Sorry, used wrong verb - rather than 'accuracy' I should have used something like 'trustworthy' or 'confidence enhancing'.
The following is a quote from a recent debate on the topic from the UK based Practical Boat Owner forum:
" Found on
http://www.defensetech.org/archives/001280.html and thought all of you might be interested by this!
US TO SHUT DOWN GPS IN CRISIS?
The White House has completed yet another piece of its never-ending review of the Clinton-era 1996 National Space Policy.
U.S. SPACE-BASED POSITIONING, NAVIGATION, AND TIMING POLICY, signed by the President on 8 December 2004, "establishes guidance and implementation actions for space-based positioning, navigation, and timing programs, augmentations, and activities for U.S. national and homeland security, civil, scientific, and commercial purposes."
In other words its a GPS policy, and pretty aggressive one at that.
The policy, which also comes in a classified flavor, reportedly resulted in a directive to the Secretary of Defense (SecDef) to develop plans to shut down civil use of U.S. GPS signals in certain emergencies and to deny advesaries access to foreign space-based satellite navigation services, such as the European Union's Galileo system.
Does anybody remember when Washington claimed that Galileo was unnecessary, because we would never shut GPS down?
The Europeans have been buzzing about what the U.S. might do to Galileo in a crisis. Publication of a new Air Force Counterspace Doctrine fueled these fears, after Peter Teets asked a rather provocative question in the foreward:
'What will we do ten years from now when American lives are put at risk because an adversary chooses to leverage the global positioning system or perhaps the Galileo constellation to attack American forces with precision?'
Comments like this have a way of being taken the "wrong way." An ugly row recently erupted after a British paper reported that European participants at a Royal United Services Institute conference thought they heard U.S. officials threaten "irreversible action" to deny hostile powers access to Galileo in a crisis--although other participants disputed that any threat was issued.
Some of the dispute can, I think, be traced to a difference in thinking about satellite navigation. Whereas Americans tend to think of GPS as a military application that civilians are permitted to use (reflecting the military origins of GPS), much of the rest of the world sees it as a global public utility. I suspect we'll be hearing a lot about this policy by Galileo's supporters."
Because there is an American Military CPS policy, in Europe there is a concern about putting putting all one's navigational needs in one basket hence the development of Galileo, although, I think it was recently agreed that The American Military could have access to switching off the system if needs exist. A lot of European countries/governments are suspicious of GPS and wish to provide a local alternative hence the appeal of Loran C if GPS should 'go down'.
However, on a slightly lighter note, from the same forums, I quote observations from an even earlier system "Decca was very accurate & was very easy to use. The best bit about Decca though was two ships navigating in reduced vis/fog/mist/falling snow etc etc , going down the same position line, but in opposite directions!! Definitely brown trouser stuff & no mistake! It used to happen a lot on harbour approaches, if one of the position lines was in a convenient place & direction. A little like a stone age edition of GPS Waypoints, where everyone is heading to the same spot in the oggin!"
GPS is undoubtable the most accurate and convenient system and is here to stay and I too have two sets on board as a backup system but I also practice pilotage skills near land and keep my charts up to date enroute - old habits die hard.
Although for Car navigation systems I can imagine it to be handy, you need more accuracy when deciding where to turn left, in a dence city. But at sea, don't think so.