Before you can expect radar overlay to line up properly, you must have the radar aligned with the bow of the boat. The installer should have done this when the unit was installed, but sometimes they don't or the settings get changed.
To adjust the radar image on your unit, it must be in installation mode. With the unit off, press and hold the [menu] key. Power the unit on while continuing to hold the [menu] key. When you see the Vx2 Furuno boat screen, then you can release the menu key. Before you adjust your heading make sure your radar has the correct antenna type. Your display was designed to support several different antennas and the system default might not be correct for your radar model. This will cause your heading alignment to be off and just correcting the alignment will still leave you with a poor performing radar. To check it, press [menu], system configuration, installation setup, radar setup, and check your antenna type. Make sure it is correct for the radar scanner/model you are using. (If not, change it, hit return and power off your unit. Then repeat these instructions) Now hit RETURN and [MENU] to return to your radar screen. Once your radar has timed in (in standby), place the radar in transmit (straight radar in heads up, NOT overlay). Once the unit is transmitting, press [menu], system configuration, installation setup, radar setup, next page. You should see a setting called "heading Align". Hit edit and turn heading align "ON". You will now see your radar again. Turn your enter knob left or right and you should see a bearing line from the center of your screen going outward. If you point this line at the radar return (object) that should be appearing at the front of your boat and hit the "SET" key, you radar heading/image will be adjusted to put that object at the front of your boat. This is best done with an object several hundred yards away from the boat that you can align the image with to the bow.
Once your radar has been aligned with the bow of the boat, you can start looking at your heading. Make sure your heading displayed in degrees, at the top of your radar screen, matches your steering compass (within a few degrees). If you have a magnetic flux gate compass or autopilot wired, you should ensure that you have your NavNet setting correct for what you have wired. If you are feeding the NavNet Magnetic data, then check under [menu] system config - installation setup - radar setup; and ensure the HEADING DATA is set to the correct type. (TRUE or MAGNETIC) After you verify that setting, you will want to ensure you are displaying the correct heading you wish to display. [menu] - system config - general setup - next page; and ensure the right type of heading you wish to display is selected. (TRUE or MAGNETIC) I recommend you display Magnetic. Then you should compare the heading numbers shown at the top of the radar with your boat steering compass and COG (Course over ground) when you are moving. All three should match within a degree or two. If you find the heading numbers displayed by the NavNet doesn't match your steering compass or COG (while moving) then it appears your heading data being sent to the NavNet is wrong. You should correct the data at the source. (ie. autopilot or flux gate might have a problem or need calibration).
Once you have aligned the radar with the bow and ensured good heading and settings, your normal and overlay alignment should be good. If not then you might have some kind of chart offset setup in your display by mistake. I would then go to a full screen plotter screen (not overlay), and hit [menu] chart setup - chart offset - reset offset. This should cover about any issue that could be causing your problem.
If you still have problems you might want to call us on the phone. You will find most of the detailed instructions on setting your radar heading in your installation manual. (not the operators manual) If you have lost your manual and need another, we have the manuals available on our web site under "Manuals & Documents" tab of the product.
You can reach tech support on the phone
East Coast 410-479-4420 (M-F 5am PST or 8am EST -to- 5 pm EST)
West Coast 360-834-9300 (M-F 8am PST or 11am EST-to- 5pm PST/8pm EST)