Lightning and Thunderstorms

[Jimnkathy]

I was wondering how safe are you in the cabin of a mac in a thunderstorm. I know it is Ideal to be home, but you never know what the weather can do. This may be a stupid question but I would appreciate some input on this subject.

THank you

Jim

[MrBarry]

There was a long discussion on just this subject a year or so ago on the aussie trailer salier forum.
General consensus was, if I remember correctly, that if there was a decent enough path from the mast to the water, you would be unlikely to be shocked/fried.
One example given was to attach a length of chain from a shroud and draped into the water......
I wonder if the wet daggerboard trunk on the M would be enough.

There was some real -life storys given in that previous discussion. I will try to locate it.


James

[Sloop John B]

You don't know what a thunderstorm is until you come to Florida. I get in bed and pull the covers over my head.

In the 26X, stay to starboard away from water storage and the center post.

[LOUIS B HOLUB]

A local elderly Harbor Master and his wife were on a sailing trip a few years back and their boat was struck by lightning. He described the damage to the boat which was substantial--hole in the hull, electronics gone, etc. The boat was saved by being near enough to shore to be towed in, pulled out of the water, and an insurance restoration put them back on the water.

The way the incident was described, they were not injured. But, the boat suffered big time.

[RICH RUYACK]

Wondering the same thing about lighting storm. The wheel is all metal do you just keep steering home and hope for the best? Hang a copper wire off the shroud and into the water. would wearing a rubber glove when steering help you?

[kziadie]

Rubber gloves wont help, but putting a teak wheel on might. The other problem is of course is that sitting on the helm seat places you right over the biggest ground conductor of the boat... the engine. I have given up trying to figure out how to protect myself if I get caught out in a bad electrical storm, there are many theories which make sense yet contradict each other. It would be easier on a boat with a keel stepped mast, but with the deck step of the Macgregor I think you place yourself in the hands of god.

Kelly

[Frank C]

Not sure, but it might be a tiny bit better on your 26X.
As Sloop observed, it has a fairly direct path ...
from the mast, to compression post, to CB bracket.

[eric3a]

..

[LOUIS B HOLUB]

I've always wondered about dissipators.

http://www.lpsnet.com/Default.asp

The lightning strike I mentioned earlier concerning the Harbor Master now has one of these on his mast. It looks sorta' like a metal bottle brush.

He is convinced it works, according to the reviews.

Lightning carries one big ole wallop, and I wonder likewise--do dissipators actually work?

[walt]

You have to pick which expert your going to believe with this stuff.

You can get opionions at either of these places and this is also where I would "put my money"...

http://www.marinelightning.com/AirTerminals.htm#DAS

http://tech.groups.yahoo.com/group/LightningProtection/

I think you will get the same answer both places, these disipators are not effective ON A BOAT. However, they may have some impact in other applications.

[RRice]

Hello, I have some video of a lightning bolt that was near my brother in laws boat. We were sailing off of Jax beach. I did not know I got ituntill i was watching the video at hom. It is posted on my photobucket page under rislandsail.

[Bransher]

walt said:

these disipators are not effective ON A BOAT. However, they may have some impact in other applications.

They are used very effectively on airplanes. We were always flying close and sometimes in thunderstorms, and after 10,000 hours of this we never had any serious problems. We did have some minor strikes that were barely noticeable. We lost a few radios, and had some pinholes burned into the trailing edges of wings and tail a few times where the lightning charge left the airplane, but nothing that you could consider dangerous. But an airplane is moving very rapidly through the air and that makes the static wicks (disipator) very effective.

Unless you own one of those fast blue hull boats, they probably would not have much effect.
But when you consider that thunderstorms are usually accompanied by strong winds..........what the heck, put them on, it's worth a try.

[blueskiesup]

Lightning strikes on airplanes, something I'm versed in!

The key to protecting an aircraft from a lightning strike is assuring the airframe is well grounded. The aircraft skin and panels must all be electrically bonded to one another well or... wammo the non-grounded panels instantly heat up as the strike conducts across the more resistive path making lots of heat...

So what about composite airplanes (fiberglass or carbonfiber)? Just below the top layer is a layer of coductive mesh or "aluminum lighting supression" ALS. The mesh is also grounded to each next door panel to assure conductivity is high enough to dissipate the amps quickly.

On an airplane strikes usually happen on the topside or the leading edges but the entire aircraft is protected in the form of a Farday cage...

On a boat it may be reasonable to assume the strike will occur at the mast and it can be conducted to the water. If you can create a low resistance path to water, you should be in good shape. At the same time you may be making yourself more susceptible to strikes. Lightning loves a nice high path to ground...

I belive I've seen some sailing vessels with big copper plates at the base of the mast on the bottom of the hull.

I would guess a typical Mac getting struck with no modification would result in a melted hull followed by relying on the foam block flotation capabilities...

By the way, I've witnessed some failed composit panel lightining tests, very cool, huge holes like a shotgun!

Sleep well!

Greg

[waternwaves]

HAving worked on composite intrapanel bonding.....

both for airframe and munitions development.

and scaled tests to determine skin effect conduction during strikes.....

AS well as working like divecoz to protect many of our government high energy and nuclear power facilities....

we found that most of the current does not go through the bonding conductors.....and the space above/between field grids becomes airgap...... each panel providing a voltage drop.

The real purpose of the interconnection of the panels is to keep the plane at the same electrical potential during normal operation.

Those small jumpers between panels have entirely too little surface area to conduct much current..... it is the area of the grid and density that determines ionization area....... This channel around the wire grid is where most of the current is conducted.


Thanks

[walt]

Im not at all an expert but wonder why the disipators would have any effect in an airplane..

The "intended" application is prevent a ground to air leader from forming - I think its probably undisputed (except maybe by the people marketing them) that they have no effect on where a strike hits which is comming from sky to ground. So they are trying to disipate a building charge in the ground before it can create high enough fields to start a leader and head upwards. Possibly a "valid" idea but maybe its often like trying to stop the tide from happening with a broom.

An airplane in the sky would have no source of charge to disipate except for the charge the disipator creates and whatever charge gets on the plane from just flying - but that is probably a drop in the bucket. Seems there just wouldnt be the big charge source available to sustain any sort of leader??

On the boat, you can have what looks like a charge buildup (saint Elmo fire, gettig shocked on shrouds ect) but I beleive its all due to being in an a electric field caused by the overhead sky charge being seperated from the beneath ground charge. Conductors take on the potentential of their midpoints and if mid points are at different hieghts, they take on different potentials - and you can have localized breakdown - or get shocked on shrouds, ect. But I dont beleive it has anything to do with pulling some sort of charge out of the water and onto the boat. Which is also why disipators on a boat seem to be a good idea - but results apparantly dont back this up.

I could be completely wrong however...