Depthfinder blanks out under 4'

[Gene Neill]

I have a Garmin 740S and an Airmar through hull transducer. Works great until the water gets scary thin (3-4') and then the depth reading blanks out.

Is there an easy way to determine whether it's the Garmin or the transducer that's at fault?

 

[centerline]

has there been an offset programmed into it?... if so, this may account for the discrepancy.

 

[hawk232]

I have a Garmin 740S and an Airmar through hull transducer. Works great until the water gets scary thin (3-4') and then the depth reading blanks out.

Is there an easy way to determine whether it's the Garmin or the transducer that's at fault?

3-4'-scary thin!! hehehehehe

in my flats boat I also consider myself scary thin when the depth stops reading, but that's at 1.3' typically!

that being said, I would guess that it is due to the "loss of resolution" from shooting through the hull. next time you are in shallow water that wont read, put the transducer over the side and see if it will pick up then. also, manually set the gain to 10ft, this will help the transducer "catch" that much faster.

that setup is capable of reading shallower. mine read 3' this past weekend and regularly reads under 2' on the flats boat (different transducer and mounted on the transom though)

 

[caguy]

You bring up a good point. I don't think I've ever checked it in really thin water. It is usually disconnected and put away before I even get back to the ramp. I was having problems with it in really deep waters 1100+. I think the problem was the frequency setup.
Thanks for bring it up. I will now do a controlled test at the ramp. Mine also is in hull but is a transom mountable transducer.

 

[Bill Roosa]

check for fouling on the hull under the transducer.