NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Pete Solon Palmer
Date: 2018 Sep 26, 17:03 -0400
I think CN is useful for coastal sailors too. If you are approaching land, and you don't know how far away it is, or where your land fall may be, then you are technically lost.
I have sailed along more than one featureless coast where I HAD to take a celestial sight to find out where on that coast I was.
Pete
-----Original Message-----
From: Brad Morris <NoReply_Morris@fer3.com>
To: globenav <globenav@aol.com>
Sent: Wed, Sep 26, 2018 12:33 pm
Subject: [NavList] Re: GNSS is not immortal
>>Please do so identify those scenarios (for GPS failure).
One scenario is that the recreational sailor has a failure to appreciate the nature of an effective Faraday cage.
The proper way to protect a handheld GPS unit from a lightning-generated electromagnetic pulse is to surround it with an insulator (e.g. inside a sealed ziplock bag or plastic case) and then surround it with the conductor (e.g. wrap in aluminum foil).This particular sailor at https://forums.sailboatowners.com/index.php?threads/faraday-cage.146943/ got it wrong: he had electronics-conductor-insulator rather than electronics-insulator-conductor.
I had a GPS wrapped in tin foil, inside a Pelican Case stored in a Ziplock bag with desicant and it still got fried.
This failure to understand the nature of an effective Faraday cage - which seems to pop up repeatedly on blue water sailing forums - has definitely led to instances where all the electronics connected to the boat's electrical system got fried by a lightning bolt, as did all the hand-held GPS units. And because of their initial misunderstanding, they come out of their experience of a lightning strike no wiser than before it happened.
I have an acquaintance who sailed single-handed around the world in her 60s. She did not carry a sextant, but rather had 5 hand-held GPS units to back up her main GPS. But because, as I discovered, she did not understand how to protect against EMP, if she HAD experienced a lightning strike, she might well have found that she had a single event that caused a catastrophic, simultaneous failure of every GPS on board.
The best back up to a GPS may indeed be another GPS...but only if you have a correct understanding of EMP and Faraday cages.
It is impossible to know how many of the 40 to 60 sailboats a year that disappear without a trace do so after a catastrophic loss of GPS navigational ability. It could range from "quite a few" to "none".
But one can at least imagine a scenario where -- no matter how many handheld units one has aboard as backups -- a GPS only approach to navigation leaves you with something very like a single-point-of-failure for a mission-critical capability required for making a landfall.
Bob
