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Lightning protection

H

haulback

New member
Might be interesting to see what everyone is doing to protect against, prevent, or otherwise discourage lightning strikes on their boats.

Last haulout I installed a medium-sized dyna-plate through the hull, below the mast (deck-stepped) to act as a grounding plate for the rig - then connected them together with a straight run of about 6 feet of 1 gauge multi-strand, tinned wire.

My personal theory about this subject is to make the boat 'unattractive' to a lightning strike in the first place by trying to prevent the build-up of static electricity that (as I understand it) would attract said strike in the first place.

Before this I have had the mast grounded to the big dyna plate, aft. But this meant that the ground wire not only took a long, rather meandering pathway through the boat to get there, but also that it shared its ground plate with my radios, weatherfax etc. So IF we were to take a strike it was guaranteed that everything aboard would be sure to be fried.

At least with it on it's own dyna-plate there is a chance some of the other stuff would not get zapped. Also electricity likes a straight line, so shortening the ground wire and eliminating all the crooks and bends in the previous run can only be an improvement as well.

There seems to be lots of different approaches to lightning protection, but I am not convinced that there is any actual 'expert' advice on the subject, that has been proven beyond a doubt, and certainly little actual anecdotal evidence to support any one method over another. ....So I have gone with what I feel makes sense.

I suppose that if a bolt of lightning has your name on it you are pretty well screwed......but if you can make your boat unattractive to it in the first place, you may escape the ones that are out there 'just looking for somewhere to go'

Jim/Haulback
 
Jim I like the idea of a lightning discussion...

The only way to make your boat "unattractive" is to shorten your mast. Grounding the mast does not make it less attractive. On a flat field the height of a tree determines the radius the circle that the tree will get nearby lightning. Taller, the bigger the "danger" circle. But I am not going to shorten my rigging.
A good grounding that you describe helps after you are hit.

The reason there are "lots of different approaches to lightning protection" and none seem to be THE answer is because lightning can vary from a little more than static electricity to bolts that could blow a house up, or blow you out of the cockpit while melting your mast. We've all seen pictures of strikes like that. Also everyone's story of what happened in a fraction of a second seems to very. We can't protect ourselves against mega-bolts, but we can protect our equipment from damage with smaller strikes.

At the top of your mast you have radio antennas and lights (anchor light, tri-color, strobe). Your forestay, backstay and shrouds, all metal, attach to the top of the mast also. When lightning strikes your mast head it will go down the mast to your dana plate but it will also go down the other lines, cables and wires. It will be in your radios, electric wiring and all around your boat. That scares me.

What I did was to put a connector on every wire and cable that comes down my mast. I do this at the bottom of the mast, inside to protect against the weather. I also have a disconnect for the SSB antenna on the back stay where it enters the boat. This allows me to separate the wires/cables from all the wiring in the boat. I think grounding the mast is a good idea and you are correct that a separate plate and closer is good but your 1 gage wire is way way too small. Can you use 1"-2" wide woven copper strap? You could add your chain plates to this if you wanted.
Making it possible to isolate every instrument as close as possible to the source of the strike is the goal. I also have disconnects for each instrument at the instrument which most come with.

In the tropics you usually see lightning coming (assuming you are on watch). If you feel you are in danger you can disconnect everything, shorten sail, and use the compass.

phil No Ka Oi
 
Ahhh, as I said, different theories abound!!!

DISCLAIMER.......I do not pretend to be an expert, or to particularly even know what the heck I am talking about. (you will notice how this does not stop me from having opinions)....These are just my thoughts on the matter and how I have tricked myself into developing a comfort zone over something of which I really have little control.

When I suggested that grounding the rig makes it unattractive, perhaps I should have said it will be 'less likely to attract' a lightning hit, if by being grounded it actually dissipates the build-up of static electricity in the rig, in the first place.

There are many reasons for lightning to strike something. The build-up of static electricity is one of them, and something a skipper can do something about. And as you say, the height of the mast is another - shortening it seems somehow unrealistic - and like yourself I choose to leave mine as it is.

I would agree that if you are hoping to DIRECT a 'strike' from the rig down to the water, as large a wire/cable/strap as possible would be best, but by then this strap may only serve to blow a bigger hole through the bottom of the boat!! The point of the 1 gauge wire in my installation is to ground the rig, hopefully preventing the build-up of a positive (or negative, I can never keep it straight) charge, BEFORE being hit.

Unfortunatly, once you are hit, it's pretty much a roll of the dice (as I see it) as to what the results may actually be, depending on severity, size and type of lightning in question.

I use my oven as a Faraday Cage to store a spare fixed and handheld GPS, an extra autopilot control, back-up computer hard drive, etc. This may, or may not prove to be effective.

Your idea about the connectors on masthead electrical wires and antennas is a good enough one, but I will probably not go that far. Seems that if you are going to try to isolate the rig from the boat, that the same will have to be done on all shrouds and stays as well......Then you are left sitting under an ungrounded, tall structure in the middle of a large flat area - Hmmmmm - Would this not actually increase your chances of being hit????

I think that if you are unfortunate enough to take a direct hit that pretty much everything will be toast anyway - I would go further and suggest it would serve well to have a back-up plan to reach your next destination that does not include the use of ANY electronics to do so.
 
Hi Jim,
Here is a great website from NOAA about lightning.
http://www.srh.noaa.gov/jetstream//lightning/lightning.htm

I am not an expert in lightning. I am an electrical engineer and many years ago had to work on high voltage wiring. It is different than regular electricity and behaves oddly. Mostly it jumps for no apparent reason and can cause burns as well as shock. My opinions are not based on knowledge of lightning so consider them opinions only.

I agree, theories abound but I don't see how the wire between the mast and the dyna plate could help. Wouldn't it conduct the positive charge up better? I personally don't think it would affect the charge on the boat. That is much bigger than the boat.

Not to be miss-undertood. I can disconnect the wires coming down my mast at the foot of the mast, but I do not isolate the rigging. My goal is to isolate the wiring from the strike. All antenna wires and electrical wires that leave the inside of my boat can be disconnected. I also can disconnect all wires from every instrument at the instrument. I will ground the mast, forestay, backstay, & shrouds to a dyna plate, but I don't think it will help prevent a strike, simply confine it if, and only if, it is small.

I like your idea of putting hand held instruments in the oven! I will do that too.
I will also hope I am never hit by lightning.

About 10 years ago, at about mid-night, lightning hit a telephone/PGE pole that was between my house and my neighbor's house. It was the loudest and brightest thing I have ever seen or heard. Everyone on the block came out to see what happened. There was a small fire but the rain quickly put it out. Needless to say we were now in the dark. It took me a very long time to be able to sleep in the bedroom near the pole again.

The curious thing is that other than damage to the pole and a near by tree, there was no damage to electrical appliances. However, a copper pipe inside the wall of my neighbor's house burst. His place was quickly flooded. Even the well grounded copper piping was damaged! High voltage jumps!

phil No Ka Oi
 
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University of Florida Lightning Study

Here is a paper from the University of Florida on lightning and boats.

http://edis.ifas.ufl.edu/SG071
ftp://mdsg.umd.edu/Public/MDSG/lightning.pdf

They actually spent some money on the issue given the the number of boats and the amount of lightning in their state. Most of the "knowledge" around is folklore given that the likelihood of a strike occurring to a given skipper more than once is fairly low and each event is pretty difficult to really learn from. The video they had was really good. Unfortunately, it looks like they moved it or took it down.

-jak
 
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