A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Mar 11, 13:49 -0700
Greg, you wrote:
"That means ownership of a boat for 25 years puts the odds at 1/10. Not good odds. EMP exposure from near strikes must then have odds higher than 4/1000 per year. "
Not necessarily in a navigationally significant way. This number, 4/1000 on average, is based on insurance claims, and the majority of these are boats that were not sailing. They were at anchor or docked in a marina (because that's where most boats are most of the time). And because these are insurance statistics, there is probably some over-reporting in some categories and under-reporting in others. For example, there's a table that suggests that a boat smaller than 15 feet in length is essentially immune from lightning strikes. I suspect that such boats are instead immune from insurance policies.
According to the article:
"nearly all of [the] claims were for damaged electronics. Here's how it normally goes. Joe and Jane Boater arrive at the marina looking forward to a lovely weekend on the water. They begin loading all their stuff onto their sailboat. Jane goes down below to put things away and says, "Joe, did you leave the breaker for the fridge off?" A bit later, Joe tries the chartplotter but it won't fire up. Then the microwave won't work. It takes awhile before the penny drops. One of them looks at the other and says, "Remember that big thunderstorm last week? Maybe our boat got hit." "
So their "normal case" is a boat moored at the marina. How often is an average boat in Florida sailing? How does that affect the statistical odds?
What about bigger vessels?? How many cruise ships are struck by lightning annually? And of the thousands of passengers aboard, nearly all of whom bring modern electronics with them (especially smartphones), how many file claims for lightning-fried devices? I can't recall a single case. Cruise ships leave Port Canaveral in Florida on a daily basis, and they are ubiquitous in the lightning-prone Caribbean. They are significantly better lightning targets than small sailboats. Yet we hear no stories of thousands of instantly fried electronic devices. They must be doing something right!
Here's a question that I posed to the group in December, 2003, just a couple of weeks after I joined NavList:
"Is there a 'lightning-proof safe'? If you're sailing across the Atlantic, and your boat is struck by lightning, you may lose all your electronics. Can you keep a spare handheld GPS in an insulated metal case? Do they market such things?"
Round and round we go! Back then, in the late Jurassic period of the Internet, there were fewer search options. But just now, I visited amazon.com and searched on "Faraday cage". There were quite a few hits. I gather that these products are mostly designed for hiding electronics rather than protecting them from lightning-induced EMP. If no protective products exist, it appears that an insurance policy is simply the cheaper option, or the odds of these events are considerably lower than it appears.
Conanicut Island USA