MacGregorSailors.com

Howdy, I have a quick question for you all. Being that this is a deck stepped mast, what happens when it gets struck by lightning? keeled masts funnel most of it strait into the water, but obviously that wouldnt be possible with a trailerable boat. Thanks, JEM

Not sure about masts on sailboats, but as far as communication towers go, there are two schools of thought.

1.) Thorough grounding of tower to earth and complete bonding of everything on the tower, to channel the current to ground.

2.) Insulate the tower from earth and it will not readily attract lightning.

Both methods work, but the second tends to allow a static charge to build on the tower, causing desensitization of receivers. I have seen damaged electronics in both situations.

I would think that the second method is what would happen on a Mac. The static build-up should not be a problem, unless you are using the backstay, mast and a return wire to the backstay as a loop antenna for an HF radio. (with an antenna tuner, of course)

Rich

Anthing from nothing to OH MY GOD!!!

It is best to disconnect all electrical on your boat. Store spair electrical in foil. Tilt the motor out of the water and Go below if possible.

There is several discussions in this forum on lightning.

One of my golfing buddies is a retired owner of one of the largest national lightning protection installers. He never had a failure! He goes by the book and so can you. Go online to www.nfpa.com (National Fire Protection Association) Click on review books. accept the agreement to not reproduce thecopyrighted material. Ask to review book 780, lightning protection. At the bottom of the page click on the index symbol and select chapter 8. That will take you page 26 which is lightning protection for marine vessels. Start there and read through page 36 so you get the explanatory passages in annex A and B, charts, drawings, and materials used.

This is the information that works for professional installers all around the world.

Take a look at this:
http://www.stewartfam.net/arlyn/lightning2.html

Our second outing on out Mac a couple of years ago, at Easter on Lake Ouachita in Arkansas, included a 5 hour lightning storm that was very intense. We were up in a hilly cove, so there were taller trees than our mast all around, but I didn't sleep that night! I purchased this lightning protection ( grounding) device (http://www.strikeshield.com) last year, but fortunately haven't had to use it yet. I did have it attached and ready to deploy a few weeks ago in Florida, but the storm never materialized. Here in the mid-south we get frequent thunderstorms, spring summer and fall. The idea behind the Strikeshield makes sense, it is well constructed, if a bit pricey. I would just as soon never have to see if it actually works!!

Good link, Brian. I really liked that guy's approach & writing style, and it's a very long, comprehensive paper. I think his conclusion was particularly noteworthy. While I'm sure it's debatable, it sure captured my subscription:

Prudence comes in different packages depending upon our needs and circumstances. This is one of those times when day sailors and those who coastal cruise on small boats ... should be careful about half hearted attempts to emulate their larger counterparts sailing in salt water.

A friend uses more graphic words and I don't want this article to lean toward the emotional, but he suggest, "If you invite the monster aboard, you better be prepared to deal with it." I think those are very wise words. Many small boat sailors use less than adequate schemes in the hopes that doing something is better than nothing... that may not be true in the case of lightning.

i went to a lecture about mountain winds last night. the speaker owns 5 sailboats, a PHD in meteorology, and works for NOAA. We asked him about this,and he said It's statistically remarkable that more sailboats don't get struck. He didn't feel there was any evidence that disipators, and other paraphanalia work, and in fact knew a manufacturer of the same who didn't put one on his own boat. Sometimes you need to ground the rigging in the water kind of like Ahab in Moby Dick, to get out of the giant capacitor effect (where your rigging is electrified with static charges).

He did talk about some really cool stuff also like steer to the edges of cumulus clouds or the spaces between them. there is always a rising column of air underneath them and great sailing air along the edges.
Beware of the edges of those giant thunderheads, especially the trailing edge. they contain some seriously disturbed air evident by their slightly upcurled edges. rolling completely over. Former cumulus compositions, these big guys are now blowing down and out because the water or "verga" dropping has cooled the air underneath. Thus the heavy air sinks. EG. He's seen two boats sailing downwind on the same lake in opposite directions.

If you invite the monster aboard, you better be prepared to deal with it." I think those are very wise words. Many small boat sailors use less than adequate schemes in the hopes that doing something is better than nothing... that may not be true in the case of lightning.

This is the theory that I operate under on mountaintops. I have commercial installations on the same mountaintop that have spent big bucks on lightning protection, including digging into solid rock and laying chemical and metallic ground systems. They have survived numerous strikes with minimal damage. Their system encourages strikes, but handles them well.

My insulating system does not attract strikes. My secret weapons are static dissipators positioned on top of the tower. These are fine wires that are bristled-out and dissipate the positive charge that accumulates on the tower into the air, before it has time to build enough potential to attract lightning. I got the idea of the dissipators from looking at the way aircraft reduce static build-up caused by passing through the air.

Rich

Richard O'Brien wrote: a PHD in meteorology, and works for NOAA . . . said It's statistically remarkable that more sailboats don't get struck. He didn't feel there was any evidence that disipators, and other paraphanalia work, and in fact knew a manufacturer of the same who didn't put one on his own boat.

I've been in a lightning storm at sea. Didn't get hit but sure thought I was going to.
Just my opinion but I think lining your shorts with aluminum foil will be just as effective as those disipators. Shiny side out, obviously.
Something as fast and powerful as lightning is going to go where it wants to go.

As a self proclaimed really smart guy and cheese connosieur, I agree with using a dissipator.

If I was to do anything, I would add a bronze brush dissipator to the top of the mast.

Grounding the mast greatly increases the odds of a strike. The high field gradient that exists before a strike will put a very high voltage potential at the top of the mast, and this charge is much, much higher if the mast is grounded , supplying the mast with an unlimited supply of electrons. This charge is what makes the mast an attractive target. If it is not charged,it is not a lightning magnet and the strike probability goes way down.

But we have sort of an intermittent ground via the mast compression post and that metal cable centerboard pendant. (if so equipped). that might explain the one instance where a 26X was struck. That was about 4 yrs ago and the lightning was reported to have made a bunch of pinholes through the hull at the waterline.

But the best idea I think, is to park your boat next to a big sailboat with a well grounded mast. Using the bear theory. You dont have to run faster than the bear, just faster than your buddy.

Of course all airplanes should be firmly grounded at all times with several double ought grounding wires. (Not to be confused with double naught which is the type of spy Jethro Boudin was, who by the way, was a fellow self proclaimed genius and champeen bug tusseler.