Airmar ST800 User Manual

INSTALLATION INSTRUCTIONSOWNER’S GUIDE &

Thru-Hull, Retractable with Valve

Speed & Temperature Sensor

Model ST800

Follow the precautions below for optimal product
performance and to reduce the risk of property
damage, personal injury, and/or death.

WARNING: Always wear safety goggles and a dust

mask when installing.

WARNING: The valve is not a watertight seal! Always
use the insert or blanking plug secured with the safety

17-396-01 rev. 04 04/04/11

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.

WARNING: 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.

CAUTION: Never use a fairing with a plastic housing;
the protruding sensor would be vulnerable to damage
from impact.

CAUTION: Never install a metal housing on a vessel
with a positive ground system.

CAUTION: A stainless steel housing must be isolated
from a metal hull to prevent electrolytic corrosion. Use
the isolation busing supplied.

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.

CAUTION: Never use solvents. Cleaners, fuel,
sealants, paint, and other products may contain
strong solvents, such as acetone, which attack many
plastics, greatly reducing their strength.

IMPORTANT: Please read the instructions
completely before proceeding with the installation.
These instructions supersede any other instructions
in your instrument manual if they differ.

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 the connections and try again. If
there is still a problem, return the product to the place of purchase.

Record the information found on the cable tag for future reference.

Part No._________________Date___________

ST800

plastic
low profile
P120 housing

Applications

• Plastic housing recommended for fiberglass or metal hull only.

Never install a plastic housing in a wood hull since 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.

• Stainless steel housing compatible with all hull materials.
Recommended for aluminum hulls to prevent electrolytic corrosion

provided the stainless steel housing is isolated from the metal hull.

Tools & Materials

Safety goggles
Dust mask
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" (plastic or metal housing in non-metal hull)

57mm or 2-1/4" (stainless steel housing in metal hull)

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 metal 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 headroom for the height of the
housing, tightening the nuts, and removing the insert.

CAUTION: Never mount the sensor directly ahead of a depth
transducer, since turbulence generated by the paddlewheel’s
rotation will adversely affect the depth transducer’s performance,
especially at high speeds. Mount side by side.

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 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 300–6 00mm (1– 2').

• Full keel sailboats—Locate amidships and away from the keel
at the point of minimum deadrise.

Anti-fouling Paint

Aquatic growth can accumulate rapidly on the sensor’s surface
reducing performance within weeks. Surfaces exposed to salt
water must be coated with anti-fouling paint. Use water-based
anti-fouling paint only. Never use ketone-based paint, since
ketones can attack many plastics possibly damaging the sensor.

It is easier to apply anti-

paddlewheel
insert

outside wall
below lower
O-ring

paddlewheel

paddlewheel
cavity

housing

exterior flange

bore of housing
up 30mm (1-1/4")

Figure 1. Anti-fouling paint

Copyright © 2006 Airmar Technol ogy Corp.

of housing

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
paddlewheel 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 3 mm 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 appropriate size hole saw, cut a hole perpendicular to
the hull from outside the hull.

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 contacts 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 sealant in the threads to seal the

hull and hold the hull nut securely in place.
Stainless steel housing in a metal hull—To prevent electrolytic

corrosion, the stainless steel housing must be isolated from the
metal hull. Slide the isolation bushing onto the housing. Apply
additional sealant to the surfaces of the bushing that will contact
the hull, filling any cavities in and around the bushing.

Installing

1. From outside the hull, push the housing into the mounting hole
using a twisting motion to squeeze out excess 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 since
electrolytic corrosion will occur. Never use wood since it will
swell, possibly fracturing the plastic housing.

plastic housing

marine sealant

on flange and sidewall

paddlewheel

insert

cap nut

(plastic)

housing

safety wire

hull nut

washer

hull

in non-metal hull

marine sealant

on flange and sidewall

BOW ►

stainless steel housingmetal housing

in metal hull

(enlarged to show detail)

marine sealant on flange

and sidewall of housing and

on isolation bushing

insert

cap nut

(plastic)

safety
wire

housing

hull nut
washer

(metal)

hull

isolation
bushing

Figure 2. Bedding and installing

Copyright © 2006 - 2010 Airmar Tech nology Corp.

2

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 counter­clockwise 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,

9- 12 mm

pour in
casting
epoxy

hull thickness

solid or hollow cylinder

Figure 3. Preparing a cored fiberglass hull

Copyright © 2006 Airmar Technol ogy Corp.

(3/8- 1/2")
larger than the
hole through the
hull’s outer skin

inner skin

core

outer skin

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 3 mm 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 51 mm 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

arrow

blanking

plug

BOW ►

paddlewheel

insert

large

O-ring

small

O-ring

shaft

flat side
of blade

faces bow

Figure 4. Replacing the paddlewheel and O-rings

Copyright © 2006 Airmar Technology C orp.

Using the Blanking Plug

To protect the 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.

1. On the blanking plug, inspect the O-rings (replace if necessary) and
lubricate them with the silicone lubricant supplied or petroleum jelly
(Vaseline
lubricated to make a watertight seal.

2. Remove the paddlewheel insert from the housing by removing the
safety wire and unscrewing the cap nut (see Figure 2). This will jack out
the insert.

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 paddlewheel insert from backing
out in the unlikely event that the cap nut fails or is screwed on
incorrectly.

®

) (see Figure 4). The O-rings must be intact and well

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 Paddlewheel Insert

Aquatic growth can impede or freeze the paddlewheel’s rotation and must
be removed. Clean the surface using a Scotch-Brite
household detergent. If fouling is severe, push out the paddlewheel 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 and mishandling in boat yards. O-rings must be
free of abrasions and cuts to ensure a watertight seal. Order a
replacement Paddlewheel, Shaft & O-ring Kit No. 33-499-01.

1. Using the new paddlewheel shaft, push the old shaft out about 6 mm
(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.

AIRMAR

TECHNOLOGY CORPORATION

4

®

scour pad and mild

®

www.airmar.com

Copyright © 2004 - 2011 Airmar Technology Corp. All rights reserved.

Servicing the Valve Assembly

Should the valve fail, remove it for servicing.

1. On the blanking plug, inspect
the O-rings (replace if
necessary) and lubricate them
with silicone lubricant or
petroleum jelly (Vaseline

®

).

The O-rings must be intact and

snap ring

valve assembly

flap valve
spring
retainer pin

well lubricated to make a
watertight seal.

notch

2. Remove the snap ring from
the valve assembly using a
screw-driver to pry the end of

housing

the ring free. Lift the ring out
(see Figure 5).

3. Slide the valve assembly
upward and out of the housing
slowly.
NOTE: The flap valve retainer
pin is a loose slip-fit and may

Copyright © 2006 Airmar Technology Corp.

Figure 5. Servicing
the valve assembly

slide out when the assembly
is removed.

4. Insert 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).

5. Clean, repair, or replace the valve assembly so the flap valve moves
freely and seats against the valve housing.

6. 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).

7. Remove the blanking plug. Slide the valve assembly into the housing
with the flap valve pointing downward. Insert the snap ring being certain

that it LOCKS INTO THE GROOVE in the housing wall.

8. Slide the paddlewheel 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/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.

9. Reattach 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 (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 an Airmar metal housing. If you have purchased a low
profile housing and prefer a flush housing, see below.

Blanking

Plug

33-481-01

Paddlewheel, Shaft & O-ring Kit 33-499-01

Obtain parts from your instrument manufacturer or marine dealer.

Gemeco (USA) Tel: [phone]

Airmar EMEA Tel: [phone]
(Europe, Middle East, Africa) Fax: [phone]

Hull Nut

or Isolation Bushing

04-004 plastic
02-030 bronze
02-530-02 stainless steel
04-186-1 isolation bushing

Housing, Hull Nut & Washer

33-340-02 plastic, low profile, P120
33-340-01 bronze, low profile, B120
33-451-01 stainless steel, low profile,

SS520

Paddlewheel

& Valve Kit

33-493-01

Fax: [phone]
email: [e-mail]

email: [e-mail]