NavList:

In http://fer3.com/arc/m2.aspx/Threats-GPS-introduction-eLORAN-FrankReed-jan-2016-g34420  Frank stated that "The best backup for a GPS is another GPS"

YouTube's "Sailing Yacht Ruby Rose" is a video travel log of a couple who have crossed the Atlantic Ocean more than once.  In a recent 2018 Q&A, they were asked about lightning stikes and ship board electronic failure.  The obvious underlying context was "what is your backup?"

The statement, in summary, was that the backup to the main GPS Chartplotter was a secondary chartplotter.  The backup to that secondary chartplotter was a series of handheld GPS based devices.  The string of devices was stated as a depth of 8 (eight) GPS position finding devices, of which the majority were battery operated.  That is, not connected to the yacht's electrical system.  The captain specifically stated that there was no sextant onboard and there was no pretense of performing celestial navigation, as that was simply a "purist's exercise". 

While a survey size of one is hardly a statistical result, the answer was informative.  Crossing the Atlantic in either direction is a non-trivial exercise.  Not knowing your position could prove fatal.  Yet this captain dismissed CN as a purists exercise.  Not worthy of his time.  His biggest fear?  Coming on watch to discover the previous watchstander as an MOB casualty, notwithstanding AIS SART.

The backup to a GPS is another GPS.  

Brad