Airmar P79 User Manual

INSTALLATION INSTRUCTIONSOWNER’S GUIDE &

In-Hull, Adjustable Angle Transducer

Model P79

U.S. Patent No. 6,201,767. EP 1 118 074

WARNING: Always wear safety goggles and a dust
mask to avoid personal injury.

CAUTION: The fiberglass hull below the transducer
must be solid. The transducer will not transmit through
coring material such as foam or balsa wood.

CAUTION: Do not use an epoxy adhesive because it
is too brittle.

17-217-01 rev. 11 12/14/10

CAUTION: Never pull, carry, or hold the transducer by
the 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.

Applications

• Fiberglass hulls only

• Recommended for high-speed powerboats and racing sailboats

• Accommodates a deadrise angle up to 22°

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

Part No._________________Date___________Frequency________kHz

Mounting Location

About Fiberglass Hulls

The fiberglass hull below the transducer must be solid. Since the
hull absorbs acoustic energy, transmitting through the hull
reduces the transducer’s performance. Fiberglass hulls are often
reinforced in places for added strength or to reduce weight. These
cored areas contain balsa wood or structural foam which are poor
sound conductors. Do not locate the transducer over coring.

Tools & Materials

Safety goggles
Dust mask
Adhesive tape
Pole
Detergent (some installations)
Weak solvent (such as alcohol)
Disk sander (some installations)
Thin sealable plastic bag (some installations)
Cable ties (some installations)
Water-based lubricant (such as K-Y® jelly) (some installations)
Angle finder or digital level
Carpenter’s square
Pencil
Silicone sealant (such as GE Silicone I or Silicone II)
Screwdriver
Petroleum jelly (such as Vaseline® brand)
Propylene glycol (non-toxic antifreeze/coolant) 71ml (2.4 fl. oz.)
Level
Grommet(s) (some installations)
Installation in a cored fiberglass hull (see page 4):

Drill
Hole saw 100mm or 4"
Miniature disk sander
Casting epoxy (Polypoxy #7035/7040) or resin
Paper cup
Stirrer

Placement

CAUTION: Do not mount the transducer near water intake or
discharge openings or behind strakes, fittings, or hull irregularities
that will disturb the water flow.

Choose a location:

• Where the fiberglass is solid (no air bubbles are trapped in the
fiberglass resin) and where no coring, flotation material, or dead
air space is sandwiched between the inside skin and outer skin
of the hull.

• Where the hull below the transducer will be in contact with the
water at all times.

• Where the water flowing under the hull is smoothest with a
minimum of bubbles and turbulence (especially at high speeds).

• Away from interference caused by power and radiation sources
such as: the propeller(s) and shaft(s), other machinery, other
echosounders, and other cables. The lower the noise level, the
higher the echosounder gain setting that can be used.

• Where the transducer beam will not be blocked by the keel or
propeller shaft(s).

• Where the deadrise angle does not exceed 22°.

• Where there is space inside the vessel for the height of the unit,
tightening the locking ring, and installing the transducer.

1/3

LWL

(Load Waterline Length)

displacement hull

pressure waves

150- 300mm
(6-12")

Testing the Selected Mounting Location

Establishing a Performance Baseline

The results of this test are used as a basis of comparison to
determine the best in-hull location for the transducer.

1. Take the boat to the maximum depth in which you will be
operating the echosounder. If deep water is not available, find a
location with at least 30m (100').

2. Connect the transducer to the echosounder.

3. Tape the transducer to a pole with the cable side up. Hold it over
the side of the boat with the active face fully submerged and
parallel to the water surface (see Figure 2).

4. Observe the echosounder’s performance and the depth reading.

stepped hull

Figure 1.

planing hulls

fin keel sailboat

full keel sailboat

Best location for the transducer

Copyright © 2005 Airmar Technology Cor p.

inboard

Boat Types (see Figure 1)

• Displacement hull powerboat—Locate 1/3 of the way back
along the LWL and 150–300mm (6 –12") off the centerline.
The starboard side of the hull where the propeller blades are
moving downward is preferred.

• Planing hull powerboat—Mount well aft, on or near the
centerline, and well inboard of the first set of lifting strakes to
ensure that the transducer is in contact with the water at high
speeds. The starboard side of the hull where the propeller
blades are moving downward is preferred.

Outboard and I/O—Mount just forward of the engine(s).
Inboard—Mount well ahead of the propeller(s) and shaft(s).
Stepped hull—Mount just ahead of the first step.

• Fin keel sailboat—Mount to the side of the centerline and
forward of the fin keel 300–600 mm (1 –2').

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

Testing the Location

While the boat is at the same site (depth of water), test the
transducer inside the hull at the mounting location. Use one of the
methods below:

A.If the transducer will be located near the stern and the boat

has a minimum deadrise angle—Clean away any build-up of
dirt and/or grease using detergent or a weak solvent such as
alcohol. Place the transducer against the hull and allow bilge
water to cover the surface where they touch (see Figure 3-A).

B.For a moderate deadrise angle—If the hull surface is not

smooth, grind it with a disc sander. Place the transducer inside
a thin plastic bag. Partially fill the bag with water and close it
tightly with a cable tie. Wet the surface of the hull and press the
active face of the transducer against it through the bag (see
Figure 3-B).

C.For any location—If the hull surface is not smooth, grind it with a

disc sander. Coat the active face of the transducer with a water­based lubricant (such as K-Y
the face firmly against the hull (see Figure 3-C). After testing,
wipe all traces of the lubricant from the transducer’s face.

Observe the echosounder’s performance, and compare it to the
baseline. Look for a stable depth reading that is similar to the
baseline. Compare the thickness and intensity of the bottom trace.

If the performance is close to the baseline, this is a good mounting
location. Remember, some energy is lost transmitting through the
hull. If the test reading differs markedly from the baseline, you will
need to find another location to install the transducer.

NOTE: If there is no reading or it is erratic, the transducer may be
positioned over coring which is absorbing the acoustic energy.
Choose another location. If no other location is available, check
with the boat manufacturer to be certain coring is present before
proceeding with the instructions for “Installation in a Cored
Fiberglass Hull” on page 4.

®

jelly). With a twisting motion, press

active face

Figure 2. Establishing a performance baseline

Copyright © 2005 Airmar Technology Cor p. Copyright © 2005 Airmar Technology Corp.

2

AB C

Figure 3. Testing the transducer at the selected location