Lowrance M68C IceMachine Installation And Operation Instructions Manual page 27

Testing Determines Best Location
Ideally, the shoot-thru transducer should be installed as close to the
transom as possible, close to the centerline. This will give you the best
performance during high speed maneuvers.
Transducer location
(high speed)
To choose the proper location for shoot-thru-hull mounting, follow these
testing procedures: (You may need a helper to complete these steps.)
1. Anchor the boat in about 30 feet of water. Add a little water to the
sump of the boat. Plug the transducer into the sonar unit, turn it on,
then hold the transducer over the side of the boat in the water. Adjust
the sensitivity and range controls until a second bottom echo is seen on
the display. (You'll need to turn off Auto Sensitivity, Auto Depth Range
and ASP. Try a range setting that is two to three times the water
depth. The harder (more rocky) the bottom, the easier it will be to get a
second bottom signal.) Don't touch the controls once they've been set.
Second bottom
Example of a second bottom signal. Unit is in 30 feet of water, with
range set at 80 feet and sensitivity set at 87 percent.
Shoot-thru-hull transducer locations for
high speed or trolling speed operation.
Transducer location
(trolling speed)
19
True bottom
Manual range setting