Airmar ST800—Retractable with Valve - Manual (Page 3)

Stainless steel housing in a metal hull—Be sure the washer
contacts the hull. Do not tighten the hull nut with the washer
against the isolation bushing, as the housing will not be firmly
installed. If necessary, sand the isolation bushing until the
washer rests against the hull.
3. Screw the hull nut in place being sure the notch on the upper
rim of the housing and the corresponding arrow on the flange
are still positioned forward toward the bow.
Plastic housing—Do not clamp tightly on the wrenching flats,
possibly causing the housing to fracture.
Plastic hull nut—Hand tighten only. Do not over tighten.
Metal hull nut—Tighten with slip-joint pliers.
Cored fiberglass hull—Do not over tighten, crushing the hull.
Wood hull—Allow the wood to swell before tightening the nut.
4. Remove any excess marine sealant on the outside of the hull to
ensure smooth water flow under the sensor.
5. After the marine sealant cures, inspect the O-rings on the
paddlewheel insert (replace if necessary) and lubricate them
with the silicone lubricant supplied. The O-rings must be intact
and well lubricated to make a watertight seal.
6. Slide the paddlewheel insert into the housing with the arrow on
the top pointing forward toward the bow. Screw the cap nut
several turns until the threads are engaged. Rotate the
paddlewheel insert until the key fits into the notch in the housing.
The arrow on the top of the insert, the cable exit, the notch in the
housing, and the arrow on the flange will all be aligned. Continue
to tighten the cap nut. Be careful not to rotate the housing and
disturb the sealant. Hand tighten only. Do not over tighten.
7. Always attach the safety wire to prevent the paddlewheel insert
from backing out in the unlikely event that the cap nut fails or is
screwed on incorrectly.
Plastic housing—Attach the safety wire to one eye in the hull
nut. Keeping the wire taut throughout, lead the wire in a counter-
clockwise direction. Thread it through one eye in the cap nut, the
eye in the paddlewheel insert, the second eye in the cap nut, and
the second eye in the hull nut. Twist the wire securely to itself.
Metal housing—Wrap one end of the safety wire tightly
around the housing and twist it together with the long end.
Keeping the wire taut throughout, lead the wire straight up and
through one eye in the cap nut. Thread the wire through the eye
a second time. Lead the wire counterclockwise and through the
eye in the paddlewheel insert. Twist the wire securely to itself.
Cable Routing & Connecting
CAUTION: If your sensor came with a connector, do not remove it
to ease cable routing. If the cable must be cut and spliced, use
Airmar’s splash-proof Junction Box No. 33-035 and follow the
instructions provided. Removing the waterproof connector or
cutting the cable, except when using a watertight junction box, will
void the sensor’s warranty.
1. Route the cable to the instrument being careful not to tear the
cable jacket when passing it through the bulkhead(s) and other
parts of the boat. Use grommets to prevent chafing. To reduce
electrical interference, separate the sensor cable from other
electrical wiring and the engine. Coil any excess cable and
secure it in place with cable-ties to prevent damage.
2. Refer to the instrument owner’s manual to connect the sensor
to the instrument.
Checking for Leaks
When the boat is placed in the water, immediately check around
the thru-hull sensor for leaks. Note that very small leaks may not
be readily observed. Do not leave the boat in the water for more
than 3 hours before checking it again. If there is a small leak,
there may be considerable bilge water accumulation after 24
hours. If a leak is observed, repeat “Bedding” and “Installing”
immediately (see page 2).
Installation in a Cored Fiberglass Hull
The core (wood or foam) must be cut and sealed carefully. The
core must be protected from water seepage, and the hull must be
reinforced to prevent it from crushing under the hull nut allowing
the housing to become loose.
CAUTION: Completely seal the hull to prevent water seepage into
the core.
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. (If the hole is drilled in the wrong location,
drill a second hole in a better location. Apply masking tape to the
outside of the hull over the incorrect hole and fill it with epoxy.)
2. Using a 51mm or 2" hole saw, cut the hole from outside the hull
through the outer skin only (see Figure 3).
3. From inside the hull, use a 60mm or 2-3/8" hole saw to cut through
the inner skin and most of the core. The core material can be very
soft. Apply only light pressure to the hole saw after cutting through
the inner skin to avoid accidentally cutting the outer skin.
4. Remove the plug of core material so the inside of the outer skin
and the inner core of the hull are fully exposed. Sand and clean
the inner skin, core, and the outer skin around the hole.
5. If you are skilled with fiberglass, saturate a layer of fiberglass
cloth with a suitable resin and lay it inside the hole to seal and
strengthen the core. Add layers until the hole is the correct
diameter.
Alternatively, a hollow or solid cylinder of the correct diameter
can be coated with wax and taped in place. Fill the gap between
the cylinder and hull with casting epoxy. After the epoxy has set,
remove the cylinder.
6. 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.
7. Proceed with “Bedding” and “Installing” (see page 2).
Operation & Maintenance
How the Valve Works
The valve is not a watertight seal! The sensor incorporates
a self-closing valve which minimizes the flow of water into the
vessel when the paddlewheel insert is removed. The curved flap
valve is activated by both a spring and water pressure. The flap
valve is pushed upward to block the opening, so there is no gush
of water into the boat. Always use the insert or the blanking plug
secured with the safety wire for a watertight seal.
3
Figure 3. Preparing a cored fiberglass hull
inner skin
core
outer skin
solid or hollow cylinder
pour in
casting
epoxy
9-12 mm
(3/8-1/2")
larger than the
hole through the
hull’s outer skin
hull thickness
Copyright © 2006 Airmar Technology Corp.