Lightening...again

[AndyEss]

Yet lightning travels 1000s of meters through the air to release its potential energy.
Our tall, conductive masts make excellent short cuts for lightning to travel those last 10s of meters.
As a side note, I am always amused when friends say the reason why automobiles are safe in lightning storms because they sit on non-conductive rubber tires. Not sure why anyone would think that a 15cm of tire air gap poses any block to electrical energy that has already leaped probably through kilometers of sky

[Dave_S]

My $0.02

No technical knowledge, probably similar to most here.

But a rule I credit myself for making up that I like is If there is a lot of argument on a subject then there are probably significant arguments to be made on both sides and most likely there are no definitive answers.

For my boat, I do nothing, however when anchored I unwittingly have made a connection that I would rather not have. I do believe that that connection makes you to some degree more likely to be hit but might incurre less damage. I read a technical paper that suggested there is some flux? reaching from earth up that the lightning follows that makes sense to me.

[BigNut]

We are currently in the US for lightning repairs after being hit on our first night on the Rio Dulce, Guatemala back in June - Texan Bay, at anchor. (We waited out the hurricane season before heading this way).
I have spent quite a bit of time since then trying to understand lightning, and to the question “Where does lightning go” the only realistic answer is “Wherever it wants to.”
Mitigation strategies might help, but that’s about it. Mitigation. There are just too many instances of weird strikes or non-strikes to make sense.
Someone witnessed the strike on our boat. They said they saw the red glow from our dual red/green bow navlight. The red light was dead. The green light (led), situated not an inch away was ok. Go figure.
That’s about all I can say re the OPs question.
But:
No one has mentioned the EMP effect. We lost electronics that were not on or even connected to the electrical system - laptops, wireless mice, drone, and the weirdest thing I still have no explanation for: 2 popcorn air poppers, both unplugged. (I still can’t think this one through, and I was too embarrassed to report them to the insurance company. It just seemed ridiculous)
Things don’t fail all at once either. It is good to wait before finalizing with the insurance company.

[cyan]

Originally Posted by tkeithlu

Grounding has no effect on whether or not you get hit.

While that seems to be the conventional wisdom, I find it curious that catamarans are statistically about twice as likely to get hit as same sized monohulls. Perhaps this "grounding has no effect" idea is more nuanced on a boat than on land, involving total waterline and surface area above water. However, there seems to be solid evidence that proper bonding of an aluminum mast to a ground plate may indeed help to avoid damage during a strike.

Originally Posted by Checkswrecks

consider connecting a regular automotive jumper cable to the vang connection at the base of the mast and just dropping the other end in the water. If too far, simply split the jumper set into a separate black piece and red piece to double the length.

...and make sure that the black end is in the water and the red end is on the mast, as about 95% of all lighning is negative lightning.
(okay, that red/black part is just a joke because electrical engineers often think they're funnier than they really are )

[daletournier]

Originally Posted by cyan

While that seems to be the conventional wisdom, I find it curious that catamarans are statistically about twice as likely to get hit as same sized monohulls. Perhaps this "grounding has no effect" idea is more nuanced on a boat than on land, involving total waterline and surface area above water. However, there seems to be solid evidence that proper bonding of an aluminum mast to a ground plate may indeed help to avoid damage during a strike.


...and make sure that the black end is in the water and the red end is on the mast, as about 95% of all lighning is negative lightning.
(okay, that red/black part is just a joke because electrical engineers often think they're funnier than they really are [emoji3])

You made me laugh[emoji1787]

Its these inconsistencies that make me not so sure of conventional wisdom.

[Frankly]

I mentioned in a recent lightning/ lightening post about a strike on an Oak tree about 50 ft from my two sail boats (IP 32 and Hunter 30 docked end to end). Both of these craft had aluminum masts with large copper ground plates just below the mast. Each boat had Freedom 10 inverter chargers plugged into the same shore power duplex receptacle. Fried the Freedom 10 on the IP and knocked out the radar on the Hunter. The Freedom 10 on the Hunter was still charging the batteries when the smoke cleared.

None of ther VHF or HF radios were effected, pretty well eliminating that either boat was a recepient of a direct hit. It was all a great mystery until the Oak tree started dying.

The mast on the Hunter was 49 ft and pretty nearly same height as the tree. Just no gurantees with Thor.

That Oak tree was 25 ft from my bed and while not asleep (to dam* much racket), I gurantee that will get your attention.


Frankly


My house metal roof (two story) was also grounded.

[Jim Cate]

I doubt if any practical grounding scheme can deal with a 100 kiloamp strike. However, good grounding can likely mitigate the effects on board from a nearby strike or a direct strike of lower energy. Every little bit may help!

Jim

[Montanan]

Originally Posted by cyan

While that seems to be the conventional wisdom, I find it curious that catamarans are statistically about twice as likely to get hit as same sized monohulls. Perhaps this "grounding has no effect" idea is more nuanced on a boat than on land, involving total waterline and surface area above water. However, there seems to be solid evidence that proper bonding of an aluminum mast to a ground plate may indeed help to avoid damage during a strike.


...and make sure that the black end is in the water and the red end is on the mast, as about 95% of all lighning is negative lightning.
(okay, that red/black part is just a joke because electrical engineers often think they're funnier than they really are )

I have read one theory about why multihulls are more likely to get struck is that they are more likely to be out on moorings and/or outer facing "T" docks and thus more isolated from other grounding targets such as a forest of monohull masts in the inner fairways and narrow finger piers of marinas, or near to shore based strike targets.

Love the remark regarding the polarity of connections of the jumper cable conductors. Sure wouldn't desire to cross the circuit polarity of the lightning strikes.

[daletournier]

Originally Posted by Montanan

I have read one theory about why multihulls are more likely to get struck is that they are more likely to be out on moorings and/or outer facing "T" docks and thus more isolated from other grounding targets such as a forest of monohull masts in the inner fairways and narrow finger piers of marinas, or near to shore based strike targets.

Love the remark regarding the polarity of connections of the jumper cable conductors. Sure wouldn't desire to cross the circuit polarity of the lightning strikes.

I'm not sure that holds true. As I mentioned earlier a cat had a direct hit here in the marina two weeks ago, it was half way down the second finger. Certainly wasnt isolated.

Also at Serangan harbour Bali several years back when I was there two cats got struck. There were many boats all on moorings, nothing particularly special about where these two boats were.

[cyan]

Originally Posted by Montanan

Love the remark regarding the polarity of connections of the jumper cable conductors. Sure wouldn't desire to cross the circuit polarity of the lightning strikes.

Well the "95% negative lightning" was actually the serious part, as clouds typically collect a negative charge at the bottom which then zaps down to a positive earth charge in most cases. Positive lightning is the scary beast, which can strike from way up high, miles from the storm, with much greater power. NOAA has a one-page summary...
https://www.weather.gov/jetstream/positive

[Alan Mighty]

Originally Posted by daletournier

I'm not sure that holds true. As I mentioned earlier a cat had a direct hit here in the marina two weeks ago, it was half way down the second finger. Certainly wasnt isolated.
.

Lightning, similar to many natural and human phenomena, is more complex than any human-devised hypothesis.

But nevertheless, the data suggests a few simple principles:

1. Larger boats are more likely to be struck than small boats. See Table 1 and Table 2 from Beth Leonard's story based on BoatUS statistics: https://www.boatus.com/seaworthy/mag...ning-facts.asp

2. Cruising multihulls are broad as well as long. That usually means that whether in a marina or an anchorage, a catamaran mast is horizontally spaced further from its nearest neighbouring masts (regardless of whether that neighbours are multi- or mono-hulls) than, say, the spacing between two monohull masts. In a forest of masts, the masts at the fringe of the forest and a mast within the forest but still relatively spatially isolated may be more at risk. See the discussion on Strike Probability by Marine Lightning Protection at: Catamarans

[Montanan]

From https://www.sailingscuttlebutt.com/2...tning-strikes/


Lightning Facts: An Analysis of Lightning Strikes
Published on February 19th, 2015
The odds of getting struck by lightning are about one in a million. But if you own a boat, the odds of it being struck by lightning are significantly higher – about one in a thousand. However, not all boats are created equal when it comes to lightning.

A just-released analysis of 10 years of insurance claims by Boat Owners Association of The United States (BoatUS) shows that certain boats are significantly more at risk than others. But which ones? And, what can you do if you’re caught on open water? BoatUS has some answers:

Let’s first state the obvious: It’s a no brainer why monohull sailboats with their tall masts pointing to the sky have significantly more lightning claims than powerboats – 3.8 chances per 1,000 versus a 0.1 chance in 1,000 for bass boats-runabouts-pontoons. The national average for the probability of a boat lightning strike claim for all types of boats and sizes is 0.9 chance per 1,000.

Size matters: It’s also not a stretch to understand why larger boats of all types – which present a larger target to the skies – are struck more often than smaller ones. A boat 40-65 feet in length has 6 chances per 1,000 while boats 16-25 feet have just a 0.2 chance per 1,000. Increasing the height of a sailboat mast from 35 to 45 feet nearly triples the odds of being hit.


Location matters, too: Where boating populations are dense and lightning is common, strike insurance claims are high. Six of the top 10 states in terms of frequency of lightning claims – Florida, Mississippi, Louisiana, Alabama, South Carolina and North Carolina – all lay within the thunderstorm hotspot in the Southeast and midsection of the country. Heading west, the frequency of lightning claims falls to about 1 chance in 10,000 along the Pacific Coast, or about 1/10th the national average.

The effect of two hulls: A multihull sailboat is almost twice as likely to have a lightning claim as a monohull. Why sailing cats get hit more is unclear, although theories include lack of a keel, more wetted surface, larger footprint, the dockage of cats at the outside edges of a marina, and higher average mast height.

[Paul L]

Originally Posted by Montanan

I have read one theory about why multihulls are more likely to get struck is that they are more likely to be out on moorings and/or outer facing "T" docks and thus more isolated from other grounding targets such as a forest of monohull masts in the inner fairways and narrow finger piers of marinas, or near to shore based strike targets.

....

I doubt that as a real reason. I sat in my cockpit in a very crowded anchorage in Panama during a wicked lightning storm. The Cat anchored close behind me took a direct hit to the mast. A mast that was fairly new to the boat as they had lost it off of Trinidad. The strike took out pretty much all electronics and near enough blinded me.

My Cat and Lightning theory is that the mast base sitting feet above the water is just too much of a calling card for the lightning gods.

[Sojourner]

Originally Posted by AndyEss

Yet lightning travels 1000s of meters through the air to release its potential energy.
Our tall, conductive masts make excellent short cuts for lightning to travel those last 10s of meters.
As a side note, I am always amused when friends say the reason why automobiles are safe in lightning storms because they sit on non-conductive rubber tires. Not sure why anyone would think that a 15cm of tire air gap poses any block to electrical energy that has already leaped probably through kilometers of sky

Because lightning can start at the ground as well and travels upward. Feelers come both up and down from the cloud. The big visible bolt doesn't come until two feelers meet. The bottom part feeler comes up from your mast, your head, a tree, etc. So I believe yes, a small air gap can prevent the bottom feeler, and then the big blast is less likely to come.

[Dave_S]

My theory on why more cats get hit is the rigging forms a 3d shape where a mono is a 2d shape.