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INSTALLATION INSTRUCTIONSOWNER’S GUIDE &
Thru-Hull, Retractable
Speed & Temperature Sensor
Models: ST200, ST550
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.
17-034 rev. 06 04/12/11
WARNING: The o-rings must be intact and well
lubricated to make a watertight seal.
WARNING: ST550—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.
Record the information found on the cable tag for future reference.
Part No._________________Date___________
ST550
Applications
• Plastic housing recommended for fiberglass or metal hull only.
Never install a plastic housing in a wood hull, since swelling of
the wood may fracture the plastic.
• Bronze housing recommended for fiberglass or wood hull only.
Never mount a bronze housing in a metal hull because
electrolytic corrosion will occur.
CAUTION: Never pull, carry, or hold the sensor by its
cable; this may sever internal connections.
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: The arrow on the top of the insert points:
• ST200—rearward toward the stern
• ST550—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
(in appropriate). If there is no reading(s) or it is inaccurate, check
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
Water-based anti-fouling paint (mandatory in salt water)
Electric drill with a 10mm (3/8") or larger chuck capacity
Drill bit: 3mm or 1/8"
Hole saw: ST200 44mm or 1-3/4"
ST550 51mm or 2"
Countersink tool (installing a P217 flush housing)
Sandpaper
Mild household detergent or weak solvent (alcohol)
File (installation in a metal hull)
Marine sealant (suitable for below waterline)
Washer or backing block (optional)
Mandatory for aluminum hull less than 6 mm (1/4") thick
Slip-joint pliers (installing a metal housing)
Grommet(s) (some installations)
Silicone grease or petroleum jelly (Vaseline
Cable ties
Installation is a cored fiberglass hull (see page 3):
Hole saw for hull interior: ST200 51mm or 2"
ST550 60mm or 2-3/8"
Fiberglass cloth and resin
or cylinder, wax, tape, and casting epoxy
®
)
Identify Your Model
The model name is printed on the cable tag.
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outside wall of insert below lower O-ring, exposed end of insert,
paint paddlewheel, paddlewheel cavity,
bore of housing, and exterior flange
Figure 1. Anti-fouling paint (ST550 shown)
Copyright © 1997 Airmar Technology Corp.
Mounting Location
CAUTION: Do not mount the sensor near water intake or
discharge openings; behind strakes, fittings, or hull irregularities
that will disturb the water flow.
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 in line with trailer rollers or bunks that
may damage the transducer’s face.
Turbulence-free water must flow under the paddlewheel at all
boat speeds. Choose an accessible spot inside the vessel. Allow
headroom for the height of the housing, tightening the nuts, and
installing the insert.
ST200 18cm (7")
ST550 28cm (11")
• 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-fouling paint before installing the sensor,
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
• Exposed end of the paddlewheel insert
• Paddlewheel cavity
• Paddlewheel
• Bore of housing up 30 mm (1-1/4")
• Exterior flange of the housing
• Blanking plug below the lower o-ring and 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, drill from the outside.
2. Using the appropriate hole saw, cut the hole perpendicular 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 (see Figure 2)
CAUTION: Be sure the surfaces to be bedded are clean and dry.
1. ST200—Remove one safety ring, the retaining pin, the
paddlewheel insert, the hull nut, and any washer.
ST550—Remove the cap nut, paddlewheel insert, the hull nut,
and any washer.
2. Apply a 2 mm (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. The sealant must extend 6mm (1/4")
higher than the combined thickness of the hull, any washer, and
the hull nut. This will ensure there is sealant in the threads to
seal the hull and to hold the hull nut securely in place.
pull ring
retaining
pin
safety
ring
housing
hull nut
washer
(optional)
hull
ST200
marine sealant marine sealant
ST550
pull ring
safety wire
cap nut
housing
hull nut
washer
(optional)
hull
ST550
plastic housingmetal housing
marine sealant
Figure 2. Bedding and installation
Copyright © 1997 Airmar Technolog y Corp.
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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 pointing
forward toward the bow and parallel to the centerline of the boat.
If the sensor is not installed on the centerline, angle the housing
slightly toward the centerline to align it with the water flow.
2. Airmar recommends a backing block or thick washer inside the
hull to distribute the force from the hull nut and provide a flat
surface to tighten against. Use a rubbery, fiberglass, or plastic
washer.
Plastic housing—Never use a wood backing block, since
swelling of the wood may fracture the plastic.
Aluminum hull less than 6mm (1/4") thick—A washer is
mandatory. Never use bronze as electrolytic corrosion will occur.
3. Screw the hull nut in place.
Plastic housing—Hand-tighten only. Do not over-tighten.
Metal housing—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 hull nut.
4. Check that the notch on the upper rim of the housing is aligned:
ST200—rearward toward the stern.
ST550—forward toward the bow.
5. Remove any excess sealant on the outside of the hull to ensure
smooth water flow under the paddlewheel.
6. After the marine sealant cures, inspect the o-rings on the
paddlewheel insert (replace if necessary) and lubricate them with
silicone grease or petroleum jelly. The o-rings must be intact and
well lubricated to make a watertight seal.
7. With the arrow on the top of the paddlewheel insert facing
forward toward the bow, slide it into the housing. Be sure to
engage the key in the notch. (Use a pushing twisting motion.)
Be careful not to rotate the outer housing and disturb the
sealant.
8. ST200—Align the holes of the housing and the paddlewheel
insert. Slide the retaining pin in place and attach the safety ring.
ST550—Screw the cap nut in place. Hand-tighten only. Do not
over-tighten.
9. ST550—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
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 an
eye in the cap nut. Loop the wire through the pull ring and twist
it securely to itself.
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
pull ring, the second eye in the cap nut and a second eye in the
hull nut. 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
9- 12 mm
pour in
casting
epoxy
hull thickness
solid or hollow cylinder
Figure 3. Preparing a cored fiberglass hull
(3/8-1/2")
larger than the
hole through the
hull’s outer skin
Copyright © 1997 Airmar Technology Cor p.
inner skin
core
outer skin
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 3).
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 the appropriate hole saw, cut the hole from outside the
hull through the outer skin only (see Figure 3).
3. From inside the hull, use the appropriate interior 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
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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” on page 2.
◄BOW
Operation, Maintenance, Repair & Parts
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 silicone grease or petroleum jelly (see
Figure 4). The o-rings must be intact and well lubricated to make
a watertight seal.
2. ST200—Remove the paddlewheel insert from the housing by
removing one safety ring and the retaining pin.
ST550—Remove the safety wire and unscrew the cap nut.
3. With the blanking plug ready in one hand, pull the paddlewheel
insert most of the way out using the pull ring. Remove the insert
and rapidly replace it with the plug. With practice, only 250ml
(10oz.) of water will enter the boat. Align the arrow on the top of
the plug facing forward toward the bow. Be sure to engage the
key in the notch. (Use a pushing twisting motion.)
4. Secure the blanking plug:
ST200—with the retaining pin and safety rings.
ST550—with the cap nut and safety wire.
Servicing the Paddlewheel Insert
ST550 converts to low-speed or high-speed operation simply by
changing the paddlewheel. The low-speed paddlewheel is
optimized for speeds up to 40kn (46MPH) and the high-speed
paddlewheel is designed for speeds up to 50kn (57MPH).
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 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 10 kn (11MPH)] 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.
arrow
pull ring
o-rings
shaft
flat side
of blade
faces bow
Figure 4. ST550: Replacing
paddlewheel and o-rings
Copyright © 1997 Airmar Technology Cor p.
Figure 5. ST200:
Paddlewheel Kit 33-114
Copyright © 1997 Airmar Technology Cor p.
Replacement Transducer & Parts
The information needed to order a replacement Airmar transducer
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.
If you have purchased a plastic housing and have a wood hull or
desire greater strength, purchase a metal housing. Lost, broken, or
worn parts should be replaced immediately.
Blanking
Model
ST200 33-412 — 04-002 —
ST550 33-414
Plug
Cap Nut Hull Nut
04-234-1 (plastic)
02-131-01 (bronze)
04-004 (plastic)
02-030 (bronze)
Obtain parts from your instrument manufacturer or marine dealer.
Gemeco Tel: 803-693-0777
(USA) Fax: 803-693-0477
email: sales@gemeco.com
Airmar EMEA Tel: +33.(0)2.23.52.06.48
(Europe, Middle East, Africa) Fax: +33.(0)2.23.52.06.49
email: sales@airmar-emea.com
Housing &
Hull Nut
33-100
(bronze B17)
Paddle-
wheel Kit
33-114
(see Fig. 5)
1. Using the new paddlewheel 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
exposed blade facing the same direction as the arrow on the
top of the insert.
3. Tap the new shaft into place until the ends are flush with the
insert.
4. Install two o-rings.
5. The remaining o-rings are placed in a similar position on the
blanking plug.
®
AIRMAR
35 Meadowbrook Drive, Milford, New Hampshire 03055-4613, USA
TECHNOLOGY CORPORATION
Copyright © 1994 - 2011 Airmar Technology Corp. All rights reserved.
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