Humminbird HDR 650 - Manual (Page 13)

Transducer Installation Overview
Find the correct section for your transducer installation type. If you have a
transom mount transducer, you can mount it on the transom (preferred), in the hull,
or you can purchase the trolling motor adapter and mount it on your trolling motor.
The included transducer is designed for transom mounting on the boat (directly
exposed to the water). On fiberglass hull boats, this same transducer can be
bonded to the inside of the hull. When mounted inside the hull, the sonar signal
actually passes through the hull of the boat. One of these two mounting
techniques will produce acceptable results on most boats. There are, however,
several situations that may demand a different type of transducer. Inboard boats,
wood or metal hulls, and sailboats often have unique transducer mounting
requirements.
9 Transducer Installation Overview