Humminbird HDR 650 - Manual (Page 25)

NOTE: The transducer must be submerged in water for reliable transducer
detection.
4. If the unit is working properly, gradually increase the boat speed to test
high-speed performance. If the unit functions well at low speeds, but
begins to skip or miss the bottom at higher speeds, the transducer requires
adjustment.
5. If you have the correct angle set on the transducer, yet lose a bottom
reading at high speed, adjust the height and the running angle in small
increments to give you the ideal transducer position for your boat. First,
adjust the height in small increments (see the illustration Adjusting the
Transducer Mounting Position).
NOTE: The deeper the transducer is in the water, the more likely that a rooster tail
of spray will be generated at high speeds, so make sure that the transducer is as
high as it can be and still be submerged in the water.
If you are still not getting good high speed readings, you may need to
disassemble the transducer mounting assembly and re-position the ratchets
(see the illustrations Transducer Knuckle Positions, Ratchets Placed in
Position 1, Ratchets Placed in Position 2, and Fitting the Mounting
Bracket Over the Ratchet).
Adjusting the Transducer
Mounting Position
Seam aligned with boat hull
Leveling the Mounting
Assembly Horizontally
Level
Le
ve
l
21 Transom Mount Transducer Installation