A78 - possible GPS issues

[silverbullet87]

I'm running an A78 on a 25ft grady white with a raymarine radome. I've noticed a large dependency between stationary targets my radar picks up vs. their location on my charts. My charts are up to date navionics charts. As you can see in the attached pictures - radar targets vs charts do not agree. I feel like the radar is accurate - and the charts are off for a few reasons.

I've tried heading straight towards a bouy or other stationary item. The radar shows it on my heading line as it should - but the chart will show it quite a way off to the right. As i get closer - the chart and radar seem to agree more.

I've also noticed when i'm going through a somewhat narrow canal - my track from earlier in the day (heading out to fish) will be significantly off. The track will be on land.

I do have radar overlay switched to radar-chart synchronization. Any ideas?

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum silverbullet87,

It is possible that your radar bearing alignment is off, and/or vessel's heading sensor is in need of alignment, and/or the vessel lacks a heading sensor and is maneuvering or under the influence of leeway. Please click here to view a FAQ addressing this subject.

[silverbullet87]

Thanks Chuck - i'll check out all of those suggestions shortly. I did notice some mention of autopilot needed to be reset. I do have an older raymarine auto pilot connected through seatalk. The A78 is somewhat new to the boat - and i've yet to get the autopilot to function properly (it seems to have a mind of it's own) I've noticed that my manual compass does not agree with the A78 heading. Is it possible there are some settings off from the previous display/communication?

[Chuck - Raymarine - Moderator]

silverbullet87,

As long as the autopilot is producing correct heading data (compare the autopilot's heading to the boat's properly calibrated (don't assume) fluid filled compass), a78 MFD has been correctly interfaced to your older autopilot, and MFD has been configured for magnetic bearings (HOME->SET-UP->SYSTEM SETTINGS->SYSTEM PREFERENCES->BEARING MODE), then the heading data specified within the MFD's Heading data item should be very close to the heading indicated by the boat's properly calibrated fluid filled compass.

[silverbullet87]

Hey Chuck,

My radar appears to be correct - and it's my charts that are off. Bearing is a solid 50+ degrees in error. I do not have an external heading sensor. I've confirmed the MFD is set to magnetic bearings. Are you saying that while the autopilot is connected through seatalk it will provide the heading, but if there is no autopilot present heading will be provided by the MFD? I'm trying to pinpoint the issue and i get minimal time on the water for testing. Thanks for your help.

[Chuck - Raymarine - Moderator]

silverbullet87,

Q1. Are you saying that while the autopilot is connected through seatalk it will provide the heading, .
A1. All Raymarine autopilots, and most other autopilot for that matter, feature a magnetic north seeking heading sensor. Should you have a Raymarine autopilot interfaced to your system, then it will indeed provide heading data to the system. Should a third party autopilot be interfaced to the system, then it may also be supplying heading data to the system. To determine whether your MFD is interfaced to a source of heading data, switch on all marine electronics (including the autopilot) and configure the MFD to display the "Heading" data item within a Databox. Should the value be something other than ---, then the MFD has been interfaced to a source of heading data which will need to be re-calibrated/aligned or serviced to permit the correct heading to be displayed. Such information will be found within the autopilot's commissioning guide.

Q2. If there is no autopilot present heading will be provided by the MFD?
A2. No. The internal GPS sensor or an a/c/e/eS-Series MFD will supply the MFD with GPS Course Over Ground (COG), not "Heading". To view more information on the differences between COG and Heading, click here.

[silverbullet87]

Hey Chuck - thanks for your help. While parked in the driveway I was able to confirm that my S1000 is providing heading data. "000" was the reading - and when I pulled the seatalk plug I got a warning that heading was lost. I went through the procedure w/ the S100 remote to "reset" the auto pilot. I'm not sure if that will reset the heading or not - but i'll check it out when i'm on the water again.

If the heading is indeed 50+ degrees off the next time i'm out - would you suggest doing the manual trim in the settings to make it correct?

[Chuck - Raymarine - Moderator]

silverbullet87,

Unlike autopilots which are designed around a magnetic north seeking flugate/heading sensor, the S1000 is designed to use GPS COG instead of magnetic heading data. Should your MFD be reporting 000 for its heading value, then it would appear that the S1000 or SeaTalk to SeaTalkng Converter is erroneously transmitting a value (000 in this case) for the Heading data item. Should you not already have done so, then it is recommended that the SeaTalk to SeaTalkng Converter's software be updated with the latest available Raymarine product software update to ensure that it is not causing Heading to be transmitted into the SeaTalkng backbone. If the SeaTalk to SeaTalkng Converter is operating with the latest software and the problem persists, it would be necessary to interface the S1000 to the system in a different manner. The S1000 will need to be disconnected from the SeaTalk to SeaTalkng Converter and as the 6" and 7" a-Series MFDs do not feature a NMEA 0183 interface, the S1000's NMEA 0183 input leads will need to be interfaced to a NMEA 0183 to SeaTalkng/NMEA 2000 Data Bridge (ex. Actisense NGW-1-STNG, etc.) which in turn would be interfaced as a spur to the SeaTalkng backbone.

[silverbullet87]

Hey Chuck - the 000 reading was unusual. Normally it will give me an actual heading value. I'll report back after my next time in the water.

[silverbullet87]

Does the S1000 have a built in GPS sensor, or does it pull GPS from the MFD or an external source?

Prior to my a78 / raydome installation - there was an older raymarine display with inputs for the S1000, and an external GPS sensor that i'm no longer using. I'm wondering if that GPS sensor was required for the S1000 to operate properly?

Also - should I still have my MFD bearing settings to "magnetic" if the S1000 uses COG?