Humminbird 998c SI - Manual (Page 35)

25 Inside the Hull Mount - DualBeam PLUS™
2. Trial installation
You will not be able to adjust the mounting after an inside the hull
transducer is installed. It is best, therefore, to perform a trial installation first
that includes running the boat at various speeds, in order to determine the
best mounting area before permanently mounting the transducer.
1. Plug the transducer into the control head, then power up the control
head. When the control head detects a functioning transducer, it
will automatically enter Normal operating mode.
2. View the sonar signal at its best by holding the transducer over the
side, immersed in the water, so that it is pointing straight down over
a known flat bottom. Use the display to benchmark against the
sonar signal that will be detected once the transducer is placed in
the hull.
3. Place the transducer body face down at the identified mounting
location inside the hull, with the end that has the mounting knuckle
pointed towards the bow of the boat.
4. Fill the hull with enough water to submerge the transducer body.
Use a sand-filled bag or other heavy object to hold the transducer in
position. The transducer cannot transmit through air, and the water
purges any air from between the transducer and the hull, and fills
any voids in the coarse fiberglass surface.
5. View the sonar signal on the display and compare against what you
observed in Step 2, making sure that the boat is in the same location
as it was during your observations in Step 2. If the results are
comparable, move on to Step 6. Otherwise, locate a new position in
the hull and repeat Steps 3 through 5.
Preferred Mounting Area
Areas of Possible Turbulence
Rivets Strakes
Transom Hull
Stepped Hull
Step Rib