2
Antifouling Paint
Marine growth can accumulate rapidly on the ultrasonic sensor’s
surface reducing performance within weeks. Surfaces exposed to
salt water must be coated with antifouling paint. Use water-based
antifouling paint only. Never use ketone-based paint, since
ketones can attack many plastics possibly damaging the sensor.
It is easiest to apply antifouling paint before installing the sensor,
but allow drying time. Reapply paint every 6 months or at the
beginning of each boating season. Paint the following surfaces
(see Figure 2):
• Outside wall of the ultrasonic insert below lowest O-ring
• Active face of the ultrasonic insert
• Exterior lip of housing
• Bore of housing up 30mm (1-1/4")
• Blanking plug below lowest O-ring including exposed end
Mounting Location
Turbulence-free water must flow under the ultrasonic sensor at all
speeds. Choose an accessible spot with a minimum of 200mm
(8") of headroom inside the vessel to allow for the height of the
housing, tightening the nuts, and removing the insert.
•Fin keel sailboats—Mount the sensor on or close to the
centerline and forward of the fin keel 150–300mm (1/2 –1').
•Full keel sailboats—Locate the sensor amidships and away
from the keel at the point of minimum deadrise.
•Displacement hull powerboats—Locate the sensor
amidships near the centerline.
•Planing hull powerboat—Mount the sensor well aft to ensure
it will be in contact with the water at high speeds.
Caution: Do not mount the sensor in an area of turbulence or
bubbles: near water intake or discharge openings; behind strakes,
fittings, or hull irregularities; or behind eroding paint (an indication
of turbulence).
Caution: Never mount the sensor directly ahead of a depth
transducer, since turbulence generated by the housing will
adversely affect the depth transducer’s performance, especially
at high speeds.
Installation
Cored fiberglass hull—Follow separate instructions on page 3.

Hole Drilling

Warning: Always wear safety goggles and a dust mask.
1.Drill a 3mm or 1/8" pilot hole from inside the hull. If there is a rib,
strut, or other hull irregularity near the selected mounting
location, drill from the outside.
2.Using the 51mm or 2" hole saw, cut the hole from outside the hull.
3.Sand and clean the area around the hole, inside and outside, to
ensure that the sealant will adhere properly to the hull. If there is
any petroleum residue inside the hull, remove it with either mild
household detergent or a weak solvent (alcohol) before sanding.
Metal hull—Remove all burrs with a file and sandpaper.

Bedding

Apply a 2mm (1/16") thick layer of sealant around the lip of the
housing that contacts the hull and up the sidewalls of the housing.
The sealant must extend 6mm (1/4") higher than the combined
thickness of the hull, washer(s), and hull nut (see Figure 3). This
will ensure there is sealant in the threads to seal the hull and to
hold the hull nut securely in place.
Figure 3. Bedding and installing
P120 plastic housing B120 metal housing
safety wire
cap nut
hull nut
washer
hull marine
sealant
marine
sealant
Figure 2. Antifouling paint
outside wall
of housing
ultrasonic
insert
housing
& valve
assembly
lowest O-ring
up 30mm (1-1/4")
active face
below
exterior lip
inside bore
ultrasonic insert