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Autopilot calculations
04-04-16, 09:15 PM (This post was last modified: 04-05-16 02:17 PM by Steve - Raymarine - Moderator.)
Post: #1
Autopilot calculations
I have the following Raymarine instruments

One S1 SmartPilot, E15016 w/ fluxgate compass
Two SmartPilot Controllers, one ST8001 and one ST8002
One E120 Chartplotter
One RS130 GPS

Both controllers are connected to the SmartPilot via SeaTalk.
The fluxgate compass is connected to the SmartPilot via its dedicated terminals.
The Chartplotter’s NMEA 0183 output is connected to the Autopilot’s NMEA 0183 input.
The GPS is connected to the Chartplotter via SeaTalkng.

The system works well.

Which of the units calculates the new heading when the chartplotter advances to a new waypoint?

Which unit calculates the crosstrack error?

Which unit adjusts the heading to reduce the crosstrack error?

Thank you
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04-05-16, 02:59 PM
Post: #2
RE: Autopilot calculations
With input by the chartplotter data, the autopilot course computer calculates the new heading to the next waypoint.

The course computer calculates the cross track error.

The course computer with the rudder data information adjusts the heading to lower the cross track error.
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04-05-16, 03:42 PM
Post: #3
RE: Autopilot calculations
Thanks Steve. I am considering upgrading some of my equipment and I wanted to get an idea on which instrument should be my focus. I sounds like the course computer upgrade should come first.

Thanks
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04-05-16, 08:34 PM
Post: #4
RE: Autopilot calculations
In my current system if the boat is on a track and there is significant compass error, current set or wind drift, the course computer adjusts the heading to provide a heading offset that enables the required COG to be achieved. This offset on my boat is usually measured in from zero to a few degrees.

If a waypoint is then encountered and the course changes very slightly, the initial heading set by the course computer is exactly equal to the new BTW. Whatever heading offset that was required is simply lost and the course computer has to go through the job of determining the offset all over again.

In my case I observe the heading offset just before the waypoint is reached. After the waypoint is reached and a new heading is set by the course computer I dial in the previous offset and get good results.

Do the new Evolution series of course computers retain part or all of the prior offset so that the operator does not have to enter the heading offset manually?
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04-07-16, 08:42 AM
Post: #5
RE: Autopilot calculations
The Evolution holds that data because it is working with more data then the S1 course computer. The EV-1 heading sensor of the Evolution autopilot system is working with virtual rudder reference data coming from the 3-axis digital accelerometer, 3-axis digital compass, 3-axis gyro digital angular rate sensors, in order to hold that course for tighter course tracking than the S1 course computer you're used to.
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