After 20 plus years my old depth sounder(Impulse) started giving erradic readings whenever I ran the diesel and also would not give good reading in shallow waters with muddy bottoms. I replaced that sounder with the Raymarine ST 60 plus this fall and the few times that I've been out it has done well. In my slip the old transducer would not give a reading since the bottom was muddy and the reflected signal was not strong enough to give a reading. That is no longer the case with the new depth finder. Also when under power the readings are now accurate. The most difficult part of the installation was running the cable from the transducer to the pedestal. The yard replaced the old thru hull and installed the new transducer which was difficult to remove due to its location and I ran the wire and installed the pod at the helm.
There were times when the old depth finder was new that the shallow alarm would activate, but that was due to either a fish or bubbles from the prop wash of another boat. It only lasted for a few moments and the reading would return to "normal". I think Raymarine has a help line and that would be my next step if unable to get good readings.