending the grounding cable, the cable has to be bent. The key is to make the bend with the largest possible radius.
As an idea, I think that boats are often hit because of corrosion in the grounding path. One ohm of resistance at a terminal point in the grounding path can generate a 10,000 volt potential if there are 10,000 amps running through it - and that is not much current for a lightning strike. Another factor is that the resistance of a corroded connection (and even one not badly corroded) can increase significantly as it heats up - possibly even becoming an open connection.
So as you examine your grounding system, look for places where there might be corrosion. Particularly check any connections where a stainless steel and aluminum are joined (such as a screw terminal).
Even though a meter is highly inadequate for this purose, it is still better than nothing in looking for a less than 0 ohm resistance path to water ground.
Great tips!
Don't think ohm putting bronze plates on the keel. no way.
Suppose I wire (what kind?) the four long stays and shrouds at the top of the mast to that blunt pointed rod I read about that extends alone above the mast.
When lightning threatens I clip four denuded battery cables to the wire above the four terminals at deck level and toss them in. What's the ohm in that, I wonder? Cheaper and simple or foolhardy and dumb?
What they say?... a strike is hotter than the surface on the sun? Are there examples of sailboats getting hit and NOTHING happens because skipper got it right? How did they do it? Of course it's not news if the boat's OK - maybe there's a clue in the one right next to yours that didn't fry? :eek:
The tricolor up there is wired in the mast. But if I wait long enough LEDs will come down in price and there will be a very small insignificant unimportant insulated wire the lightning won't be interested in. Right?
I have put a copper plate on the bottom of the boat, just under the locker. My lightning lines are tied to that. There is a plastic heat dissipator pad in the electrical connection on the inside so the heat generated by the current passing through is not dissipated by the fiberglass
Although I have no empirical evidence to prove this, I am reasonably confident that the electrical connection between the masthead fittings and one or all of the shrouds is usually solid. Those connections tend to work thereby wearing off any corrosion build up. Plus the masthead fitting is aluminum, as is the spar, so there wouldn't be electrolysis.
Where the problem can occur is at the foot of the mast and the shrouds - in my opinion. In the Ariel, inside where the grounding cable is tied to the chainplates is where I have seen corrosion, and, in fact, had to replace my connectors because they were eaten away with corrosion. The wires inside the connectors were super green, and many of the strands were broken as I recall. If all six shouds are tied together at each of the six chainplates using the #6 wire, you're probably in good shape.
What I don't like in the Ariel is that the ground wire on my boat was tied to a small screw on the water intake fitting. That seems too small for me - and I fear the fitting would be blown out - although apparently that has never happened.
The wire to use for lightning is #6 stranded copper, with Anchor (non-corrosive) terminal fittings to connect to the chainplates (and the pulpits and the lifeline/stanchion assembly). As for the tricolor, the lightning would probably bypass it totally, preferring the path of the very low resistance of the mast and shrouds.
Battery cables with one end clipped onto the shroud and the other dangling in the water are good - although I have heard the wetted area in the water is not adequate. You're more fortunate in salt water than we are in fresh water because saltwater is more conductive.
As for boats being hit without damage, yes it happens frequently, and it has happened on my Ariel (many years ago). It is called St. Elmo's fire. The stays hum and can even glow (the "fire" in St. Elmo's fire). When that happens, the boat is discharging the cloud precluding a voltage buildup to cause a lightning strike. The old square wooden square riggers had St. Elmo's Fire happen all the time.
Incidentally, I have been reading about Ben Franklin (the book by Isacsson - great book) and his experiments with lightning. In the book it is pointed out that one of Franklin's findingss was that a rounded surface (your tri-color for example) won't dicharge anything. The key to a lightning rod is to have a point - and that goes to how the static dissipators work. They form a plethora of points to discharge any accumulated positive charge so the masthead does not electrically attract the negatively charged clouds.
iee e e! matey.
from Dan's fourth http above we find we can purchase a StrikeShield product that is pretty much an exact up grade from the 'battery cable'.
They have a narrow cuplike head on the water end and a flat plate you strap to the mast with flat nylon. Port and starboard doodahs will cost you an amazing $799. There is nothing in the specs (excuse me!) that suggests what this money gets you. You can buy a single one for about half that: the "Plain Jane" model.
You could no doubt solder up the ends of a couple b. cables to flat curved metal pieces that you nylon tie to the mast base or hose clamp for real tight contact. Maybe the water end could be larger rectangles of copper plate soldered to the cable. Since the ends are relatively small rectangles of the copper plate, might think of sandwiching the cable between two pieces and clamping with machine bolts.
Dan's info above suggests that rigging is a poor conductor because of the 'broken' conductors in the wire, toggles, etc. But I'm not certain why the mast top is any better, since the spike or brush would have to be linked to the mast head, the mast head is probably bedded in aluminum oxide, and then another connecting link to the mast metal itself. Just saying: there seem to be a number of interruptions on the top of the mast.
If you want to neutralize the sailboat's highest point with water-ground, imco the best way would be a single unbroken conductor from the spike above the mast down the mast or the rigging to the water. Don't know what that conductor is, anything less is problematic.
Maybe StrikeShield has saved some boats. Since none of this guarantees the safety of the humans aboard during a thunder storm, the best commercial fix for that could be to get one of those Plain Jane's and strap it to your leg. :D
[continuing self talk here:
Another unanswered point with the battery cable / strikesheild protection method is that it creates a break in the lightning's path to the water. Aluminum oxidizes readily - to get a good connection I guess you'd have to scrape the mast to bright metal before connecting the cables. (?) When aluminum wire was popular it became apparent it caused fires in homes. Often it was the connectors, but sometimes it melted and burned in the insulation. Anyway it is a LINK problem, if not perfect could imco side flash and/or blow out at the fitting on the mast.
That imco is the problem with connecting the mast at the base to the water. Seems to me you are giving 100,000,000 volts the opportunity to toast the mast. And any body close to hand!
I'm pretty convinced that a unbroken run (lamp cord?) from top to bottom is what to look for for protection. Anyone with an opinion?]
Hi Everyone,
We had an electrician check out our wirng/electrical system today because we have recently been re-wiring the entire boat. The elctrician told us that we don't need the ground/bonded wire, the wire that connects to the chainplate from the negative bus. He said we don't need it because we don't have any metal under water and we were wondering if that was for sure true?
Thanks for input!
-Anthony/Bina
Got any thruhulls, seacocks?
How about the rudder post, rudder fastenings, bolts, gudgeon, and rudder shoe?
There is still considerable controversy over bonding all metal parts together on a saltwater boat. Your electrician may be the other camp that believes underwater metal should be isolated from each other because varying potentials might cause galvanic corrosion when wired together.....etc.
Ariels have had bronze corrosion on the ruddershaft in the rudder tube which could be caused by using manganese bronze rod (which is a brass) rather than silicon bronze - where the zinc leeches out because the potential exists in the metal alloy. Wiring pieces together here probably wouldn't help and might make things worse.
Do the SEARCH mode and find out about zincing and where to place zincs - probably your best protection. It would be very good to know what has worked for long time A/C skippers because I have read it is also possible to screw things up by OVER zincing! :eek:
In the most recent issue of Seaworthy, the Boat US Insurance Magazine, under MAILBOAT Letters/ Lightning Protection there is a reprint of a portion of a letter from me, and their response. My letter reads:
On the issue of lightning strikes, your article did not mention the issue of electricqal resistance between a sailboat masthead and the water. For example, there may be excellent conductivity between the hasthead and the chain plates (through the aluminum mast and the stainless steel shrouds), and the keel being well grounded, but a couple ohm resistance in the electrical connection between the chain plates and the grounding cable to the keel could, in the event of a lightning strike, build up tens of thousands of volts across that corroded connector and cause the lightning to jump.
The response of the editors was as follows:
A good point and one that highlights one of the reasons why boatbuilders hesitate to install lightning protection systems. Conductivity in the entire system must be near-perfect and over time, corrosion creeps in around connections, increasing the resistance to a point that lightning protection is no longer effective.
There are a couple other letters there plus the article frm the previous issue for those that are interested.
Perhaps the authority, IMO, on the issue of lightning strikes is a book by Michael V. Huck Jr. "Lightning and Boats - A Manual of Safety and Prevention" published by Seaworthy Publications, Brookfield, Wisconsin. Address is 17125C West Bluemound Rd., Suite 200, Brookfield, WI 53008.
Theis, on the subject of this thread, makes imco a very good clear point here.
I am only a student of the problem. The lightening protection system on my sailboat will never get the constant attention it needs. How would I do it? Go aloft with a meter and a magnifier? It is to me a rather gerried collection of assumptions, anyway. If I am depending on connections of bolts and rigging parts what's the fix to get better connections? Something in a spray can?
The hatch is wide open for a genuine invention to appear on the market, like a single or pair of dependable UNBROKEN runs of cable? from the top to the ground. Perhaps it could be a diy upgrade rather than an obscenely priced doodah. Perhaps it could be weight saving sacrificial aluminium cable that can be renewed easily.
1) The lightning protection system is completely separate from
2) the grounding of a boat's electric system. And I believe
3) the bonding of underwater metals, if you choose to do it, is a separate system as well.
To me that means no sharing of any wires or cables or grounding plates.
If someone could set me straight in very simple english, on this once and for all I'd be grateful. Tho still a curmudgeon. :D
One ohm more of resistance here:
I feel that if at all possible I have to keep the lightning strike outside the inside of the boat. I feel that NO wire runs connected to the strike safety system should exist inside the cabin. I feel the mast base should not be wired to ground thru the interior space. I feel that bolting a bronze plate to the hull that is somehow connected to the rod on top of the mast is asking for trouble. One ohm out might spell disaster. I feel the faraday cage effect should somehow be incorporated into the safety system to ensure as much as we know that no side flashes are possible in the event of a strike. To me that means use the rigging. That means get the strike to ground without impedance. Or as somebody has pointed out, have such a good ground that lightning is uninterested in my little ship.
ebb,
I think you bring up very good points.
In my particular example and I don't believe that the original Pearson wiring was designed for lightning.
My commander is completely stock, with no toilet plumbing or any other through holes except for the drains in the cockpit.
The only thing I have are wires running from the aft chain plates to the negative bus bar. Thus far, I have come up with the following reasons for these wires:
1. They were put in every ariel/Commander and were perhaps necessary on more complex versions of the boat such as internal engines and such. ( For corrosion protection?) But on my stripped-down version, they are completely unnecessary?
2. the wiring was designed to somehow reduce corrosion from the chainplates? perhaps the original designers felt this was important? But it adds a further question, why were only the rear chain plates grounded/bonded? and shouldn't bonding be only required on underwater components, not shrouds and chain plates?
3. This was some sort of attempt at a lightning protection system? But this would not make any sense either because the wires terminate at the negative bus bar which runs to the battery only? Making this a very unlikely scenario.
Are there any other reasons that anyone can think of why these wires would exist? So far I think that number 1 is the most likely reason. and if this is the case it would seem that I could remove these wires.
Any thoughts? Does anyone else's but have the similar wiring configuration? My ground wire was a 10guage green wire.
Capt,
Yep, I got 'em that way on my Ariel, both aft lowers wired in to the system. Don't know if it helps, but doesn't seem to hurt either. HOWEVER, I did used to have a #10 wire connected from the system to my starboard thru hull seacock (bronze). First year in my new marina, and I saw etching on the outer seacock plate when we pulled the boat that winter, so I removed the wire and have had no trouble since. "Hot" marina, I guess, as it went for forty years with no etching. Just for sh*ts and giggles, I also put in a battery disconnect switch each for the motor and the system, and I open both when I leave the boat.
A few years ago, lightning did hit #199 at the dock, but only toasted the radio and fused the "on" switch, which drained my new battery, and I replaced both. No further damage. THAT'S when I put the disconnect switches in.
Carry on...
Dan
Been six years since this thread was posted.
Anybody for a fresh start?
Here is a paper on the subject with some scary diagrams from EM Thomson of the U of Florida - 2010.
google>
SGEB - 17/SG071:Lightning & Sailboats
also see google>
SailboatOwner.com - Strikeshield lightning ground
for a rebuttal.
Maybe some practical feedback is in order?
___________________________________________________________________________________________________
google>
Lightning Protection - Cruisers & Sailing Forums
imco some excellent posts of actual experiences, observations, explanations and consequences of this most dangerous phenomenon.
Most agree there is no way to prevent a hit.
There seems to be no concensus on the best way to minimize damage from a strike - but reading these entries may persuade.
My concern still is:
What is the best and most economic mechanical lightning strike diverter for our specific Ariel/Commander?
Most important: What is the safest procedure a sailor can do to protect himself - and crew - on his boat when there is lightning in the area?
This is a bit of a hot button topic for me because – most of my life – I’ve been dealing with lightning in one way or another. And sometimes I get a little, well, impatient with the folklore surrounding it.
Ever since Ben Franklin invented the lightning rod (his kite experiment wasn’t intended to “discover” electricity) people have been saying: “there ain’t nothin’ folks can do to prevent lightnin’ damage.” In fact, some of the religions of the time preached that: “if it’s God’s will to smite your house with fire from the sky, it’s sinful to interfere!” Ironically, then as well as now, it’s often churches that burn to the ground most frequently from lightning strikes. If you live in the Southeast, take a good look at the roof ridge line of any nearby church. See all those lightning rods? Some are hidden, but ask the curator what that decorative-looking ball in the middle of the church’s spire is for, and (if the pastor isn’t within earshot) he’ll tell you that the ball is made of glass, and that it’s there so if the spire takes a lightning hit the ball will shatter from shock heating, and then that’s his cue to inspect the lightning arrestors and grounding system.
I was a broadcast engineer for many years in Nebraska. We had a five tower array that was on a hilltop, making it the highest object in a 60 mile radius (kinda like being a lonely sailboat out in an ocean of corn). And I’d sit there peering out the window while the towers took hit after hit – sometimes so powerful that the bolt would split into five forks and hit all the towers simultaneously. The transmitter building lit up like the inside of a giant flashbulb, and the metallic smell of ozone filled it for several minutes. Twice the 100 kilovolt-amp transformer, owned by the power company just outside, exploded with a tremendous thud, a shower of blue sparks and green copper plasma – only causing me to shrug and start the diesel generator. And while that energy would leave burn spots on the inside of the transmitter cabinets, all the tiny delicate transistors in that building didn’t suffer any damage at all. Why? In two words: Grounding and Bonding.
There were other times that I’d listen to loud snaps coming from inside the transmitter, while I watched arcs jump across the Johnnyball guywire insulators at the tower, in response to lightning strikes that I could see discharging miles away. It’s called “induced lightning” and it’s caused by the magnetic field created from several million amps being discharged vertically ground-to-sky (the principal direction of a lightning discharge). Anyone familiar with the inner workings of an air core transformer will recognize the effect. The current gets “induced” in any vertical conductive object some distance away… Like an aluminum sailboat mast. It doesn't take a direct hit to cause damage.
One of the things that people noticed after Ben started selling his rods was that buildings with them seldom seemed to use them because the buildings got hit less frequently. A lot of knowledge has been acquired since then, and we know today that a sharp pointed conductive object will dissipate the charge in the air immediately surrounding those rods, delaying or preventing the discharge from selecting exactly that location to finally breakdown the natural insulation of the air. Someone noticed quite a few years ago that barbed wire seemed to protect fence posts from lightning hits because it had lots of really pointy conductive surfaces. Later, someone invented the “brush looking thingy” that concentrated lots of sharp points in one place (http://www.lightningmaster.com/) in order to prevent a strike from occurring. And smart people started putting them at the tops of their sailboat masts.
The next time you’re on an airliner, take a window seat behind the wing and look closely at the training edge of the wing. You’ll see lots of furry looking protrusions about the diameter of a pencil sticking out of the trailing edge (see image). Those are static dischargers, and they’re there to discharge the buildup of electrical charges from playing havoc with the radios. They work on the same principal as those brush looking things people put on top of their masts. Yea, right, companies like Boeing spend umpteen dollars each to put those little suckers on their airplanes ‘cause they’re bunk ;-) You’ll see them on ALL airplanes that are certified to fly on instruments – all the way down to little Cessnas and Pipers - because the FAA requires them to be there (that’s what I was taught in school as part of becoming an instrument-rated commercial pilot). They work. And airplanes in flight don’t even have ground connections!
Technically, by the way, “lightning rods” are properly called “air terminals.” An air terminal performs two duties: 1) Prevent a lightning strike from occurring by discharging the developed difference of electrical potential of the air immediately surrounding it, thus making the area less attractive to a strike and; 2) provide a safer path to ground should a strike still occur. While the task of providing a safe path to ground is obvious and well understood - even though Ben Franklin observed the preventative action of a sharp-pointed object* - many people are still unaware of the preventative capacity of air terminals. A good path to ground isn't necessary to gain the benefits of strike prevention (bonding is still important). In fact, it's impossible in some applications to have any ground at all (like with aircraft in flight).
There is a great deal of assembled knowledge on how to protect boats from lightning in the National Fire Prevention Association (NFPA) standard number 780: http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=780. The NFPA are the same people who write the National Electrical Code, and they know a thing or two about keeping electricity from burning things up. I suggest consulting them first before factoring in all the other folklore.
So what should someone do in cases where they don’t have good lightning protection? 1) Go by the surplus store and buy some steel ammo cans. They’re cheap. Disconnect your radios completely and put them in the ammo cans when you aren’t using them. 2) If you’re caught out without ammo cans, put the radios in anything metal that completely surrounds them. If you have an oven on board, that’s a great location. If you don’t, then carry a roll of aluminum foil for just that contingency. Wrap the completely disconnected radios in foil. If you take a hit, plan on replacing the coax cables running up your mast because they will likely have conductive arc paths burned in them between the center conductor and the outer braid, lowering the breakdown voltage thereafter (that only a "megger (http://wiki.answers.com/Q/What_is_a_megger_test)" - not a low voltage ohm meter - will ever detect). Are your radios acting oddly after that last thunderstorm...? If you don't like the prospect of replacing all your coax, buy a coax switch that shorts your antennas and coax when they aren't in use and has arc protection for when you are using them (or forget to throw the switch at the slip): http://www.hamradio.com/detail.cfm?pid=H0-008459.
I’m currently in the San Francisco area. People don't rightly concern themselves much with lightning here. One could live an entire lifetime here without ever seeing even one of the thunderstorms that I witnessed on a weekly basis during Nebraska summers. In fact, if you really enjoy (or want to avoid) thunderstorms, there’s a map of how frequently lightning strikes occur in the United States: http://www.lightningsafety.noaa.gov/lightning_map.htm. (For real lightning aficionados, there’s no place like Central Africa.)
As for your own personal safety: averaged out over many years (http://www.nws.noaa.gov/om/hazstats.shtml), do you know which single natural phenomenon's death rates ranks right up there with cold weather, tornadoes, hurricanes, floods, earthquakes, and even volcanoes? Until the weather service recently started keeping records on heat related deaths, ranking neck-and-neck as the top killer was lightning. In a fiberglass boat, it isn't practical to seal yourself inside a metal can. There are some advantages to metal-hulled boats…
----
*Franklin wrote: "...upright Rods of Iron, made sharp as a Needle and gilt to prevent Rusting, and from the Foot of those Rods a Wire down the outside of the Building into the Ground;...Would not these pointed Rods probably draw the Electrical Fire silently out of a Cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible Mischief!" Following a series of experiments on Franklin's own house, lightning rods were installed on the Academy of Philadelphia (later the University of Pennsylvania) and the Pennsylvania State House (later Independence Hall) in 1752.
pbryant sir, thanks for your splendid reply!
While waiting to see if anyone else was going to post, couple days ago, up here in Sonoma we had some tall dark cumulus move in overhead and produce some loud claps of thunder.
I'm OK with the fuller brush static dissipater that Forespar sells.
You mount it onto your masthead with a couple screws.
However it can't work unless it is grounded. I'm guessing.
Our masts are deckstepped, so we have to create a path for ground.
Some guys talk about using 'welding wire' to make direct bonding connections.
I imagine that from the stem of this electric wick I'd connect it with welding wire to the two shrouds and the two stays. (What's the galvanic corrosion separation between stainless and copper?) The method of attaching the copper to the shafts of the dissipater and the rod is a problem.
I'd have a sharppointed Benji lighting rod that would also be connected in the same way.
Don't believe you can have one without the other.
At the turnbuckles on deck we have another problem.
I thought that a heavy duty alligator-clip battery cable could be attached to the wire above the turnbuckle and tossed overboard into the water. Backstay, forestay, and upper shrouds.
Aligator clips don't make a good connection.
However the static dissipater and the lightning rod aren't going to work unless there is
FOUR SQUARE FEET OF COPPER somewhere on the hull. Right, we need an absolute ground.
Don't know if it has to be 1/4" thick plate, or foil, or copper paint.
SO, can each of the four battery cables be altered so one square foot of copper is attached to the part in the water. I assume it could be a hollow square cube, or a plate, or some copper water pipe, or even a coil of wire? Would that take the place of 4 squares of copper attacted to the hull?
If any version of this seems feasible, can we talk about it? How to do it?
I know it's all conjecture but, specific to the Ariel/Commander, could this 'portable' system be effective at all?
//www.kp44.org
Peterson Cutter Wedsite
scroll to the bottom of their Welcome page to their great list of articles and links:
Lightning Protection on Sailboats
Hello Ebb,
Excellent questions! Here is a summary of what I've learned over the years. (In two parts due to size limits).
There are two short-but-good sources of information pertaining to lightning protection systems that I suggest reading before making an investment in time and materials:
- Lightning & Sailboats, University of Florida, http://edis.ifas.ufl.edu/pdffiles/SG/SG07100.pdf. A good description of the behavior of lightning and basic design of a lightning protection systems for sailboats. (Free document.)
- NFPA Standard 780, http://www.nfpa.org/catalog/product.asp?pid=78011&order_src=B484. Contains detailed descriptions of recommended wire gauges, fastener types, etc., as well as good advice on technical design details. ($41.50)
A sailboat in seawater having a modest lightning protection system isn’t the worst place to find yourself during a thunderstorm. I once found myself in a metal rowboat in a freshwater lake named “Molnbyggen“ in northern Sweden; while Thor hurled lightning bolts from a rapidly developed thunderstorm directly overhead. I was surprised at how fast a rowboat can go with someone rowing for his life! Later, when I asked if the name of the lake meant anything in English, I was told: “Why, yes. In English it means: ‘the cloud builder’.”
Here are some basic principals I’ve learned over the years:
- You don’t have to achieve perfection to gain some benefits. Any protection is better than none at all. When it comes to lightning protection, many people have a difficult time getting past a feeling of futility. But it’s not an “all or nothing” situation.
At the risk of stating the obvious, the likelihood of sustaining damage from lightning is inversely proportional to the distance of the lightning. More distance = less risk of damage. From a probabilistic standpoint, there’s lots of lightning at a distance, and much less nearby. So, if your lightning protection system is only capable of withstanding distant strikes, you’ve still solved most of the problem.
Since damage to delicate electronics like radios can be caused by a strike far away – while certainly not the ideal configuration - connecting a thin wire to the bottom of your mast and throwing the other end in the water will still dissipate the small induced currents caused by distant strikes that are much more frequently encountered, and it will also allow your mast to neutralize some of the difference of potential (voltage) between the mast top and the surrounding air. A small investment will protect your vessel and its electronics from most lightning hazards.
Cheap and dirty is better than nothing. If you buy an arc welding clamp, several feet of battery cable from which you remove all of the insulation, connect the wire to the clamp, connect the clamp to a shroud line or stay above the turnbuckle, and toss the other end of the wire into the water; you will have some protection from lightning.
Everything else I’ll write here is only a refinement of that design.
- Use flat copper braid or (slightly better) copper strap wherever possible and avoid sharp turns wherever you can. Lightning is made up of mostly very low frequency (VLF) energy, with some minor radio frequency (RF) components spanning the entire radio spectrum into the gigahertz range[FONT="][1][/FONT] (http://www.pearsonariel.org/discussion/#_ftn1). Since lightning behaves like RF energy, the two factors you have to overcome are DC series resistance and RF inductive reactance. RF travels on the surface of conductors because of something called skin effect (http://en.wikipedia.org/wiki/Skin_effect).[FONT="][2][/FONT] (http://www.pearsonariel.org/discussion/#_ftn2) RF travels better on a flat conductor (like copper strap) than on a round conductor (wire) because the surface area (the “skin”) is greater with a flat conductor for a given amount of copper (you get better results for the same investment in copper). A flat conductor or plate also has less effective series inductance because of complicated conditions that would take a long time to explain. Suffice it to say that inductance is bad. The worst possible arrangement for conducting lightning would be a coil of wire. It would appear to lightning as effectively as if it weren’t there at all.
RF sees a sharp 90 degree bend as a quarter turn of an inductor, which detrimentally increases the impedance of the overall lightning protection system. This is why NFPA Standard 780 specifies a minimum radius for bends in conductors.
But referring back to point 1, don’t give up if you can’t use strap or avoid sharp bends.
Also, from a cosmetic standpoint, flat copper strap is usually easier to conceal flush to a surface than is round copper wire. After making sure you have really solid connections, feel free to paint the strap. By the way, if you run your copper bonding strap down the bottom of your bilge (which is a convenient way to interconnect the fore and aft halves of the vessel), don’t paint it. Any water in the bilge will slosh over the copper, and you may find your bilge smells better as a consequence. Copper has long been used to repel sea life from hull surfaces, but it is also a fungicide and bactericide – copper interferes with the metabolism of microbes (https://secure.wikimedia.org/wikipedia/en/wiki/Antimicrobial_properties_of_copper). That’s a long topic by itself.
You want to use pure, electrical grade, copper for all conductors. I’ve never heard of using “welding wire”, but if it isn’t pure copper, avoid it. Since an aluminum mast represents such a massive lightning "downwire" to conduct a strike, I wouldn't fret over it being aluminum instead of copper. Just provide a really good bond at the base of the mast, and it'll do fine. Because of skin effect, it doesn't matter that the mast is hollow. If running a conductor from the mast base isn't convenient, providing a "water terminal" (submerged plate) at your stern, and connecting your backstay to that terminal is actually a good configuration because you can provide a smooth path to the plate that avoids any sharp bends. So far as the electrical properties for conducting lightning are concerned, I wouldn't worry too much about bypassing the turnbuckle, but you may have a mechanical problem after a hit: your turnbuckle may become seized by being welded in place. A clip-on bypass can be used when the boat is unattended and when you anticipate penetrating a storm. Be sure to provide a bonding wire from the plate to the rest of your protection system.
- Use robust bronze clamps or brazed (silver-phosphorous-copper) connections. Do not depend on soldered (tin or lead-tin) connections. Solder melts at a very low temperature and has higher electrical resistance than copper. During a direct or close by lightning strike, most of the electrical heating will be concentrated at the soldered junctions (because of skin effect), and because of solder’s higher resistance, the solder will instantly boil and vaporize. Think of soldered connections as being fuses that “blow” during a lightning strike, opening the electrical connection that carries the lightning when you need those connections most. Lightning strikes consist of several repetitive “strokes” (called “restrikes”), and your soldered connections will vanish after the first stroke in a direct hit. But again, if you have to solder, we’re back to point 1 above. Don’t give up here! You’ll still get some protection.
The preferred materials for fasteners are bronze and stainless steel, in that order.
- Assuming you don’t have an unlimited budget, tailor your investment to the actual risk (do a “risk/benefit analysis”). The west coast of the US is one of the safest places to be with regard to lightning, while the Gulf States and the southeastern Atlantic coast are the most dangerous. NASA recently produced a map based on lightning observations from space: http://earthobservatory.nasa.gov/IOTD/view.php?id=6679. While a more-is-better approach to lightning protection is valid, you can reach a point of diminishing returns where additional money is better spent on other safety items.
[FONT="][1][/FONT] (http://www.pearsonariel.org/discussion/#_ftnref1) NASA,
Review of Measurements of the RF Spectrum of Radiation from Lightning: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19870001225_1987001225.pdf. Ever since Apollo 12 was nearly taken out by a lightning hit during launch, NASA has had a deep interest in lightning phenomena. Some very interesting background info on lightning can be found here: http://thunder.msfc.nasa.gov/primer/.
[FONT="][2][/FONT] (http://www.pearsonariel.org/discussion/#_ftnref2) Skin effect is a very substantial factor. In fact, even at the extremely low frequency of AC power – 60 Hertz – it’s pointless to use a wire thicker than 2/3rds of an inch because none of the current will flow through the center of a conductor that’s any thicker. In RF work, we often use hollow copper tubes instead of wire for conductors because a solid wire would be a waste of copper. If you ever have the opportunity to inspect something conductive that has been only slightly damaged by lightning you will probably notice that its surface is singed but its center is undamaged.
Part two, continued.
5. Bond every potential lightning conductor to a single-point ground. In the radio broadcasting business, we call that point the “common ground.” The old folklore adage that: “electricity takes the path of least resistance,” is just wrong. If it were true, then turning on whatever appliance draws the most current (has the least resistance) in your home would cause all of the electricity to bypass everything else. Then every time you turned on your electric oven in your home – all your lights would go out!
There’s something called Kirkhoff’s Laws (http://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws) that explain the effect in detail, but the short version is: when conductive paths are available, electricity flows through every one of those available paths. The current flow in each path is inversely proportional to the resistance of that path. More resistance = less current.
The reason you want to choose a common point ground is to prevent current from flowing through unexpected and inadequate paths. When that happens, it’s called a “ground loop,” and if you aren’t careful you can have thousands of amps flowing through a thin conductor that will get hot enough to ignite a fire or ruin expensive electronics. In installations lacking a common ground design, it’s not uncommon to see the outer braid (“shield”) of a coax cable become the primary path for a lightning discharge, and the expensive radio at the other end of that cable converted into so much charcoal. And the prospect of a fire at sea ranks at the top of my list of Things to Avoid.
You accomplish a common point ground design by selecting one point, and one point only, to connect all your circuits that should be at ground potential. That’s usually done with a buss bar or One Big Badass Bolt (the negative terminal on your battery is a good choice) connected to the biggest conductor you can afford, which is then connected by the shortest and straightest path possible to your ground plate submerged in the water. Everything metallic that could become a secondary path for lightning (engine, metallic through-hulls, keel bolts/cables, mast, standing rigging, battery (one terminal only please – commonly the negative terminal), etc., is connected by wires radiating from that common point. And if you're tempted not to ground some delicate piece of electronics while thinking: ”but these wires are insulated, so lightning can’t pass into them,” remember that the lightning already passed through several thousand feet of air to reach your vessel. A few millimeters of 600 volt-rated insulation won’t offer any realistic impediment.
Side strikes: When you hear stories like: “Lightning hit the house, and then flew from the fireplace across the living room into the opposite wall,” that’s a “side strike”. If you tore out the drywall, you’d find electrical wiring, a water pipe, or some other conductor directly beneath the point hit by the lightning. Preventing side strikes is another purpose for bonding everything together. A side strike in your boat could produce a hole punched in the hull below the water line, or worse, pass through you.
6. Provide as large a conductive surface area as possible through which to discharge the energy into the water. “More is better,” but the generally accepted bare minimum is 2 square feet.
Please don’t consider using your propeller as the primary discharge surface, and then connect your lightning discharge wire (“downwire”) to the engine. The resistance between your engine and your propeller might measure “zero ohms” at the milliamp of current from a volt-ohm meter, but a lightning strike will cause an enormous current (often tens of thousands of amps) to flow through your engine’s main bearings, frying them.
Copper paint on your hull is great for repelling marine organisms. It is worthless as a lightning conductor. You need nearly pure copper to conduct electricity.
An added side benefit of all this efforts is – your radios will work better in a storm and during very low humidity conditions. Since the time that boats had masts, mariners have observed in darkness a bluish glow occasionally coming from the tops of their masts. They named the effect "Saint Elmo's Fire (https://secure.wikimedia.org/wikipedia/en/wiki/St._Elmo%27s_fire)." The scientific name for the effect is "coronal discharge" and it requires several thousand volts of difference of potential between the boat and the air to generate this visibly glowing plasma -- which usually occurs exactly where you have mounted your VHF antenna. The current is extremely low, and the discharge shouldn't damage a well designed radio, but you'll be lucky if you can hear anything besides static on the receiver while it's occurring. Placing one of those "brush looking" static dissipators at the top of your mast will cause the discharge to opportunistically favor developing around the dissapator instead of around the tip of your VHF antenna.
Equipment sources:
These are reliable sources I have used in the past. You may find cheaper deals elsewhere, so I encourage you to shop around.
- Copper plate, braided wire stap, copper buss bars, copper strap, bronze fasteners, and brazing rod. Georgia Copper: http://www.gacopper.com/.
- Antenna lightning arrestors (use at the antenna end of the coax): Polyphaser. Superbly effective and used widely by the US military for, let’s just say, “other purposes” as well as for lightning protection. They are so effective in fact that it may be illegal to export their product to certain countries. Alpha Delta: These arrestors have replaceable arc chambers. I don’t recommend using them at the antenna only because you won’t want to climb your mast to perform an arc chamber replacement. But they are fine at the radio end of the coax. Both products are available from DX Engineering: http://www.dxengineering.com/Sections.asp?ID=48&DeptID=19
- Fasteners, clamps, and other accessories: http://www.lightningrodparts.com/
- Grounding plate: You don’t need anything fancy. An 18 inch X 18 inch copper plate will do. I personally hate through-hulls – I loose sleep over any hole I make in the hull. However, this is an interesting approach to providing a large surface area to ground: http://www.ropeantenna.com/Grounding%20Plate.htm. To avoid through-hulls, I hang two pieces of 2 inch wide copper bar stock, submerged 3 feet into the water, from the outboard engine port on either side of the engine. That combination provides 2 square feet of surface area (there are 4 surfaces on the 2 bars). I feel 2 square feet of surface area is adequate for seawater. In fresh water, you will need more.
If I haven't covered all of your questions, please advise.
-Patrick Bryant, S/V Jubilee, Ariel #75
FCC Licensed: Commercial Radio Operator, General Class; Amateur Radio Operator, Extra Class (N8QH (http://www.qrz.com/db/N8QH)); Global Maritime Distress and Safety System Maintainer with Ship RADAR endorsement