Chip Hindes wrote:Based on the data, I'm very happy to conclude it's not a problem. If there's a lightning bolt out there with my name on it, so be it.
Chip
Chip Hindes wrote:I prefer to save my worrying for stuff that actually might happen.
I understand... I've been riding 40 years and never needed a helmet... been driving that long too, and never needed a seatbelt. That's true for most who ride or drive.
Me too, but these 6 lane Highways used to be 2 lane country roads.
The 4 thousand people who used to live here has grown to 44 thousand now . WE used to slow down and stop on yellow now we blast through on the red lights as though its our right . They say Motor vehicle deaths are rising at an alarming rate have lighting strikes increased as well? I ware my seatbelt now and always have since I bought that New 1976 CJ5 with the 304 V8 . I still don't wear a helmet though. I am sure I am safer on the Mac than I ever was in that CJ5
Chip Hindes wrote:With 5,000+ X boats out there, the huge majority of which have the same system as me (i.e. no lightning protection system at all) ...
- So far, to my knowledge, not so much as a single anecdote of an actual lightning strike. ...
- Based on the data, I'm very happy to conclude it's not a problem. ...
No mystery there at all ... thanx to Roger's studious attention to the principles of lowest-cost suppliers, the Mac's mast is the least cost and least conductive aluminum stock available anywhere on this (or nearby) planet(s)!
Is keeping the mast ungrounded the simple answer for a small boat in fresh water? No. A ground system would likely reduce damage and side flashing if the mast does take a hit. How can there be a ground system without grounding the mast? By use of an arrestor, a small air gap or dielectric that will provide for an isolated mast but yet provide a bridge to a lightning protection system. Will the lightning still hit the mast if its not grounded? Yes, statistics indicate that the ungrounded mast while less likely to be hit will still take the hit. In my early survey conclusions, 100% of sailboats that were hit either grounded or ungrounded, took the hit to the mast. Because ground systems in small freshwater sailboats are likely inadequate, its unwise to attract lightning to them, so using an arrestor makes sense. The arrestor should be placed in the ground conducting path from the mast base to the water. On a small boat in fresh water, it has been suggested that the most effective ground is a long copper strip. Small boats however need something flexible and easy to store.
One idea is to use copper welding cable. Not only would it meet the easy to store requirement, but It would be very quick and easy to deploy when needed. With 8-10 feet of bare wire on each end and the insulation left on the out of water section, the wire would be wrapped a couple of turns around the base of the mast and then each end draped over the sides passing against the side shrouds being sure that the stripped sections are not against the shrouds. The ends would of necessity need to be as long as possible, but short of the outboard prop. The insulation left on the cable becomes the arrestor, keeping the mast ungrounded but yet providing a short bridge to carry the hit to the grounding wire. Some small holes in the insulation where it wraps around the mast would provide a spark gap while holding the cable from bonding. With two turns of cable around the mast and equal sections on each side, the rubber covered cable shouldn't need any further effort to remain in place. This would afford twenty feet of ground strap, a good conductor without connections and an arrestor which should provide a ready pickup for a lightning discharge.
It seems this may be a good approach.. not grounding the mast but providing a path in case it is hit.
Something to think about:
My mom said when she was little, they lived on a hill with a row of houses that were all alike. One owner had lightning rods installed on there house, obviously not installed or grounded properly, because the house with the lightning rods was struck by lightning 3 times ( and caught on fire) while the other houses were not.
Maybe you can "attract" (more like provide a path) the lightning such as on a show I saw a while back where they launched model rockets with wires attached in order to cause a lightning bolt when conditions allowed.
The arrestor as described in the Stewart article is much like the arrestors used on power lines and would leave the mast ungrounded.
Greg,
I agree totally. That is the only approach that makes any sense to me, if you are going to do anything.
A fully grounded mast will increase the odds of being hit dramatically, since the charged cloud overhead will pull charge from the water up the ground cable and put a concentrated high opposite charge at the top of the mast, making it a much more attractive target. You do not want a direct connection between mast and water, but the bridgable gap will still afford some personell protection in the event of a strike. The method Arlyn descibes sounds like the best way to accomplish this I've heard of.
I saw the same show about the rockets with grounding wire being fired into the air to attract lighting and they got hit darn near every time. They also were measuring electric field strength to help determine when to fire the rockets. I was amazed at the strength of the electric fields. something like 5-10 KV per foot of air or something.
Last edited by craiglaforce on Fri Feb 04, 2005 5:50 pm, edited 1 time in total.
While what I know of eletricity would lead me to agree with you guys, and disagree with "the experts," about whether grounding "attracts" lightning, let me point out what I see as possible problems with the Arlyn solution.
Divecoz and Darren can correct me if I'm wrong, but arrestors I've seen have a gas-filled tube designed to ionize and conduct very quickly when higher than normal voltage (electrical pressure) is applied across them. I question the speed at which the air between the welding cable and mast will ionize, not to mention how quickly the insulation will vaporize and remove its resistance to conductivity, relative to a commercial arrestor, especially since the buildup of electrons that causes ionization probably isn't the greatest at the mast base but more at the compression post base.
The Arlyn solution, while possibly reducing the size and "attractiveness" of the attachment spark off the mast, relative to a grounded mast, might not prevent it. It appears to me that anything with mass, whether grounded or not, is going to polarize under the presence of the large negative charge at the cloud base, with positive ions at the top and a buildup of electrons at the bottom. Specifically, this solution doesn't address the buildup of electrons on the compression post and chainplates in the cabin, and it will be these electrons that first leave the mast and chainplates, and seek a path, from the pressure (voltage) of the huge number of electronics present at the top of the mast once a strike leader hits it. If the welding cable doesn't conduct immediately and heavily, it won't be able to relieve the pressure (voltage) on the electrons in the compression post and chainplates.
At the instant the strike leader contacts the mast top, there are several paths current can follow... the mast, any of the stays, as well as through the air around them. The saying "electricity follows the path of least resistance" doesn't tell the whole story. It also follows the path of most resistance. And it follows any other possible paths with resistance between the least and the most. What the resistances determine are the amount of current flowing through those paths, and hence the amount of power that will be dissapated in each.
Without a ground on the mast, there is no path for current, so one will have to be made by ionization, which is occuring between the lower end of the mast and anything connected to it, and any object with free electrons near them, especially objects between them and ground, as a result of the differences in potential. The Arlyn solution is betting the gap to the welding cable will ionize, the insulation vaporize, and conduct first. I personally don't think that's a sure bet, especially with MacGregors lampcord in the cabin ceiling, running by the compression post and grounded through the DC system and outboard or outboard mount.
There are a couple of other issues I have with it. One, wrapping the cable at the mast base is asking lightning to turn 90 degrees, probably not a good idea. As Divecoz says, make it easy for it, and if you do it, wrap it high with the cable angling down and out from the mast. Another issue is whether his considerable length of uninsulated ends provides sufficient dissapation and edge area. The corrosion problem of uninsulated and untinned copper exposed to sea water also may become a problem. And finally, the ungrounded mast doesn't provide the "cone" or as someone described it, "sieve" of protection, reducing the chances of strike on a stanchion, pulpit, or lifeline.
This is why I earlier said it sounded a bit like whistling in the dark to me.
[quote] personally don't think that's a sure bet, especially with MacGregors lampcord in the cabin ceiling, running by the compression post and grounded through the DC system and outboard or outboard mount. [/quote]
Is the motor frame grounded to the DC system? I would not have thought this was the case unless modified by the owner as part of a bonding system.
Personally, I would never want an electrically bonded system.
Lightning hit the power line coming into our house's kitchen when I was a kid (our house was near the crest of a small mountain). It blew a hole through the refrigerator power cord insulation and went to ground about 3 feet away from my feet. There was a small black burn mark on the linoleum floor and the fridge quit working. We thought the fridge was dead, but upon fixing the cord, it resumed working. At least in this case, lightning was happy to turn a corner and blow a hole through insulation.
It also shattered the kitchen light bulb.
It was LOUD!
AFAIK, all outboards use the chassis for negative ground. That's how spark plugs work... one side depends upon the powerhead for a path for current. Lightning may turn a corner, but I wouldn't bet my life on it.
Lightning may turn a corner, but I wouldn't bet my life on it.
-Moe
I believe most of us have at one point or another in our individual posting's either stated or admitted that lightening arrest/grounding is a crap shoot at best. There are just too many variables. Too much room for error. I agree,. . . to just wrap wielding cable around a mast and expect the strike to follow your desired path, 360 degrees or more is asking a bit. . . much. We are instructed to use a radius of no less than 12 inches to change direction of desired path by not more than 90 degrees depending on cable size and type etc on and on and on ... Its when you have those microsecond hesitation's in the flow that you produce eminence heat btw. Someone mentioned two leads, one off each side, then they better have the same length, same conductivity relative to ground. Heat generation, even when "the system" works has caused fires.
Fires and Boats, Whiskey and Motorcycles . . never the two should meet!
Your luck is running so bad your one of say 4 sailboats in all the USA that is hit by lightening. Immediately your luck changes and you survive the initial hit/strike your "system" performed exactly the way you intended it to / hoped it would /guessed it might !
( which one of the three choices you choose btw depends on just how honest you are with yourself ) and it does provide a path of egress. All is well, with your soul , you crawl back out from under the covers smiling , till. . .till, you smell smoke DANG smoke from burning resin or electrical wiring somewhere somewhere your now fighting a fire maybe a big fire maybe not, but a fire all the same . Variables variables, what did you do first, deploy your "system " ?? Or try to Unplug everything you could . If your luck is running this bad ,what would make you think that 500,000 Volts has to make physical contact with your electrical system to start a fire, to burn everything beyond use and maybe beyond recognition. Part of Everything could be you . What ever your industry you hear about things going wrong , things that should not have happened that way . Things that defied theory and logic . Same goes for my industry . I'll choose not to ground and pray I am not the 1 out of a million or so to take a hit.
My apologies to any who decide this is too long. But I do hope it helps clarify some erroneous information that is out on the net.
While I agree that the number of witnessed lightning discharges to sailboats is low, and if your number is up it is up......
And, I would never presume to state for another whether or not they need a protection/dissipation system.....
All I am trying to put out here is how to safely carry a strike if it comes to your boat. I am obviously not recommending a system for every boat or instance. Let others justify the needs. I concentrate on the technical aspects. The Physics and the engineering details.
So let me go on record heresimply for definition purposes, I leave it to others to decide if they should have a system. But if you are trying to protect a sailboat. Get the discharge off the deck..
Additionally, once the mast is placed at ground potential.. The threat of a strike does increase, because the protected area of ground potential is increased , and extends around the boat several (I have seen estimates are as low as 3 and as high as 10) mast heights around the boat. Not as much as one observes on dry land. Since the surrounding saltwater is also at the same potential. For a boat on freshwater lake..The draw area could be considerably larger A pristine clear clean mountain lake with low turbidity and 50 -75 ft of water visibility (Tahoe, Chelan, Crater et. Al.) you would need almost an impossibly large dissipation system to distribute sufficient charge to protect the boat. In those locations, Probablity of Lightining activity and strikes are relatively low (compared to reservoirs in Kansas, Missouri, Great lakes, and sailing in Florida etc. and I think for most, the decision would be not to deploy in low turbidity, low conductivity water. For boating almost everywhere else in lowland lakes, and saltwater, conductivity of the water is high enough to use a dissipater approximately equal to the surface area of the mast, if it has many edges. Since almost every other sailboat in the harbor is larger than me, I dont feel that I need to deploy any system when adjacent to taller masts.
What I describe is the absolute minimum of engineering elements to do this safely. Several people have marketed systems for sailboats/powerboats, and successfully sold them, and with so few strikes, the effectiveness of some said systems is hearsay at best.
The Mac mast is similiar to other aluminum and steel elements which have survived direct strikes. Signposts, fenceposts, scaffolding and structural elements have frequently been analyzed after direct hits to determine the damage sustained. Further investigation has shown that charge has diverted and jumped when the mechanical boundary at the drain system has changed (typically to a high resistance connection or an element with significantly less or insufficient surface area).
The basic problem with any system that uses a circular cross section cable is insufficient surface area. Even a 4/0 cable only has a surface area of less than an order of magnitude (In.^2/In.) less than just the exterior surface of the mast. With a large strike, This can result in flashover, with charge penetrating fiberglass decks, hulls etc. Optimizing the drain/dissipation system to have a contiguous surface bond and to have the same or greater surface current carrying capacity than the collector can divert as much charge as the mast can carry. The purpose being to keep the charge out of the cabin. As Moe pointed out some of that charge from the strike is traveling down the stays, boom and every other metal surface in the boat. A grounded drain plaited sheath, and dissipation system can remove charge otherwise accumulating on the mast. Perhaps one could figure out a rigid pipe system with sufficient surface area, but that would be even larger to carry and deploy.
Bringing the charge on deck before attenuation is wrong. Better to divert to a dissipation/ ground plane. 20,000 gallons of conductive saltwater around the boat is a much better attenuator than anything on the boat. ((Just for fun, calculate how much energy it takes to boil that water in a few microseconds, even lightning is rarely that powerful., )
The reason I do not recommend an air gap or dielectric on the mast to drain connection is simple. It is the wrong location. Pure and simple.
Fore and back stays are already conducting some charge down toward the boat..., The proper place for a dielectric (or any other device which absorbs part of the charge to ionize a material to induce plasma) is between the rod and the system that is being protected. (In an unprotected mac's case, the mast or the stays are hit first.) You simply cannot do that with the Mac mast unless you are willing to mount a rather large rod above the mast and place the dielectric between the mast and the rod mount. Few are going to do this. Systems which place a dielectric on Deck invite the potential buildup which will Ball, (Potential difference across a large area builds up because of the lack of conductor surface area) , and the water vapor in the air flashes steam or disassociates to component gasses (The Ozone generation of strikes) (In many strikes this process occurs multiple times in microseconds as hydrogen and oxygen nuclei are stripped and thrown around. (the concussive effects of thunder)) that travels along with the plasma. (the mechanical force behind the fireball effect). This also occurs when lighting discharges onto moist surfaces as the liquid water is flashed to steam or plasma..
The Idea of a dielectric is good. The positioning is absolutely critical, but unless you are going to put it in above the mast and stays and below the lighting rod, it is worse than useless on the deck of a MAC.
Secondly, Since the mast is already bring the charge on deck, The last thing you want is an additional resistance/ capacitive connection , That charge will perforate fiberglass easily if allowed to build and nail that cabin compression post, wiring, and every other piece of metal within a few inches and then down into the ballast tank etc. Better to provide a easy path to ground.
Thirdly, The charge is traveling on the surface of the mast, to conduct that charge easily, Where much of the charge is actually traveling along an ionized channel adjacent to the metallic surface, the drain dissipation system surface area needs to be approximately equivalent to the mast. One or two welding cables is not sufficient. IMHO.
If people are interested we can get into Recorded strike measurements, plasma Flow/dynamics, formation and separation energy, Electron mobility and the ratings of various dielectrics.
If one was truly worried and wanting to lessen risks of flashover inside the cabin, one could also replace the stainless steel mast compression post with a non conductive structural element along with the addition of a dissipation system. Or modify the pipe to include a large spacerblock or sheath for additional dielectric isolation.
Again I am not trying to say any individual should or should not have a system. But if you have a system, it should be sufficient for intended application.
Other ways to lessen the risk during an electrical storm, dry clothing, sit in the center of the boat away from metal, and obviously turn off all electrics before the party starts.
All of the above can greatly improve your chances and lessen damages in a strikeBut cannot absolutely eliminate risk in all configurations.
Anecdotes aside
I have a relative who was hit while on a utility pole. There are no guarantees in life. But the single 4/0 stranded aluminum ground wire/connections was insufficient to safely carry all of the surface charge. And that was a relatively small strike. And yes he lived. Which means absolutely nothing about whether any individual strike will killAll can under the right conditions. And like many other hits which have been examined The clamp to wire connection blew, not the clamp to rod. At the time, The investigators could not even determine if the clamp had been blown out in a previous strike since inspection of the surrounding system showed several dozen clamps had failed. After additional statistical hocus pocus. There never was a determination whether or not failed bonding termination was a contributing factor to the accident. Now many utilities inspect each pole on some schedule and maintain some equipment damage history and reports. Others monitor strikes to service conductors. The primary reason service conductors can take a strike is their long lengths, Thats how they get sufficient area to take direct strikes and not always fry.
In summary. You wont find me putting in a arrestor, gas discharge tube, etc inches from my head while hiding in the cabin. I am going to dump that charge overboard soon as possible.
Last edited by waternwaves on Mon Feb 14, 2005 3:05 pm, edited 1 time in total.
From two lightning strikes to boats I crewed...I am not sure any 'grounding' method on a fibreglas boat will be perfect.
I was on a 32 footer glas boat which had a grounding system from the mast and rigging down to the lead keel. We were anchored up on Lake Superior during a powerful lightning storm. Just as the storm ended and the sun started to come out, the mast got hit...the radio antenna was vaporized down to the mast...'side leaders' jumped from the massive grounding wires into the boat's electrical system...frying all of the electronics...smoke began to ooze out of the fixtures (luckily no actual fires...just melted wires)...but weirdly it didn't cross to the starting circuits and the engine.
We inspected the boat carrying fire extinguishers but didn't need to use them.
The cap'n on the boat moored next to us asked if anyone had gotten hurt, we told him no. He said he was looking at our boat when the bolt hit. He wasn't looking at the mast top so he didn't see the flash up there but he was looking at our hull when it hit. He saw multiple fingers of blue shooting out of our fibreglass hull at the waterline all along the water line. he figured with that much current exiting the boat, we must surely have gotten zapped ourselves.
My cap'n's eyes got wide and he swung over the side to look at the water line and began to swear. He stripped down, put on a mask and snorkel and dove over into that !@# cold water. He quickly swam around the boat and said we had to get back to the marina asap which wasn't very far away.
As soon as we had the hull up on the marine hoist, we could see multiple craters in the gelcoat and even into the mat-layers...only a couple of the craters actually penetrated all the way through the hull. Some of the current had jumped through the hull from the electrical wiring. Since it only took about 1/2 hour to get back and put the boat up...we only had a small of water actually get in the boat.
It took about a month before all the repairs were finished.
I guess the moral to this story is if the bolt has enough amperage it will flow through darn near everything on its way to ground. When the boat's owner bought it, one of the selling points was the massive grounding the manufacturer had installed...but it didn't do any good.
So I guess I am going to hook connected welders cable over the side when lightning comes...just to feel that I was doing something...and I am going to make sure that I have the most effective boat insurance. That money is still alot cheaper than if I had to pay for the repairs myself.
My wife is still nervous about me and electrical storms since she says 'everything comes in threes'
