Lightning Strikes

[markpierce]

Got lightning rod. Wonder if it can protect the boat's electronics? Doubt it.

It's to the right of the VHF antenna, behind the anchor light:

[ka4wja]

Jbaffoh,
All of your questions are answered in the pages I provided links to....

Originally Posted by Jbaffoh

What I'm wondering, is whether a grounded mast is more likely to be stricken than an ungrounded mast. I understand grounding and bonding to minimize damage. But what is the research? Is there any correlation between frequency of strikes on grounded/bonded versus insulated?

But, in a nutshell, a grounded mast is NOT more likely to be struck, to the contrary it is LESS LIKELY to be struck.....Although the data shows a small advantage for grounded masts, any advantage is a good thing, at least in my opinion!!!
This is all backed-up by both the science/engineering AND decades of real-world data (both on boats and on shore).....
Please read the data....
Whether you choose to believe or disbelieve the data is up to you.....






sokari,
You're welcome....

Originally Posted by sokari

Hi John, thanks for the input but in your experience noted above, are the electronics being protected by some kind of Faraday's cage and that's why they suffer no damage?

No, as Wotname wrote there are no "faraday cages".....just a well grounded tower and coaxes grounded as the enter the building...We don't even have any lightning arrestors, etc.....just good grounding...
(On my home antenna tower, which is less well grounded, I do have lightning arrestors attached to the coaxes as they get to the ground, and even though I've taken a few direct strikes in the past few years, I've not suffered any damage....)



And, sokari, I actually appreciate you trying to read all the data, and trying to understand the facts.....as in the past I've been frustrated by these "lightning discussions".....
To be clear, I'm not telling anyone what to believe, just providing the science/engineering data, as well as my own real-world decades-long experiences....
(my 65' tall alum mast and shrouds on my Annie Laurie are well grounded, so I do practice what I preach!!!)


Keep your head down in those T-Storms!!!
Fair winds...

John
s/v Annie Laurie

[Paul L]

Originally Posted by markpierce

Got lightning rod. Wonder if it can protect the boat's electronics? Doubt it.

It's to the right of the VHF antenna, behind the anchor light:

Is it an issue that your VHF antenna is higher than your lightening rod?

[offshorer]

can somebody please recommend the best way to ground a boat?

[ka4wja]

Originally Posted by offshorer

can somebody please recommend the best way to ground a boat?

offshorer,

As all boats are a bit different, precisely where / how you'd run the grounding wires and place/mount a grounding plate (or use a external keel, etc.) will be "boat specific".....
BUT....
But, all the general info, data, procedures, recommendations, results, etc. (even wire gauge recommendations!) are right there for you in the links provided.....


Fair winds..

John
s/v Annie Laurie

[noelex 77]

Originally Posted by Jbaffoh

What I'm wondering, is whether a grounded mast is more likely to be stricken than an ungrounded mast. I understand grounding and bonding to minimize damage. But what is the research? Is there any correlation between frequency of strikes on grounded/bonded versus insulated?

It is very common myth that bonding the mast must increase the risk of lightning strike. In fact the opposite is true although the benefit in reducing the average number of strikes is quite small. Viking sailor has given a good explanation of why, but it's worth emphasising again that bonding (slightly) decreases, not increases the risk of a strike.
It is an important message because the myth stops people grounding their boats and even causes them to disconect existing grounding systems. A great pity when as are significantly increasing the chance of severe structural damage in the event of a strike.

[Jbaffoh]

John, Viking & noelex: Thank you for taking the time to explain this so clearly.

[sokari]

Many thanks to everyone for their input. There's certainly a lot to think about and consider. I appreciate everyone's suggestions. Cheers.
Rosemary

[Amanin]

Originally Posted by Viking Sailor

Lightning is not random or mysterious. It is a governed by the laws of physics and is generally well understood.

What makes lightning seem mysterious is that it occurs in an electrostatic environment that humans are not even aware of until their hair stands on end or their is a bright flash in the sky. We are so ill equipped to sense this environment that we take shelter under a tree in a rain storm. If we could see in this environment the tree would glow as it leaves striped away electrons from the passing air and water molecules. And, we could watch these ions rise toward the sky as a charged cloud passes overhead. Then as this process builds a local charge difference between the tree and the air a small "leader discharge" occurs creating a highly conductive ionized path of superheated air reaching upward towards the cloud. Suddenly, the negatively charged bottom portion of the cloud has a discharge path to ground. WHAM! Lightning.

This process is not limited to just trees, it also happens to air currents that get deflected upwards, and to boats that are not properly bonded. However, if the boat is properly bonded then any charge buildup is conducted to ground and no lightning. This sounds good, but there is a problem. You see, there are two form of lightning. What was described above is the most common form of lightning. There is another form of lightning that goes between the negatively charged ground and the positive ions in the cloud. Two interesting things about this form of lightning is that it's comparatively rare, and it is a lot more powerful then the common type. It turns out that a well bonded boat acts as a skyward extension of this negatively charged ground and slightly improves the chance that lightning will occur.

To complicate this picture further there are two ways in which clouds can be charged. The most common is with the top positively charged and the bottom negatively charged. However, the reverse is also possible. This is of course not helpful in preventing a lightning strike when the boat is bonded. Fortunately, this cloud configuration is quite rare.

The above explains why bonded boats are less likely to be struck by lightning but never the less still do get hit. Also, it is the invisible paths that are forming that result in the near misses that are so often reported. So, no mystery here. Just good old physics.

A very low-tech "precaution" against a lightning strike might be canvas olive oil sacs tied to the bow, slowly releasing olive oil to the sea. Traditionally, this was used by 16th century meditarenean pirates, who believed that olive oil made their boats invisible to lighning. Maybe some good old physical explanation to this?

[Viking Sailor]

Originally Posted by Amanin

A very low-tech "precaution" against a lightning strike might be canvas olive oil sacs tied to the bow, slowly releasing olive oil to the sea. Traditionally, this was used by 16th century meditarenean pirates, who believed that olive oil made their boats invisible to lighning. Maybe some good old physical explanation to this?

Amanin,

I have to confess that the 16th century was slightly before my time. However, it is known that wooden ships with rope rigging were poor conductor of static electricity. A fact exemplified by the reports of St. Elmo's fire about the rigging on this type of ship. St. Elmo's fire is ionized air (plasma) in the presents of an electrostatic field. It is nearly always associated with lightning storms. And, in olden times, the use of oil on water was a common way to reduce wave action in a storm. It is likely that the use of oil would also help suppress the generation of ionized air molecules do to the interaction of air and waves. Of course it should be noted that the sailors of that time may have simply come to an erroneous conclusion about the effect of oil and lightning. Just saying.

[Jbaffoh]

Originally Posted by Amanin

A very low-tech "precaution" against a lightning strike might be canvas olive oil sacs tied to the bow, slowly releasing olive oil to the sea. Traditionally, this was used by 16th century meditarenean pirates, who believed that olive oil made their boats invisible to lighning. Maybe some good old physical explanation to this?

It's well known that 16th Century pirates were at the cutting edge of physics. After all, Newton wasn't even born until the 17th Century, and Georg Ohm and Tesla until the 19th Century.

[BMWshoe]

On a run from Florida to the Bahamas, my 60' mast took what we thought was a direct hit. The boat and all through hulls were thoroughly bonded - she was custom built by a well known boat manufacturer where I was the general manager. The VHF antenna was vaporized. Every thing electronic, or with electric wires was destroyed. Batteries, light bulbs, navigation, radios, AC units, TV, all instruments- fried. No damage to boat structure except where molten drops of metal landed on the deck.
Seconds before the hit we saw a significant increase in the digital readout of wind speed. (much higher than the actual wind that I estimated at 50 knots). Static charge!

[smaarch]

I suffered a direct masthead strike about 12 years ago.
the route the strike took is telling
the solutions aren't so obvious.

a 1976 Pearson 30
deck stepped mast (i.e. mast is not directly grounded)

the strike vaporized everything at the top of the mast . vhf antenna, windex, anchor light. the strike found the wiring harness inside the mast and followed it thru the boat. not a good thing!
it eventually found the biggest piece of metal........the engine.

all the grounds in this boat are lead to the thru-hulls. not acceptable by today's understandings.

the strike found its ground at the bronze raw water intake

lucky on several points
the strike fried the electric fuel pump (gasoline atomic 4) without igniting fuel.
the bronze raw water thruhull disintegrated in hand during the insurance survey. apparently electric charges effect the metallurgy of bronze. lucky the boat didn't sink.

after this event, ive read various strategies and they all seem inconclusive.
everything from masthead dissipators, hanging a chain off the backstay, grounding etc.
some writers even point out this may attract a strike.

the only conclusion i've come to is the thru hull grounding is definitely not a good idea.
and like other posters stated, i still havent completely gotten over this and prefer not to be on board when threat of a strike exists. In fact cut a sail short yesterday because of Tstm alert. something unlikely before.

[noelex 77]

it is always difficult to know with lightning, but my conclusion from your description is that had been grounded you would probably have suffered less damage.
Most of the damage you had was from the energy escaping via the engine and thru hulls. The thru hulls are particularly dangerous as the lightning can vaporise the fitting and leave a large hole below the waterline as you ( almost) found out. If your boat had been grounded there is a good chance the energy would have left the boat in the safest way.

Originally Posted by smaarch

some writers even point out this may attract a strike.

It is a common myth,that grounding will attract a strike when it overall slightly reduces the chance of a strike. I would be interested in any links you can provide that support a contrary view.

Originally Posted by smaarch

the only conclusion i've come to is the thru hull grounding is definitely not a good idea.
.

Just to clarify bonding or grounding thru hulls is completely different to grounding the boat to reduce lightning damage. It's unfortunate that "grounding" can be used to describe both and this leads to some confusion.

[westwinds]

Originally Posted by skipmac

Had not heard of the company but if founded by a lightening researcher from UF it must be Martin Uman. He is certainly considered one of the best if not the best expert in the field world wide.

Has a cool setup for his research. He has a facility in the area with bunkers full of test equipment and a launch pad for model rockets that trail a grounded wire when fired. When thunderstorms are in the area they shoot at it with the rockets and capture strikes pretty often. Sort of a modern version of Ben Franklin's kite and key. I think if anyone could come up with a system to minimize the risk and damage from lightening strikes Uman might be the one.

The following in my own words is taken from the first chapter of The Art and Science of Lightning Protection by Martin A Uman published in 2008 and printed by Cambridge University Press. Uman has also published over 200 research papers and was Chair of the Department of Electrical and Computer Engineering from 1991 to 2003 at the University of Florida and currently holds the rank of Distinguished Professor. Chapter 2 is Lightning Damage, Chapter 3 General Methods for Lightning Protection: Faraday cages, topological shields; and more practical approaches: cone of protection and rolling sphere methods. Chapter 4 Structure Protection: air terminals and down conductors. Chapter 5 Structure Protection: grounding. Chapter 6 Surge Protection for Electronics in Low Voltage Electrical Systems. Chapter 7 Humans and Animals. Chapter 8 Lightning Warning. Chapter 9 Airships, airplanes, and Launch Vehicles. Chapter 10 Ships and Boats, Chapter 11 Trees. Chapter 12 Overhead and Underground Power and Communication Lines. Chapter 13 Lightning Elimination. Chapter 14 So, What Do WE Know and What Don’t We Know About Lighting Protection?

Discharges between clouds are more common than cloud to ground and is a concern to aircraft. Cloud to air also exists. For sailboats we are of course concerned with cloud to ground, or should I say water. A radio tower, a building, and a sailboat have different construction so I am thinking we have to be careful generalizing between these various structures. Also, saltwater conducts electricity about 1000 times better than freshwater. Of the four types of cloud to ground lightening, nearly 90% is cloud to ground initiated by a negatively charged downward propagating leader while about 10% of the lightening occurrences, the cloud to ground is initiated by a positively charged downward propagating leader. Two other types are rare. One is upward initiated from tall towers and mountaintops and is a positive charge. Using as an example the type of lightening occurring 90% of the time, electrons move in a step fashion with a 50 meter length jump, a pause for a microsecond, and then another step of about 50 meters downward until this negatively charged stepped leader makes connection with a separate positively charged upward moving leader that starts from the ground and moves upward sometime after the cloud to ground leader has become established. On these downward and upward negatively and positively charged leaders, branches are produced. When a positive and a negative branch intersect, current flow with an average of 30,000 amps flow and a lightening strike point is determined. It is difficult to predict the time and place for this connection because electrons have low mass so these free electrons are very mobile compared to atoms that have lost one electron. After a stroke occurs, other strikes follow the exact path of the original strike up to the last when the strikes occurring near the end will again have more than one strike within a lightening bolt occurs 80% of the time with 3 to 5 strikes being most common and the whole lasts a few tenths of a second. 40 to 50 microseconds separate the strikes with more than half the continuing strikes lasting more than 40 microseconds. The continuing strikes follow the original path with no branching has smaller peak currents averaging 10,000 to 15,000 amps where the original strikes were above 30,000 amps on average with 100,000 amps near the maximum. Towers 100 meters high are hit by these normal negative downward propagating leaders and are four times more likely to be hit if more than twice as tall as another tower. Towers 400 to 500 meters have another type of lightning, which initiate as positively charged upward going leaders from the tower and can have first strike as high as 300,000 amps.
Most lightening is over land and caused by heating from the sun causing moist air to move upwards. On the west coast of the United States, the Pacific Ocean current from Alaska cools air so little lightening exists. Central and southwest Florida has 90 days per year with lightening storms. The number of strikes for a year averages about 15 per square kilometer. There are 2.7 square kilometers in a square mile. With this density, a house is likely to be hit once every 50 years in Florida.