Lightning

[Quiet Magic]

Ever since this season started I have had my mind stuck on how to prevent lightning damage. I have asked many knowledgeable sailing freinds but never really got a definite answer. So my qusetion is, what is the best way to prevent lightning from causing bad damage.

Steve C.​

 

[gareth harris]

Ground the mast.
This means running a thick electrical cable (1/0 or 2/0 AWG), which has a strong connection to the mast, straight down to a copper plate under the hull. Doing so greatly reduces the danger to the crew, and reduces the likely damage. A strike will still most likely destroy any electrical mast fittings, and anything electronic on the boat (unless it is in a metal case such as a biscuit tin or oven), but statistically everyone will most likely sail home.

A strike is highly unpredictable, so there are some other things some recommend but are not universally accepted.
Creating a Faraday cage by running cables (4 AWG) from each shroud to the central grounding cable can protect crew inside. The problem with doing this is that it may encourage the charge to follow a route other than the main path straight down through the mast, and may destroy the shrouds, or take a path through the hull and sink the boat.
There are devices on the market designed to dissapate charge on the boat as it builds, preventing it building to the point lightning is attracted. They are used on power lines, but there is disagreement about how effective they are on a boat grounded to an infinite ion source (the ocean).

If you are looking for something that does not involve hauling the boat, look at www.strikeshield.com, which is a quick fix and probably fairly effective.

Gareth
Freyja E35 #241 1972

 

[Chris Miller]

Also...

Also, unplug from shore power when the boat is at the dock. If somebody who is plugged in or the marina gets hit, you have less of a chance of being affected. Otherwise a nearby strike could spike the shore power cable and fry all of your systems.
Chris

 

[Quiet Magic]

I would have never thought of that...

Thanks guys. Those where some great pionts or me to think about, I would not have thought of that shore power thing in a million years. Now I have two more questions:
1. what are these things I see on top of peoples masts. they look like little wire brushes(I think some one told me they were there to dispurs static)?

2. And how do you install a grounding plate?​

Steve C.

 

[gareth harris]

The bottle brushes you mention are the devices I was describing designed to dissapate the charge from the boat before it builds to a high intensity. There are no statistics available that show whether or not they work on sail boats.

The manufacturers are adamant that they do, I have also read articles ridiculing the idea. Looking at the basic physics, it does seem unlikely to me that the bottle brush can release ions faster than they travel up a grounded mast - but that is just a gut feeling, to the best of my knowledge, nobody has conducted experiments on the extent to which charge build up is reduced.

I have heard a number of people say they help keep the boat clean by keeping birds away.

To install a grounding plate, you need to drill through the hull, which is a job I recommend to be left to experts if you are not sure of what you are doing.

Gareth
Freyja E35 #241 1972

 

[hodo]

Just wanted to say this brought back memories of a trip to Sequim Bay, years ago. with lightning strikes in the surrounding hills, I looked around and decided the best thing we could do was drop the mast. It was a 27'. We had a much easier time sleeping that night. Hodo

 

[footrope]

Witnessed a strike in 1998

Funny you should mention Sequim Bay, hodo. After I saw this thread I went to the 48° North magazine website (http://www.48north.com/) to see if the article CRACKBLAM! by John McPhee was still posted in the Article Archive. It isn't. Interesting story of a strike on a Ranger 29 at Port Ludlow, Washington (of all places) on the morning of July 5th. John is a friend of mine, and my ex- and I were anchored about 50 yards away.

I was coming out of the companionway when they were hit - worried about my own chances of a strike as the storm came over us. I saw their VHF whip come down on their deck - just a few blobs of yellow molten steel. :eek:

There were many, many boats tucked back there with us that morning - including a raft of three boats in the 40-60 foot range about the same distance away. It impressed me that the tallest object isn't necessarily the most likely to be affected - it's all in the physics, sure - but there are many factors other than height.

I'll try to get 'official' permission to attach a copy of the article, but I don't think John or the magazine will care. You can also request 48° North to send you a copy. When he was refitting the boat he elected to go with a sintered plate grounding solution. Another interesting note: The Atomic 4 started right up once they recovered their senses enough to motor over to the marina. Everything else electrical was toast.

 

[escapade]

To ground or not to ground......

I have also heard that keeping everything isolated to prevent a buildup of potential is a way to deal with lightening. For what it's worth, my old '75 E27 was lightening grounded from the factory & mt '80 E30+ & '88 E34 are not. From what I've been able to gather there are good reasons for either approach and NOTHING that is garunteed to work every time! Your best bet is to say a prayer & keep your finger's crossed. I've been very lucky (this will probably jinx me now!) never to have been hit in 17 years. Most people never get hit, some get more than once. Go figure. Just my $.02 worth.
Bud E34 "Escapade"

 

[Emerald]

Anyone have any idea if hanging jumper cables off your shrouds and stays into the water does any good either in the case of a strike or to help dissipate static charge? On a deck stepped mast, I am doubting that I could really run a heavy enough wire in a straight enough line to a grounding plate - I am under the impression that lightning dosn't like to turn and can "jump" from one object to another.

I feel like I've heard the horror story of blowing a hole in the hull of the boat via a grounding plate (and then sunk). That said, I'll never forget almost being hit many years ago on my father's Tartan 34. We were at anchor and the rigging started to buzz. As this buzzing got louder my dad went below and disconnected the VHF antenna from the radio and connected it over to a grounding plate through the hull. When he did this, he got a zap that knocked him backwards, and at the same precise moment the buzzing stopped. From what we've been able to gather, we were building the static charge in the rigging that was moments away from being a strike, and when my Dad switched over the connection on the grounding plate, we/he dissipated the charge.

Also, any ideas on using the engine (diesel) prop shaft as a ground?

I don't like lightning....


-David
Independence 31
Emerald

 

[gareth harris]

Saying a prayer and keeping fingers crossed never seems to work for me....

There is some talk that grounding the mast may be a two sided coin, in that it encourages your boat to be struck. But I think the difference it makes is really not high, if even significant (again, I have not seen any experimental evidence). What there is plenty of evidence for, is that if you are struck, your odds of living and sailing home are a lot higher with a good grounding system. For those of you on fresh water, the plate needs to be a lot larger, but the principle is the same.

There is no cheap way of doing that - jumper cables on the shroud encourage the strike to go where you do not want it to go, the shroud, which can make the mast drop; plus the cables may disintegrate before all the charge is in the water, negating their use completely. The amount of charge in a strike can vary widely, such systems may handle a small strike without major damage, but I would not trust the shroud afterwards. Engines in Ericsons are generally not under the mast, and most likely the electrical systems required to run will be destroyed if it is part of the path to ground.

I have no commercial interest in www.strikeshield.com, but if you are not willing to install the cable and plate in the boat, they have the best alternative I have seen. Not cheap. In San Diego bay a complete waste of money; in Pensacola bay, very good value for money (I once watched from my boat as a tree was struck less than 100 yds away, then a transformer 200 yds away a few seconds later).

Gareth
Freyja E35 #241 1972

 

[u079721]

Welding cable anyone?

On my E-38 it was a fairly easy matter to connect the mast to one of the keel bolts for the external keel, which I am told works well as a giant grounding plate.

But I also practiced a trick I learned from a circumnavigator I met a few years back. He kept a 10 foot length of welding cable, the type with many small diameter wire strands, attached to his backstay with a hose clamp. The idea was of course to provide the most direct route to the water for any lightning strike on the mast.

The top inch of insulation was removed, and then held in contact with the backstay with the hose clamp. The other end was stripped of insulation and splayed out to give maximum surface area. He swore by it, and it seemed easy enough to do. So for the combined 300 or so nights I spent cruising and anchoring in the North Channel I kept this rig attached to my backstay, and would throw in into the water if an electrical storm came up.

We were never struck, so I can't say whether it worked, but it was simple, cheap, and easy to remove when I didn't want it in the way.