NavList:

Re the GPS being hacked (or otherwise being down), I don't know how often it happens but it is a very real possibility.  See attached notice that I picked up at Ala Wai boat harbor on Oahu in 2012. The US navy was messing with the GPS and it could not be relied upon in the vicinity of Kauai much of the time for several weeks.  Dead reckoning was enough to make the overnight  passage from Oahu to Kauai, but it felt good to have the sextant on board too!