Turn on the hand held GPS which has a built in chartplotter feature and procede in confidence..
OH solar flares knocking out the sat signals......generally this is a short lived event but I have to say the odds of that happening while I was on SW ledge would be pretty slim and I would generally know about it prior to heading to a place like that.
(Like last year in the fall the signal did go down but not altogeter)
I would probably look at my compass though IF all this happend.
You know the compass is not ammune to atmospheric/geo events either. Years back I recall once watchin the compass go nuts off Montauk, asked my dad...can a compass break? It cleared up after a few revs...But to this day I have no idea what caused it.
Have you ever seen the compass do odd things?
Remember, all those ships that ran aground/collided in the NE graveyard all had a compass...Some crashed directly into islands head on....while looking at thier compass.