Humminbird 998c SI - Manual (Page 26)

16 Transom Mount - DualBeam PLUS™
3. Continue to hold the bracket on the transom of the boat, and use a
pencil or marker to mark where to drill the two mounting holes.
Mark the drill holes near the top of each slot, making sure that your
mark is centered in the slot.
4. Make sure that the drill bit is perpendicular to the actual surface of
the transom, NOT parallel to the ground, before you drill. Using a
5/32” bit, drill the two holes only to a depth of approximately 1”.
NOTE: On fiberglass hulls, it is best to use progressively larger drill bits to reduce
the chance of chipping or flaking the outer coating.
3. Assembling the Transducer and Initial Mounting
In this procedure, you will assemble the transducer using the hardware
provided, then mount it and make adjustments to its position without locking
it in place.
NOTE: You will initially assemble the transducer and the pivot arm by matching
the two ratchets to a numbered position on the transducer knuckle. Further
adjustments may be necessary.
1a. If you already know your transom angle, refer to the chart below for
the initial position to use to set the ratchets. If your transom is
angled at 14 degrees (a common transom angle for many boats) use
position 1 for the ratchets. In either case, go to step 2.
or...
1b. If you do not know your transom angle, measure it using a plumb
line (weighted nylon string or monofilament line) exactly 12 inches
long. Hold the top of the plumb line against the top of the transom
with your finger, and wait until the line hangs straight down. Using
a ruler, measure the distance from the bottom of the plumb line to
the back of the transom, then use the chart.
-2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Transom Angle (°)
Bead Alignment
Number
1 4 2 5 3 1 4 2 5
25 26 27
3
28 29 30
1
Measured Distance (x)
1.1cm
1/2“
0.0 cm
0“
2.5 cm
1“
4.3 cm
1 5/8“
5.9 cm
2 3/8“
7.6 cm
3“
9.3cm
3 5/8“ 11.1cm
4 3/8“
12.9cm
5“
14.9cm
5 7/8“
16.9cm
6 5/8“
Using the Mounting Bracket to Mark the Initial Drill Holes
Mark Initial Drill Holes
Fourth Hole
Third Hole
NOTE: The third hole should not be drilled until the angle and height of the
transducer is finalized, which you will not do until a later procedure.