Chart Plotter/Auto Pilot Heading Errors

[Witzend]

Hey Rich, Fluxgate Compass was swung in May during commissioning. It was done in the upper Elk just South of the C&D canal entrance. I tried to pick slack tide with little wind, but there may have still been some current. The apparent errors were noted in the middle of the bay just opposite the Sassafras river heading N/E pointing at Turkey Pt. My bow was pointing right at the point, but the heading vector (HDG) was pointing to the middle of the Elk river. I then pointed at Sandy Pt. on Spesutie Island. The HDG vector was again pointing ~5 deg. NE of the Pt. So it would seem it is off ~ the same at a different heading. I hear ya on the anomalies in the area, could be to blame for some of it. I will play with it some more. I know this is a bit anal, but would like to get it a little closer if possible.

 

[kloudie1]

Remember that a fluxgate will respond to the odd can of beans or any other magnetic substance close to the sensor. Those will definitely un-calibrate it if added or subtracted after calibration.

 

[rpwillia]

Swung the compass

When I installed the S1, I did the calibration. I may have erred with caution as 10 degrees of difference may be the max and 2-5 may be more realistic. I just don't worry about it that much. I am also a river sailor so land is visible in one form or another all the time. One other consideration is the fluxgate, gps antenna and compass while all mounted in the stern are a few feet away from each other.

 

[Witzend]

I have finally solved the problem, apparently you need to set the time offset first. I'm not sure why this was causing the problem, but it corrected the heading error, or what Raymarine calls "crabbing"

 

[Bill Roosa]

time offsets and compasses

the time offset tells the computer what part of the world you are in (east coast in this case). It can then consult its deviation table for the standard deviation for that area. Why can't it get that automagically from the GPS?? Well some don't have the GPS connected (can't imagine why but mine came that way) and the time offset is the only way to caliprate it without GPS. I think there is a page in the setup/calibrate sequence that askes if the GPS is up and running and do you want to use that (in-lue-of) the time offset.

Also I remember a NTM that warns of large magnetic disturbances in the top of the bay.

 

[Witzend]

The C90W has GPS included, so it is a mystery as to why the offset is not automaticly applied, furthermore, I had to use 7 hours for the offset to get the time to display EST..
You would think it should have been based on UTC time that would have needed a 5 hours offset, not 7? I'm aware of the magnetic disturbance at the top of the bay, I'm wondering if Iron Hill is contributing to the problem.