VHF and plotter showing different positions

[Seaflyer02]

ICOM 411 displaying different position to my Garmin 172C.

I read a thread on this recently but unable to find it. Can anybody point me in the right direction or explain what I need to do please?

[Pikey Dave]

Are they both using the same position format dddmmss/ dddmm.mmm?

[Seaflyer02]

Hi PD,


I have sent you a PM.

[Bobg]

I have had this problem on different GPS equipment quite a while ago, but I cannot remember the full details. The main reason is the chart datum being used WG824?? and the other one.
Sometimes a correction factor is applied to the GPS position for certain charts. Check the two devices have the same chart datums. If they are giving you different distances and directions to a waypoint, also check that a compass corrections been applied to one of the devices

[Seaflyer02]

Hi Bobg,


I will check the datum like you suggest.
What I don't understand is, the plotter sends the position data to the VHF because the VHF does not have any position info. So surely the VHF should not be showing anything but the same position info has the plotter?


It will be a couple of weeks before I can try anything with it at the moment.

[willk]

A VHF may retain a previous position if no new input is provided - you may have a networking issue. Does the VHF's displayed position change as the vessel moves?

[Pikey Dave]

Originally Posted by Seaflyer02

Hi Bobg,


I will check the datum like you suggest.
What I don't understand is, the plotter sends the position data to the VHF because the VHF does not have any position info. So surely the VHF should not be showing anything but the same position info has the plotter?


It will be a couple of weeks before I can try anything with it at the moment.

Afaik, there's no option to change the datum on the vhf. It just displays the data sent via nmea0183. This makes sense as the datum is only relevant when transferring a position onto a chart.

[j.i.wilson]

Like when the coastguard receives your position from the vhf and attempts to find you?

Sent from my SM-N9005 using RIB Net mobile app

[Pikey Dave]

Originally Posted by j.i.wilson

Like when the coastguard receives your position from the vhf and attempts to find you?

Sent from my SM-N9005 using RIB Net mobile app

Eh? Not sure what you mean with that one

[Seaflyer02]

Originally Posted by willk

A VHF may retain a previous position if no new input is provided - you may have a networking issue. Does the VHF's displayed position change as the vessel moves?

PD has suggested I try this also. I would have thought when the electronics are powered down the VHF would not keep any previous position data?

Fingers crossed and it sorts its self out when the boats moving, either way I will report back when I have tried it.

Thanks for your suggestion

[willk]

Originally Posted by Seaflyer02

PD has suggested I try this also. I would have thought when the electronics are powered down the VHF would not keep any previous position data?

I've seen it happen. VHFs remember things like your MMSI and channel names, so they don't loose all data when powered off. I can't speak for your VHF.

[Poly]

Originally Posted by Seaflyer02

PD has suggested I try this also. I would have thought when the electronics are powered down the VHF would not keep any previous position data?

Fingers crossed and it sorts its self out when the boats moving, either way I will report back when I have tried it.

Thanks for your suggestion

If it has "out of date" position info it will 1. Show it somewhere on the display 2. Alert you after a period of time.

[Seaflyer02]

Finally found my old thread.
I switched the electronics on while getting ready to launch. Once launched I checked both displays and they were still different.
We had a run for about twenty minutes then stopped to check once again, both showing the same position!


Thanks everyone for your help with this.