Garmin mis match of radar over chart

[Greg QS]

Any one having problems with the overlay of Garmin radar over the chart not reading correctly? I may have a solution to that. A 9 step process.

 

[ksanders]

Generally radar vs chart overlay problems are because of inaccuracies in your heading sensor.

 

[twistedtree]

I agree with Kevin, but very curious what your 9 step process is, and what was off?

 

[ScottC]

On my RayMarine e127, there is actually a function in setup that's used to align the chart and the radar overlay.
I would like to think Garmin has a similar feature. So, if you haven't yet, look around carefully in the setup/customization options. And it's best to make sure you're zoomed-in to perform this alignment.

 

[MYTraveler]

The only mismatch I have seen (my primary heading sensor is a satellite compass, so no alignment of that necessary), was chart inaccuracies. Chartplotter showed a rock, radar put it in a different place (range and bearing were both significantly off, but if I had been approaching differently, only bearing would have been off, suggesting radar alignment problems). Off Baja with Furuno equipment.

 

[twistedtree]

The only mismatch I have seen (my primary heading sensor is a satellite compass, so no alignment of that necessary), was chart inaccuracies. Chartplotter showed a rock, radar put it in a different place (range and bearing were both significantly off, but if I had been approaching differently, only bearing would have been off, suggesting radar alignment problems). Off Baja with Furuno equipment.

I think identifying chart inaccuracies is probably the best use of radar overlay, and your example of Mexico is a classic. I don't care for overlay otherwise, finding that the radar return tends to obscure chart features, and chart features obscure radar returns.

As for alignment, there are a couple that I am aware of.

First is that the heading sensor needs to be aligned with the boat's actual heading. So if the sensor says the boat is pointing due north, the boat needs to actually be pointing due north. All the sensors I have encountered have adjustment provisions, assuming the sensor has been installed to already be in pretty close alignment.

The second adjustment is telling the radar when it's aligned with teh boat's heading, i.e. pointing straight ahead. Again, when installed you need to physically sling the radar with the bow of the boat, and all I have encountered then have configuration adjustments to make corrects so it's spot on.

Assuming you are in an area with known good charting, the overlay should then be spot on. If not, it's because one or both the compass and radar are not aligned correctly.

On commercial radars, there is one other adjustment that tweaks the distance to a target, but I haven't seen that on pleasure boat radars.

 

[ksanders]

A good way to check if the overlay/radar mis match is your equipment, or the charts, would be to check where the AIS reports other boats position vs where the radar shows they actually are.

 

[MYTraveler]

I think identifying chart inaccuracies is probably the best use of radar overlay, and your example of Mexico is a classic. I don't care for overlay otherwise, finding that the radar return tends to obscure chart features, and chart features obscure radar returns.

As for alignment, there are a couple that I am aware of.

First is that the heading sensor needs to be aligned with the boat's actual heading. So if the sensor says the boat is pointing due north, the boat needs to actually be pointing due north. All the sensors I have encountered have adjustment provisions, assuming the sensor has been installed to already be in pretty close alignment.

The second adjustment is telling the radar when it's aligned with teh boat's heading, i.e. pointing straight ahead. Again, when installed you need to physically sling the radar with the bow of the boat, and all I have encountered then have configuration adjustments to make corrects so it's spot on.

Assuming you are in an area with known good charting, the overlay should then be spot on. If not, it's because one or both the compass and radar are not aligned correctly.

On commercial radars, there is one other adjustment that tweaks the distance to a target, but I haven't seen that on pleasure boat radars.

Good point. I had failed to realize that my sat compass could be mounted to not point straight forward. The builder installed that during commissioning, as well as the backup magnetic sensor. That magnetic sensor and a bunch of other stuff were only roughly aligned, but the sat compass was perfect. I incorrectly assumed that technology solved that problem.

 

[twistedtree]

Good point. I had failed to realize that my sat compass could be mounted to not point straight forward. The builder installed that during commissioning, as well as the backup magnetic sensor. That magnetic sensor and a bunch of other stuff were only roughly aligned, but the sat compass was perfect. I incorrectly assumed that technology solved that problem.

I think if any care has been given to the physical installation, any adjustments will be a degree or less. But it's really nice when everything lines up correctly on the charts and radar, adn when you can see where things REALLY are in Mexico

 

[sjisailor]

I think identifying chart inaccuracies is probably the best use of radar overlay, and your example of Mexico is a classic. I don't care for overlay otherwise, finding that the radar return tends to obscure chart features, and chart features obscure radar returns.

As for alignment, there are a couple that I am aware of.

First is that the heading sensor needs to be aligned with the boat's actual heading. So if the sensor says the boat is pointing due north, the boat needs to actually be pointing due north. All the sensors I have encountered have adjustment provisions, assuming the sensor has been installed to already be in pretty close alignment.

The second adjustment is telling the radar when it's aligned with teh boat's heading, i.e. pointing straight ahead. Again, when installed you need to physically sling the radar with the bow of the boat, and all I have encountered then have configuration adjustments to make corrects so it's spot on.

Assuming you are in an area with known good charting, the overlay should then be spot on. If not, it's because one or both the compass and radar are not aligned correctly.

On commercial radars, there is one other adjustment that tweaks the distance to a target, but I haven't seen that on pleasure boat radars.

This exactly matches my experience, that it depends first in real world alignment with 'forward' and then can be fine adjusted with the rotational offset calibration option in radar / overlay settings.

I second the feeling that chart overlay otherwise makes both the chart and the radar less useful. I separate them on two displays (usually, or in split windows on one display otherwise).

I also believe in running the radar pretty much all the time when underway. Both for practice and monitoring (and even the minor value of having it detected). Just turn it off in port!! Recently watched a 48" Furuno continuously painting the marina, not good.

 

[Greg QS]

What I have been seeing is the chart and all radar contacts on the chart overlay are 4-5 degrees to port. Even ais contacts.
Garmin had me do a fine compass adjustment .
have the radar on overlay on a second screen.

vessel, autopilot, auto piolet setup , compass setup, yes, fine adjustments .

at this point the fine adjustment can go up or down by 1 deg. Press accordingly till all things line up perfectly.
I had to call several time to get the right tech that new the answer. This solved my issue anyway