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Larry Larry is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 5,275
Default Autopilot NMEA question for gear heads

"Roger Long" wrote in
:

Any tips or experience interfacing and using one of these autopilots
with a GPS also appreciated.

--
Roger Long


The autopilot doesn't do the navigating. The chart plotter does the
navigating and sends out directional messages to the autopilot via the
network from its calculations taken from GPS position data. i.e. "We
want to go to this waypoint. We are headed in this direction, so we need
to turn the boat 48.5 degrees to starboard to head that way. Our course
over ground to the waypoint shows there is 1.8 knots of current trying to
drag us off course, so we need to subtract that from the boat heading.
Yo! Autopilot! Turn 44.5 degrees to starboard or I'll tell the captain
to replace you!" Autopilot, terrified of being turned into marine scrap,
comes about smartly 44 degrees to starboard, as measured on its compass
I'm convinced, causing an awful gybe because you got cheap and didn't buy
the network wind instrument so Chart Plotter could tell the slaves it
needed to gybe to the new course. The chart plotter makes constant
course corrections and tells the autopilot what to do to make it happen.

Autopilots aren't all that smart, if you haven't guessed that already.
All this is to force you to buy more boxes...GPS boxes...Chart Plotter
boxes...Speed boxes...Gyrocompass boxes...Compass boxes...Wind
boxes...etc. The more boxes, the more data. The more data, the smoother
that turn is because Chart Plotter and Autopilot can see their rate-of-
turn lots more often than waiting on the calculated ROT from the slow GPS
updates. The more boxes, of course, the more profits. Boats are full of
boxes...

Hope the gybe didn't pull apart the traveler that needs replacing....(c;

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