Airmar S300 User Manual

INSTALLATION INSTRUCTIONSOWNER’S GUIDE &

Thru-Hull, Shorty™ with Valve

Speed & Temperature Sensor

Models: S300, ST300

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

17-274-01 rev. 04 04/14/11

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

CAUTION: Never pull, carry, or hold the sensor by its
cable; this may sever internal connections.

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.

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

Part No.:___________________Date___________

Low Profile P371

Flush P398

Pretest

Connect the sensor to the instrument and spin the paddlewheel.
Check for a speed reading (and the approximate air temperature if
applicable). If there is no reading(s), check all the connections
and repeat the test. If there is still no reading(s) or it is inaccurate,
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 minimum 10mm (3/8") chuck capacity
Drill bit 3mm or 1/8"
Hole saw 51mm or 2"
Countersink tool (installing a P398 flush housing)
Sandpaper
Mild household detergent or weak solvent (such as alcohol)
File (installation in a metal hull)
Marine sealant (suitable for below waterline)
Additional washer [aluminum hull less than 6mm (1/4") thick]
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

Applications

• Recommended for fiberglass or metal hull only

• Never install a plastic thru-hull housing in a wood hull, since
swelling of the wood can possibly fracture the plastic.

• Low profile P371 recommended for cruising sailboats and
planing hull powerboats

• Flush P398 recommended for racing sailboats and high-speed
powerboats

• Minimum headroom required: 153mm (6")

• Accommodates hull thickness:
Minimum 6mm (1/4")
Maximum 25mm (1")

Mounting Location

CAUTION: Do not mount near water intake or discharge openings;

or behind strakes, fittings or hull irregularities that may disturb the
water flow.

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

Turbulence-free water must flow under the paddlewheel at all
boat speeds. Choose an accessible spot inside the vessel. Allow
a minimum of 153mm (6") of headroom for the height of the
housing, tightening the nuts, and removing the insert.

paddlewheel
insert

housing

bore of housing

up 30mm (1-1/4")

outside wall below
lower O-ring

paddlewheel

paddlewheel
cavity

exterior flange of housing

washer
(some
installations)

sealant on flange
and side wall

paddlewheel
insert

cap nut

safety
wire

housing

hull nut

hull

arrow

Figure 1. Anti-fouling paint—low profile shown

Copyright © 2004 Airmar Technology Corp.

• Fin keel sailboats—Mount on or near the centerline and
forward of the fin keel 300 –600mm (1–2').

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

• Displacement hull powerboats—Locate amidships near the
centerline.

• Planing hull powerboats—Mount well aft to insure that the
sensor is in contact with the water at high speeds.

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 types of plastic 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

• Paddlewheel cavity

• Paddlewheel

• 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

Figure 2. Bedding and installing—low profile shown

Copyright © 2000 Airmar Technolog y Corp.

Bedding

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. The sealant must extend 6 mm (1/4") higher than the
combined thickness of the hull, any washer(s), and the hull nut
(see Figure 2). This will ensure there is 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 sealant. Align the

arrow on the flange of the housing pointing forward toward the
bow (see Figure 2). If the sensor is not installed on the centerline

of the boat, angle the housing slightly toward the centerline to
align it with the water flow.

2. From inside the hull, slide any washer(s) onto the housing.

NOTE: Some installations do not have a washer.

Aluminum hull less than 6mm (1/4") thick—Use an additional
rubber, plastic, or fiberglass washer. Never use wood, since it
will swell, possibly fracturing the plastic housing. Never use
bronze, since electrolytic corrosion will occur.

3. Screw the hull nut in place, being sure the notch on the upper
rim of the housing is still positioned forward toward the bow. Do

Installation

Cored fiberglass hull—Follow separate instructions on page 3.

Hole Drilling

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.
P398—This flush model requires countersinking the housing to
create a “seat” in 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.

2

BOW ►

detail

large

O-ring

small

O-ring

Figure 3. Paddlewheel insert—no paddlewheel shown

Copyright © 2000 Airmar Technology Cor p.

key

notch

not clamp tightly on the wrenching flats, possibly causing the
housing to fracture. Hand tighten only. Do not over tighten.

Cored fiberglass hull—Do not over tighten, crushing the hull.

4. Remove any excess sealant on the outside of the hull to ensure
smooth water flow under the paddlewheel.

5. After the sealant cures, inspect the O-rings on the paddlewheel
insert (replace if necessary) and lubricate them with the silicone
lubricant supplied (see Figure 3). 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. Seat it into place with a
pushing twisting motion until the key fits into the notch. The
arrow on the top of the insert, the notch, and the arrow on the
flange of the housing will all be aligned. Be careful not to rotate
the housing and disturb the sealant.

Screw the cap nut several turns, then check that the insert’s
arrow is still facing forward toward the bow. Continue to tighten
the cap nut. 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. Attach the safety wire to one eye in the hull nut.
Lead the wire in a counterclockwise direction and thread it
through one eye in the cap nut. Twist the end securely to the
wire (see Figure 2).

Cable Routing & Connecting

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 4).

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 is 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” on page 2.

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

CAUTION: Completely seal the hull to prevent water seepage into

the core.

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.

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,

Operation & Maintenance

CAUTION: Do not remove the screws on the top of the sensor.

To remove the insert, unscrew the cap nut. This will jack the insert
up. Then remove the cap nut and insert as a single unit.

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/temperature 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 (see Figures 1 and 5). Always

install the paddlewheel insert or blanking plug secured with the
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 build-up on the paddlewheel is
suspected due to inaccurate readings from the instrument.

9- 12 mm

pour in
casting
epoxy

hull thickness

solid or hollow cylinder

Figure 4. Preparing a cored fiberglass hull

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

Copyright © 2000 Airmar Technol ogy Corp.

inner skin

core

outer skin

3

1. Inspect the O-rings on the blanking plug (replace if necessary)
and lubricate them with the silicone lubricant supplied or
petroleum jelly (Vaseline®) (see Figure 3). The O-rings must be
intact and well lubricated for a watertight seal.

2. Remove the safety wire from the cap nut (see Figure 2).

3. To remove the paddlewheel insert from the housing, unscrew the
cap nut. This will jack the insert out of the housing. Do not unscrew
the screws. Replace the paddlewheel insert with the blanking plug.
Seat it into place with a pushing twisting motion until the key fits
into the notch in the housing. Screw the cap nut in place and hand
tighten only. Do not over tighten (see Figure 5).

NOTE: If the flap valves do not move freely and block the
blanking plug from being inserted, clean the valve assembly so
the flap valves move freely and rest against the valve housing.
In the unlikely event that the flap valves cannot be freed, you
may need to push the flap valves down or break them off.

4. Reattach the safety wire to the cap nut to prevent the insert
from backing out in the unlikely event that the cap nut fails or is
screwed on incorrectly (see Figure 2).

Winterizing

After the boat has been hauled for winter storage, remove the
blanking plug to let the water drain away before re-inserting 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®
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 10kn (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. A replacement Paddlewheel Kit 33-350-01 is
available.

1. Using the new paddlewheel shaft, push the old shaft out about
6mm (1/4"). With pliers, remove the old shaft (see Figure 5).

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 in the new shaft until the ends are flush with the insert.

4. Install one large and one small O-ring.

5. Place the remaining two O-rings in similar positions on the
blanking plug.

Sensor Replacement & Parts

The information needed to order a replacement Airmar 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.

detail

key

blanking
plug

paddlewheel
insert

large

O-ring

small

O-ring

cap nut

small
O-ring

paddlewheel
shaft

paddlewheel
(flat side
of blade
faces bow)

housing
with valve
assembly

detail

flap valves

notch

Figure 5. Maintenance

Copyright © 2000 Airmar Technol ogy Corp.

Lost, broken, and worn parts should be replaced immediately.

Part

Airmar Part Number
Blanking Plug 20-288-01
Paddlewheel Kit 33-350-01
Cap Nut 04-011
Hull Nut 04-004
Housing (P371), Valve, and Hull Nut Kit 33-361-01

Obtain parts from your instrument manufacturer or marine dealer.

Gemeco Tel: [phone]

(USA) Fax: [phone]

Email: [e-mail]

Airmar EMEA Tel: [phone]

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

Email: [e-mail]

®

AIRMAR

TECHNOLOGY CORPORATION

4

35 Meadowbrook Drive, Milford, New Hampshire 03055-4613, USA

www.airmar.com

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