Airmar ST800 Technical Document

17-396-01 rev. 05 09/15/15
Thru-Hull, Retractable with Valve
Speed & Temperature Sensor
Model ST800
Applications
•Plastic housing recommended for fiberglass or metal hull only.
Never install a plastic housing in a wood hull because swelling
of the wood can possibly fracture the plastic.
•Bronze housing recommended for fiberglass or wood hull.
Never mount a bronze housing in an aluminum hull because
electrolytic corrosion will occur.
Pretest
Connect the sensor to the instrument and spin the paddlewheel.
Check for a speed reading and the approximate air temperature. If
there are no readings or they are inaccurate, check all the
connections and try again. If there is still a problem, return the
product to the place of purchase.
Tools & Materials
Safety goggles
Dust mask
Ear plugs
Water-based anti-fouling paint (mandatory in salt water)
Electric drill with 10mm (3/8") or larger chuck capacity
Drill bit: 3mm or 1/8"
Hole saw: 51mm or 2"
Sandpaper
Mild household detergent or weak solvent (such as alcohol)
File (installation in a metal hull)
Marine sealant (suitable for below waterline)
Additional washer [for aluminum hull less than 6mm (1/4") thick]
Slip-joint pliers (installing a bronze housing)
Grommet(s) (some installations)
Cable ties
Installation in a cored fiberglass hull (see page 3):
Hole saw for hull interior: 60mm or 2-3/8"
Fiberglass cloth and resin
or Cylinder, wax, tape, and casting epoxy
Mounting Location
Turbulence-free water must flow over the paddlewheel at all boat
speeds. Choose an accessible spot inside the vessel. Allow a
minimum of 280mm (11") of space for the height of the housing,
tightening the nuts, and removing the insert.
CAUTION: Do not mount the sensor directly ahead of a depth
transducer, because turbulence generated by the paddlewheel’s
rotation will adversely affect the depth transducer’s performance,
especially at high speeds. Mount side by side.
Record the information found on the cable tag for future reference.
Part No._________________Date______________
Follow the precautions below for optimal
product performance and to reduce the risk of
property damage, personal injury, and death.
WARNING: Always wear safety goggles, a dust
mask, and ear plugs when installing.
WARNING: The valve is not a watertight seal! Always
use the insert or blanking plug secured with the safety
wire for a watertight seal.
WARNING: The O-rings must be intact and well
lubricated to make a watertight seal.
WARNING:Always attach the safety wire to prevent
the insert or blanking plug from backing out in the
unlikely event that the cap nut fails or is screwed on
incorrectly.
WARNING: Immediately check for leaks when the
boat is placed in the water. Do not leave the boat
unchecked for more than three hours. Even a small
leak may allow considerable water to accumulate.
CAUTION: Plastic housing—Never use a fairing
with a plastic housing. The protruding sensor would
be vulnerable to damage from impact.
CAUTION: Bronze housing—Never install a metal
housing on a vessel with a positive ground system.
CAUTION: Never pull, carry, or hold the sensor by its
cable. This may sever internal connections.
CAUTION: The arrow on the top of the insert must
point forward toward the bow to align the paddlewheel
with the water flow.
CAUTION: Never use solvents. Cleaners, fuel,
sealant, paint, and other products may contain
solvents that can damage plastic parts.
IMPORTANT:Please read the instructions
completely before proceeding with the installation.
These instructions supersede any other instructions
in your instrument manual if they differ.
low profile
P120 housing
plastic
OWNER’ S GUIDE & INSTALLATION INSTRUCTIONS

CAUTION: Do not mount the sensor in line with or near water
intake or discharge openings; behind strakes, fittings, or hull
irregularities that will disturb the water flow.
•Displacement hull powerboats—Locate amidships near the
centerline.
•Planing hull powerboats—Mount well aft to ensure the sensor
is in contact with the water at high speeds.
•Fin keel sailboats—Mount on or near the centerline and
forward of the fin keel 300–600mm (1–2').
•Full keel sailboats—Locate amidships and away from the keel
at the point of minimum deadrise.
Anti-fouling Paint
Surfaces exposed to salt water must be coated with anti-fouling
paint. Use water-based anti-fouling paint only. Never use ketone-
based paint, because ketones can attack many plastics possibly
damaging the sensor.
It is easier to apply anti-fouling paint before installation, but allow
sufficient drying time. Reapply paint every 6 months or at the
beginning of each boating season. Paint the following surfaces
(see Figure 1):
• Outside wall of the insert below the lower O-ring
• Paddlewheel
• Paddlewheel cavity
• Bore of the housing up 30mm (1-1/4")
• Exterior flange of the housing
• Blanking plug below the lower O-ring including the exposed end
Installation
Hole Drilling
Cored fiberglass hull—Follow separate instructions on page 3.
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 a 51mm or 2" hole saw, cut a hole perpendicular to the
hull from outside the boat.
3. Sand and clean the area around the hole, inside and outside, to
ensure that the marine 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
CAUTION: Be sure the surfaces to be bedded are clean and dry.
Apply a 2mm (1/16") thick layer of marine sealant around the
flange of the housing that will contact the hull and up the sidewall
of the housing (see Figure 2). The sealant must extend 6mm (1/4")
higher than the combined thickness of the hull, washer(s), and
hull nut. This will ensure there is marine sealant in the threads to
seal the hull and hold the hull nut securely in place.
Installing
1. From outside the hull, push the housing into the mounting hole
using a twisting motion to squeeze out excess marine sealant
(see Figure 2). Align the arrow on the flange of the housing to
point forward toward the bow. If the sensor is not installed on the
centerline, angle the housing slightly toward the centerline to
align it with the water flow.
2. From inside the hull, slide the washer onto the housing.
Aluminum hull less than 6mm (1/4")thick—Use an additional
rubbery, fiberglass, or plastic washer. Never use bronze
because electrolytic corrosion will occur. Never use wood
because it will swell, possibly fracturing the plastic housing.
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.
Bronze 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. The O-rings must be intact and well lubricated to make a
watertight seal. After the marine sealant cures, inspect the
O-rings on the insert (replace if necessary) and lubricate them
with the silicone lubricant supplied.
2
Figure 2. Bedding and installing
cap nut
washer
hull
safety wire
housing
hull nut
insert
marine sealant on flange
bronze housing in non-metal hull
(plastic)
marine sealant on flange
paddlewheel
and sidewall of housing and sidewall of housing
BOW ►
Figure 1. Anti-fouling paint
outside wall
bore up 30mm (1-1/4")
exterior flange
O-ring
below lower
insert
housing
paddlewheel
paddlewheel
paddlewheel
cavity
Copyright © 2006 Airmar Technology Corp.
B120
plastic housing
P120
Copyright® 2006 - 2015 Airmar Technology Corp.

6. Slide the 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 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 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 insert, the second eye in the cap nut, and the second
eye in the hull nut. Twist the wire securely to itself.
Bronze 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 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 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” 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 marine 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 insert is removed. The curved flap valve is
activated by both a spring and water pressure. Water pushes the
flap valve upward to block the opening, so there is no gush of
water into the boat. Always install the insert or the blanking plug
secured with the cap nut and safety wire for a watertight seal.
Using the Blanking Plug
To protect the paddlewheel insert, use the blanking plug:
• When the boat will be kept in salt water for more than a week.
• When the boat will be removed from the water.
• When aquatic growth buildup is suspected due to inaccurate
readings from the instrument.
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.

4Copyright © 2004 - 2015 Airmar Technology Corp. All rights reserved.
1. The O-rings must be intact and well lubricated to make a
watertight seal. On the blanking plug, inspect the O-rings
(replace if necessary) and lubricate them with the silicone
lubricant supplied or petroleum jelly (Vaseline®) (see Figure 4).
2. Remove the insert from the housing by removing the safety wire
from the cap nut. Unscrew the cap nut to lift the insert (see
Figure 2). Remove the insert with a slow pulling motion.
3. Slide the blanking plug into the housing. Screw the cap nut
several turns until the threads are engaged. Rotate the blanking
plug until the key fits into the notch in the housing. Continue to
tighten the cap nut. Hand tighten only. Do not over tighten.
4. Reattach the safety wire to prevent the blanking plug from
backing out in the unlikely event that the cap nut fails or is
screwed on incorrectly.
Winterizing
After the boat has been hauled for winter storage, remove the
blanking plug to let the water drain away before reinserting it. This
will prevent any water from freezing around the blanking plug and
possibly cracking it.
Servicing the Insert
Aquatic growth can impede or freeze the paddlewheel’s rotation and
must be removed. Clean the surface using a Scotch-Brite®scour pad
and mild household detergent. If fouling is severe, push out the shaft
using a spare shaft or a 4D finish nail with a flattened point. Then,
lightly wet sand the surface with fine grade wet/dry paper.
The water lubricated paddlewheel bearings have a life of up to 5
years on low-speed boats [less than 10kn (11 MPH)] and 1 year
on high-speed vessels. Paddlewheels can fracture and shafts can
bend due to impact with water borne objects. O-rings must be free
of abrasions and cuts to ensure a watertight seal. Order a
replacement Paddlewheel, Shaft & O-ring Kit, 33-499-01.
1. Using the new shaft, push the old shaft out about 6mm (1/4"). With
pliers, remove the old shaft (see Figure 4).
2. Place the new paddlewheel in the cavity with the flat side of the blade
facing the same direction as the arrow on the insert top.
3. Tap the new shaft into place until the ends are flush with the insert.
4. Install a large O-ring near the top and a small O-ring near the
paddlewheel.
5. Place the two remaining O-rings in similar positions on the blanking plug.
Servicing the Valve Assembly
Should the valve fail, remove it for servicing.
1. The O-rings must be intact and
well lubricated to make a
watertight seal. On the
blanking plug, inspect the
O-rings (replace if necessary)
and lubricate them with
silicone lubricant or petroleum
jelly (Vaseline®).
2. Remove the insert/blanking
plug from the housing.
3. Remove the snap ring from
the valve assembly using a
screw-driver to pry the end of
the ring free (see Figure 5).
4. Slide the valve assembly
upward and out of the housing
slowly.
NOTE: The flap valve retainer
pin is a loose slip-fit and may
fall out when the assembly is removed.
5. Push the blanking plug into the housing. Screw the cap nut several
turns until the threads are engaged. Rotate the blanking plug until the
key fits into the notch in the housing. Continue to tighten the cap nut.
Hand tighten only. Do not over tighten. Reattach the safety wire (see
Figure 2).
6. Clean, repair, or replace the valve assembly so the flap valve moves
freely and seats against the valve housing.
7. To reinstall the valve assembly, first reassemble the flap valve in the
valve housing with the retainer pin and spring in place (see Figure 5).
8. Remove the blanking plug. Slide the valve assembly into the housing
with the flap valve pointing downward. Install the snap ring being certain
that it LOCKS INTO THE GROOVE in the housing wall.
9. Slide the insert (or the blanking plug) 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 insert (or the blanking
plug) until the key engages the notch in the housing.Be sure the arrow
on the top is facing forward toward the bow. Continue to tighten the cap
nut. Hand tighten only. Do not over tighten.
10.Reattach the safety wire to prevent the insert/blanking plug from
backing out in the unlikely event that the cap nut fails or is screwed on
incorrectly (see Figure 2).
Replacement Sensor & Parts
The information needed to order a replacement sensor is printed on the cable
tag. Do not remove this tag. When ordering, specify the part number and date.
For convenient reference, record this information on the top of page one.
Lost, broken, and worn parts should be replace immediately. If you have
purchased a plastic housing and have a wood hull or desire greater
strength, purchase a bronze housing.
Paddlewheel, Shaft & O-ring Kit 33-499-01
Obtain parts from your instrument manufacturer or marine dealer.
Gemeco (USA) Tel: [phone]
Fax: [phone]
email: [email protected]
Airmar EMEA Tel: [phone]
(Europe, Middle East, Africa) Fax: [phone]
email: [email protected]
Blanking Plug Hull Nut Housing, Hull Nut & Washer Paddlewheel
& Valve Kit
33-481-01 04-004 (plastic)
02-030 (bronze)
33-340-02 (plastic, P120)
33-340-01 (bronze, B120) 33-493-01
Figure 4. Replacing the paddlewheel and O-rings
arrow
flat side
of blade
shaft
faces bow
large
O-ring
small
O-ring
Copyright © 2006 Airmar Technology Corp.
paddlewheel
insert
blanking
plug snap ring
valve assembly
flap valve
spring
retainer pin
housing
notch
Figure 5. Servicing
the valve assembly
Copyright © 2006 Airmar Technology Corp.
BOW ►
35 Meadowbrook Drive, Milford, New Hampshire 03055-4613, USA
•www.airmar.com