Lightning diversion on deck stepped mast

[jskamer]

I know there’s a lot of other threads and opinions on this topic, I’m mainly interested to know what other people have installed on their boats. My 2004 Jeanneau Sun Odyssey 43 has a deck-stepped mast, which does not seem to be electrically connected to the compression post. There does not seem to be any grounding of the rig from the factory. Would it help to use big battery cables to connect both main shrouds to a keel bolt, or is this useless as the path of least resistance is likely through te mast?

Thanks for any insight in what others have done in a similar setup!

[GordMay]

NFPA 780, the Standard for the Installation of Lightning Protection Systems, specifies the size of the down conductor [Main Conductor Cable], for
Class I [<75Fy Hi] installations as:
Copper: Minimum Gauge is 2 AWG [35 mm2], with a minimum individual strand size of 17 AWG.
The IEC 62305-3 standard specifies: Copper: 50 mm2 [1/0 AWG].

[barnakiel]

Undrounded boats sometimes drop chain lengths from the chainplates to well below water level. I think the backstays can be just as good and less damaging to gelcoat.


b.

[Benz]

I simply don't supply a path to ground. My deck-stepped mast has no connection to the water (or the compression post, since it's a handy grab-post inside), and my synthetic shrouds are non-conductive.
So unless the lightning cares to travel along the thin layer of water on a rainy deck, the mast is just an uninteresting pole in the sky to it.
Did Central America in rainy season (when most boaters avoid it because of lightning), and did not get struck. Caribbean, Florida, New England summer--no strikes yet.
Not saying it's foolproof: could get struck tomorrow--my experience is just one data point.

[coopec43]

I've seen lightning hit the ground about 20M (10 O'Clock) in front of the car I was driving.

A metal mast is no more likely to be hit than a timber mast.

What happens when lightning strikes a yacht mast?
A small diameter conductors melt; wooden masts explode; and air gaps that are bridged by an arc start fires. On boats, radio antennas may be vaporised, and metal thru-hulls blown out of the hull, or the surrounding fiberglass melted, with areas of gelcoat blown off.22 July 2022

The odds of a boat being struck by lightning in the US are about one in 1,000, but in Florida lightning is so frequent that the chances of lightning damage to boats are about four times higher.10 Apr 2024
https://www.thetimes.com/uk/article/...acht-9w7325hpq


Type of Boat Chances per 1,000

Multihull Sailboat ....... 6.9
Monohull Sailboat ...... 3.8
Bass Boat ................ 0.1
Runabout.................. 0.1
Pontoon Boat............. 0.1

Overall Average ......... 0.9

https://www.boatus.com/expert-advice...k-by-lightning

[BobFord]

I'm so pleased to see this post re lightning . For many years I've asked the questions but there seems to be no experience out there - Anyhow , here we go - Aluminium cat , a hinged copper rod ( 2 ) from the Mast Compression Post to below water level. Questions - will this allow a lightning charge ( say field charge ) to dissipate safely ? Will the all aluminium boat shell act as a Faraday cage ? I've deployed this for many years but it is not easy to judge results , if any !!! Comments and opinions most welcome .

[NorthCoastJoe]

I have similar questions but a very different boat. All aluminum hull and deck with aluminum compression post, that is also part of my keel lifting device so its very thick aluminum.
So aside from the contact between the mast and its step everything is welded in a monolithic structure. With that my mast should be very well grounded.
But what happens if we take a hit? Will devices in the boat be damaged that are shut down with double pole switches. I would think most of the energy will travel straight through. Maybe toast the wood work around the mast step?

[barnakiel]

Watching Luna Rosa NOT getting hit I am bound to understand boats get hit by pure accident, not by design (of their grounding system).


btw mind that charge had Luna Rosa and Emirates to choose from - as well as a good couple dozen spectator boats - some of which had masts as high or higher (and surely well grounded) than the AC boats


God bless AC for that video. It cured me of my intellectual worries if not of my primal fear.


b.

[BobFord]

Originally Posted by NorthCoastJoe

I have similar questions but a very different boat. All aluminum hull and deck with aluminum compression post, that is also part of my keel lifting device so its very thick aluminum.
So aside from the contact between the mast and its step everything is welded in a monolithic structure. With that my mast should be very well grounded.
But what happens if we take a hit? Will devices in the boat be damaged that are shut down with double pole switches. I would think most of the energy will travel straight through. Maybe toast the wood work around the mast step?

Sounds logical , Joe . Agreed to isolate all electrical leads , where possible. I would love to define the Faraday effect . I have had (2) "field effect ", hits ,in past years but GRP cat. Dudded radios and frig ?? Melted antenna . Funny quote - I asked the Electrical Engineer , when he fitted out ( 12 y.o. ) , about lightning - his advice ," wear thongs and steer with (2 ) wooden spoons ".

Not sure whether he deserves a Nobel prize !! Cheers, Bob

[Uricanejack]

Our mast was hit by lighting.
I've never been in the vicinity of a stun grenade. I imagine the effect would be quite similar.
I was blinded, deafened and slightly stunned.
No trace of where it hit was visible.
No problems with ant electronics or radios.
Compass completely bamboozled. Huge errors and deviations after.

[coopec43]

Originally Posted by BobFord

I'm so pleased to see this post re lightning . For many years I've asked the questions but there seems to be no experience out there - Anyhow , here we go - Aluminium cat , a hinged copper rod ( 2 ) from the Mast Compression Post to below water level. Questions - will this allow a lightning charge ( say field charge ) to dissipate safely ? Will the all aluminium boat shell act as a Faraday cage ? I've deployed this for many years but it is not easy to judge results , if any !!! Comments and opinions most welcome .

I've done a lot of reading on the subject and even so called experts can differ in their views.

There are also a lot of people who consider themselves expert. I just started to read an article which started off "Your chances of being hit by lightning are about 1 chance in a 1000,000. Really!

There are a lot of good articles out there but I suggest you examine source/author before accepting their view. Here is one that appears to be pretty "authoritative":


Lightning Protection on steel hulls and superstructures

https://www.trawlerforum.com/threads...uctures.67595/

Apparently ships get hit quite often with no ill effects,

[coopec43]

Originally Posted by barnakiel

Watching Luna Rosa NOT getting hit I am bound to understand boats get hit by pure accident, not by design (of their grounding system).

btw mind that charge had Luna Rosa and Emirates to choose from - as well as a good couple dozen spectator boats - some of which had masts as high or higher (and surely well grounded) than the AC boats

God bless AC for that video. It cured me of my intellectual worries if not of my primal fear.

b.

But multi hulled yachts get hit more often?

While Alteza (now Sweet Escape) was supremely unlucky, the chance of a yacht being struck aren't that remote. BoatUS Marine Insurance analyzed 10 years of claims and came up with odds of one out of 145 for multihulls, one out of 263 for monohulls and one out of 667 for motor yachts.3 Sept 2024

https://www.dockwalk.com/safety/what...k-by-lightning

[GordMay]

Originally Posted by coopec43

...
There are also a lot of people who consider themselves expert. I just started to read an article which started off "Your chances of being hit by lightning are about 1 chance in a 1000,000. Really! ...

YES, really!

According to the US National Weather Service [NWS] Storm Data, over the last 30 years (1989-2018) the U.S. has averaged 43 reported lightning fatalities per year. Only about 10% of people who are struck by lightning are killed, leaving 90% with various degrees of disability. More recently, in the last 10 years (2009-2018), the U.S. has averaged 27 lightning fatalities [est. pop 330,000,000].
Odds of Becoming a Lightning Victim (based on averages for 2009-2018):
Odds of being struck in a given year (estimated total deaths + estimated injuries): 1 in 1,222,000.
Odds of being struck in your lifetime (Est. 80 years): 1 in 15,300.
NWS ➥ https://www.weather.gov/safety/lightning-odds

According to the US Centers for Disease Control and Prevention [CDC]: “About 40 million lightning strikes hit the ground in the United States each year. But the odds of being struck by lightning in a given year are less than one in a million, and almost 90% of all lightning strike victims survive...”
CDC ➥ https://www.cdc.gov/lightning/data-research/index.html

According to the National Lightning Safety Council [NLSC], the odds of being struck in a given year (estimated total deaths + estimated injuries) are 1 in 1,600,000.
Odds of being struck in your lifetime (Est. 80 years) 1 in 20,000.
NLSC ➥ http://lightningsafetycouncil.org/Odds.pdf

Of course, these simple statistics don't tell the entire story, and Your Expectations May Vary.





“Lightning Science: Five Ways Lightning Strikes People” ~ NWS
➥ https://www.weather.gov/safety/lightning-struck

[coopec43]

I think we are comparing apples with oranges.

I said "Your chances of being hit by lightning are about 1 chance in a 1000,000. Really"

I'm talking about the boat being hit and you appear to be talking about getting killed? Anyhow I'll go along with what the Insurance actuary has to say.

"Here's the good news and the bad. According to reports from our BoatUS Marine Insurance claim files, the odds of your boat being struck by lightning in any year are about one in 1,000. Some states, such as Idaho, have no lightning claims (no surprise)"

I have also read that the average yacht located in Florida could expect to be hit twice in it's lifetime. ?????


Looking at this map there is currently a lot of lightning activity off the West Coast of Mexico but none over Florida.

https://www.lightningmaps.org/#

[coopec43]

Apparently out in the open ocean there is little chance of being zapped. But what about The Great Lakes?

Look at the map.

https://www.researchgate.net/figure/...fig1_354549112