I've got the GPS version 580 and have had no issues. Your transducer should be sticking down about 1/4" below the level of the boat and have a slight angle twards the front of the boat (the back of the transducer should be lower than the front/transom part). Farther away from the prop the better. If you boat is a flat bottom or ModVee with a bunch of ribs/strikes on the bottom then you will have issues with it reading fish accurately at any speed over ~7-10mph like I do. Mine Still keeps bottom lock at 38mph WOT for depth readings though.