I have a Lowrance X51 that has been on my boat now for over a year and has worked fine. Now when I pick up the speed in the boat - anything over 5 to 10 MPH - the depth reading will start blinking and remain the same regardless of the depth of water. When I slow down it seems to correct itself. I have tried adjusting the sensitivity but that doesn't seem to correct the problem. The transducer is a transom mount.