Originally Posted by balp
Is the setup so just repeating incomming gps signals would work? Or does thet need to be generated?
for a complete description of my setup (perhaps more than you want to know).
The Raymarine ST4000+ supports three modes of operation:
- Basic Autopilot mode, where the controller keeps the boat on a constant heading. This requires no external inputs, but works more effectively if the autopilot receives SOW (paddlewheel) or SOG data, because the controller will modify its gain to compensate for changes in the boat's responsiveness at high/low speeds
- Track mode, where the controller minimizes XTE on a plotted course. In this case, it also uses SOG data to calculate and compensate for current and drift and to modify its gain to compensate for changes in the boat's responsiveness at high/low speeds
- Wind vane mode, where the controller takes wind data and keeps a constant heading relative to the wind direction. I do not have an electronic wind transducer, so I do not use this mode.
I use the first two modes. I use basic mode over a large range of speeds from full cruising speed to idling the motor
directly into the wind while I raise/drop my sails
. I am having great difficulty tuning the controller to hold a constant heading over the full range of speeds. I believe that feeding SOG data to the autopilot would help this greatly.
The track mode requires XTE, BTW, and DTW to function, and also works better if it gets SOG or SOW. But it basically works fine without the SOG data, so it's less of a concern. However, I need to continue receiving XTE, BTW, and DTW from OpenCPN for this mode to work.
By the way, the track mode works very nicely
in OpenCPN by simply right-clicking at a point on the chart and selecting "Go to here" from the drop-down menu. It is so easy that I am using it a lot more than I expected to.
You can see from my schematic in the link above that I could feed my GPS info or
OpenCPN's chartplotter info to the Autopilot. I cannot feed both unless I buy a multiplexer. The GPS will feed SOG but not XTE, BTW, or DTW because you need a chartplotter to plot waypoints. If OpenCPN were modified to also send SOG data to the autopilot (by repeating RMC or VTG data that it receives from the GPS), I could have everything needed without having to buy a multiplexer.