Just put a straight edge up under your hull that comes across the transducer. As stated before simply adjust the transducer to be level with the hull but just a slight amount lower into the water then the hull bottom. A simple straight edge will get you adjusted up in no time. If you have an aluminum hull with rivets then a very slight tilt in the direction shown in your pic might be needed to clear away air bubbles from the rivets. But only a very slight tilt!