Transom mount transducers—while they are the easiest to install, can be the hardest to get working properly at speed. Fine
adjustments are needed for good high speed performance.

Please check the following for troubleshooting your transom mount transducer:

• Transom mount transducers will not work at any speed if they are installed on a powerboat boat with inboard motors,
  or any sailboat.
• If you have a single engine outboard, or I/O, make sure that the unit is mounted on the starboard side of the boat, so it is
  free from most prop wash.
• If you have a twin, or triple engine outboard, or I/O make sure that the unit is mounted between the motors, as low as
  possible, either on the flat section of the keel (if any), or slightly left or right of the vee.
• If you are still seeing poor performance at speed, this usually indicates that the transducer needs to be mounted lower
  so that more of the face of the transducer is in contact with the water at speed.
• To make this adjustment, loosen the mounting screws, and slide the transducer 1/2″ lower and re-test. You may need to
  re-drill holes. If you do so, be sure to seal the old holes with manufacturer approved, below the waterline caulking or
  epoxy.
• You also may want to add another plastic wedge (supplied with the installation kit) so that when looking at the side of
  the transducer the back or stern of the transducer is noticably lower than the bow or front of the transducer. This angle
  will not affect depth readings. Doing this adjustmant will help keep the transducer in hard contact with the water at
  higher speeds.

The picture below illustrates lowering and angling your transom mount.