Vexilar LC-507 - Manual (Page 7)

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just in front of the transducers. They will disturb the water and
scramble the reading. The 107 kHz transducer is more susceptible
to this effect than the 400 kHz transducer, so it is a good idea to place
it closer to the center of the transom.
FOR EACH TRANSDUCER, FOLLOW THESE
INSTRUCTIONS TO OBTAIN A PROPER
INSTALLATION.
After you attach the mounting bracket to the transducer, hold it
up to the boat where you are planning to mount it (see figure 6).
Mark the four holes on the transom, or mounting plate, so that when
the bottom of the transducer is flush with the bottom of the boat the
holes are located at the bottom of the bracket slots. This gives you
room to "fine tune" the position of the transducer and optimize your
reading after you've put the boat back in the water. Drill out the
holes and install the transducer bracket assembly. Tighten the screws
down securely. Be sure to seal any holes drilled into the transom
with silicone to prevent water from leaking into the boat.
Route the transducer cord up to the unit taking the same care as
you did when you routed the power cord. Make sure that the cord
is restrained and not allowed to flop around in the wind. This can
cause stress on the wire inside the cable, and possible breakage. Plug
the transducer connector into the back of the unit and screw the
retaining ring down tight.
After you have put the boat back in the water confirm that you
can maintain a bottom reading at all boat speeds. If not, loosen the
bracket screws and tilt the transducer some more. Keep the front
edge flush with the boat, but drop the back edge down a little more.
If changing this angle several times does not clear up the reading,
loosen the mounting screws and slide the transducer down, slight-
ly. Repeat these adjustments until you get a clear reading. Make sure
that all mounting screws are tight. Finally, fill any gap between the
transducer and the hull with silicone to prevent a rooster tail from
shooting up behind the boat.