Furuno 8252 problem

the void is normally created when there is an obstruction, like a sat dome or something ... is there?

Troubleshooting is easy, first get a roll of aluminum foil and make a tall hat. Stand on the bow or the dock in front of the boat. For short range calibration, stand in a tender while zig zagging out in front of the bow.

Seriously though, is this a new thing? It just looks like the "shadow" behind an obstruction. Or, is the boat trimmed with the bow unusually high? Is sector blanking turned on for some reason?

Depending what kind of boat you're running, radars on most sport boats are wedged downward in front so it's not looking for airplanes when on plane. With it set at 24nm at idle speed the signal is probably glancing off the water in front of the boat.

Theoretically it should exist at all ranges, but the degree of being able to discern it will differ because of signal strength and is probably (hopefully) not visible able at most ranges. Sort of like looking for weather, but in reverse. It's usually at around the 24nm range that you see weather best. BTW, it does disappear when you come up on plane right?

Back to basic troubleshooting .... is this a new issue? Does it only occur in heading up? Does the blank sector follow the bow when in north up? Does it occur at all gain settings? Does it occur at all range settings? If the unit was working fine earlier, have you done any work on the boat or fiddled with the menu settings on the radar?

What does the Furuno tech say?

Is the radar angled on top of the hardtop at all? Is it possible that the radar is picking up 300 degrees of atmosphere (with the gain turned all of the way up), and the other section the signal is bouncing on the water? Why do you want the gain turned all of the way up anyways?

It appears to be picking up objects in the clear area. Is it functioning fine with the gain turned down?

Back to fundamentals, is this a new installation? If not, was it working properly until recently?

Have you done any work on or around the antenna or added anything to the boat forward of the antenna?

Ah, looking for birds ... did it ever work before? Is this a new problem? How long has this "blank" sector been an issue?

Can't say I've ever seen birds at 6 to 12nm's. Seems that might require a flock supplied by Alfred Hitchcock. However, if you wedge it up so you can see them at idle speed and that range, that's about all you'll see when up on plane. Picture a line running straight out from your roof. Where it hits the water (or another object) is where you radar will wash out. Raise the angle and you'll get a clear picture, but then you'll be looking at airplanes and your propwash when on plane. It sounds like your radar is operating normally.

If you want to see birds, turn the "tune" up (off of auto), then start turning the gain up. I've won several tournaments and fished many, we never bothered looking for birds. We're too busy looking for fish. Rarely will you pick up birds on your radar several miles away, run there, and find them on top of something by the time you get there......

So, the story finally comes out ... it sounds like someone wedged the front of the thing up thinking they would have an air surveillance radar system.

Seeing birds with a marine radar beyond a couple of miles is expecting a bit too much and mounting the radar with that in mind eliminates the purpose for which that radar was made, as is so obvious.

On top of that, it looks like the thing is wedged up higher to starboard than port. Return it to level and if you ever see a bird within about 3 miles consider it a plus.

Actually, they're usually wedged down in front on boats with a high bow rise. Otherwise birds and airplanes would be all that was seen while on plane. The tilt to one side is the result of the boat rocking. It's working fine. When I'm in the ocean I continually adjust the range between .5nm & 6nm (most time spent at 1.5nm) with an occasional sweep at 24 nm to check the weather. Anything else is just a curiosity. If I were fishing I'd be more interested in the birds I can get to before they finish desert. I might spend a bit of time at 1.5 to 3nm to look for those birds, but I'd be more inclined to use the naked eye except on a calm night.