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rexposeidon 15-04-2008 19:56

lightning strike prevention/protection against?
Does anyone know or have recommendations to help deflect an at sea lightning strike? Or can you direct me to the correct thread. Thanks.

Alan Wheeler 15-04-2008 22:33

You can't. A lightning bolt has most likely traveled 10miles through the air on it's way to the ground. It is in the millions of Volts and millions of amps. The presence of your boat means nothing to it. We have discussed this subject in great depth and if you do a search, you will find enough reading to keep you happy for hrs.
Sadly we had a guy killed here in NZ just yesterday. He was out riding his horse and was struck. Both he and His Horse died.

maxlev 16-04-2008 01:09

Sure was heaps of lightning up north yesterday.
300 per hour weatherman rekoned.

After one massive flash thought I'de lost the solar panel or controller.
A bit of checking with multimeter, solar panel OK, controller turned off but battery not fully charged.
Soon after a very strong gust came through spinning the air generator big time which sorted the solar controller glitch.
Fixed for free.

claire 16-04-2008 02:00

You can't really avoid lightning strikes, but you can somehow limit the damage to your boat, I think, with the following preventive measures:
1. ground the mast and/or shrouds
2. disconnect both positive AND negative leads to the expensive equipment like radios, auto-pilot, chart plotter etc.
3. Stick the laptops in the oven

This is what we concluded from our experience with 2 lightning strikes, one year apart. The first one was not a direct strike, we had the mast grounded and lost "only" the wind indicator.
The second one was a direct hit, the only one at our anchorage during the whole thunderstorm, coming from "nowhere". The mast was not grounded, that time. We hear an explosion noise, the electric panel started smoking, most LEDs dead. Everything on top of the mast blew up, the mirrors in the bathrooms, close to the shrouds, exploded, all electronics except the GPS was dead. One engine control panel lost the warnings. The speed Xducer was mostly destroyed and water started leaking in slowly....
A close look at the damage showed that it had reached the electric and electronic systems through the ground wires. Obviously, the lightning strike energy took all the possible routes to ground and I am convinced that there would have been less damage if the mast had had a good direct connection to the water.
Since then, we have installed a 2 wire connector to the auto-pilot, easily reachable in case of intense thunderstorm.

Alan Wheeler 16-04-2008 02:17

The Direct hit must have been terrifying.
I was close to a direct hit once. I will never forget that Earth shattering explosion and the huge blue flash that lept at least a ft out of the light bulb without shattering the glass. The Telephone being blown off the wall.

the lightning strike energy took all the possible routes to ground and I am convinced that there would have been less damage if the mast had had a good direct connection to the water.
I doubt it. You simply can not provide a large enough conductor for that kind of Current flow and Voltage pressure. It will still take every other conceivable path to ground if it can easily find it.
You are correct about laptop in the Oven. That's the best place for every electronic component if you can get it there.
The problem is, there are too many variances with each and every storm. The result is how and what becomes energised. Sometimes grounding only makes you more of a target. Sometimes it seems the higher point never gets hit, sometimes it does. We even have photo's here in that Gallery that show hits to mast in a Marina full of masts and some higher and some lower. Why it chose that one, no one knows. It still has Scientists baffled at the odd behaviour of lightning. Just when they think they have it cracked, some one comes up with some evidence of something that defies their theory. Kinda cool that really.

Viking Sailor 16-04-2008 02:42

There is no way to prevent lightning from striking a boat. There are techniques that can be used to increase the chance that you will not be injured and the boat will not be sunk by a lightning strike. However, even using these techniques, the boat's electronics and electrical equipment will still be at risk of damage.

The major risk during a lightning strike is when the lightning seek a path to the sea that goes through you or the hull of your boat. This is known as a "flashover" event. Lightning will take ALL possible paths to get from ANY metal object above the waterline to the sea. To prevent "flashover" events all metal objects aboard should be connected to a common seawater ground. This includes stays, shrouds, air terminal, mast, poles, sail tracks, lifelines, stanchions, anchor(s), anchor chain(s), tanks, through-hulls, electrical components, electronic equipment, RF grounding plates, engines, etc. The size of the wires making these connections depends on their length, stress, and thermodynamic characteristics. As an example, the recommended wire size for the connection from the masthead located air terminal should be #4 GA tinned copper. However, an old stainless steel backstay would work as good or better. For the other connections #8 GA tinned copper or equivalent should be adequate.

Some common sense is required when making these connections. If an anchor is laying on a already grounded anchor roller then it too is grounded. However, the bitter end of the anchor chain connected to that anchor should also be taken to its own ground. That way a "flashover" event is less likely to occur between the pile of chain and seawater that includes someone in the v-berth and hull of the boat.

BTW, if you use low inductance connections to connect the above items together you will by default have a very good RF ground system. Low inductance connections can be made using copper or stainless steal tape and braid. The stainless will last longer.


fastcat435 27-05-2008 14:35

Getting your deck wet with seawater will help and give your boat a lot of grounding
Just put on your deck wash

GordMay 28-05-2008 02:50

As others have implied, “Lightning Protection” is a misnomer; which might be better termed “Lightning Mitigation”.

Lightning Protection - ABYC Recommendations (see Standard TE-4, formerly E-4)
Lightning Protection - ABYC Recommendations

Boomp 28-05-2008 05:02

There is so much information and from what I've seen, most electronics will be destroyed but people have a good chance because of the wire cage around them. [rigging, mast etc.] My mast is grounded but I have a metal box and keep a portable vhf and hand held gps and cell phone in it for backup. It offers the same protection as a microwave oven or reg. oven. At least w sailboats we can get back in!

cabo_sailor 28-05-2008 06:31

I read something about this some time ago and since it seemed reasonable I tend to believe it.

As everyone has stated - lightning goes where ever it durn well pleases.

What I heard was that if your boat is properly bonded you increase somewhat the chance of taking a hit but decrease the potential for damage.

If the boat is unbonded you decrease somewhat the chance of taking a hit but increase the chance of damage such as blowing out a thru hull.

For the record, my boat is bonded.

As a small anecdote, when I bought my first boat I found a 5 foot lenghth of foam pipe insulation in the cockpit. I enquired as to its purpose and the PO told me that when there are T-storms in the area he placed it over the wheel to protect him from lightning!! :dork:


jackdale 28-05-2008 10:05


Originally Posted by rexposeidon (Post 152969)
Does anyone know or have recommendations to help deflect an at sea lightning strike? Or can you direct me to the correct thread. Thanks.

Take a look at Lightning protection of boats and marine facilities.


Beausoleil 04-06-2008 07:25


Originally Posted by jackdale (Post 166665)

I'll preface this by saying I've never had any contact with Dr. Ewen Thompson - in the past I've read his paper on marine lightning mitigation, and have found that he has left the University of Florida to start up his own company, Marine Lightning Protection, Inc. My interest in lightning protection began when I got my amateur radio license in 2001 and installed my HF system at home.

After pouring over data from marine lightning strikes over the years, he's come to the conclusion that the lightning bonding system on a boat should really be more like that of a commercial building - perimeter grounding conductor connected to ground rods every few feet. The old ABYC recommendation of a 1ft^2 grounding plate mounted on the outside of the hull just isn't sufficient. I'll include a quote from the conclusion of his paper:

"The U.S. code for lightning protection of boats is seriously inadequate. Downconductor conductance should be specified as that of #4 gauge copper rather than the #8 gauge presently quoted in order to minimize the risk of overheating and melting. The 1-ft^2 ground plate is shown to be hopelessly inadequate to prevent side flashes in fresh water. The magnitude of the potential gradients involved is 2 orders of magnitude larger than the breakdown value if we ignore the effect of breakdown in the water and points to no simple solution to this problem. In salt water, a 1-ft^2 ground plate is inadequate. The concept of a cone of protection with a 90 apex angle is not applicable to the attractive effect of sailboat masts because it underestimates the probability of a strike occurrence by an order of magnitude."

His company's website says they've worked with the National Fire Protection Association (NFPA) to publish a new version of Chapter 8 (Marine Protection) of the NFPA 780 Installation of Lightning Protection Systems. His company is working with some manufacturers to build in from the start a perimeter bonding system. Since it's a significant effort to install after manufacture, I'm thinking about a similar system on our boat. We've got quite a few bronze thru-hulls, and it's possible to form a "perimeter" loop using them. I may actually contact Dr. Thompson with some specifics of our boat - particularly the diameter and location of each thru-hull, and see what kind of improvement we could expect to see over our existing 1-ft^2 external ground plate. In fact, there's enough info in his paper for me to whip out my old HP-15C scientific calculator and run the numbers myself...

I may just have to whip out the $US38 for a copy...

Any of our board readers here have any work experience with NFPA 780 and NEC lightning bonding systems? Comments?

GordMay 04-06-2008 08:18


Originally Posted by Beausoleil (Post 168744)
...Any of our board readers here have any work experience with NFPA 780 and NEC lightning bonding systems? Comments?

Dr. Thomson’s opinions generally represent the overwhelming consensus viewpoint of informed professionals & academics.

easterly 04-06-2008 11:03

Has anyone looked into lightning mitagation systems on aircraft? The radome on the front of the planes is fiberglass and they have very expensive electrions behind them. When lightning strikes the fiberglass radome, happens 100s of times a year, it is mitigated by closely spaced small metal disks glued to the surface. The lightning jumps the gaps creating an ionized path that it will follow. The fiberglass/electronics are saved. The same thing should work on a sail boat. Mast ungrounded, closely spaced small metal disks glued to the exterior of the hull from the shrouds/chain plates down to the waterline. I am going to do this on my boat. I figure that if hundreds of planes are hit every year and none of them have fiberglass radome/electronic damage it must work. If the disks stay on at 500mph they should stay on at 8 kts. It may be worth looking into. Any comments?

GordMay 04-06-2008 11:05

An aircraft, which cannot be solidly grounded to earth, is not a boat, which can (be).

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