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Old 09-07-2015, 09:54   #1
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Information needed by NFPA 780 on lightning damage

In a previous post Colemj made a distinction between the main strike and the surge component of a lightning strike to his Manta 40. This observation evolved into a discussion on lightning grounding that raised some very fundamental questions. Answers are needed but the science is presently lacking.

In three weeks at the NFPA 780 Lightning Protection Technical Committee meeting the Watercraft Task Group will be discussing grounding in water via immersed grounding conductors. Since many members of this forum have had first-hand experience with lightning strikes, accounts of your damage can provide exceedingly valuable data to help in this investigation.

Specifically, we are interested in any first-hand objective observations or accounts of physical damage that may relate to the current flow into the water. Of particular relevance are any melted or blackened fitting, pitting or blackening on any immersed part such as a ground plate, keel ballast, propeller shaft or strut, rudder, submerged electrodes,etc., and damage to engine electronics. A list of damaged, and undamaged, electronics (transducer, make, model #, if available) is also of interest. Photographs are especially useful. Please include the location where the strike happened. All of these observations will be presented to NFPA and considered by the Watercraft Task Group.
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Old 09-07-2015, 10:27   #2
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Re: Information needed by NFPA 780 on lightning damage

The BoatUS data, http://www.boatus.com/seaworthy/magazine/2015/january/lightning-facts.asp, shows that multihull sail boats are more likely to get struck by lightning than mono hulls.

Quote:
Table 1. The probability of a lightning strike by type of boat, 20032013

Type of Boat.............................. Chances per 1,000
Multihull Sailboat
.............................. 6.9
Monohull Sailboat.............................
3.8
Trawler/Motoryacht
.......................... 1.5
All Overall Average.........................
0.9
Bass Boat, Runabout, Pontoon Boat
.. 0.1
This seems to suggest that the extra water line length of the boats is increasing the odds a sail boat getting hit by lightning.

If that is true, then larger boats should be getting hit more often than smaller boats. The link has the following data :

Quote:

Table 2. The probability of a lightning strike by size of boat, 20032013

Type of Boat................Chances per 1,000
0-15 Feet.......................
0
1625 Feet.....................0.2
2639 Feet.....................
2.1
4064 Feet.....................6
It certainly looks like the larger the water line the greater the odds of being hit. Flip side is that in the second chart, it appears that multihulls and mono hulls have been grouped together. It would be interesting if the hull length chart had been split between mono and multi hulls.

Is there a grounding method that could be done, or improved, to reduce the odds of being hit? Does the longer water line increase the flow of positive charges flowing in the streamer? If so, can that flow be minimized or stopped?

Later,
Dan
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Old 09-07-2015, 13:55   #3
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Re: Information needed by NFPA 780 on lightning damage

Saw a friends 40 ft sloop after it was hit in Costa Rica. The boat was hit while the owners were off. It was at anchor with an all chain rode attached to a polished stainless steel Bruce type anchor. The boat suffered the typical almost all electronics failures. When the anchor was raised one side of it was still polished stainless looking. The other side was entirely rainbow tinted, as you would see on over-heated metal. Presumably the major portion of the strike exited through the chain and out one side of the anchor.
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Old 10-07-2015, 01:26   #4
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Re: Information needed by NFPA 780 on lightning damage

Quote:
Originally Posted by dannc View Post
The BoatUS data, http://www.boatus.com/seaworthy/magazine/2015/january/lightning-facts.asp, shows that multihull sail boats are more likely to get struck by lightning than mono hulls.
I'm not sure that's what the data says. I think the data says that more BoatUS insured multihull boats make lightning damage claims than mono hull boats. If a boat is struck but not damaged then BoatUS would not have that in their files. There may be a big difference in saying what ratio of boats were struck vs. what ratio of boats suffered enough damage to warrant an insurance claim.

Assuming that all sailing boats are struck equally often (admittedly not established as fact but I think it likely) there could be several reasonable explanations why monos are less often damaged. Among them is many monohull boats have huge metal bits embedded in salt water. This could be a very effective way to get the current from the lightning strike out of the boat without damage. Whereas, multi hull boats typically don't have big metal appendages immersed in salt water. If fiberglass or cold molded construction then the multi hull boat could be "insulated" from the water making it harder for lightning induced current to dissipate.
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Old 10-07-2015, 21:30   #5
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Re: Information needed by NFPA 780 on lightning damage

Quote:
Originally Posted by EwenT View Post
In a previous post Colemj made a distinction between the main strike and the surge component of a lightning strike to his Manta 40. This observation evolved into a discussion on lightning grounding that raised some very fundamental questions. Answers are needed but the science is presently lacking.

In three weeks at the NFPA 780 Lightning Protection Technical Committee meeting the Watercraft Task Group will be discussing grounding in water via immersed grounding conductors. Since many members of this forum have had first-hand experience with lightning strikes, accounts of your damage can provide exceedingly valuable data to help in this investigation.

Specifically, we are interested in any first-hand objective observations or accounts of physical damage that may relate to the current flow into the water. Of particular relevance are any melted or blackened fitting, pitting or blackening on any immersed part such as a ground plate, keel ballast, propeller shaft or strut, rudder, submerged electrodes,etc., and damage to engine electronics. A list of damaged, and undamaged, electronics (transducer, make, model #, if available) is also of interest. Photographs are especially useful. Please include the location where the strike happened. All of these observations will be presented to NFPA and considered by the Watercraft Task Group.
You need a check list to get a fair accounting. Otherwise, much will be missed.

Thread on this here on CF.
Have you suffered a lightning strike? - Page 4 - Cruisers & Sailing Forums

MODERATOR - should these be merged?
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Old 15-07-2015, 10:33   #6
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Re: Information needed by NFPA 780 on lightning damage

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Originally Posted by Nicholson58 View Post
You need a check list to get a fair accounting. Otherwise, much will be missed.

Thread on this here on CF.
Have you suffered a lightning strike? - Page 4 - Cruisers & Sailing Forums

MODERATOR - should these be merged?
A checklist is a good idea. However, I am interested in any and all observations and am afaid that a checklist could miss a detail that turns out to be crucial.

Merging the two threads could be a good way to increase the reach of this topic.
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