So you see a thunderstorm coming...

[Catketch]

I've read that you can ground your mast to the water by connecting one of your shrouds, via jumper cables, to a piece of metal (at least one foot diameter) and submerging it. The theory is that this creates a cone of safety around the mast that encloses the boat within it.

My 33' sailboat had a heavy cable grounding the mast to a large metal plate exposed in the keel and I was caught out in several severe thunderstorms and never struck. This could either have been because the grounding plate theory works or complete dumb luck.

Anybody have any thoughts/experiences with this kind of system?

 

[walt]

I don’t know if you meant to imply that the ground on the shrouds protects the mast from a lightning strike (i.e., cone of protection) but I don’t think it works this way at all. Before a strike, some sort of grounding on the mast can have some effect on the corona current that happens in a high electric field but how much that affects taking a strike is questionable.

The cone of protection normally referred to that you get with a mast is because the mast is more likely to take the strike than anything under the cone of protection. This is a good thing since if your sitting in the cockpit and a strike comes down with your number, its way better that it connects with the mast than the top of your head. Its how the charge is handled once it contacts the mast that is important..

In an earlier post about the lightning fatality (same boat as I have), sounds like some local knowledge had the victim climbing back on the boat and Ill assume he was using an aft metal boarding ladder. I’m going to add the ladder to the list of potentially unsafe locations on the sailboat during a storm. We don’t know exactly what happened but odds are that the mast did work as the cone of protection and took the strike rather than the victim. But at the bottom of the mast (ungrounded on these boats), there may have been a side flash from the bottom of the mast to the ladder - possibly aided by a portion of the ladder being in the water which would be normal if it were used for boarding. Note that the ladder in the water still did not ground the mast and likely had no influence on getting the strike in the first place. Ionized air just happens easily with this much energy and makes a very competitive conductor.

The goal of a lighting protection is to attempt to not have an uncontrolled side flash and in the simplest case, it’s just trying to provide a path to ground that out competes with the ionized air side flashes. The shrouds are electrically connected to the mast but are not at all a very "competitive" way to try and discharge the mast because of both the resistance, inductance, skin effect, etc of the shroud. A battery cable clamped to the mast and just dangling over the side of the boat into the water could have been effective in discharging the mast and saved a life - no way to know for sure.

The now somewhat abandoned zenpole idea referenced earlier (and in the attached picture of my 15 foot rotating mast sailboat) also does nothing more than attempt to be the most competitive way to discharge the mast into the water surface and in this case, there are multiple four gauge wires connected to the mast at the end of each wire are multiple sparking electrodes that are kept just above the water surface. Long story about why the sparking electrodes (they just re-create the spark at the water surface where it then propagates and finds the positive surface charge) but it’s basically this same technology as here http://www.marinelightning.com/Siedarc.htm

 

[Piotr]

I also read that the lightning dissipators (they look like a chimney sweeper's brushes) used on the tall antennas can be installed on the top of the mast. Apparently, the structures protected by these have statistically signifantly fewer lightning strikes than the unprotected structures.

 

[justsomeguy]

I also read that the lightning dissipators (they look like a chimney sweeper's brushes) used on the tall antennas can be installed on the top of the mast. Apparently, the structures protected by these have statistically signifantly fewer lightning strikes than the unprotected structures.

Did the maker of these dissipators supply the statistic you cite?

 

[FourPoints]

Did the maker of these dissipators supply the statistic you cite?

In cell tower work it's a well established fact those dissipaters do in fact make a small difference. Adding those will reduce the electrical potential that builds up on a particular structure (assuming the dissipater is of large enough size for the object being protected). They are often installed on certain types of antenna clusters that have particularly sensitive receivers since the electrical potential build up on the antenna can cause static discharge and blow the receiver.

On the flip side though, whenever there is a nearby lighting strike those dissipaters also can act as collectors, and it makes that same equipment more susceptible to an actual lightning strike.

So they do in fact help dissipate the electrical charge that builds up on the tower / equipment / mast and thus reduce the chance of a strike, but when a strike occurs, it is more likely to strike the dissipater vs something else nearby since there is already an established electron flow and charged particle cloud in their area, which lightning loves.

 

[MrBill_FLL]

one of the boats I crew on was hit last year, and had that brush on the top of the mast. (dufor 34)

that took out the fridge, wind/speed indicator, and A/C. That was at the slip of a big marina... (but otherwise, there was no damage to rig, or hull !)

the basic question is are you more or less likely to get a lighting strike if you have a 'grounded' boat.

I think you are more likely.. but you are better off if you are hit with a 'ground' and much worse if you are hit, and ungrounded.

 

[Jackdaw]

In an earlier post about the lightning fatality (same boat as I have), sounds like some local knowledge had the victim climbing back on the boat and Ill assume he was using an aft metal boarding ladder. I’m going to add the ladder to the list of potentially unsafe locations on the sailboat during a storm. We don’t know exactly what happened but odds are that the mast did work as the cone of protection and took the strike rather than the victim. But at the bottom of the mast (ungrounded on these boats), there may have been a side flash from the bottom of the mast to the ladder - possibly aided by a portion of the ladder being in the water which would be normal if it were used for boarding. Note that the ladder in the water still did not ground the mast and likely had no influence on getting the strike in the first place. Ionized air just happens easily with this much energy and makes a very competitive conductor.

Walt, here's what I know.

The boy was walking in the water (perhaps knee deep) when the bolt hit. He was not in the actual process of boarding. First-hand reports say the boat was NOT hit. No one on the scene could identity where the bolt struck, but the boat had none of the typical damage of a strike, either on the mast or structure.

 

[Piotr]

Did the maker of these dissipators supply the statistic you cite?

Possibly...

 

[walt]

The boy was struck as he climbed back to the boat.

This is what I had read a few posts back..

edit

I watched the video that was posted earlier again( http://minnesota.cbslocal.com/2012/0...ikes-sailboat/


It looks like the 26 classic is beached with the bow first and the account seems to indicate that the grandfather, mother and boy were all in the water at the time of the strike. So.. we just dont know what happened, could have been the orientaition of how they were standing and the gradient of the current in the water.. or that the boy was just shorter so more of his body in the water.. just dont know.

 

[Jackdaw]

This all reminds me, the night this happened were were at anchor in the Apostle Islands, about 75nm east of where the boy was struck in Duluth. We watched the storm roll by, most just to the north of us. The sat weather show strike locations for the last 30 minutes. No where to go at this point, just hunker down.

 

[walt]

Using the ladder when it’s partly the water probably is a bad thing - but from that example, for sure being in the water near a sailboat during a storm is on the "avoid" list.

I’ve had five encounters with lightning myself - one where I actually took a good shock while windsurfing when the shore was struck fairly close to where I was sailing. I was on a short board plane having a good time, big shock - big wipeout.

Last year at this time I was worried about my house burning down (2 miles from a big fire) so am thankful for the weather we are getting in CO .. but am just terribly sad about the tornados in OK. But this makes me remember one of the strangest lightning experiences I have had.

I have attached a picture I took five years ago from my Mac 26S. At the time I took this picture, I had taken my sails down and had an old outboard that was hard to start regardless but this particular time it would just not start and it seemed as if the ignition timing was off. There was a lot of lightning to go along with the water spout. I could hear buzzing on the boat electrical parts and would get shocked if I touched the outboard. I think this was screwing up the electronic ignition control. So I was thinking I was either going to get electrocuted by lightning from working on the chunk of metal partly in the water (outboard) or I was going to hit by the water spout. It came right at me for a long time but fortunately turned just about the same time I got the outboard started...

The other three cases involve land sailors on dry lake beds and corona current..

 

[Sumner]

A very dramatic shot and I wouldn't of wanted to see that coming at the boat,

Sum

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[Doc_holiday]

Yeah but if you caught it just right you could have exceeded the hull speed.

 

[Piotr]

Yeah but if you caught it just right you could have exceeded the hull speed.

Thanks, Doc - just fell on the floor gasping for air....

 

[Tony E]

So I took the Sailboat out last weekend for the first time ever and wouldn't you know it in the late afternoon clouds starting forming and lighting and thunder were miles away but coming out way. I quickly ducked into a coulee off of the lake that had hills on each side of me and that's where we spent the night. I think the main thing with lighting is pay attention to your surroundings and the weather and be always respectful of mother nature as she can always "Kick our butt" when she wants to. If you see a storm possibly forming and coming then get out of there and head for safer territory and don't be a fool and stay out on the lake as you are a floating lighting rod and you are just asking to meet your maker. Anyway, after an hour or so the thunder and lighting passed and the sun came out and all is well.