Humminbird XTH 9 DB 74 P Manual page 2

Plastic Thru-Hull Transducer
3.
Attaching the Transducer
Before attaching your transducer, you will need to decide which type of installation to use:
• For a standard installation, where there are no major obstructions and the deadrise is less than 8 degrees, use
the included leveling block (uncut), and mount it inside the hull. Drill the hole perpendicular to the hull.
• For an installation that needs to minimize the impact of a small obstruction, but where the deadrise is less than
8 degrees, use the included leveling block (uncut), and mount it outside the hull. Drill the hole perpendicular to
the hull.
• For an installation where the deadrise is greater than 8 degrees, use the included leveling block, cut at the
appropriate angle, to compensate for the deadrise. Drill the hole perpendicular to the waterline.
1. From the outside of the hull, drill a small pilot hole (smaller than the centering bit of your drill bit or hole saw), at
the mounting location you selected in procedure 2.
CAUTION! Before you drill, make sure you are drilling in the correct orientation according to the installation guidelines
above.
2. Use the pilot hole (from the outside of the hull) to drill a 1 1/8" hole that is sized to fit the threaded stem of
the transducer:
NOTE: For installations where the deadrise is less than 8 degrees, where you will not be cutting the leveling block, drill the
hole perpendicular to the hull.
NOTE: For installations where the deadrise is greater than 8 degrees, and you will be cutting the leveling block at an angle,
drill the hole perpendicular to the waterline.
3. Thoroughly clean and deburr the drilled hole and clean the outside of the hull.
4a. If the deadrise is less than 8 degrees, you will not be cutting the leveling block; install it either on the inside of
the hull (standard installation) or on the outside of the hull to compensate for small obstructions.
4b. If the hull angle is greater than 8 degrees, you should cut the included leveling block and use both pieces to
level the transducer. The block should be cut to match the angle of the deadrise of the hull. The leveling block
included with your transducer can accommodate a maximum deadrise angle of 25 degrees.
CAUTION! Use only the leveling block included with this transducer. Do NOT use a wooden leveling block, as any swelling
of the wood might cause the plastic on the transducer to shatter.
NOTE: You should cut the leveling block into two equal pieces: one which mounts outside the hull and is shaped to match
the profile of the transducer, and one which mounts inside the hull and provides a level surface for the fasteners. The
thinnest wall of the outside leveling block must be at least 1/8".
NOTE: A separately-purchased fairing block can also be used to create a hydrodynamic waterflow around the transducer
body. The design and fabrication of this block varies greatly with different hull shapes; therefore, it should be customized by
a qualified marine technician.
5. Feed the cable through the hole, then temporarily install the transducer to check the fit.
6. Apply a generous amount of marine-grade silicone sealant or slow-curing epoxy inside the drilled hole and along
the mating surfaces of the transducer housing. Also, seal the mating edges of the leveling block.
7. Make sure that the narrow (thin) end of the transducer is pointing forward. Insert the transducer into the drilled
hole from outside the boat, then install the nut onto the threaded stem from inside the boat.
NOTE: This type of transducer is directional in nature and must be aligned with the front of the boat (the direction of travel)
and parallel to the center line. Failure to align the transducer properly will result in incorrect bottom readings and incorrect
fish locations (see the illustration Correct Orientation of Transducer).
8. Hand tighten the nut ONLY until the assembly is firmly seated, then tighten NO MORE than 1/8 of a turn extra.
OR...
Standard Installation
Leveling block (can
also be positioned
outside of the hull)
Apply Marine Adhesive
Sealant to all mating surfaces
Installation for deadrise angle greater than 8°,
using a cut leveling block to level transducer.
Cut-leveling blocks
1/8"
Minimum
Apply Marine Adhesive
thickness
Sealant to all mating surfaces
Correct Orientation of Transducer
Hull
Hull