The last three years of nautical almanacs on my shelf say otherwise. We own two, an Astra IIIB and a nice Freiberger from the '70s.
I know enough about solar physics to know that our projected cruise falls near a flare maximum (it's cyclic) and that not only do these "sun storms" have the potential to screw up
GPS, they can cause the atmosphere itself to heat up, expand and create drag on LEO satellites...like the
GPS constellation.
Solar flares cause GPS disruptions
Solar flares will disrupt GPS in 2011 - tech - 29 September 2006 - New Scientist Tech
I recall well 1989 when a burst of solar radiation took out the electricity in Eastern Canada. It pooched
GPS for a few days, but in '89, few people were using it "recreationally".
So the sextant (and the maintenance of the skills to use it) are simply representative of good seamanship. One should always have multiple (or at least more than one) methods of ascertaining one's position.
GPS is ONE such nav aid. Sextants are another. Depth contours are a third. Coastal pilotage is yet another. Hell, I can find my latitude with a stick, a protractor and a calendar, even on a boat. If my
GPS is showing me I'm sailing atop Mount Terror, I know nothing of use to me as a navigator.
EDIT: Here's some recent examples of outages due to flares:
Solar flares ate my GPS | Register Hardware
GeoCarta: GPS Outage Due to Solar Flare; Are More to Come?