Specifications

Chapter 9-12 EQ33 Installation and service
which holds the transducer away from the hull and which directs the flow of
aerated water around the sides of the transducer rather than over the face of
the transducer.
On deep keeled vessels, care must be taken to ensure that the transducer beam
will not be blocked by any part of the keel. Although the appropriate mount-
ing location that meets all requirements depends on the type of vessel and its
normal operating speeds, a practical choice is usually somewhere between one
third and one half of the vessel’s water line length from the bow. Levelling
blocks may be designed accordingly to meet this requirement.
 The more the transducer protrudes from the hull, the better the results will
be.
Particularly at lower frequency operation (50kHz), interference from propel-
ler noise can be a significant problem. This can be seen as an increase in the
“noise” on the echosounder display when the propeller speed is increased. To
help reduce this, the transducer’s mounting face may be angled slightly for-
ward on the order of 3-5°. The goal is to incline the transducer so that a line of
sight along the transducer’s radiating surface passes below the propeller.
 Keeping the propeller clean and free of any nicks or roughness will assist in
minimizing interference from propeller noise due to cavitation.
Sources of noise to consider:
Water/air
noise
Acoustic noise Electrical noise
Air bubbles
Tu rbulence
Propeller
Main engine
Reduction gear propeller
shaft
Generators auxiliary
engines
Power plant for freezers
Hydraulic pumps
Rudder engine
Bow thruster
Stern thruster
Noise from electrical cables
Noise from generators
Poor grounding of instrument
Radiated noise from other
instruments
Dc – Dc converters
Electrical winches
Neon lights
etc.