My main SI transducer is mounted well above the hull bottom such that it's completely out of the water at planing speed, so it loses its picture at about 6 mph. That's a pretty common approach, especially on fiberglass hulls, to protect the expensive transducer from impact. I have a shoot-through-hull 2D transducer for high speed running, and it works fine at any speed I would run in water where I feel the need to pay attention to it.