|Topic Review (Newest First)|
|08-16-2006 10:57 AM|
Thanks saildog...yep...I am just waiting till I return from Argentina to sail back from the keys to Fort Lauderdale where my dock is...
thanks again for the help...
|08-16-2006 08:06 AM|
Obviously a metal vessel is going to fare a bit better, as the hull can act as a ground plane... the best type of metal vessel would be a copper-nickel alloy boat, which is exceptionally rare.
Some electronics can be protected by simple enclosure in an all metal box. The box acts as a faraday cage and removes the ability for the pulse to destroy the contained electronics... I have used a pressure cooker for the "box".
The real debate is whether an ungrounded fiberglass vessel is more or less likely to get struck. If grounding a fiberglass vessel makes it more likely to get struck, I see no point in doing so. Lightning strikes are relatively rare phenomenon, and I'd prefer they stay that way, with respect to me and my boat. However, if lightning does strike, the chances of serious damage seem to be much higher on an ungrounded boat, as the lightning has to create a path to ground, rather than follow an existing path.
|08-16-2006 12:23 AM|
No sh*t, I was there
My Dad is a retired EE with a lot of experience with tracking antennas of all sizes. You know, those big dish shaped things mostly seen in the movies and documentaries. Lightning was a bug issue with them since they were large and usually in the middle of a field. Anyway, they used dissipators and grounding. The ground connections were welded to the assembly to prevent the possibility of corrosion degrading the grounding path. At that time he said NASA had barbed wire running the roof perimeter of the acres of the large two story buildings they had at Cape Kennedy. The purpose was as a dissipator with all of the little points oin the barbed wire.
We talked about sailboat strikes recently. He considers it foolish to not have a dissipator for on anchor or underway. That is when it will help you reduce the known induced potential that rolls along beneath the storm cloud. Your mast is a huge target without much else around. The higher the potential voltage induced on an object the greater the probability of a strike, so the dissipator will reduce your strike probability. On the other hand when in the crowded marina, he said that unless most of the boats in your marina have a dissipator, it won't matter if anyone does. The marina tends to become one huge target at the edge of land where the masts are the only tall objects around. In that case all the boats tend to have roughly equal chances of being hit since they are so close together.
My boat was struck while underway on the Chesapeake several years ago . I must say it was a fascinating experience but not recommended. After that I first talked to my Dad and decided to install the $80 bottle brush dissipator during the repairs. In my subsequent research I found a lot of controversy but there was some common ground. The US Navy has researched the subject extensively to the point of going offshore and actually attracting lightning strikes. I've seen up close pictures of a bolt striking the deck. From the Navy research the common conclusion is that during a lighning storm the very best boating place to be is on a metal boat. The surrounding metal tends to conduct the strike charge safely to ground. They suffer very little damage to vessel or crew. Based on that it would seem that more grounding is better than less, but maybe it doesn't extrapolate to the minimal case of a fiberglass boat.
At the other end of the safety spectrum is the small fiberglass power boat. Typically the strike will hit the cabin top but then it might pass through an individual standing underneath it.
In between the two extremes of the safey spectrum with the metal boat on the safest end and the fibeglass powerboat on the riskier end is the fiberglass sailboat with it's "cone of strike protection" extending down from the tip of the mast to the deck. It's no surprise that the mast takes the strike and you want to be away from it but not too far so you are inside the cone. I talked to a couple who were riding out a storm on anchor when the boat was struck. They were sitting on the settees and saw a bunch of small ball lightning spread across the cabin sole and dissappear into the cabinets beneath them. I saw a hit on a power pole once and a ball lighting the size of a basketball went down the street of a few hundred feet in a couple of seconds.
For lightning protection I'd prefer a metal hulled vessel. It is known that cars take lightning strikes and nobody is hurt as long as they are not touching metal attached to the car's body. Unfortunately metal boats seem to have serious long term maintenance issues. So a few years ago I came up with the idea of a fiberglass hull with an extra layup inside of a metal mesh. When I discussed it with my Dad, he thought it had the potential to give the vessel enough conductivity to protect it's occupants and structure well. I'd really like to know if practically speaking this can be done, or would any metal mesh cause structural problems inside the rest of the layup. Possibly the mesh weight could offset by less fiberglass due to added strength from the mesh. It certainly could make for an interesting yet expensive experiment. Another way to go is if you started with a project boat that you had to gut the interior anyway. Then you could line all of the exposed hull and cabin with a light metal mesh before reassembling the interior. In both of the mesh designs, the interior would be come a Faraday cage so your cell phone would no longer work. Oh well.
As for the onboard electronics, they are just at the mercy of the electromagnetic pulse. The strike itself is actually a subsecond series of extremely high voltages pulses. Any conductor laying radially from the strike can pick up huge induced voltages and that is all it takes to fry solid state equipment. Physically unplugging equipment will protect it from surges that enter the vessel power distribution wiring, but will not protect it from the induced voltages within the equipment itself. Even a strike in the water a hundred feet abeam has been known to wipe out all of the electronics from induced charges.
I'll finish this with one more point from a true story of my friend with the C&C 37-40+, a very nice performance cruiser. A few years ago he decided to buy that particular model and bought one on the hard in Florida. Before closing, it took a strike causing much damage including an extra hole below the water line. At least it wasn't in the water. Anyway, the seller wasn't up to making proper repairs so my friend walked on the deal. Being persistent, he soon found another one in the Cayman Islands. This one was intact without extra holes below so he quickly aquired it and for the last few years it has been berthed a few piers in front of my boat.
A few Saturday nights ago we had a really nasty storm sweep through our marina while we were in the slip. The next morning I found out that one of the close strikes that we heard that night was on his boat in the slip and they were onboard . The boat is on the hard now with the mast unstepped for rewiring. Attached is a picture of his vhf aerial which landed in a temporarily maleable state so that it wrapped around his slipmate's starboard safety rail. So far the repair estimates are about $15K. Several vessels surrounding his also have significant electrical damage.
My point from this story is that besides whatever else you do about the lightning issue, make sure to have good luck. In my friend's case having purchased the same model twice and having both of them hit within a few years is quite a statistic. His luck in the strike extended to the point that no one was hurt, and that of course is the most important.
|08-15-2006 11:28 PM|
|sailingdog||Congrats on the boat.. I take it you just got her...|
|08-15-2006 11:09 PM|
Thanks guys for all the input, the first thing I did was kiss my wife and throw a life jacket on her. I then told her to stay below and let me and bro fix things on-top...!
I did not put a life jacket on neither my brother, he and I were too concerned with my wife and fixing our situation... the problem with being a marine (me) and my brother a navy seal medic...we forget about our own safety for the safetly of others...!
I am now in Buenos Aires, but the first thing we will due when I return is practice safetly measures and storm condtion procedures.
Our instructor told us because we got the boat and ourselves back to the dock safetly we passed his test...HAHA...he said he would not charge me for the rental but show us what to do next time this occurs..with our 30ft Lippincott...!!!
thanks again bros...
|08-15-2006 10:55 PM|
There is too much unknown variation in what happens in a lightning strike. While grounding a boat may offer some additional protection, it may also increase the potential for getting struck. Basically, lightning protection is a crapshoot....if you think it helps.... do it...if not, don't bother.
That said, I have read a few articles which seem to point to boats having a lightning ground system surviving with less damage than boats without one. Also, a good lightning protection system setup may offer a bit more protection to the passengers on the boat.
|08-15-2006 06:50 PM|
I have read articles by 'experts' claiming that dissipators don't work. I don't recall the author of how he reached that conclusion.
I also recently read that a one foot square plate should be attached to the underwater surface and grounded to the engine and only the engine. Bonding the metal fittings together, the article said, only increases the oportunity for lightning to blow a hole in the boat.
I'll see if I can find some research on the topic. I'd like to know.
|08-15-2006 11:07 AM|
This would be a heated debate.
If you ground your boat, You WILL increase the odds of getting hit. I do not know how this can be an argument. Electricity looks for the easiest path to ground. Now that being said, not grounding your boat does NOT mean you will not get hit. Martha Bliss has a Catalina 400 that is not grounded. She has been hit twice, though I do not think either was a direct strike.
Lightning does not have to hit your boat to take everything out. All it has to do is hit close.
To ground or not to ground is a very debated subject. Most offshore boats (Valiant, etc) ground. If you are out at sea in a storm, you are probably the highest point out there. I find most production/coastal cruisers do not ground.
If I were going offshore a bunch, I would ground my boat. You are increasing your chances of being struck, but will give the lightning a clear exit point from the boat likely reducing the possibility of serious damage. If I were going to be coastal primarily and in areas where there should be taller objects, I would not.
Another option (and this one is very debatable) is to put a charge dissipating item on top of your mast. It looks like a metal bottle brush. THere are better ones and worse ones, but in general the theory is that it diddpiates the charge build up the preminates a strike. Thus, your neighbor gets struck!!! Ha! Ha!
I did put one of these on my last boat in S Florida and I never got struck. S Florida has got to be the lightning capitol of the country. THat being said, was that because of the disspator or was it because I was just lucky???? Who knows.
PS If you do use the disspator, you are SUPPOSED to ground your stick. I could not bring myeself to do that. I preferred running to the other side of the marina, throwing a chain around the forestay of another owners boat, and tossing the other end in the water. He never could figure out why he got struck so much. I told him to try a dissipator, it might help.
|08-15-2006 10:45 AM|
|astraeus||I know this is a little off topic...but, does anyone have any first or second hand accounts of lightning hitting a sailboat? I've heard sailors debating whether or not to ground the mast. The advocates of not grounding the boat say that it increases the chances of being struck (not sure I buy this argument). My boat is not grounded, but I carry wire to run off the shroud in case of electrical storms.|
|08-15-2006 12:38 AM|
CD & FG have it right... first thing you should do is put on PFDs for everyone. That way, if the wind knocks you down, or someone goes overboard, they have a chance.
Lightning is a real danger... so try to get the boat anchored and then hide out in the cabin, as far away from the chainplates and mast as possible.
Reefing—the old adage about when the right time to put in a reef is when you first think about it is very true. Always better to reef early, and have too little sail up, than to reef too late, and maybe not be able to get the sail area reduced.
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