if your set up follows suit, your 2 d images will suffer greatly, everyone I have seen with that set up has poor 2 d returns. the fish ID symbol function doesnt work correctly either. I can understand the reason for wanting to know the depth you are running in, but cant you just look at your map card and see the depth? If your unsure of how deep it is.. do u really want to be running thru it in the first place?
not trying to be critical here. just trying to understand .

why do you need to hammer down, and run around the lake seeing how deep it is. ?

I have recently just begun having a problem with my 1198 at the console losing bottom on mid-high speed runs. My setup is as follows: two 1198s connected by ethernet, with separate gps antennae, and y cable for transducers for the console unit, with the si/di transducer mounted on the hull, and the shoot thru hull transducer inside sump area of my Ranger Z521, installed at Ranger factory. The boat and units are three years old and have always read fine up until now for showing bottom depth and readout correctly on the 2d view. As Doug has suggested, for runs across the lake, i use the split screen view of map and 2d sonar. Does it matter if the 2d is in clear mode or max mode in regards to readouts at high speed? What are some possible causes for the readout to be intermittenly failing all of a sudden on digital and 2d readout when it has always worked fine in the past three years? Shoot thru hull transducer going out?