Posted: Sun Aug 31, 2008 12:59 am Post subject: Connection from GPS to Autohelm ST1000 : Result of seatrial
I have been able to test the latest version 1.41 with the following setup:
- Garmin GPS eTrex legend with a complete route including more than 15 waypoints and sharp turns. The GPS outputs NMEA signals.
- Autohelm ST1000 connected with Seatalk
- ideal sea conditions, no current
The first conclusion is that the bridge is able to perfectly send the needed information from the GPS to the ST1000. Please have a look at the following screenshots of the ST1000:
Bearing to next waypoint
Cross-track error : in this case the boat is left of the track
Distance to waypoint
The second conclusion is that the ST1000 is able to steer according to the information, steering toward the destination and minimizing the crosstrack errors.
I forced the boat out of the track in order to see how the autopilot would correct the situation. Please have a look at the following charts, they show the error correction algorithm:
You need to know that for this 60 degrees angle error, the autopilot will need as much as 0.8 nm before reaching the right track again. The maximum cross track error was 0.2 nm. This error correction is thus very slow, much slower than a manual correction.
When the waypoint is reached and the GPS starts heading for the next waypoint, the ST1000 sounds the next waypoint alarm and will make sharp turn once the captain clears the alarm.
There was a few strange phenomenons I would like to share with other members of the forum:
- the ST1000 stopped reacting to the GPS for 10 mins and claimed that no navigation position is available. I was able to get the NMEA messages during this time and the most strange is that they show that the bridge has both the NMEA and the Seatalk connection (the ST1000 sends $IIHDM messages). I don't know why this happened!
The other surprising reaction is that sometimes the "waypoint advance" function did not work. The ST1000 did ignore the waypoint change indicated by the GPS. As a result the ST1000 made the "slow" turn above instead of the sharp turn. I would like to know from other members of the forum whether this could be due to some "intelligence" in the ST1000? Could it be due to the prior usage of "manual corrections"?
Thanks again for this great functionality of the bridge!
Joined: Mar 26, 2006 Posts: 417 Location: Mannheim / Germany
Posted: Tue Sep 23, 2008 3:58 pm Post subject:
sorry - i'm currently moving into a new house.
Everything is packed So I currently can't try it myself.
I have tried it on a charter boat last june - and I didn't have that "unavailability" Problem.
I would like to test it again - but that takes a bit of time until I have unpacked all my stuff again.
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