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Old 24-01-2015, 07:52   #31
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Re: New lightning stats from BoatUS Insurance

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Originally Posted by colemj View Post
Here is how that works (this is from direct experience of having our VHF antenna take a strike): The lightning hits the antenna, travels down the coax to the radio, jumps onto the negative side of your DC system and proceeds to take out anything and everything connected to your DC system until it finds its way out through your DC bond to water (typically through the engine). You will lose not only the electronics, but your alternator, windlass, possibly starter, fridge, inverter - where it may jump over to your AC side and start wreaking havoc there, etc.

It can become very expensive in milliseconds after hitting the VHF.

But put this in perspective - how many close lightning storms are you experiencing in SF Bay area? For comparison, in Panama these occur every night and often in the day for 6 months of the year.

Mark
Personally I don't think it would matter if a powerfull bolt hit the VHF antenna or not. Powerfull lightening induces eddy currents in surrounding metal (or any conductor) up to 20 feet away from the actual path of the bolt. In fact, these currents can be so strong that they can kill a person that has not been directly struck or flashed over. If you search Youtube, there is a video of lightening striking a soccer field during a game. Players that are over 20 feet away from the strike are injured from these currents.

Here is a really good laymens document on current lightening study and ground based protection systems.

http://www.weighing-systems.com/Tech...Lightning1.pdf

Personally, I beleive lighting protection system on a boat are ineffective due to both flashover and induced currents. Even though you provide a low impedence path to ground there are other wires (VHF coax, mast light) within the induced current radius. Powerfull stikes will kill eletronics regardless of the main bolt traveling within those circuits.

Some electronics are much more sensitive as well. Anything with MOSFETS is most likely going to die. Unfortunately, tons of electronics use MOSFETS these days (charge controllers for example).
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Old 24-01-2015, 08:08   #32
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Re: New lightning stats from BoatUS Insurance

Lightning protection systems are mainly concerned with protecting the boat structure, not the electronics. They attempt to provide a path to ground that does not include passing through the hull or skin fittings. A minor component of some of these systems include surge arrestors on electrical panels and circuits, but this isn't the major focus.

A massive strike will take out uninvolved electronics like you say. However, less massive strikes aren't always so catastrophic provided you can keep the actual strike out of the electrical system and get it to ground. A stern or arch-mounted VHF antenna, LED nav lights wired with 18g wire, and the small wire on the wind instrument helps to keep the lightning out of the electrical system should the mast be struck.

Mark
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Old 24-01-2015, 08:59   #33
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Re: New lightning stats from BoatUS Insurance

Everything that I have read on this subject suggests there are no rules, it just does what it does. Some boats have massive bills after a direct strike, others get away much lighter and it has little to do with how they are set up. It is completely unpredictable.
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Old 29-01-2015, 08:44   #34
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Re: New lightning stats from BoatUS Insurance

At first glance these numbers seem high, but I wold like to see the numbers broken down. Others in this thread mention some interesting things such as how higher latitudes have less strikes. While this sounds reasonable, that implies that the incidence of strikes is much, much higher in some areas. In an area like Florida, it suggests that a marina of 250 to 500 slips should see one strike a year. It certainly suggests that we as a group don't think enough about, let alone prepare for lightning strikes.

In terms of the numbers, I would like to see how many boats they looked at and where these boats were. It is possible that the sample was not evenly distributed and thus the numbers appear higher than they actually are. As Mark Twain said, there are lies, damned lies, and statistics.
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Old 29-01-2015, 09:19   #35
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Re: New lightning stats from BoatUS Insurance

The best write up on boat lightning protection/issues I have seen is by Kasten, Lightning Attenuation Onboard. This is only a part of his long article discussing grounding plates.

Quote:
The ABYC states: "An exterior grounding plate of copper, copper alloys, stainless steel, or aluminum may be provided by means of a plate which has an area of at least one square foot." Ewen Thompson's research indicates that in salt water, a grounding plate of one square foot in area is probably sufficient, but that in fresh water even two square feet or more may not be enough to provide a sufficiently low resistance in the event of a direct strike. If the grounding plate is not large enough, the result will be that a lightning strike will seek additional pathways to ground, and the danger of side flashes will be dramatically increased, along with possible severe damage to the hull, equipment, and people.


A grounding plate should be solid, rather than the sintered bronze type often used as radio grounds. The sponge-like structure of the sintered bronze plates may, in the event of a strike, allow the instant formation of steam, which could blow the plate apart, resulting in possible severe damage to the surrounding hull.



Thompson does not consider a grounding plate to be the ideal shape for dissipating a strike, nor does he consider its typical location near the keel to be optimum. This is in part because a square plate has a limited amount of "edge" but also because of the tendency of lightning to seek the water's surface. Rather than using a square grounding plate located down low, Thompson favors using long grounding strips, located closer to the water's surface.
One certainty about lightning, is that there is no certainty. Having said that, my guess is that multi hulls are hit more often than mono hulls is because there is more water line on a multi hull vs a mono of the same boat length.

This is just a guess based on the need to use a long, thin grounding strip vs a square grounding plate per Kasten/Thompson near the waterline. If a long grounding strip is better at handling a strike, I wonder if the long water line lengths on a multi hull somehow attract lightning.

Later,
Dan
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Old 29-01-2015, 09:39   #36
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Re: New lightning stats from BoatUS Insurance

I've seen a couple of lightning strikes, they seemed logical, until I saw one strike the ground in the middle of a baseball field, with all the metal light poles around and fences etc, you wouldn't have though it would hit the ground in the middle, but it did.

You have to be very careful about statistics, for example are these numbers of lightning strikes, or insurance claims? Might be the multi fleet is newer on average and more likely to be insured for example.
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Old 29-01-2015, 09:51   #37
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Re: New lightning stats from BoatUS Insurance

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The statistics given in terms of strikes per 1000 boats, not the absolute number of strikes. So if most multis are in Florida, while the monos are more evenly distributed up and down the eastern seaboard, the multis will have a higher odds of getting hit. That may not be the whole story, but I think it is a part of the explanation.


Good point. I don't know where the highest incidence of lightning is on the globe. Florida is the highest in the U.S.
Yes... and also one wonders if these data are from Boat US claims? and if so, where is Boat US insurance more prevalent? I'm guessing Florida?
It is interesting though that boats with a keel are more likely (if that's really true) That would reinforce the thinking that a grounded rig attracts lightning..
If anyone saw the film about viewing the earth/collecting data by satellite from space ...about everything from temperature to lightning to sea currents... the view from space of lightning was amazing... it's a constant light show around the globe... never really stops flashing....on the film...
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Old 29-01-2015, 10:10   #38
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Re: New lightning stats from BoatUS Insurance

It seems logical that a composite or wooden mast is less likely to take a hit but is this really the case? I imagine that anything on the mast such as an antenna, radar, exposed wire, steel rigging, etc. would negate or reduce the benefit of a non metal mast. I would nonetheless like to see if there are any figures for metal versus non metal masts.
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Old 29-01-2015, 10:40   #39
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Re: New lightning stats from BoatUS Insurance

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It is interesting though that boats with a keel are more likely (if that's really true) That would reinforce the thinking that a grounded rig attracts lightning.
How are you reading the stats this way? Multis were listed 2x as likely to be hit and they don't have keels.

Moreover, the mast on a keel boat isn't necessarily grounded/bonded to the keel.

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Old 29-01-2015, 10:43   #40
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Re: New lightning stats from BoatUS Insurance

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Originally Posted by colemj View Post
How are you reading the stats this way? Multis were listed 2x as likely to be hit and they don't have keels.

Moreover, the mast on a keel boat isn't necessarily grounded/bonded to the keel.

Mark
Whooops! I got it backwards.. too late to correct it...
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Old 18-12-2016, 04:52   #41
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Re: New lightning stats from BoatUS Insurance

So my question is why are Trawler/Motoryacht only at 1.5% when many are as tall or taller than many sailboats. Many of the boats in FL have huge tuna towers with VHF and other attennas rising much higher than the tower.
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Old 18-12-2016, 05:31   #42
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Re: New lightning stats from BoatUS Insurance

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So my question is why are Trawler/Motoryacht only at 1.5% when many are as tall or taller than many sailboats. Many of the boats in FL have huge tuna towers with VHF and other attennas rising much higher than the tower.
Just looking around the marina here, I don't ses any trawlers or motoryachts sticking up any where near the height of the masts on even the smallest sailboats (and that includes the game fishing boats).
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