I have HDSI on the Terrova and can routinely scan and see walleyes at 10 mph, but it takes alot of screen time to get to that point. (plus, it helps to know that they are there to begin with) It not uncommone for me when fishing alone to set the boat straight, climb up to the bow and watch the SI. Steer with the Terrova, see a pod of eyes, hit spot lock, casually walk back to the console, pull the boat out of gear, shut motor off while spot lock takes me back to position. Its not optimum,because it takes the boat a fee time to correct itself, positioning wise, but its effective..