I moved my 788ci HD from the console to the bow and added the XTM 9 DI 25 T to the trolling motor. My question is why is there a major difference between the depth shown on the new 998c HD. They are never even close if the console shows 21' the 788 may show as much as 27'. I looked on the 788 to see if there is some way to adjust to being run from a new transducer but didn't find any thing. The 998 is only running off the 2D transducer XP 9 20, SI transducer has not is still MIA. Search didn't show any similar problems. Thanks

Is one of the transducers shooting through the hull? Sometimes you can get bad depth readings due to the epoxy or air bubbles/gaps.

I have not epoxied it in yet. I have water around it and a sand bag on top of it. It seems like the in hull is pretty close to right. The TM is the one that is all over the place.

Ok I think I have it figured out. I checked the 998 at the console with the flasher and they are reading the same depth but 788 up front is still about 7' difference. Reset the 788 to defaults and all three are reading the same at least today they were.

Maybe you had it set for saltwater? Since it's denser than fresh, the sonar travels though it at a different speed. That's why they have that setting on the fishfinders, to compensate for it. It would make your depth off by a greater percentage the deeper the water. So, if 21' showed 27', then 10.5' would have shown 13.5', 42' would show 54', etc.

That, or you had a offset inadvertently put in (keel offset or some other term). That would be a linear offset. so if 21' showed 27', 10' would show 16', 1' would show 7'!
Kind of scary that it may have been telling you you had more water under you than you did.

Either way, a reset would have cleared it.