New lightning stats from BoatUS Insurance

[DotDun]

Striking Lightning Facts - Seaworthy Magazine - BoatUS

New numbers, not vastly different than what's been reported previously.

The probability of a lightning strike by type of boat, 2003–2013
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

The probability of a lightning strike by size of boat, 2003–2013
Type of Boat--------Chances per 1,000

0-15 Feet--------------------0
16–25 Feet-----------------0.2
26–39 Feet-----------------2.1
40–64 Feet------------------6

[colemj]

Interesting - I think that last set of numbers is new? At least I don't remember them in the previous data.

Since most multihulls are >40', perhaps this helps explain the mono/multi hit rate difference?

It would be illuminating to see the mono/multi data presented by length.

Mark

[ronbo1]

The article in Seaworthy has more detail, in particular, why multis have more claims than monos. The first reason seems the lack of a grounding keel.

Ronbo

[colemj]

The article states this:

"Understanding why multihulls get hit so much more frequently than monohulls is more problematic. Several theories have been put forward including the lack of a keel, the increased wetted surface area, the larger footprint, the location of catamarans at the edges of marinas, the overall size of catamarans, and the average height of their masts. Unfortunately, we do not yet have enough data to be certain of what is driving this finding."

If it is indeed due to the lack of a grounding keel, then that is even more interesting and would put to rest the "ground/not ground" argument with regard to lightning.

Mark

[DotDun]

Indeed, the ground/not ground theories don't have much corroborating data to back them up.

Dr. Ewen Thomson is leaning towards the theory of "sparking surface discharge electrodes" for protection. It makes one wonder if this works, that the pure footprint on the surface of the water that a multihull presents is what causes the attraction. To me, a monohull of more weight would have more actual 'wetted surface' of hull to water, more being under the water than at the water line comparatively.

Marine Lightning Protection Inc.

[Bluesailor]

It is obvious why larger boat get hit by lightning more often. They have higher masts than the smaller ones.

[colemj]

Originally Posted by Bluesailor

It is obvious why larger boat get hit by lightning more often. They have higher masts than the smaller ones.

Taller boats certainly fit your hypothesis, but most catamaran rigs are similar in height to those of equal length monos. Most are actually a bit shorter since they carry more sail area for a given length.

It would be nice to see multi/mono hit data sorted by LOA.

Mark

[travellerw]

I read a hypothosis somewhere that postulated multihulls get hit more often as they are more frequently found in shallower water. This means they are closer to the negative charge (earth) and thus the lightening takes this path. Its an interesting hypothosis. I think its paritally backed up by the fact that boats are rarely (not never) struck in deep water.

The authors suggestion was that if you were on a multihull during a lightening storm, you should move to deeper water. It couldn't hurt.. Heck it seems less silly than hanging chain over your stays.

Personally my gut feeling is its much more complicated (many factors) than we realize.

[robert sailor]

I read a report that multi's were being hit in marina's and even when right beside a mono with a taller mast. There has been all sorts of speculation why this happens but as far as I can see no solid conclusions just lots of speculation. The only thing for sure is that multi's do get hit at a much higher rate. I'm sure over time this will get figured out.

[colemj]

Originally Posted by travellerw

I read a hypothosis somewhere that postulated multihulls get hit more often as they are more frequently found in shallower water. This means they are closer to the negative charge (earth) and thus the lightening takes this path. Its an interesting hypothosis. I think its paritally backed up by the fact that boats are rarely (not never) struck in deep water.

The authors suggestion was that if you were on a multihull during a lightening storm, you should move to deeper water. It couldn't hurt.. Heck it seems less silly than hanging chain over your stays.

Personally my gut feeling is its much more complicated (many factors) than we realize.

I don't believe that hypothesis could stand up to fact. For it to work, 50% of multis would have to always be in shallower water than monos. Including ones at docks and ones in anchorages that don't have shallow areas. It's hard to believe that could be the case.

Then there is the relative thing - monos in 10' of water are safer than multis in 6'?

I don't think it is a fact that boats are rarely struck in deep water - just that on average, boats are rarely in deep water. Certainly lots of stories about people on passage suffering lightning strikes.

I still think having strike data on equal LOA mono/multi may help narrow the theories.

For example, multi's are twice as likely to get struck overall than monos, but the percentage of all multis <40' is very low, while the percentage of all mono's <40' is very high. Yet overall, boats >40' are 3x more likely to be struck than boats <40'.

Difficult to see the above relationships being coincidental.

Mark

[ronbo1]

I believe these statistics are based on claims. Larger boats usually have more expensive electronics which don't fare well when zapped hence more claims than smaller less equipped boats.

Though lightning travels wherever it wants, it generally takes the most direct route to ground. A monohull mast grounded to the keel provides that route. A multi's mast loses that advantage and may suffer more from side flash damage.

But lightning seems to defy logic.

[Ziggy]

There are more multis in lower latitudes than further north. Lighting strikes are a lot more frequent in lower latitudes (e.g., Florida, the lighthing capital of the world). This may explain, at least partially, why more multihulls get struck.

[Dhillen]

Lightning is indeed not well understood. I was on my boat in the marina in CT many years ago at the height of summer when the black clouds rolled through. I watched lightning ignore all the high pointy metal masts and strike the ground between a car and a dumpster (both metal). This made me realize all the stuff I learned in Boy Scouts about lightning was ********, namely, it always strikes the highest object and that it is attracted to metal.

Also, I know quite a few boats that have suffered direct hits from lightning or side hits, and all of them were at anchor (usually in lightning-prone areas such as FL, Panama or Malaysia). I know of nobody, nor have I heard of anybody, getting struck while crossing the ocean. I guess it has happened but I have not, as yet, heard of a reliable account of this.

We have been out at sea with lightning striking all around us, left, right and frickin' center (Andaman Sea) but despite our 70 foot mast being metal and easily the tallest point for hundreds of miles around we thankfully were not touched.

It is scientific fact, however, that trailer parks attract tornadoes.

Dhillen

[colemj]

Originally Posted by ronbo1

Though lightning travels wherever it wants, it generally takes the most direct route to ground. A monohull mast grounded to the keel provides that route. A multi's mast loses that advantage and may suffer more from side flash damage.

But wouldn't this contradict the statistics that multis are struck twice as often as monos?

Originally Posted by Ziggy

There are more multis in lower latitudes than further north. Lighting strikes are a lot more frequent in lower latitudes (e.g., Florida, the lighthing capital of the world). This may explain, at least partially, why more multihulls get struck.

That would make sense only if the number of multis in lower latitudes were twice the number of monos. I don't think this is the case.

BTW, while FL may be the lightning capital of the USA, I can assure you that it is not that of the world! We have been in places that Floridians there cannot believe…

Mark

[DotDun]

from Wikipedia....strikes/km2/yr