Humminbird 998c SI - Manual (Page 32)

22 Transom Mount - DualBeam PLUS™
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.
If you do change the transducer position, re-trace the position of the
mounting bracket before proceeding.
NOTE: It is often necessary to make several incremental transducer adjustments
before optimum high speed performance is achieved. Due to the wide variety of
boat hulls, however, it is not always possible to obtain high speed depth
readings.
6. Once you have reached a consistently good sonar signal at the
desired speeds, you are ready to lock down the transducer settings.
Force the pivot to the Up position to gain access to the mounting
screws, then re-align the mounting bracket against the transom of
the boat to match the traced silhouette. Check the bracket position
with the level again to make sure it is still level, then mark the third
mounting hole using a pencil or marker. Unscrew and remove the
mounting screws and the transducer assembly and set aside.
7. Drill the third mounting hole, using a 5/32” drill bit. Use a marine-
grade silicone sealant to fill all three drilled mounting holes,
especially if the holes penetrated the transom wall.
NOTE: On fiberglass hulls, it is best to use progressively larger drill bits to reduce
the chance of chipping or flaking the outer coating.
8. Re-position the transducer assembly
against the transom of the boat, then
hand-install all three screws. Make
sure that the transducer location and
the pivot angle have not changed,
then fully tighten all three mounting
screws. Snap the pivot back down. If
you have performed the preceding
procedures correctly, the transducer
should be level and at the right
height for optimal operation.
Fully Tighten All Three
Mounting Screws