Thanks everyone for your help. I asked Grady customer service and was told 20 degrees at the transom. I'm amazed at the knowledge the Great Grady members have and their willingness to share it with others. I'm doing some glass and wood repairs and thought I would replace an old thru hull transducer with a airmar B164 while I had it apart. It will be hooked to a garmin GSD22 sounder & 5212 Chartplotter.Has anyone had any experience with this transducer?