Vexilar FL-10 - Manual (Page 7)

7
After the boat is launched, put about a half inch of water
in the bilge and set the transducer into the the water. Moving
it even an inch in any direction can effect the quality of the
reading drastically. Move it around until you get the best
reading. Be sure to try this when the boat is on plane and
running at top speed. Mark the best spot.
To install the transducer, first clean the spot of mud and
oil and then dry it thoroughly. Using an epoxy* or silicone
glue, make a puddle, about the same size as the transducer,
on the inside of the hull. Place the transducer in the glue and
press it down firmly, gently twisting it back and forth,
making sure that there are no air bubbles in the glue between
the transducer and the hull. It is important that you let the
glue dry completely before turning the unit on.
Run the transducer cord up to the unit. Before you plug
the transducer connector into the inline jack, it is
recommended to spray some lubricant or dab some common
petroleum jelly inside. This will help prevent long term
corrosion.
* If your hull is aluminum, use silicone. This material will flex with
the hull at high speeds and in rough water.