Furuno GP-1670F Operator's Manual page 158

13. INSTALLATION
3. Using a 4 mm, #23, or 9/64" bit, drill three holes 22 mm (7/8") deep at the locations
indicated. To prevent drilling too deeply, wrap masking tape around the bit 22 mm
(7/8") from the point.
Fiberglass hull: Minimize surface cracking by chamfering the gelcoat. If a cham-
fer bit or countersink bit is not available, start drilling with a 6mm or 1/4" bit to a
depth of 1 mm (1/16").
4. If you know your transom angle, the bracket is designed for a standard 13° tran-
som angle.
11°-18° angle: No shim is required. Skip to step 3 in "Adjustments".
Other angles: The shim is required. Skip to step 2 of "Adjustments".
If you do not know the transom angle, temporarily attach the bracket and sensor
to the transom to determine if the plastic shim is needed.
5. Using the three #10 x 1-1/4" self-tapping screws, temporarily screw the bracket to
the hull. DO NOT tighten the screws completely at this time. Follow the step 1-4
in "How to attach the sensor to the bracket", before proceeding with "Adjust-
ments".
Adjustments
1. Using a straight edge, sight the underside of the sensor relative to the underside
of the hull. The stern of the sensor should be 1-3 mm (1/16-1/8") below the bow
of the sensor or parallel to the bottom of the hull.
Note: Do not position the bow of the sensor lower than the stern because aeration
will occur.
2. To adjust the sensor's angle relative to the hull, use the tapered plastic shim pro-
vided. If the bracket has been temporarily fastened to the transom, remove it. Key
the shim in place on the back of the bracket.
2°-10° transom angle (stepped transom and jet boats): Position the shim with
the tapered end down.
19°-22° transom angle (small aluminum and fiberglass boats): Position the
shim with the tapered end up.
transom
3. If the bracket has been temporarily fastened to the transom, remove it. Apply a
marine sealant to the threads of the three #10 x 1-1/4" self-tapping screws to pre-
vent water seeping into the transom. Screw the bracket to the hull. Do not tighten
the screws completely at this time.
13-10
11º transom angle
2º-10º
NO SHIM
angle
shim with
taper down
YES YES
parallel parallel
12º-18º transom angle
NO SHIM
YES
NO
slight
angle
angle
reversed
19º-22º
transom
angle
shim with
taper up
YES
parallel
NO
angle too
steep