jgoucher
Please see an old post of mine below for you to try.
Guys
Some of this may be coming from "Surface Clutter" setting. I was playing around with this the other day and if you set "surface clutter" lower than 5 it starts to jumble up the depth reading. On a setting of "1", forget it, .....the depth reading will jump to double or triple which (if your on auto max depth) will flicker the sccreen back and forth for max depth. This only happened when I was in 13 ft or less though. On a setting of 5 it started jumping when I got in 3 ft of water. So, it appears that if your running shallow water you'll need to have "surface clutter" set higher than 5 to keep this from happening.