Instruction manual

Installation and service Chapter 12-19
Due to the varying design of ship’s hulls and different operating speeds, there
can be great variation in the amount of air bubbles which are carried beneath
the hull. These bubbles tend to be carried close to the hull as they pass aft. For
this reason, it is desirable for the transducer to be mounted on a fairing block
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. Leveling
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 (38 and 50kHz), interference from
propeller 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
forward 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
Turbulence
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.