Radar troubleshooting - X and S don't agree, which is right?

Greetings all,

I’m a relatively new mate (1 year as OOW), and I haven’t run across this before in training. We’re anchored and the captain is ashore; this issue was noticed by another mate this morning just before watch handover. We have had work done on the radars over the past few days.

[B]Problem:
[/B]EBL bearings on the X and the S band radars don’t agree. [B]

Observations:[/B]
The ship’s heading on the radar agrees with the gyro.
The GPS coordinates for both ownship and targets agree between radars.
Ranges to both the cursor and to fixed objects agree.
Target SOG and ranges agree.
BUT, target bearings to ownship and target COG are off, both by about 10 degrees.

[B]Question:[/B] How can I tell which one is correct?

I’ve tried a few things, but I’d like to see what the internet says. Any insight or advice you have would be very much appreciated. Thanks!

are you using true north one on and magnetic north on the other?

and the edit; just read it again and see it says both radars agree on own ships heading so nevermind. Next question, how far apart are radars from each other, and how far away are targets? If youre on a ship with a beam over 100 ft and have a radar on each side of the house and youre in the bay targeting everything running right across your bow, I can see some deviation there. Im not going to bother with the math for you but try a target 10 miles away and try a target 1 mile away and compare…

Some radars can switch between true and relative bearings. Might be worth checking on that. Do you have ARPA with the radars? If so, Try tracking a target and compare bearings.

http://www.ibiblio.org/hyperwar/USN/ref/RADONEA/COMINCH-P-08-05.html

I found an old Navy link, which has some good info on radar limitations. Go to page 92 for a section on radar bearings. I’m not sure how much difference horizontal antenna separation would make for close reflections. Would depend on how far apart they were - big ship? Pulse width and frequency have an effect. The shorter the wavelength (x-band), the narrower the beam width.

I have seen on some radars there is an adjustment to align the heading line with the lubber line of the vessel.

The rough, “in-the-field” tweak is to point the bow of the boat at an object and adjust the potentiometer until the head up flash is also pointing at the object reflection on your radar screen.

[QUOTE=aryk4;162241]Greetings all,

I’m a relatively new mate (1 year as OOW), and I haven’t run across this before in training. We’re anchored and the captain is ashore; this issue was noticed by another mate this morning just before watch handover. We have had work done on the radars over the past few days.

[B]Problem:
[/B]EBL bearings on the X and the S band radars don’t agree. [B]

Observations:[/B]
The ship’s heading on the radar agrees with the gyro.
The GPS coordinates for both ownship and targets agree between radars.
Ranges to both the cursor and to fixed objects agree.
Target SOG and ranges agree.
BUT, target bearings to ownship and target COG are off, both by about 10 degrees.

[B]Question:[/B] How can I tell which one is correct?

I’ve tried a few things, but I’d like to see what the internet says. Any insight or advice you have would be very much appreciated. Thanks![/QUOTE]

I’d say pull out the manual and do some reading.

What do you mean “target bearing to ownship” How are you getting that? If the bearing (or the reciprocal) to a target differs you can resolve it by visual bearings.

The EBLs don’t match, you can find out which one is in error by taking a visual bearing.

[QUOTE=Flyer69;162276]I have seen on some radars there is an adjustment to align the heading line with the lubber line of the vessel.

The rough, “in-the-field” tweak is to point the bow of the boat at an object and adjust the potentiometer until the head up flash is also pointing at the object reflection on your radar screen.[/QUOTE]

This is what we have on our vessel. I’ll never forget the time it dropped out after a darken ship. Started coming in the hole in the wall and holly crap it was 45 degrees off. Gyro input was correct but this little box allowed you to tweak the display. At 45 degrees it needed more than a tweak. :slight_smile:

[QUOTE=aryk4;162241]Greetings all,

I’m a relatively new mate (1 year as OOW), and I haven’t run across this before in training. We’re anchored and the captain is ashore; this issue was noticed by another mate this morning just before watch handover. We have had work done on the radars over the past few days.

[B]Problem:
[/B]EBL bearings on the X and the S band radars don’t agree. [B]

Observations:[/B]
The ship’s heading on the radar agrees with the gyro.
The GPS coordinates for both ownship and targets agree between radars.
Ranges to both the cursor and to fixed objects agree.
Target SOG and ranges agree.
BUT, target bearings to ownship and target COG are off, both by about 10 degrees.

[B]Question:[/B] How can I tell which one is correct?

I’ve tried a few things, but I’d like to see what the internet says. Any insight or advice you have would be very much appreciated. Thanks![/QUOTE]

Re-reading this you’re are saying that the heading markers on both radars agree but the EBLs don’t but that you can’t determine which radar is incorrect. Seems like a visual bearing would tell you but what happens when you align the EBL with the heading marker?

Just make sure you captain doesn’t know you have been poking radar innards with a screwdriver :smiley:

If you have a Furuno radar, Radar Menu>Initial settings>Heading Align. If you have another brand/model, check the manual or email a technician/service company. Getting into the Initial Settings menu isn’t discussed in the Operations Manual or the Installation Manual - probably because there’s a lot of damage that can be done there. PM me if you have a Furuno and need help getting to the Initial Settings menu.

There are many reasons for such bearing diference between radars.
Briefly.

The difference on bearings is not directly related with wave length ( S ,X or T )
Location of radar on the mast ( greater difference as the target gets closer )
Heading line alignment error. ( you can correct it through service menus ) do not mix with gyro heading it comes from gyro itself.
Check with ECDİS ( use radar overlay function )
Take visual bearing and compare with both radars ( ı believe you’ve already done it )
If you are too close to the shore ( i.e. rivers or eustuaries ) such difference do occur try visuals or PI.

Capt. Melih AKGUL, MNI

[QUOTE=aryk4;162241]Greetings all,

I’m a relatively new mate (1 year as OOW), and I haven’t run across this before in training. We’re anchored and the captain is ashore; this issue was noticed by another mate this morning just before watch handover. We have had work done on the radars over the past few days.

[B]Problem:
[/B]EBL bearings on the X and the S band radars don’t agree. [B]

Observations:[/B]
The ship’s heading on the radar agrees with the gyro.
The GPS coordinates for both ownship and targets agree between radars.
Ranges to both the cursor and to fixed objects agree.
Target SOG and ranges agree.
BUT, target bearings to ownship and target COG are off, both by about 10 degrees.

[B]Question:[/B] How can I tell which one is correct?

I’ve tried a few things, but I’d like to see what the internet says. Any insight or advice you have would be very much appreciated. Thanks![/QUOTE]

Does no one use a bearing circle anymore? I’ve had a magnatron go out and the radars were almost 90* off, it was pretty easy to tell which one was bad.

Is one giving you ARPA info and the other giving you AIS info?

Hello again!

Problem was solved, so I’m posting the update:

We lined up on a natural transit to verify the gyro - all good!
We then introduced a offset in the transmission settings (it was a password-protected setting) to make the EBL on both units line up on the ship’s heading marker.
Both units were “fixed” by the chief mate and were better than they were when the problem was first noticed, but both were still off by about 2 degrees each.
This seems to have fixed everything.

FYI, our max beam is only 9.75m, and the radars antennas are vertically aligned.

No magnetron failures here…this time. Thanks for the input!