Airmar P79 - Manual (Page 2)

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.
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 water-
based lubricant (such as K-Y
® jelly). With a twisting motion, press
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.
2
inboard
Figure 1.
pressure waves
1/3
full keel sailboat
displacement hull
(6-12")
fin keel sailboat
150-300mm
LWL
Best location for the transducer
(Load Waterline Length)
stepped hull
planing hulls
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 300–600mm (1–2').
• Full keel sailboat—Locate amidships and away from the keel
at the point of minimum deadrise angle.
Figure 2. Establishing a performance baseline Figure 3. Testing the transducer at the selected location
A B C
active face
Copyright © 2005 Airmar Technology Corp.
Copyright © 2005 Airmar Technology Corp. Copyright © 2005 Airmar Technology Corp.