T&T: NAV Mode and Autopilots

[Jim Ague]

NAV mode is good. I used it all the time in those wide open spaces.  But it 
does depend on nonfailure of GPS, or LORAN.

One time we were traveling down the Chesapeake Bay, headed to Solomons 
Island, in NAV mode. Shortly after NAV turned us into the Pautuxent River, 
near the Pautuxent Naval Air Station and still on track, Derreen made a hard 
turn to starboard. A postanalysis after manually finishing the trip, showed 
that the GPS had relocated us 30 miles to the south, somewhere near St Marys 
on the St Marys River.

Since Derreen's GPS receiver continued to work properly thereafter, I 
assumed the problem was with the satellites, or perhaps the Air Station was 
having some fun.

Others report the same kind of problem going under the bridge on the Severn 
near the Annapolis Naval Academy. I don't know. That' not a place where I'd 
be in NAV mode.

-- Jim Ague