Join Date: Jan 2000
Thanked 18 Times in 10 Posts
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as sailingfool said, most GPS unit have this feature with a programmable threshold for movement. If you get a GPS with "differential" they're very accurate. I forget what the manufacturers advertise but I've cruised by nav aids entering locals areas and my gps unit (a Furuno) showed the navaid a few feet from the boat when it was in fact "a few feet" from the boat.
I have not had to rely on it in the fog but after seeing it perform I would trust it.