Lightning Protection

[JusDreaming]

After the boat and us being struck by lightning, I am considering some form of lightning protection. The problem is there is no consensus. If you ask 100 sailors, 50 say it works, and 50 say it either attracts lightning, or is a waste of time and money

[Pblais]

There is little consensus on the subject. It depends on how you are struck. A large direct strike is potentially very serious no matter what you do. A near strike can through induction wipe out a lot of your electronic equipment even if no physical damage is seen. A small hit and the path to ground can make a set of strange damages. Having a clear ground path seems to be a good idea for most situations, but a lot depends on where you are and how you get hit. Places like south Florida make enough lightning to export and i can't see how you could do enough but doing something sensible I think that is proportional to the area you sail in seems to be a good idea. Don't forget you can get struck through your shore power cable as easy as the mast.

My neighbor here at home and on my dock has been hit twice in 4 years and the last time he got his house and boat hit and it never struck either directly. I in the same strike got nothing. This last time he did add an arrestor to his radio cable. That it seems had been the root of losing all his electronics in both strikes. Cost about $150 and only adds a 0.5 db drop in radio signal strength. It's too early to tell if it has helped.

He also had this whole time one of those puffy metal balls on the top of the mast. They may help but he has been hit twice so it is easy to see why there are so many opinions. My own opinion is that not all lightning is the same and none of it acts 100% predictable. I think it's clear you don't fly kites with metal line in an electrical storm but what works is not always the same in every case or every situation. There is no magic protect you from all lightning solution.

[Viking Sailor]

Lightning protection is not intended to protect boat instruments or electronics. It is intended to protect the crew and the hull. The real hazard from lightning strikes are flashover events that occur inside the hull between ungrounded metal objects located below the waterline.

[44'cruisingcat]

The argument goes, that if you have a lightning conductor you are more likely to be struck than if you don't. How accurate this might be is anyone's guess, lightning is so unpredictable. I intend to build in a conduit from the mast base down through the bridgedeck floor, and have a suitable length of copper rod which I can pass through the bridgedeck floor, into the water, and bolt to the mast when a thunderstorm is coming.

As VS says, at least that might offer some protection from having thru-hulls blown out, and damage of that nature.

[GordMay]

Denny:
Your poll begs the question of what you mean by lightning “protection’.

If you mean devices like bottle brush and other style lightning (static/ionic) “dissipaters”, you’ll find little controversy among informed sources - they don’t work.

If you mean, what I call a lightning “mitigation” system (grounding), consisting of a robust air terminal, down-conductor, ground electrode, and bonding cables - they reduce the harmful effects of a lightning strike. The purpose of lightning protection is to reduce the damage to the boat and the possibility of injuries or death to the passengers from a lightning strike.

Lightning protection systems do not prevent lightning strikes. They may, in fact, slightly increase the possibility of the boat being struck.

[Cruisingdad]

(this is a brief except from a thread I wrote on another forum)

My opinions:

Dissipators, such as the bottlebrush, have had marginal effects. Many now opt instead for a lightning rod with a very sharp tip on top. The current theory (highly debated) is that by grounding your boat, you decrease your chances of being struck because you can bleed off the potential. I personally find this difficult to believe - but that is the saying.

Grounding a boat or not grounding is a serious consideration. I feel that a poorly gounded boat poses more of a danger than a boat that is not grounded at all. Either do it, and do it all the way... or do not do it at all. All metal must be grounded, including toe rails, tie rods, and especially your steering mecahnisms. #8 was once recommended, but now that has been chaged to #4 (IIRC) for a straight run from the mast. DO not use your keel as a grounding plane and FOR GOD's SAKES DONT USE A DYNOPLATE*** unless you plan on swimming afterwards. The more surface area exposed to the saltwater, the better. Special plates have been developed to do this. They should not be painted. A seperate lead, #8-#4, should be run to ground the diesel/prop. It should be independent of the main run, preferably running perpendicular with its own lead and outside of the remainder of the boat grounding (stanchions, etc). The third leads can all be tied together and run to a similair ground plate.

The reality of doing a correct and proper job on grounding a vessel has been severly overlooked by most sailors & manufactureres (and especially motorboaters). It is very involved and moderately expensive. As the odds of being struck are very small, it may be the best money you have ever wasted. However, for anyone in very electrical prone areas such as South Florida, the islands, or the Northern part of South America, it should be highly considered. Those travelling offshore should also strongly consider it.

Just my opinions.

- CD

*** A bronze dynoplate is porous. That poricity gives it more surface area which makes an very good ground for "low voltage" items such as SSB. However, in a lightning strike, the very high energy causes the water inside those pores to rapidly heat up, then boil. That boiling water creates steam and pressure, which often cannot be released from the pores quickly enough. THus, the plate will explode - often taking a chunk of the hull with it. You will sink quickly. Dynoplates are dangerous lightning grounds and should not in any way be connected with your lightning grounding system in my opinion. Still, I am amazed when I see "offshore" boats whose lightning ground is a dynoplate.

Web Sites of interest to those interested in grounding (or not):


Lightning Attenuation Onboard
Marine Lightning Protection Inc.
NASD: Boating-Lightning Protection

[GordMay]

Actually, current opinion favours a rounded (1/2" dia.) lightning rod (air terminal).

[Cruisingdad]

Hi Gordon,

The newest research shows that a blunted tip works best. I bleieve this work was done out of the Univ of SW Fl. A year or two ago, they were saying a very sharp point. For some time, the bottle brushes.

Did you ever get the feeling they have not perfected the science behind lightning strikes yet?? (smile).

My point has always been: Instead of following the neatest, latest, and greatest theories on how NOT to get struck, better to plan on what to do with the lightning if you ARE struck.

Agreed?

- CD

[Viking Sailor]

Originally Posted by Cruisingdad

DO not use your keel as a grounding plane and FOR GOD's SAKES DONT USE A DYNOPLATE*** unless you plan on swimming afterwards.

Does anyone have first, second, or even third hand knowledge of a Dynoplate failing or exploding due to lightning?

[Cruisingdad]

THis is not the first hand knowledge that you are looking for, but:


The ABYC suggests the use of a grounding strip, rather than a plate. The ABYC rule states: "A grounding strip shall have a minimum thickness of 3/ 16 inch (5 mm), and a minimum width of 3/4 inch (19 mm)." A strip approximately one inch (25 mm) wide and 12 feet long (3.7 m) has nearly six times the amount of edge area exposed to the water, which will improve the dissipation of charges. "The grounding strip, if used, shall extend from a point directly below the lightning protection mast, toward the aft end of the boat, where a direct connection can be made to the boat's engine."

"An equalization bus on the inside of the boat, paralleling the grounding strip on the outside of the boat, may be used as the lightning ground conductor." ABYC encourages use of two bolts at each end of the strip, extending between the external strip and the internal equalization bus, a metal strap inside the boat substantially parallel to the exterior lightning ground plate, and connected to the lightning ground plate at each end. Secondary lightning conductors can be connected to the
equalization bus.

[Cruisingdad]

A grounding plate, if used instead, should be solid, rather than the sintered bronze type often used as radio grounds. The sponge-like structure of the sintered bronze plates may, in the event of a strike, allow the instant formation of steam, which could blow the plate apart, resulting in possible severe damage to the surrounding hull.

(Sorry, it would not let me post it all on one post... something squirrely I guess).

You can find this by reading the first link I provided. Sorry for the multiple posts... I could not get it all on one post!

- CD

[Viking Sailor]

Cruisingdad,

My question pertains to whether or not exploding Dyanoplates are a fact or a myth.

[Cruisingdad]

My guess is that you feel it is a myth. Why?

[Viking Sailor]

No, the question is a honest one. If they do cause hull damage then they shouldn't be on our boats. On the other hand, if they do cause hull damage you would think there would be lots of first hand reports.

p.s. I am in no way associated with Dynoplate.

[Cruisingdad]

Sorry, Viking, I know the question was an honest one. I will give you my perspective:

First, I have not been struck directly. I have not seend a plate explode first hand. However, I think the science and explanation is valid. Too many people have said it for it to have not happened, in my opinion. Now, I think Sailboat US said something like 4 sailboats/1000 a year are struck, that does not give us much of a pool to choose from!!! HAHA!

If I recall correctly, the first time I was corrected about using the Dynoplate was with Cedar Mills (Valiant Yachts). It seems they had a V-42 struck and had the plate blown apart, but I will have to verify that before I stand behind it - so do NOT USE THIS AS EVIDENCE! I will find out for you this weekend as I head up there and harrass them.

In the meantime, if you are using a plate as a ground, please do your own research. The Dynoplate is not just my opinion, it is published by many others that know a lot more about it than me on the web. I will see about getting you a first hand account.

- CD