"Roger Long" wrote in news:45c39114$0$1339
:

That's not what the manual for the ST1000 says. The GPS can tell it
the
bearing, distance, and track error. The ST1000 has a logic circuit to
resolve this into a new heading.



Like I said, the chartplotter tells it how to steer the boat. A GPS
receiver puts out lat/long/time and calculates course and speed if it has
a little display with a crumb line. You can tell the simple GPSes with
simple displays what waypoint lat/long you'd like to go to and it will
make a waypoint IT can steer the autopilot to. There's no way to input a
waypoint lat/long into the autopilot that has a few course change buttons
and simple controls. $GPAP data coming from the simplest GPS tell it
what to do:
$GPAPA - Autopilot Sentence "A"
$GPAPB - Autopilot Sentence "B"
$GPASD - Autopilot System Data
So, the little GPS you put the waypoint into is the chartplotter, whether
it has a $200 map plug into it or not.

The autopilot has no computing capacity to store waypoints, do great
circle calculations, etc. On your simple installation, I'd like to
recommend the Garmin 76Cx handheld GPS/Chartplotter in its little snapin
mount at your helm. Power is not an issue. It uses so little it will
still give you full navigation on its own batteries if yours fail. It
comes with America Recreational chart, but the CD has all the bigshot
charts you can load into its standard microSD 128MB memory card. The CD
program loads the 76Cx from your laptop, and you activate the charts you
want to BUY online for it.

Now you have a full-featured chartplotter to run the nav solutions and
tracking on that's really neat. I installed one on my buddy's sailboat,
and he also has a Jolly Boat (fiberglass rib boat with 40hp outboard).
We bought a second snap-in GPS mount for the Jolly runabout and you just
pop the 76Cx out of your pocket into whichever boat you're on and have a
full navigator, even on a boat with a 40hp Yamaha outboard....overkill?..
(c;

The little autopilots I know of only have a fluxgate compass to steer
with.

Larry
--
Democracy is when two wolves and a sheep vote on who's for dinner.
Liberty is when the sheep has his own gun.