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Old 01-18-2008
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Being Hit By Lightning - To Ground or Not

So I’ll admit I’m a bit paranoid about getting hit by lightning. I’ve been hit twice, once at Cape Lookout, NC on a Grady-White 23’ Gulfstream and the second time at Three Mile Harbor on Eastern Long Island on our Little Harbor 38. In both instances we were around a lot of other boats that had anchored late afternoon, perhaps a little earlier than normal to ride out the night and oncoming squall lines.

On the Little Harbor, we were a sailboat among a lot of other sailboats so that we got hit, well that’s the way it goes I suppose. On the Grady, we were surrounded by numerous sailboats. All we had was 15 foot outriggers on the hard top which I had grounded with #4 cable to the engine block. The Grady is a well-made boat but even they do nothing out of the factory regarding lightning grounding. My take is that since I did such a great job grounding I turned us into a really good antenna to “pull down” a strike. When we were hit, my wife and I were standing under the hardtop with the curtains down. Behind us, shards of white hot metal burst onto the deck from the super heated terminal where the # 4 wire connected to the outrigger base. Our loran and depth sounder got fried through the ground wire and transducer presumably, because the power wires were disconnected. Our Icom radio survived intact.

Regarding the strike to the Little Harbor, it is of course a well grounded boat with a bonding system. Even so, as the storm approached I took a battery jumper cable and clipped one end to the base of the port shroud and let the other end dangle in the water. Just after we went to bed I saw and heard that instantaneous “crack” followed by a loud “twang” which I was quite sure was from the sound of the rod rigging (like most things, it has its own unique sound). In the morning when I came up on deck, sure enough, there on the deck lay the 36” whip antenna and part of the base from the top of my mast, having been blown out of its base and bent into a 90 degree angle from being super heated. Where the battery cable had been clipped onto the rigging there was a minor scorch mark (Nitronic rod is pretty tough stuff). Other than my Xantrex Pathmaker being fried (it was the only piece of electronics that’s really hard to get at and disconnect) all the electronics were fine as I disconnected everything going to the electronics including grounds this time.

I guess my take at this point, other than the fact that my wife especially hates sailing in lightning, is that I still would rather be well grounded than not as we’ve had well contained damage each time. I must admit that even with my small sample and relatively small amount of time I get to spend on the water, it does seem to me that being well grounded increases the chances of being hit. It’s just that I’ve heard some really horror stories regarding the damage to boats that are not properly grounded. Does anyone have any experience using one of the lightning / static dissipater products, protecting electronics with a power conditioner, or any other thoughts or experiences with lightning?

Last edited by marinedtcomRob; 01-18-2008 at 07:46 PM.
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Old 01-18-2008
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One technique we used in the ole south - that actually works, is taking your cables and doing a loose knot at a point closest to the power source. The knot creates a magnetic field that causes the cable to blow apart there - but doesn't allow the rest of the current to travel any further...That is a very low tech solution for protecting gear. However this is good reading: Link

For most in hull grounding to be effective on a fiberglass boat, one of the techniques was the copper plate running for to aft with additional copper looping from port to starboard to create a Faraday Cage...

There is nothing to prevent a lightening strike - just various techniques to minimize the effect...if your boat is properly grounded, and such...(and seems there are tons of products that promote something that aides etc for it)... none of them are lightening proof...and usually due to the mast and the tallest structure and usually the backstays and forestays are not grounded out to the water - there is only one direct path and that is in the boat and out whatever path your boat has....
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Old 01-18-2008
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Rob-

The only real way to protect electronics is to disconnect them and store them in a metal box. The voltage surge induced in the wiring is what fries the equipment normally, and not much can prevent that.

There are basically two schools of thought on lightning grounding and bonding.

The first is to ground the mast and all large above deck metal objects, like stays, shrouds, stanchions, pulpits and pushpits. This, in theory, should create a region of safety. The grounding system should use a thick ribbon or foil of copper to connect the metal to a grounding plate on the exterior of the keel.

The second school is to leave the boat completely ungrounded. The reasoning is this... grounded boats tend to get hit more often. So, by leaving the boat entirely ungrounded, you reduce the chance of getting hit. However, there is a downside to this... ungrounded boats generally suffer much more damage when they do get hit.

So either you ground and increase the risk of getting hit, and minimize the amount of damage a hit will do, or don't ground and minimize the chance of getting hit, but risk far more damage if it happens.

The static brushes are basically lightning phobe placebo equipment. For those to actually work, they would need a decent path to ground and a solid ground connection...

Power conditioners don't work, since the lightning power surges can occur in the wiring leading into the equipment, and it doesn't have to be power wiring... the mic cord on a VHF set could fry the electronics if the lightning induced surge is high enough.

As for the Nitronic rod being blow out... not completely surprised given stainless steel's generally high resistance to electricity. It is roughly only 3% as conductive as copper... and as such tends to heat up quite a bit under the very high voltage/amperage of a lightning strike.
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Last edited by sailingdog; 01-18-2008 at 07:57 PM.
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Old 01-18-2008
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Saildog

My boat has a bonding plate on the hull not on the keel but to the left of the shaft tube the hull is only 1/2" thick in that area, It is small maybe 3x8". The engine and chain plates are conected to it, the mast is not. I want to connect the mast also but am concerned about the small size of the bonding plate, the run the wire would take along the bottom inside of the hull and all the keel bolts it would have to pass by? What would you recomend?

Could I Just hook the mast to the first keel bolt?

Last edited by Stillraining; 01-18-2008 at 08:50 PM.
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Old 01-18-2008
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Rob...I've never seen any convincing evidence that any of the masthead products work. Power conditioners that WORK are expensive but may be worthwhile for individual high cost items...SSB's, Plasma TV, PC's etc. if you are in an area that is hit with regular T-storms...(Florida & the Chesapeake come to mind!). I agree with your conclusion that a properly grounded boat is the way to go...and I also like to hang around boats with taller masts (g)
I've never been hit myself...but have been in the company of those that have and these grounded boats had significant damage to electrical components but remained with masts upright and afloat. Meeting those two criterea is sufficient for me...the rest is all insurance!
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Old 01-18-2008
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Stillraining-

It really depends on what your keelbolts are made of and whether you have an encapsulated keel or not.

Stainless steel keel bolts are not going to do the job very well. Either is an encapsulated keel. Personally, I wouldn't use a keel as a grounding plate... there are serious possible problems with doing so.

BTW, A grounding plate should have at least four feet of linear edge to dissipate the charge. The bonding plate you have doesn't sound to be large enough to do a proper job, especially since the mast isn't connected to it.
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Old 01-18-2008
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well I have such a device, as well have boat grounded as well and have to admit that whether its been luck in a storm or the brush on the top of my mast, but touch wood never got struck. Have talked to other sailors on the Ottawa river from the Nepean Yacht club who have also had good safe times in lightening storms, and hench the reason for my brush a top my mast.
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Old 01-18-2008
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Dog:

From what I've read, your correct about the 4' of linear edge. Its the edge of the ground plate that discharges the strike to the water. However, the 4' is for salt water. If you sail in fresh water, the number doubles or triples in length.
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Old 01-18-2008
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OK , So if

I was to manufacture a larger plate with larger attachment bolts and backing plate, and attach my main mast to it. The cable I would have to runn would be laying in the bilge for about 20' horazontal. This is my mane concern as everythin I read say's to form as straight a path down to the water as possibal. I dont want current trying to blow a hole in my hull as it runs that 20' to the bonding plate. I will try to post a picture.
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Old 01-18-2008
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Here's a picture

of the bilge that runs from the mast step ( right at the top of the picture is the mast step tunnel )most of the length of the boat ,into the engine compartment to the shaft tube.

You can see the keel bolts there are 18 of them and yes they are SS.
The bonding plate bolts are barly visibal to the far left edge of the sole hatch cut out on the left side,( second picture ) there is no backing plate, will be changing that!!

Oh by the way another cncern is thoes are my fuel tanks on both sides of the bilge , Im standing on the starboard tank.( Fiberglass )
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Last edited by Stillraining; 01-18-2008 at 11:20 PM.
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