For a long time it has bothered me that the Autopilot display, the Raymarine GPS control Head, and the Garmin Multi-function display are never exactly in synchronization. On my trip to Yorktown with Al and on my trip to Cambridge I was bothered that something just didn't seem right. This was the first times I had gotten underway since installing the Actisense.
Totally by accident I discovered that the Raymarine GPS thought the year was 1995. Apparently the unit could not calculate the year 2015. This means that all of the almanac data driving the GPS is wrong. Prior to installing the Actisense this might have been a big deal. I am not sure. But subsequent to the install it became a very big deal. Since the only OEM data bridge between NMEA 0183 and NMEA 2000 puts NMEA 0183 data on the NMEA 2000 bus but not vice versa the old (circa 1995) Raymarine GPS data was isolated to the autopilot computer.The network equipment used the NMEA 2000 GPS units for data. Not so after the bridge was installed. I discovered that all of the equipment thought it was 1995! A couple of interesting things:
1) Since the GPS knew the correct time but the incorrect date all the current and tide information was wrong.
2) GPS satellites must be in pretty stable orbits - the location data was pretty close (or it was all getting it from somewhere, I am not sure.)
My solution was to set the NMEA 2000 network preferred source for the GPS to the NMEA 2000 GPS units. What a difference. Reboot picked up 1.5 knots of speed!
Tomorrow I will experiment with disconnecting the old GPS unit to see if all of the data then becomes in sync. Or, knowing Raymarine the autopilot will most likely stop working forcing me to purchase a new one (because I am sure they can't fix the old one - that would not cost enough money! Yes, I love Raymarine like I love hemorrhoids.
Part 2 is here: http://blog.sailboatreboot.com/2015/07/do-you-really-know-what-time-it-is-part.html
Fair winds and following seas :)