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Philip OUVRY writes:
 > For maritime users in small craft a GPS accuracy of 100 metres is
 > more than sufficient.  Provided you can find the fairway or safe
 > water buoy at the approaches to ones destination or the entrance to
 > the harbour, it is far safer to navigate by sight (i.e. pilotage)
 > rather than by 'head-down' reference to the GPS.

Slavish adherence to any one source of navigation information, be it
the display of a GPS or the human eye, will sooner or later lead to
problems.  The prudent mariner will continually compare one source of
information with another to be sure of having reliable information.

 > Out at sea an accuracy of one mile is quite sufficient.

Er, I'd even argue that three miles is quite enough.

 > There are occasions when a greater accuracy would be useful such as
 > an anchor position in a crowded anchorage.  There is no real need
 > to know the boat's position to an accuracy of 30 metres or less.

While perhaps 15 meter accuracy seems superfluous for small boats, one
of the more important benefits of SA being disabled is speed accuracy.
Remember that every time the satellites danced and, albeit briefly,
had 30 foot sailboats moving at 20 or 30 knots, speed averaging and
log functions were corrupted by these false motions.  Without SA,
speed and distance covered are going to be closer to reality than when
SA was enabled.

Rick
S/V One With The Wind, Baba 35

   

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