I have a TZTl12 MFD, DRSd4nxt radar, NMEA2000 network and have added a Maretron SSC300 fluxgate compass. The compass has been calibrated using Maretron N2KAnalyzer and all appears to be in order. When cruising off plan the chart and radar plot align perfectly. When up on plane the radar plot shifts left when traveling east and right when traveling west. Is there anything in Furuno setup that needs to occur? Any ideas? I have asked Maretron the same question.
Radar overlay doesn't match chart
- Thread starter Hotspur
- Start date
No, the Furuno will use the heading to conduct overlay. The more the heading swings off the more the overlay will be off. I saw another brands flux compass do as you describe. It was related to the boat pitch and roll. As long as the boat was level and stable the heading was good. If we increased the throttles and the boat pitched up, the heading would go flying off 20 degrees and slowly stabilize to be correct. When we lowered throttles, the heading would fly the other directly 20 degrees and then stabilize. It was not only a problem for the overlay but a big issue for the autopilot as well.
What you are seeing is pretty typical for the newer generation MEMS based heading sensors, although, more likely it would behave like Johnny pointed out and eventually settle again.
Other effects are a very nervous heading when the boat rolls or pitches and all these effects are worse at high latitudes.
In general, classic gimballed flux-gate compasses, especially when assisted by a rate giro still do much better than any of these new devices. What you have is not a flux-gate compass, but one based on MEMS chips (micro-electro-mechanical-systems) that have become very cheap, given that they are in every smart phone.
But technically it is a real challenge to combine these to get a result as good as from a gimballed and oil dampened flux-gate system. The gimbals keep the compass coils level and the oil avoids crazy swings. The short term deviations, due to slow swinging, are sorted out by the rate giro that only needs to look at the yaw axis.
The fixed mount MEMS based magnetometer will not be horizontal all the time and since the earth magnetic field, especially in higher latitudes is not at all oriented horizontal a non level sensor gets a much different reading. This gets pretty complicated to compensate, as you need the accelerometer to determine from the force of gravitation, what the orientation of the system is to then correct the magnetometer. But the accelerometer is also exposed to actual acceleration forces and can only over time average out where the center of earth is. Again that time needs to get bridged by the rate giro.
All this is very compute intensive and overly sensitive to the classic sources of compass error and I have yet to see a MEMS implementation that gets near the classic rate giro assisted flux-gate sensor in performance. I have found one that uses 3 separate analogue output accelerometers and they do the integration in analog circuitry, rather than complex computing and they seem to do much better.
This is probably the reason why Furuno sticks to proven flux-gate designs with their heading sensors, that really perform very well.
Other effects are a very nervous heading when the boat rolls or pitches and all these effects are worse at high latitudes.
In general, classic gimballed flux-gate compasses, especially when assisted by a rate giro still do much better than any of these new devices. What you have is not a flux-gate compass, but one based on MEMS chips (micro-electro-mechanical-systems) that have become very cheap, given that they are in every smart phone.
But technically it is a real challenge to combine these to get a result as good as from a gimballed and oil dampened flux-gate system. The gimbals keep the compass coils level and the oil avoids crazy swings. The short term deviations, due to slow swinging, are sorted out by the rate giro that only needs to look at the yaw axis.
The fixed mount MEMS based magnetometer will not be horizontal all the time and since the earth magnetic field, especially in higher latitudes is not at all oriented horizontal a non level sensor gets a much different reading. This gets pretty complicated to compensate, as you need the accelerometer to determine from the force of gravitation, what the orientation of the system is to then correct the magnetometer. But the accelerometer is also exposed to actual acceleration forces and can only over time average out where the center of earth is. Again that time needs to get bridged by the rate giro.
All this is very compute intensive and overly sensitive to the classic sources of compass error and I have yet to see a MEMS implementation that gets near the classic rate giro assisted flux-gate sensor in performance. I have found one that uses 3 separate analogue output accelerometers and they do the integration in analog circuitry, rather than complex computing and they seem to do much better.
This is probably the reason why Furuno sticks to proven flux-gate designs with their heading sensors, that really perform very well.
Quitsa
Furuno Super Fan
Might be a little =late for you to make this point as you have acquired the Maretron unit. One of the performance feature of my new radar with the heading input coming from the new SCX-20 satellite compass that has impressed me is what a great job it does of matching the chart in overlay mode.
I never saw anything like this previously with various magnetic/fluxgate compass whether the Furuno PG700, Gamin, Airmar GH2183 or Simrad. With the SCX-20, the radar image precisely tracks the chart whether the boat is moving or not and in rough or calm seas. Both shorelines and objects such as buoys and bridges are right on top of the chart position.
I never saw anything like this previously with various magnetic/fluxgate compass whether the Furuno PG700, Gamin, Airmar GH2183 or Simrad. With the SCX-20, the radar image precisely tracks the chart whether the boat is moving or not and in rough or calm seas. Both shorelines and objects such as buoys and bridges are right on top of the chart position.
I just started running Timezero as my sole display of my Furuno DRSD NXT and DFF1. I have been using the Airmar GH2183 for heading. Definitely an issue as others have noticed on a boat that moves around (planing small fast boat)... The issues went away with the SCX-20.
It was a difficult ($$$) decision to get rid of the Airmar, but worth it..
It was a difficult ($$$) decision to get rid of the Airmar, but worth it..
