I am a little confused as to where we are on GPS accuracy. I thought the Government was dropping the scrambling on the satelite signals so accuracy would be quite high and differentials no longer needed. Que pasa?
From what I read in Sail, Selective Availability was turned off on May 1. This means that the accuracy of the civilian GPS is now +/- 10 meters vs the old +/- 100 meters. There was an article in Sail or Cruising World a couple of months back testing the difference between GPS now and GPS+differential and a new Raytheon only system. The GPS alone could get withing a few yards of the target whereas with differential or the Raytheon system got within a few feet. IMHO GPS by itself is pretty good now. Jim Covey
On a recent trip to SF Bay, I entered quite a few channel markers as waypoints as I passed them (within 30'-50' or so). On the way back, the GPS "spotted" them within about the same tolerance. I don't see a need for anything closer as far as navigation goes.
SA on every once in a while. Which will give you a lot less accurate position than you might be used to. The have done it here in Long Island Sound a few times this summer.......But most of the time it is very accurate ever since this spring.
I recently sailed 130 nm putting in all the waypoints I needed in advance. The GPS was highly accurate. I tested it by putting in my home waypoint sitting in my living room. When I drove home from work the next day it tracked perfectly. In fact, It read .1 nm in my driveway and read 0 when I was back on my couch. Magellan handheld.
I have a Garmin 12 - SA is definitely off, has been off for months. My receiver is routinely accurate down to 20 feet, sometimes as low as 10, and every once in a while out to 40 feet. Any way you slice it, it is a fantastic peice to technology and should be on your boat at all times. 149.oo at walmart, 129.00 at West Marine with a discount. Rob
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