Lightning protection

Don S/V ILLusion · Oct 10, 2014

Kudos for spelling it correctly. There was a recent discussion on lightning on the Cruisers Forum in which many of those giving advice used the term "lightening" as in decreasing weight.

Always an interesting debate in which I have nothing constructive to add but yet another question.

Are there degrees to efficacy of grounding systems and is lightning attracted to the best among a number of masts?

Chief RA · Oct 10, 2014

Don: I have been taught all my electronic technician/engineer life that "current seeks the path of least resistance". With that in mind I do not intentionally ground my boat to the water so that my boat is the path of least resistance! Of course this generates much debate as you imply, but it is what I have come to believe. Later, Chief

jrowan · Oct 13, 2014

I do not believe that lighting protection attracts lightning strikes, it only creates a straight path for the current to discharge safely. Benjamin Franklin invented the first lighting rod & cable protection system to prevent the replacement Philadelphia State House from burning down again, after is was replaced due to fire from a lightning strike.

A 40 foot + tall aluminum mast is already an excellent attractor of lighting on its own.
The basic idea of a lighting protection system is to wire the base of the mast through to the keel with heavy cable bonding to discharge electricity safely, so it doesn't burn a hole through the hull instead. No system is perfect, but a system is definitely better then non. The higher the gauge of wiring & heavy bonding strips the better, but also makes it expensive to install. Catalinas are easier to install lighting protection since we have lead keels. Talk to a marine electrician for specific recommendations & costs.

Chief RA · Oct 13, 2014

I am both a degreed Electronic and Industrial Engineer and I just stated what I think. Chief

The Garbone · Oct 15, 2014

I wonder what the ohmic if value is from the jacket of my VHF coax cable to the prop shaft/keel.

Unless you have a metal boat that is what we are talking about as the mast themselves and chainplates are atop a fiberglass and wood hull which are pretty good insulators. My guess is a bond to the keel from the mast or a chainplate would help bleed off electricity from a near miss.

A direct strike, well what happens happens, your electronics will most likely eat it ground or no. I took sailing lessons from someone who was on a boat that got hit. She said some of the woodwork below caught on fire and made sure to have her mast grounded after that.

Jackdaw · Oct 15, 2014

I think Chief and JR are talking about two different things:

1) Does a grounding system minimize damage/injury in the event of a strike?
2) Does a grounding system make a strike more likely?

For #1 I think yes it can. Lots of anecdotal evidence supported by basic science.
For #2 maybe, not sure anyone can say for sure. I've seen lightning strike in the water, surrounded by masts of all types less than 100 feet away.

The simple truth is that lighting is an amazing amount of electricity and very unpredictable. Anyone that speaks in absolute terms when it comes to lighting is forgetting this fact.

chrisings · Oct 20, 2014

I'm with Chief. Let's keep in mind that a lightning bolt contains 1 billion volts and possibly 10,000 ampere. No amount or size of electric cable installed on our boats can handle that.

Maine Sail · Oct 20, 2014

Chief RA said:
Don: I have been taught all my electronic technician/engineer life that "current seeks the path of least resistance". With that in mind I do not intentionally ground my boat to the water so that my boat is the path of least resistance! Of course this generates much debate as you imply, but it is what I have come to believe. Later, Chief

The only good set of data we have on this, collected by Dr. Ewen Thompson, suggests that unbonded boats are hit slightly more often, not less. In my own pool of lightning strikes, on customers boats, the same holds true... This summer was a light strike year for me and it was a 3:1 ratio.. Three unbonded boats hit to one bonded boat...

Chief RA · Oct 29, 2014

Just got back from Bodega Bay and retrieved my boat and put her away in her boat house.
I really don't much care what a Dr. says as I have more education than a Dr. level and always drew top level doctorate pay while teaching electronics in college anyway.
My learned education/experience indicates that the best grounded boat gets to be the primary attractant/source!
Thats all I have to say about it. Chief