Airmar M42 User Manual

INSTALLATION INSTRUCTIONSOWNER’S GUIDE &

Sealcast

™

and Cast Resin Transducers

Models: M42, M155, M163, M172, M177, R155

IMPORTANT : Please read the instructions completely

before proceeding with the installation. These
instructions supersede any other instructions in your
instrument manual if they differ.

CAUTION : NEVER USE SOLVENTS!

Cleaners, fuel, paint, sealants, and other products may
contain strong solvents, such as acetone, which attack
many plastics greatly reducing their strength.

17-011 rev. 05 10/05

Mounting Location

Carefully study the hull to determine the best mounting location.

•Away from the propeller(s) and shaft(s), other machinery, and
other echosounders to minimize the effect of noise on the
echosounder display. The lower the noise level, the higher the
gain setting that can be used.

• On the side of the hull where the propeller(s) blades are moving
downward. The upward motion of blades generates pressure
waves and pushes bubbles up against the hull. By mounting on
the downward side, the hull shades the transducer from this
effect (see Figure 1).

• Where the transducer beam will be unobstructed by the keel or
propeller shaft(s).

• Where there is a minimum deadrise angle.

• Where there is adequate headroom inside the vessel for the
height of the stuffing tube and tightening the nuts.

• Locate the transducer about 1/3 aft LWL. Generally, this
provides the best compromise between obtaining aeration-free
water away from the bow and minimizing propeller noise (see
Figure 2).

Caution : Do not mount in an area of turbulence or bubbles:

Near water intake or discharge openings,
Behind strakes, fittings, or hull irregularities.

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

Part No._________________Date___________Frequency________kHz

M155

Stuffing Tube

Choosing the Stuffing Tube

Warning: A stuffing tube is required for all installations.

Caution : The stuffing tube must be compatible with the hull material

The stuffing tube seals the hull forming a water-tight conduit for
the cable. Choose a stuffing tube based on the hull material and
diameter of the transducer cable. Airmar stuffing tubes are
available from your marine dealer (see table below).

Fiberglass hull —The stuffing tube

fiberglass, not in coring.

Aluminum hull —Use a stainless steel stuffing tube.

bronze stuffing tube as electrolytic corrosion will occur.

Stuffing Tube

Material

bronze

stainless steel

steel weld to steel hull up to 0.5” D 38mm (1-1/2") 33-818

a. Requires the tube to be isolated from the hull with non-electrically conductive spacers.

Hull Material Cable Diameter

fiberglass
wood

fiberglass, wood
steel, aluminum

a

Installing the Stuffing Tube

After determining the best mounting location, install the stuffing tube.

Follow the installation instructions that came with the stuffing tube.

must

be installed in solid

Never

use a

Hull Hole
Diameter

up to 0.47” D 44mm (1-3/4") 33-511-01

up to 0.47” D 26mm (1") 33-819

Airmar

Part No.

Tr ansom View

pressure waves

aeration, cavitation, and turbulence

slope of hull

deadrise angle

parallel to waterline

fairing

- corrects for the deadrise angle
of the hull, so the transducer
beams shoots straight down

- mounts the transducer deeper
in the water for clean flow
over the transducer’s face

Figure 1. Mounting location and deadrise angle

AIRMAR

®

1/3 aft

LWL

(Load Waterline Length)

AIRMAR

®

Figure 2. Mounting location on displacement hull

▲

AIRMAR

®

cutting

cavity

guide

Figure 3. Airmar fairing

Bow

➣

arrow points

toward bow

backing block (2)

77mm (3")

deadrise shape

deadrise shape

fairing

Figure 4. Fabricating a fairing

and backing blocks

Fairing

Nearly all vessels have some deadrise angle at the transducer’s
mounting location. If the transducer is mounted directly to the hull,
the sound beam will be tilted off the vertical at the same angle as
the deadrise. If the deadrise angle at the mounting location
exceeds 10 ° a fairing is strongly recommended (see Figure 1).

•Orients the sound beam straight down by mounting the
transducer parallel to the water surface.

• Mounts the transducer deeper in the water for clean flow over
the transducer’s face.

AIRMAR Polymer Fairing

Made of a high impact polymer with an integrated cutting guide,
the Airmar fairing is easy to cut with a band saw and shape with
hand tools (see Figure 3). The fairing also has a center cavity for
the stuffing tube and cable service loop.

Model (see cab
M155, R155, M172 33-147
M177 33-145

Fabricating a Fairing & Backing Blocks

A fairing is usually constructed of an oily wood such as mahogany
or teak. Shape the fairing to match the outline of the transducer
(see Figure 4). Cut a 75mm x 150mm (3" x 6") hole in the center
of the fairing for the stuffing tube and the cable service loop. Place
the transducer over the fairing and using the transducer as a
guide, drill two holes for the threaded rods.Backing blocks are
mounted inside the hull to provide a level surface for tightening the
nuts that hold the threaded rods. They are fabricated to match the
interior deadrise angle. Drill a hole through the center of each
backing block.

le tag) Airmar Fairing Part No.

➣

®

band saw
table

deadrise
angle

AIRMAR

77mm (3")

blunt
end

Bow

Figure 5. Cutting an Airmar fairing

Model (see cab

le tag) Hole Diameter
M42 13mm or 1/2"
M163 10mm or 3/8"

Cutting the Fairing

Warning : The fairing must be installed parallel to the keel to

ensure proper boat handling and water flow over the transducer.

1. The stuffing tube will be centered in the cavity of the fairing (see
Figures 3, 4 & 6). Measure the deadrise angle of the hull at the
stuffing tube using an angle finder or a digital level (see Figure 1).

2. Tilt the band saw table to the measured angle and secure the
cutting fence (see Figure 5).

Caution : The arrow will be pointing forward toward the bow

after the fairing is installed (see Figure 3).

M177 —This fairing is symmetrical.

3. Place the fairing on the table so the cutting guide rests against
the fence. The arrow will be pointing toward you for installation
on the port side and away from you for installation on the
starboard side of the boat (see Figure 5).
fairing on the band saw so the angle cut matches the intended
side of the hull and not the mirror image.

Warning : Always wear safety goggles and a dust mask.

4. Recheck steps 1 through 3; then cut the fairing.

5. Center the stuffing tube in the cavity of the fairing.
fairing is parallel to the keel (centerline). Shape the fairing to the
hull as precisely as possible with a rasp or power tool.

6. The remaining section of the fairing with the cutting guide will
be used as the backing block inside the hull. It will provide a
level surface for tightening the nuts on the threaded rods.

Be sure

to orient the

Be sure

AIRMAR

cutting
guide

fence

the

®

backing block

service loop

transducer

2

cable

compression nut

hull

fairing

cable

forward view

stuffing
tube

Figure 6. Threaded stem stuffing tube installation

Bow

➣

backing block

fairing

transducer

—stainless steel stuffing tube shown

flanged nut

or

nut & washer

threaded rod (2)

nut (2) & washer (2)

nut (2) & washer (2)

rubbery washer (2)

nut (2) & washer (2)

plug (2)

AIRMAR

®