Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.
Does it give a picture sitting still but not under way? If so I would suggest checking the number one issue would be air/turbulence in the water which can be caused by chines, thru-hull fittings, bulk heads, anything forward of the ducer or near it that can cause turbulence as well as too close to the leg/unit/drive, tabs etc.
If not the above then check how the ducer is mounted, I will need to know if thru-hull, in-hull flush mount or if transom mounted.
Next would be to check the connectors ESP if you have an extender cable between ducer cable and main unit, check the connections for bent pins, corrosion, etc. You could also have a bad main unit.
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