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EQ33-2 Installation and service
10.5.2 Determining the position for the transducer
The EQ33-2 is a sophisticated piece of electronic equipment, but how well it
will perform under actual operating conditions will be largely dependent upon
the location of the transducer and how it has been installed.
Careful consideration, therefore, must be given to selecting the mounting loca-
tion and on deciding the method of installation that best suits the vessel.
Air bubbles and turbulence caused by the vessel's movement through the water
will seriously degrade the transducer's performance. Therefore the transducer
should be located well clear of any water intake or discharge line and also
clear of any projection along the hull line which might disturb the smooth flow
of water. It is of profound importance for good performance of the EQ33-2 that
the water flowing over the transducer be free of bubbles and aeration. If the
transducer face is clean but the performance degrades with increasing vessel
speed, then aeration of the water flowing under the transducer may be the
cause of the poor performance.
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. 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.
Chapter 10-11
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