Garmin 400C fishfinder not displaying properly

[Bonker43]

I have a Garmin 400C fishfinder that does not display properly in freshwater. While motoring at speeds over 8mph the display shows the bottom looking like a jagged mountain range when it should be displaying it as flat. Garmin has been unable to help. Attached it a picture of my transducer position. Anyone have a suggestion.

 

[Silvertip]

Disturbance caused by the unit next to the Garmin. Transducers do not like and cannot shoot through air. Any bubbles caused by rivets or other things adjacent to or in line with the transducer causes issues.

 

[Bonker43]

Thanks Silvertip, I'll move the speedometer unit over a few inches.

 

[Silvertip]

why not just remove it and tie it out of the way for a test. If that's not the problem you reinstall it. No additional holes to fill.

 

[Bonker43]

thanks again, going to work on it tonight.

 

[Fed]

A screen shot would help.
It could simply be an undulating bottom combined with a slow chart speed, try speeding up the chart.
Do you know the bottom is flat, did you go down & see it?

 

[Bonker43]

When I travel at speeds less than 8 mph the unit works properly and shows the flats and drop offs etc. I am going fishing Saturday and will try adjusting the chart speed to see if by doing so and moving the speedometer unit fixes my problem. Thanks for the assistance.

 

[Fed]

Pictures can be very deceiving but I had a close look at the one you put up and to me it looks like the hull has a huge hook in it, that may be a contributing factor by lifting the stern.

 

[Bonker43]

Pictures can be very deceiving but I had a close look at the one you put up and to me it looks like the hull has a huge hook in it, that may be a contributing factor by lifting the stern.

HI Fred, I'm not sure what you mean by a "huge hook" but the hull is smooth and formed properly.

 

[Fed]

It's probably nothing Banker, see how the water test goes & take a few pictures of the screen if you can.

 

[Bonker43]

It's probably nothing Banker, see how the water test goes & take a few pictures of the screen if you can.

HI Fred,

I did the water test with the speedometer unit removed. The fishfinder worked perfectly in some ares of the river but the image reverted back to the jagged display in others even though the river bottom was flat. I've attached a picture to show you what the incorrect display is showing.

 

[Bonker43]

Pic attached

 

[Fed]

That simply looks like a bottom with ~6 foot undulations compressed by a slow chart speed or high boat speed or both.

 

[Bonker43]

That simply looks like a bottom with ~6 foot undulations compressed by a slow chart speed or high boat speed or both.

Hi Fred, I appreciate the help. I will continue to adjust the settings and hope I find the correct set up. Thanks.