Following Routes - Simrad AP28



The Navnet 3D does not appear to be sending route information to the auto pilot. I have erratic behavior because when a route is activated the boat may not always follow it. The Simrad auto pilot works fine in auto mode, but loses position in the follow route mode; NAV mode. In some cases when the boat follows a route it suddenly losses course information and begins to drift off course. If you dodge it is very difficult to get back on the route. Sometimes you can not get into NAV or sometimes the boat will severely over correct to get back on a route. The result is broad S turns until it finds its track. Seems to be a communication problem between the two units.
If you are losing NavData to your pilot, I would recommend that you first ensure you are running the most current version of NN3D software. (2.07) Next, I would evaluate the NMEA 2000 (SimNet) network for architecture errors. If you are still getting “No NavData” on your Simrad unit and you are convinced you have a good network, then you might have a NMEA 2000 data problem with the pilot or the MFD. You can always have the unit tested at our factory service center. More common than not, it isn’t normally the MFD. If you send the MFD in for testing, I would also recommend you send the autopilot course computer in for testing. If this is a new system, the error would most likely be with the NMEA 2000 networking/installation. What NMEA 2000 PGNs do you have turned on? Do you get “Nav Data error” on your pilot immediately when doing navigation or at random intervals? If you are not getting the error then you most likely getting data but the pilot has some other issue. We see broad S turns and issues with our pilot when there is a heading or hydraulics issue. There are also many setting in the pilot that effects the response of the pilot. What has Simrad told you about the pilot?
Regarding the severe course correction after dodge: after resetting a course following a dodge, the default behavior for the Furuno is to cause your boat to do an abrupt perpendicular turn until it gets back on the route line, then another abrupt perpendicular turn to resume following the route line. This is, of course, silly behavior - particularly for a sailboat, and particularly when just dodging a log or something floating in the water.

The remedy is to reset the route before resuming AP operation. To do this, right click on the route and select "reset route" (or something like that - I don't have it in front of me).

I REALLY wish there was a way to change the default behavior for this because the default Furuno chose is actually dangerous for a sailboat and has never been relevant in my use.

I have also experienced the same severe course correction intermittently...and I can say it is dangerous for a motorboat too! I agree it ought to be put forward as a software enhancement.
How aggressive the AP is at 'getting back on track' is a function of the AP, not the chart plotter. The chartplotter sends cross track error and direction (right or left), the AP decides how aggressively to eliminate the XTE. In my experience, the AP can be set as to it's level of aggressiveness.
Thanks for the responses. This boat also has twin Volvo Ips 900s. I found a similar issue on the Hull Truth relating to the new Furuno time zero touch screen. In that case the user was told to turn on PGN 129285. My research tells me that the nav/route data out of NMEA0183 port 3 cycles every 4 seconds.  Simrad told me to install an AP10. Then the AP10 converts this data to NMEA2000 which is about 20 times faster, which then has to get to the SG05 computer (IPS) and apply math.  The biggest delay is because of the NMEA0183 data rate.  If the NN3D had PGN 129285, it would be significantly faster. 

So now the auto pilot is handshaking better with the NN3D. This has eliminated the "no auto pilot computer" error messages I was getting sporadically. This is not a perfect solution since I am still getting the hard S turns for course changes even after resetting the route. Also I am missing waypoints by 100 yards or more. I also have a simrad backup NSE 8 chart plotter, which if used as the auto pilot source works perfectly. The issue seems attributable with the NN3D. By the way all this equipment is new and running current software. Help.
Interesting. I have a NN3d and Simrad AP24 with an AC12 computer and it behaves perfectly. It would seem that the Simrad SG05 gateway has different requirements to the AC12. Perhaps Simrad could explain why the SG05 requires an additional PGN.
The SG05 is the required interface between the EVS (Volvo Penta Electronic Vessel control) and the AP 28. My understanding is that Furuno does not have an auto pilot that works with IPS. To make matters worse I changed the SG05 control unit already to play it safe, but that was not the problem. I have been working on it since I got the new boat about a month ago. My Furuno installer is positive the issue is PGN129285. Simrad changed the SG05 for me two weeks ago. Thanks for the input.
Sorry but I think your installer is wrong. PGN 129285 contains Route information. It doesn't contain navigation information such as course to steer, cross track error etc which are required by autopilots. The pilot should be able to get everything it needs from PGN's 129283 & 129284 in order to follow a route. For what it's worth I also have the NN3D output water depth and speed PRNs which the autopilot uses also. Good luck with it.
(gdfisher) I agree. I think the installer is wrong about the PGN. I also agree with dotdun that "How aggressive the AP is at 'getting back on track' is a function of the AP, not the chart plotter." The Furuno pilot has settings to tell it to return to the original track or to resume a more direct course to the waypoint. Many times after dodging to return to the original course line would be a violent maneuver. The Furuno pilot also lets you limit max degrees that a turn is allowed to be.

IPS drives are special. Our Furuno NavPilot currently is not compatible with IPS drives. I am sure this is one reason why the installer picked the Simrad for this installation. When it comes to the NN3D talking to the Simrad autopilot; some of the comments about update rate to the Simrad is no longer correct. There was a Simrad data rate requirement to the autopilot that the NN3D was not meeting. This in the past could be worked around by using a Simrad AT10 NMEA 0183 to NMEA 2000 adaptor so that it would meet the data rate requirement. This is old information. With newer NN3D software, the NMEA2000 data rate from the NN3D works fine with the Simrad Pilot. This is one reason why I keep asking what software is used in the NN3D. If using 2.07 software, then the NN3D should communicate fine with the Simrad.

Overall, this case seems more like an autopilot issue that is being blamed on the Furuno plotter. IPS drives are complex. I am sure Simrad can help you with this problem more than we can. If Simrad can provide us some clear data on why the problem is ours, please provide it so we can get this over to our engineers. Overall, I would suggest that you ensure you have current software in the NN3D and that it is wired to the pilot correctly by NMEA 2000. We have many folks running the Simrad pilots in this manner without problems.
1) I agree with Johnny and Gene133, the violent turns are an autopilot issue. PGN 129285 will not help. But, read #2.

2) In my experience, I have witnessed a Simrad autopilot perform a little odd when they are fed BTW in true and don't have magnetic variation information available to them. Remember, the AP is using a magnetic compass, if you pass it BTW in 'true', it must know the magnetic variation in order to steer the boat properly. It's also been my experience that NN3D sends BTW using 'magnetic', so what I'm stating here is a little confusing why you are having problems. The reason I bring this up is that you state what I believe is a second problem in that your arrival to WPs are 100 yards off. This is indicative of the AP missing magnetic variation. You can turn on PGN 127258 on the NN3D for the NMEA2000 port and this will supply magnetic variation on the NMEA2000 network from the same source as the navigation data, I have witnessed some instances where this is important. My thinking is that the AP would then have all the data it needs.

FWIW, my experience with RM APs is that they will not engage if fed a BTW in 'true' and they don't have magnetic variation available. I have no experience with Furuno APs.
I agree with dotdun. I forgot to mention that I have the Magnetic Variation PGN turned on.
Thanks for the input. I will re verify the settings. Last time I checked all were set to magnetic. Its possible that when the Simrad guys installed the AP10 the settings were changed. Funny thing is that my backup chart plotter is a Simrad NSE 8 which works perfectly with the auto pilot.
Ah, correction: I agree with gdfisher that 129285 won't work.

Gene133: So now I'm confused, you installed a AT10? Why? NN3D supports NMEA2000 directly. I found the AT10 has issues.
I am willing to believe that the return to course problem is with the Simrad AP and will look into it. The only thing I can say is that when the pilot is being controlled by a computer running Coastal Explorer, the violent return to course behavior does not happen following a dodge.

And section 5.10 "Restart Navigation" in the MFD8 operator manual shows exactly this violent behavior as the normal operation. There is a figure that illustrates how the course will be resumed if one does not reset the route first. The figure shows normal operation as a direct perpendicular turn back to the original route followed by a perpendicular turn back onto the original route heading.

The chartplotter sends (3) main parameters to the AP. They are bearing-to-waypoint, distance-to-waypoint, and cross-track-error. XTE is simply how far the current position is (in meters) right or left of the track line. APs do consider other parameters like waypoint lat/long, waypoint name, speed-over-ground, heading, etc. My point - there is no parameter transmitted to the AP that states how aggressive to turn, that's totally a function/calculation of the AP.

When you restart a track, it moves the track to line up current position -> waypoint, eliminating the XTE and the follow-on (aggressive) turns to get back on track.

I hope this helps.
The AP 10 is necessary to get route information to the autopilot from the IPS system. The Simrad SG05 needs PGN 129285. It looks like the only way to get routes to work is by adding the AT10 which is a Simrad part to integrate with the Simrad SG05. To follow routes you have to fiddle with arrival waypoint circle on the NN3D. Yes when you dodge you have to restart the route facing the next waypoint before you re engage the auto pilot.
Gene133":2jw5ieuj said:
The AP 10 is necessary to get route information to the autopilot from the IPS system. The Simrad SG05 needs PGN 129285. It looks like the only way to get routes to work is by adding the AT10 which is a Simrad part to integrate with the Simrad SG05. To follow routes you have to fiddle with arrival waypoint circle on the NN3D. Yes when you dodge you have to restart the route facing the next waypoint before you re engage the auto pilot.

I have no experience with the IPS. But, for the life of me, I can't figure out what the SG05/IPS would do with a complete route set (PGN 129285).

BTW, the AT10 does NOT support PGN 129285.

The NN3D communicates with the Simrad course computer, which then communicates with the IPS via the SG05. Both NN3D and course computer support NMEA2000, that is the only connection needed between those boxes, the AT10 is useless in this scenario and can/could be detrimental since is doesn't perform all translations properly (in my experience). If you need NMEA0183 data on the NMEA2000 network, a better plan would be to use the NN3D to perform this function.

Good luck with getting this sorted out.
Dotdun is right, the AT10 does not support that PGN.
As far as dodging.... There is a difference between dodging with the dodge buttons and disengaging your autopilot and re-engaging a route in progress.
Well now I can confirm that after installing the AT 10 and a new SG05 supplied by Simrad the routes are working properly. The only issue is that at higher speeds over 20 knots the boat will over correct at least 3 times before its on course. The XTE is as much as 400 feet. I have a waypoint arrival circle of 250 feet. The SG05 is required to interpret rudder information from the Volvo IPS. Furuno advises that the SG05 needs PGN 129285. While its not perfect at least its working, but there is a lot of stuff between the auto pilot and the NN3D.